- Email: [email protected]
Highly efficient and humidity stable perovskite solar cells achieved by introducing perovskite-like metal formate material as the nanocrystal scaffold
Journal of Power Sources 402 (2018) 229–236
Contents lists available at ScienceDirect
Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour
Highly efficient and humidity stable perovskite solar cells achieved by introducing perovskite-like metal formate material as the nanocrystal scaffold
T
Guozhen Liua,b, Liangzheng Zhua,b, Haiying Zhenga,b, Xiaoxiao Xua,b, Ahmed Alsaedic, Tasawar Hayatc,e, Xu Pana,∗, Songyuan Daia,c,d,∗∗ a Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China b University of Science and Technology of China, Hefei 230026, China c NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia d State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China e Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan
H I GH L IG H T S
G R A P H I C A L A B S T R A C T
PLMF was firstly introduced into the • PSCs as a new-type scaffold additive. perovskite films with • High-quality fewer grain boundaries can be achieved.
PCE was boosted from 16.45% to • The PLMF. 19.17% by adding 3 mg ml devices with PLMF showed sig• The nificantly improved humidity stabi−1
lity.
A R T I C LE I N FO
A B S T R A C T
Keywords: Perovskite solar cells Film quality Scaffold additive Photovoltaic performance Humidity stability
Crystallinity and morphology of perovskite absorber layers are important factors for influencing on the performance and stability of perovskite solar cells. Here, a perovskite-like metal formate (PLMF) material is firstly introduced as the scaffold into the perovskite precursor solution to improve the quality of perovskite films by effectively controlling the crystallization process in the course of the perovskite growth. The results show that the perovskite films with PLMF exhibit well-organized crystallinity and compact morphology, and therefore decreased grain boundaries which will notably reduce the electron-hole recombination and the defect points exposed to humidity. Finally, the photoelectricity properties have been significantly improved. The device with 3 mg ml−1 PLMF achieves a power conversion efficiency of 19.17% with less hysteresis under AM 1.5G solar illumination, which shows a 16.53% increase than the pristine one (a power conversion efficiency of 16.45%). Importantly, the device with 3 mg ml−1 PLMF displays excellent stability compared to pristine device under 40 ± 5% and 70 ± 5% relative humidity (RH) in the dark, maintaining about 85% and 60% of the original efficiency after about 1000 h at room temperature, respectively. This work offers a potential way by employing scaffold additive to improve the performance and stability of perovskite solar cells.
∗
Corresponding author. Corresponding author. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China. E-mail addresses: [email protected] (X. Pan), [email protected] (S. Dai). ∗∗
https://doi.org/10.1016/j.jpowsour.2018.07.014 Received 28 February 2018; Received in revised form 24 June 2018; Accepted 2 July 2018 0378-7753/ © 2018 Published by Elsevier B.V.
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
1. Introduction
2. Experimental
In the last few years, organometal trihalide perovskites have attracted unprecedented attention owing to their low defect density, wide absorption band, long diffusion length and high charge carrier mobility [1–4]. Since 2009, the power conversion efficiency (PCE) of perovskite solar cells has rapidly increased from 3.81% to more than 22% [5,6]. Furthermore, perovskite solar cells have become the fastest-advancing photovoltaic devices, due to the advantages of high efficiency, simple manufacturing process and low-cost advantages [7–9]. Despite perovskite solar cells have displayed many outstanding properties in the field of photovoltaic application, the instability especially at the condition of moisture prevents them from the further practical development [10–13]. To further improve the performance and stability of perovskite solar cells, many efforts, such as optimizing the preparation methods, replacing the materials of charge transport layer and promoting the contact of different layers, have been made [14–16]. Meanwhile, it has been proved that the defects which are easily formed at the grain boundaries and on the surfaces of the inferior films can not only cause more nonradiative recombination centers but also deleteriously impact charge carrier lifetime [17,18]. Therefore, high-quality perovskite films with dense connected grains, including proper stoichiometry, low surface roughness and less grain boundaries play important roles to fabricate outstanding performance and stable solar cells [19,20]. Generally, high-quality perovskite light absorption layers are gained by changing the compositions of precursor solution suitably, controlling the experiment conditions accurately and employing solvent-engineering skillfully [21–24]. It has been reported that controlling the crystallization process in the course of the perovskite growth is one of the important issues for improving the quality of films and achieving highly efficient and stable perovskite solar cells [25,26]. Alternatively, using an appropriate additive can fabricate excellent crystallinity perovskite films with large grain size and full surface coverage. The superior perovskite films with low bulk defect density and reducing carrier recombination are beneficial for the PCE and stability of devices [27–30]. Wang and co-workers [29] found the 2-Pyridylthiourea additive added into the precursor solution can promote the transform of 2-D PbI2 to tetragonal perovskite crystals and improve the quality of the perovskite films. Finally, a CH3NH3PbI3-based device with the highest PCE of 18.2% and better stability were obtained. Besides, other additives, such as 1,8-diiodooctane [31], terephthalic acid [32], lithium iodide [33] and polyethyleneimine [34], have been introduced into the perovskite films to improve the photovoltaic performance. However, the reported PCE and stability by the method of adding additives are not very satisfactory, it remains an apparent challenge to develop a simple and effective additive to control the crystallinity and morphology of perovskite and improve the PCE and stability distinctly. In this work, to control the crystallization during the growth of the perovskite, a new-type scaffold additive, perovskite-like metal formate (PLMF), is introducing into the perovskite light absorption layer. PLMF, which owns a three-dimensional perovskite-like structure, is used to promote the crystallization of perovskite films. It can be found that the morphology of perovskite film with PLMF additive can be obviously improved and the surface becomes more uniform and compact. With fewer grain boundaries, the rate of electron-hole recombination and the defect points exposed to humidity can be significantly reduced, and therefore the improved photoelectricity properties. Eventually, the device with 3 mg ml−1 PLMF has a PCE of 19.17% with less hysteresis under AM 1.5G solar illumination. Moreover, the humidity stability of the devices under 40 ± 5 and 70 ± 5% RH is significantly increased.
2.1. Materials and preparation Formamidine iodide (FAI): FAI was prepared by stoichiometrically reacting formamidine acetate with hydroiodic acid (57 wt% in H2O) and then were stirred in the ice bath for 2 h. The solution was evaporated at 55 °C using rotary evaporation under reduced pressure for 1 h. Then the powder was washed with anhydrous ether and purified by dissolving in ethanol. After filtration and drying at 60 °C, the pure FAI powder was obtained. Synthesis of perovskite-like metal formate (PLMF): The PLMF (Ni (CHOO)3 [NH2(CH3)2]) was synthesized by the mixture of NiCl2*6H2O (1 mmol), DMA*HCl (DMA*HCl = dimethylamine hydrochloride, 1 mmol), NaCHOO*2H2O (3 mmol), H2O (8 mL) and DMF (8 mL), which was heated in a Teflon lined autoclave (20 mL) at 140 °C for 3 days. Some green precipitation was separated out the solution after slow cooling to room temperature. The product was filtered from the solution and washed by ethanol. Preparation of the PLMF/perovskite precursors: The 1.3 M Pb2+ of (FAPbI3)0.85 (MAPbBr3)0.15 precursor solution was prepared from dissolving the corresponding lead iodide (PbI2), lead bromine (PbBr2), formamidinium iodide (FAI) and methylammonium bromine (MABr) powders in DMSO and DMF mixed solvent (DMSO: DMF = 1:4 by volume). The PLMF/perovskite precursor solutions were obtained by mixing the PLMF suspension (20 mg mL−1) and the precursor solution of perovskite with different volume ratios. All the solutions were stirred at 70 °C for 6 h and filtered with 0.45 μm PVDF filters before using. PbI2 was purchased from TCI. Other materials were purchased from Alfa without further purification. 2.2. Device fabrication Fluorine-doped tin oxide (FTO) glass substrates were cleaned sequentially by sonication in detergent, ultrapure water and ethanol for three times. By spray pyrolysis at 460 °C, the TiO2 compact layer was coated on the FTO. The precursor solution for spray pyrolysis is including 0.4 mL bis(acetylacetonate), 0.6 mL titanium diisopropoxide and 7 mL isopropanol. Then, TiO2 mesoporous layer was spin-coated on the substrate with a speed of 4000 r.p.m. for 20 s TiO2 paste for mesoporous layer with 30 nm is diluted via ethanol (ethanol: TiO2 = 5.5: 1). After the spin coating, TiO2 mesoporous layer was sintered at 510 °C for 30 min. Next, the perovskite and PLMF/perovskite precursor solutions were spin-coated with firstly speed 1100 r.p.m. for 15 s, secondly 4500 r.p.m. for 38 s in an air flowing glovebox. A small amount of chlorobenzene (about 120 μL) was fast drop-casted on the perovskite layer during15 s before finishing the spin coating procedure. The substrate was heated at 105 °C for 60 min on a heating platform. The HTL was spin-coated on the substrate with 3000 r.p.m for 20 s, the HTM solution is composed of spiro-OMeTAD (73 mg), 4-tert-butylpyridine (29 μL), Li+ salt (LiTFSI, 17 μL) and cobalt (III) salt (8 μL) in chlorobenzene solvent (1 mL). Finally, Au electrode (about 60 nm) were deposited on top of the HTL via thermal evaporating. 2.3. Characterization EDX and films morphology was measured by a field-emission scanning electron microscope (SEM) with a Schottky Field Emission gun. The X-ray diffraction measurements of the perovskite films were obtained by an X'Pert MPD PRO (PANalytical) and the 2θ range were from 10° to 40°. The absorption spectra were collected by an
230
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
pristine perovskite and PLMF/perovskite films exhibit typical characteristic peaks of (FAPbI3)0.85 (MAPbBr3)0.15 mixed perovskite crystal (β-phase) including three strong diffraction peaks at about 14.2°, 28.4° and 31.9°, which can be validly indexed as (110), (220) and (310) crystal face, respectively [36]. Furthermore, the films with PLMF have the notably increased characteristic peaks. Especially, when the additive amount is 3 mg ml−1, the intensities of peaks at 14.2°, 28.4° and 31.9° are stronger. In addition, the FWHM values of the characteristic (110) peak are shown in Fig. 2 (c). As can be seen, the PLMF-3 perovskite film owns the smallest FWHM value, implying its superior crystallinity with preferred orientation at the (110) direction [37]. The results demonstrate that PLMF additive can enhance the crystallinity of perovskite which will have a beneficial influence on the optoelectronic properties. Presented in Fig. 2 (d) are the UV–vis spectra. As the additive amount increasing from 0 to 3 mg mL−1, the absorption of perovskite shows an obvious enhancement which potentially attributes to the impact of PLMF additive on the uniform surface morphology and preferred orientation crystal structure. However, when the additive amount continues to increase to 5 mg mL−1, there is a certain extent decline of absorption compared to PLMF-3 which can correspond to the decrease of crystallinity [38]. As shown in Fig. 2 (e), steady-state fluorescence (PL) spectra were utilized to study and characterize the light-generated electrons and holes properties of pristine and PLMF perovskite films. To eliminate the influence of electron transport layer and FTO on charge injection, the films were prepared on the glass. Under an excitation wavelength of 473 nm, the fluorescence peaks of the two kinds of films all appear at about 775 nm, which are consistent with the related literature. Besides, in comparison to the pristine film, the PLMF-3 film presents a higher fluorescence peak, suggesting high quality with enhanced crystallization and fewer trap sites [39]. A uniform and compact perovskite film suggests less defects on the surface which is beneficial to the efficient transport of charges in devices [40]. Fig. 3 (a) and (d) show the cross-sectional SEM images of pristine and PLMF-3 devices. Compared with the pristine, PLMF-3 perovskite film is much smoother and owns fewer grain boundaries, which will effectively reduce the centers of carrier recombination and improve the photoelectricity properties [41]. The top view SEM images of pristine and PLMF-3 films at different magnifications are presented in Fig. 3 (b), (e) and (c), (f). The film with 3 mg mL−1 PLMF exhibits enlarged and well-organized grain. By introduced PLMF, the morphology of perovskite film can be remarkably improved and the surface becomes more uniform and compact. As a structure template additive, PLMF is a kind of porous material with regular channel and clear direction of organic ligands and metal ions. During the initial phase of crystallization, the perovskite crystal will arrange in order around organic ligand and metal ions of PLMF template. Hence, the perovskite crystals can grow orderly and the films will become more compact with fewer grain boundaries. Nevertheless, when the content reaches 5 mg mL−1, the excessively high concentration of PLMF trapped in the
Ultraviolet–Vis spectrophotometer (UV–vis, U-3900H, HITACHI, Japan). The steady-state PL spectra measurements were carried out on a spectrofluorometer (photon technology international) and studied by the software Fluorescence. The exciting wavelength of 473 nm was excited by a standard 450 W xenon CW lamp. The transient absorption spectra (TAS) were tested on LKS (Applied photophysics) with repetition rate of 5 Hz and the laser device energy of 150 μJ/cm2. The excitation light and probe light wavelength were 500 nm and 760 nm, respectively. Electrochemical impedance spectroscopy (EIS) was performed at −0.9 V under dark by using an Autolab analyzer (Metrohm, PGSTAT 302N, Switzerland) with a frequency range from 1 Hz to 1 MHz. J–V curves were measured on a solar simulator (Newport, Oriel Class A, 91195 A) with a source meter (Keithley 2420) at 100 mW/cm2 illumination AM 1.5G. By masking a black mask, the active area for each device was controlled at 0.09 cm2. The setup was calibrated with a certified silicon solar cell (Fraunhofer ISE) prior to measurements. The incident photon to current efficiency (IPCE) were recorded on an IPCE measurement system (Newport Corporation, CA) with dual Xenon/ quartz halogen light source and measured in DC mode with no bias light used with the wavelength from 300 to 900 nm. The humidity aging tests were performed in two containers with the relative humidity of 40 ± 5% and 70 ± 5%. The containers remained at ambient temperature under dark. 3. Results and discussion Fig. 1 (a) and (b) show the structure of the perovskite-like metal formate (PLMF), Ni(CHOO)3 [NH2(CH3)2], which has a network threedimensional structure. It has been synthesized by a solvothermal method [35]. In the compound, each asymmetric unit includes a nickel ion, bonding to a formate group (CHOO−), and an unordered dimethylamine (DMA) cation. In addition, the nickel ions are bridged by a three-atom group CHOO−, a three-dimensional tortile perovskite-like structure is forming, and the DMA cations exist in the center of each cage. The scanning electron microscope (SEM) image of the PLMF sample is shown in Fig. S1. In Fig. S2, the energy dispersive X-ray (EDX) spectroscopy is employed to evaluate the chemical compositions of PLMF sample. The schematic diagram, which illustrates the films preparation process from the perovskite precursor solution with PLMF, is shown in Fig. 2 (a). Before one-step deposition method, the precursor solution was firstly sonicated for 15 min and then stirred continuously for 6 h at 70 °C. After spin-coated on the m-TiO2 layer, the films were annealed at 105 °C for 60 min. To study the influence of PLMF additive on the morphology of perovskite films and the performance of solar cells, three different additive amounts 1, 3 and 5 mg mL−1 were selected. For simplicity, they were named as PLMF-1, PLMF-3 and PLMF-5, respectively. In this study, we employed (FAPbI3)0.85 (MAPbBr3)0.15 mixed perovskite as the pristine, which has been reported achieving excellent PCE. The XRD patterns, as shown in Fig. 2 (b), were utilized to reveal the effect of PLMF additive on the crystallinity of perovskite films. All the
Fig. 1. (a) The perovskite-like structure and (b) three-dimensional structure of perovskite-like metal formate (Ni(CHOO)3 [NH2(CH3)2]).
231
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
Fig. 2. (a) Schematic diagram of the fabrication process for perovskite films with PLMF. (b) The XRD patterns of perovskite films with different amounts of PLMF and the magnified XRD patterns of the (110) peak. (c) The dependence of full width at half maximum (FWHM) for the (110) peak. (d) UV–vis spectra and (e) PL spectra of perovskite films with different amounts of PLMF.
Fig. 3. (a, d) Cross-sectional scanning electron microscope (SEM) images of pristine and PLMF-3 devices. (b, c, e, f) Top view SEM images of pristine and PLMF-3 perovskite films.
232
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
Fig. 4. (a) Normalized TA responses of TiO2/perovskite films with 0 and 3 mg mL−1 PLMF. (b) Nyquist plots of PSCs with 0 and 3 mg mL−1 PLMF at V = −0.9 V in the dark. Fig. 5. (a) J–V curves of PSCs with different amounts of PLMF. (b) J–V curves of PSCs with 0 and 3 mg mL−1 PLMF under reverse and forward scan directions. (c) Incident photo to current conversion efficiency (IPCE) spectra of PSCs with 0 and 3 mg mL−1 PLMF. (d) The PCE histogram fitted with a Gaussian distribution of the devices with 0 and 3 mg mL−1 PLMF over 30 measured devices.
recombination occurring in perovskite layer will be slower [43]. After fitted at single exponential decays, the carrier lifetime of PLMF-3 film with 193 ns is longer than the one of pristine (142 ns), which indicates higher quality of PLMF-3 film. Furthermore, electrochemical impedance spectra (EIS) were employed to analyze the charge recombination and charge transfer behavior in the devices, Fig. 4 (b) shows the Nyquist plots of the pristine and PLMF-3 devices measured at voltage of −0.9 V in the dark. According to the Nyquist plots, the low frequency featured resistance is attributed to the recombination resistance (Rrec) and the high frequency should be assigned to the charge transport resistance (Rct) [44]. Clearly, compared with pristine, the PLMF-3 device owns a higher Rrec and a lower Rct, indicating the properties of decreased carrier recombination between electron transporting layer and perovskite layer and enhanced carrier transfer. As testified above, the PLMF additive is advantageous to obtain the perovskite films with more uniform and preferred orientation crystal structure. The current–voltage (J–V) curves of PSCs with different amounts of PLMF additive under AM 1.5G illumination are presented in Fig. 5 (a) and the corresponding parameters are presented in Table 1. The device without PLMF additive shows an optimal PCE of 16.45%, a short-circuit current (Jsc) of 21.59 mA cm−2, an open-circuit voltage
Table 1 Photovoltaic parameters of perovskite solar cells with different amounts of PLMF. Device
Jsc (mA cm−2)
Voc (V)
FF (%)
PCE (%)
Pristine PLMF-1 PLMF-3 PLMF-5
21.59 21.67 22.17 21.75
1.04 1.07 1.08 1.05
73.56 77.45 79.79 74.93
16.45 18.00 19.17 17.15
films will make a negative impact on the photoelectric properties of device and even cause the phase separation between the PLFM nanocrystals and perovskite. The film turns to be coarse and the redundant PLMF appears and distinctly disperses on the surface (Fig S3), which is the reason for resulting from the decreased absorption. To make further study of the quality of the films with and without PLMF, as shown in Fig. 4 (a), transient absorption (TA) spectra was carried out to investigate the electron and hole recombination behavior in the perovskite layer, which can affect the photovoltaic performance of the devices [42]. It is universally acknowledged that a longer carrier lifetime means a longer decay lifetime, and the speed of charge 233
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
Fig. 6. (a) Normalized efficiency variation curves of unsealed perovskite solar cells with different amounts of PLMF (a) under 40 ± 5% RH and (b) 70 ± 5% RH.
Fig. 7. Schematic view of the crystal growth process of pristine and PLMF perovskite thin films.
(Voc) of 1.04 V, and a fill factor (FF) of 73.56%. Fascinatingly, the device with the PLMF presents a significantly increased performance. The PLMF-3 device shows the best performance with an optimal PCE of 19.17%, a Jsc of 22.17 mA cm−2, a Voc of 1.08 V, and FF of 79.79%. The PLMF-3 device has an obvious enhancement of Jsc because of the enhanced absorption which is ascribed to its improvement of the uniform and compact perovskite absorption layer. The Voc increased from 1.04 V to 1.08 V due to the reduced defect-induced recombination and improved charge transport in the PLMF-3 device [38]. However, when the content reaches 5 mg mL−1, the excessively high concentration of PLMF trapped in the films will make a negative impact on the performance of device. The PLMF-5 device displays a declining PCE of 17.15%. Besides, the common hysteresis phenomenon connected with the changes of the defect state in the interface and the ferroelectric effect which can influence the photovoltaic performances of PSCs. The J–V curves and the corresponding parameters of the devices based on pristine and PLMF-3 under different scan directions are shown in Fig. 5 (b) and Table S1, respectively. By adding the PLMF, the hysteresis effect of the J-V curves becomes more negligible due to the reduction of spontaneous radiative recombination among trap states [45]. The IPCE spectra of pristine and PLMF-3 PSCs are summarized in Fig. 5 (c). The PLMF-3 PSC shows higher IPCE than pristine between 350 and 750 nm. The integrated currents of pristine and PLMF-3 are 20.71 and 21.61 mA cm−2, respectively, which are in good agreement with the corresponding values in Fig. 5 (a). To evaluate the reproducibility of photovoltaic performance, Fig. 5 (d) shows the PCE histograms of pristine and PLMF-3 PSCs fitted with a Gaussian distribution. Each histogram consists of 30 measured devices. It displays that the PLMF-3 devices exhibit an impressive average PCE about 17.93%, compared with 15.61% for the pristine devices, demonstrating that PLMF-3 devices have an evident improvement PCE and outstanding reproducibility. At present, stability is a key challenge for PSCs especially the ability of resistance to humidity [46,47]. Therefore, the humidity stability of
unsealed devices with different amounts of PLMF was investigated. All the aging tests were carried out in dark. Fig. 6 (a) shows the normalized efficiency variation curves of the unsealed devices tested under 40 ± 5% RH at room temperature. At the first 250 h, all the devices keep good stability. Whereas, the pristine device begins to degrade and the PCE decreases by 40% after about 1000 h. While, for the device with PLMF, the PCE shows a slower decrease and retains about 80% of the original efficiency after aging for about 1000 h. In addition, when tested under 70 ± 5% RH at room temperature (Fig. 6 b), the device with PLMF presents more significantly stability than pristine one by attributing to its high-crystallinity and fewer defects. After aging for about 1000 h, the PLMF-3 device still retains about 60% of the original efficiency, while, for the pristine device, the value of PCE decreases by 80% under the same conditions. The enhanced performance and stability of PSCs with PLMF may be attributed to the structural property of the scaffold additive. Fig. 7 shows the schematic view of the crystal growth process of pristine and PLMF perovskite thin films. PLMF nanocrystal material, with a periodicity three-dimensional perovskite-like structure, can effectively control the crystallization process in the course of the perovskite growth because of its organized micropores. For nucleation, because of the existence of ordered template with directional arrangement of organic ligand and metal ions in the precursor solution, the dispersal of Pb+ becomes more ordered, leading to evenly distributive nucleation centers. Then, for growth, perovskite crystallites will grow in their preferred direction during the initial phase of crystallization around the organic ligand and metal ions [48,49]. Because of the fewer defects on the surface and at the grain boundaries, the defect points exposed to humidity can be reduced obviously, which can lead to the improved stability of devices under moisture. The existence of steady PLMF, which acts as a regular scaffold, can further improve the stability. As a result, the devices based on the perovskite with PLMF absorber layer present improved humidity stability and photoelectricity properties.
234
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
4. Conclusions
[16] J. Jiang, Z. Jin, J. Lei, Q. Wang, X. Zhang, J. Zhang, F. Gao, S. Liu, ITIC surface modification to achieve synergistic electron transport layer enhancement for planar-type perovskite solar cells with efficiency exceeding 20%, J. Mater. Chem. 5 (2017) 9514–9522. [17] C. Besleaga, L.E. Abramiuc, V. Stancu, A.G. Tomulescu, M. Sima, L. Trinca, N. Plugaru, L. Pintilie, G.A. Nemnes, M. Iliescu, H.G. Svavarsson, A. Manolescu, I. Pintilie, Iodine migration and degradation of perovskite solar cells enhanced by metallic electrodes, J. Phys. Chem. Lett. 7 (2016) 5168–5175. [18] W. Nie, H. Tsai, R. Asadpour, J.-C. Blancon, A.J. Neukirch, G. Gupta, J.J. Crochet, M. Chhowalla, S. Tretiak, M.A. Alam, H.-L. Wang, A.D. Mohite, High-efficiency solution-processed perovskite solar cells with millimeter-scale grains, Science 347 (2015) 522–525. [19] G.A. Al-Dainy, S.E. Bourdo, V. Saini, B.C. Berry, A.S. Biris, Hybrid perovskite photovoltaic devices: properties, architecture and fabrication methods, Energy Technol. 5 (2017) 373–401. [20] J. Ye, H. Zheng, L. Zhu, X. Zhang, L. Jiang, W. Chen, G. Liu, X. Pan, S. Dai, Hightemperature shaping perovskite film crystallization for solar cell fast preparation, Sol. Energy Mater. Sol. Cell. 160 (2017) 60–66. [21] D. Bi, W. Tress, M.I. Dar, P. Gao, J. Luo, C. Renevier, K. Schenk, A. Abate, F. Giordano, J.-P.C. Baena, J.-D. Decoppet, S.M. Zakeeruddin, M.K. Nazeeruddin, M. Grätzel, A. Hagfeldt, Efficient luminescent solar cells based on tailored mixedcation perovskites, Sci. Adv 2 (2016) e1501170. [22] H. Wang, J. Lei, F. Gao, Z. Yang, D. Yang, J. Jiang, J. Li, X. Hu, X. Ren, B. Liu, J. Liu, H. Lei, Z. Liu, S. Liu, Magnetic field-assisted perovskite film preparation for enhanced performance of solar cells, ACS Appl. Mater. Interfaces 9 (2017) 21756–21762. [23] W.-T. Wang, S.K. Das, Y. Tai, Fully ambient processed perovskite film for perovskite solar cells: effect of solvent polarity on lead iodide, ACS Appl. Mater. Interfaces 9 (2017) 10743–10751. [24] N.J. Jeon, J.H. Noh, W.S. Yang, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Compositional engineering of perovskite materials for high-performance solar cells, Nature 517 (2015) 476–480. [25] R. Linblad, D. Bi, B.-W. Park, J. Oscarsson, M. Gorgoi, H. Siegbahn, M. Odelius, E.M.J. Johansson, H. Rensmo, The electronic structure of TiO2/CH3NH3PbI3 perovskite solar cell interfaces, J. Phys. Chem. Lett. 5 (2014) 648–653. [26] J.-H. Im, I.-H. Jang, N. Pellet, M. Grätzel, N.-G. Park, Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells, Nat. Nanotechnol. 9 (2014) 927–932. [27] T.-H. Chang, C.-W. Kung, H.-W. Chen, T.-Y. Huang, S.-Y. Kao, H.-C. Lu, M.-H. Lee, K.M. Boopathi, C.-W. Chu, K.-C. Ho, Planar heterojunction perovskite solar cells incorporating metal–organic framework nanocrystals, Adv. Mater. 27 (2015) 7229–7235. [28] Y. Wu, F. Xie, H. Chen, X. Yang, H. Su, M. Cai, Z. Zhou, T. Noda, L. Han, Thermally stable MAPbI3 perovskite solar cells with efficiency of 19.19% and area over 1 cm2 achieved by additive engineering, Adv. Mater. 29 (2017) 1701073. [29] M. Sun, F. Zhang, H. Liu, X. Li, Y. Xiao, S. Wang, Tuning the crystal growth of perovskite thin-films by adding the 2-pyridylthiourea additive for highly efficient and stable solar cells prepared in ambient air, J. Mater. Chem. 5 (2017) 13448–13456. [30] F. Han, J. Luo, H.A. Malik, B. Zhao, Z. Wan, C. Jia, A functional sulfonic additive for high efficiency and low hysteresis perovskite solar cells, J. Power Sources 359 (2017) 577–584. [31] P.-W. Liang, C.-Y. Liao, C.-C. Chueh, F. Zuo, S.T. Williams, X.-K. Xin, J. Lin, A.K.Y. Jen, Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells, Adv. Mater. 26 (2014) 3748–3754. [32] X. Hou, S. Huang, W. Ou-Yang, L. Pan, Z. Sun, X. Chen, Constructing efficient and stable perovskite solar cells via interconnecting perovskite grains, ACS Appl. Mater. Interfaces 9 (2017) 35200–35208. [33] H. Luo, J. Wu, Q. Liu, J. Huang, Y. Tu, J. Lin, M. Huang, Addition of lithium iodide into precursor solution for enhancing the photovoltaic performance of perovskite solar cells, Energy Technol. 5 (2017) 1–7. [34] Q. Dong, Z. Wang, K. Zhang, H. Yu, P. Huang, X. Liu, Y. Zhou, N. Chen, B. Song, Easily accessible polymer additives for tuning the crystal-growth of perovskite thinfilms for highly efficient solar cells, Nanoscale 8 (2016) 5552–5558. [35] X.-Y. Wang, L. Gan, S.-W. Zhang, S. Gao, Perovskite-like metal formates with weak ferromagnetism and as precursors to amorphous materials, Inorg. Chem. 43 (2004) 4615–4625. [36] H. Zheng, G. Liu, L. Zhu, J. Ye, X. Zhang, A. Alsaedi, T. Hayat, X. Pan, S. Dai, Enhanced performance and stability of perovskite solar cells using NH4I interfacial modifier, ACS Appl. Mater. Interfaces 9 (2017) 41006–41013. [37] X. Li, D. Bi, C. Yi, J.-D. Décoppet, J. Luo, S.M. Zakeeruddin, A. Hagfeldt, M. Grätzel, A vacuum flash–assisted solution process for high-efficiency large-area perovskite solar cells, Science 353 (2016) 58–62. [38] G. Xing, N. Mathews, S.S. Lim, N. Yantara, X. Liu, D. Sabba, M. Grätzel, S. Mhaisalkar, T.C. Sum, Low-temperature solution-processed wavelength-tunable perovskites for lasing, Nat. Mater. 13 (2014) 476–480. [39] M. Yang, T. Zhang, P. Schulz, Z. Li, G. Li, D.H. Kim, N. Guo, J.J. Berry, K. Zhu, Y. Zhao, Facile fabrication of large-grain CH3NH3PbI3-xBrx films for high-efficiency solar cells via CH3NH3Br-selective ostwald ripening, Nat. Commun. 7 (2016) 12305. [40] J.S. Yun, A. Ho-Baillie, S. Huang, S.H. Woo, Y. Heo, J. Seidel, F. Huang, Y.B. Cheng, M.A. Green, Benefit of grain boundaries in organic–inorganic halide planar perovskite solar cells, J. Phys. Chem. Lett. 6 (2015) 875–880. [41] R. Long, J. Liu, O.V. Prezhdo, Unravelling the effects of grain boundary and chemical doping on electron-hole recombination in CH3NH3PbI3 perovskite by timedomain atomistic simulation, J. Am. Chem. Soc. 138 (2016) 3884–3890. [42] Q. Shen, Y. Ogomi, J. Chang, S. Tsukamoto, K. Kukihara, T. Oshima, N. Osada,
In summary, a significative method is adopted to enhance the crystallinity and morphology of perovskite films via employing a perovskite-like metal formate (PLMF) material, Ni(CHOO)3 [NH2(CH3)2], as a scaffold additive. It is found that PLMF, acting as an ordered scaffold, is beneficial for the crystallinity of perovskite and can promote to form a uniform and compact absorber layer with fewer grain boundaries. As a result, photoelectricity properties are improved due to the improvement of quality of the perovskite films and the decreased electron-hole recombination. Compared to the pristine device (a PCE of 16.45%), the device with 3 mg ml−1 PLMF additive exhibits a PCE of 19.17% with less hysteresis under AM 1.5G solar illumination. Moreover, the device with 3 mg ml−1 PLMF shows excellent stability compared to pristine device under 40 ± 5 and 70 ± 5% RH after about 1000 h. Thus, the PLMF additive provides an easy strategy for improving the performance and stability of PSCs. Acknowledgements This work was financially supported by the National High Technology Research and Development Program of China under Grant No.2015AA050602, STS project of Chinese Academy of Sciences (KFJSW-STS-152). Appendix A. Supplementary data Supplementary data related to this article can be found at https:// doi.org/10.1016/j.jpowsour.2018.07.014. References [1] M. Liu, M.B. Johnston, H.J. Snaith, Efficient planar heterojunction perovskite solar cells by vapour deposition, Nature 501 (2013) 395–398. [2] H.-S. Kim, C.-R. Lee, J.-H. Im, K.-B. Lee, T. Moehl, A. Marchioro, S.-J. Moon, R. Humphry-Baker, J.-H. Yum, J.E. Moser, M. Grätzel, N.-G. Park, Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%, Sci. Rep. 2 (2012) 591. [3] L. Zhu, Z. Shao, J. Ye, X. Zhang, X. Pan, S. Dai, Mesoporous BaSnO3 layer based perovskite solar cells, Chem. Commun. 52 (2016) 970–973. [4] Q. Chen, H. Zhou, Z. Hong, S. Luo, H.-S. Duan, H.-H. Wang, Y. Liu, G. Li, Y. Yang, Planar heterojunction perovskite solar cells via vapor assisted solution process, J. Am. Chem. Soc. 136 (2014) 622–625. [5] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskites as visible-light sensitizers for photovoltaic cells, J. Am. Chem. Soc. 131 (2009) 6050–6051. [6] W.S. Yang, B.-W. Park, E.H. Jung, N.J. Jeon, Y.C. Kim, D.U. Lee, S.S. Shin, J. Seo, E.K. Kim, J.H. Noh, S.I. Seok, Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells, Science 356 (2017) 1376–1379. [7] J. You, L. Meng, T.-B. Song, T.-F. Guo, Y. Yang, W.-H. Chang, Z. Hong, H. Chen, H. Zhou, Q. Chen, Y. Liu, N.D. Marco, Y. Yang, Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers, Nat. Nanotechnol. 11 (2016) 75–81. [8] J. Liu, J. Lin, Q. Xue, Q. Ye, X. He, L. Ouyang, D. Zhuang, C. Liao, H.-L. Yip, J. Mei, W.-M. Lau, J. Power Sources 301 (2016) 242–250. [9] Y. Wu, X. Yang, W. Chen, Y. Yue, M. Cai, F. Xie, E. Bi, A. Islam, L. Han, Perovskite solar cells with 18.21% efficiency and area over 1 cm2 fabricated by heterojunction engineering, Nat. Energy 1 (2016) 16148. [10] J.H. Kim, S.T. Williams, N. Cho, C.-C. Chueh, A.K.-Y. Jen, Enhanced environmental stability of planar heterojunction perovskite solar cells based on blade-coating, Adv. Energy Mater 5 (2015) 1401229. [11] H. Back, G. Kim, J. Kim, J. Kong, T.K. Kim, H. Kang, H. Kim, J. Lee, S. Lee, K. Lee, Achieving long-term stable perovskite solar cells via ion neutralization, Energy Environ. Sci. 9 (2016) 1258–1263. [12] Y. Rong, L. Liu, A. Mei, X. Li, H. Han, Beyond efficiency: the challenge of stability in mesoscopic perovskite solar cells, Adv. Energy Mater 5 (2015) 1501066. [13] B. Conings, J. Drijkoningen, N. Gauquelin, A. Babayigit, J. D'Haen, L. D'Olieslaeger, A. Ethirajan, J. Verbeeck, J. Manca, E. Mosconi, F.D. Angelis, H.-G. Boyen, Intrinsic thermal instability of methylammonium lead trihalide perovskite, Adv. Energy Mater 5 (2015) 1–8. [14] F. Xie, C.-C. Chen, Y. Wu, X. Li, M. Cai, X. Liu, X. Yang, L. Han, Vertical recrystallization for highly efficient and stable formamidinium based inverted structure perovskite solar cells, Energy Environ. Sci. 10 (2017) 1942–1949. [15] Q. Jiang, L. Zhang, H. Wang, X. Yang, J. Meng, H. Liu, Z. Yin, J. Wu, X. Zhang, J. You, Enhanced electron extraction using SnO2 for high-efficiency planar-structure HC(NH2)2PbI3-based perovskite solar cells, Nat. Energy 2 (2016) 16177.
235
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
K. Yoshino, K. Katayama, T. Toyoda, S. Hayase, Charge transfer and recombination at the metal oxide/CH3NH3PbClI2/spiro-OMeTAD interfaces: uncovering the detailed mechanism behind high efficiency solar cells, Phys. Chem. Chem. Phys. 16 (2014) 19984–19992. [43] Q. Shen, Y. Ogomi, J. Chang, T. Toyoda, K. Fujiwara, K. Yoshino, K. Sato, K. Yamazaki, M. Akimoto, Y. Kuga, K. Katayama, S. Hayase, Optical absorption, charge separation and recombination dynamics in Sn/Pb cocktail perovskite solar cells and their relationships to photovoltaic performances, J. Mater. Chem. 3 (2015) 9308–9316. [44] H. Zhang, J. Mao, H. He, D. Zhang, H.L. Zhu, F. Xie, K.S. Wong, M. Grätzel, W.H. Choy, A smooth CH3NH3PbI3 film via a new approach for forming the PbI2 nanostructure together with strategically high CH3NH3I concentration for high efficient planar-heterojunction solar cells, Adv. Energy Mater 5 (2015) 1501354. [45] H. Cho, S.-H. Jeong, M.-H. Park, Y.-H. Kim, C. Wolf, C.-L. Lee, J.H. Heo, A. Sadhanala, N. Myoung, S. Yoo, S.H. Im, R.H. Friend, T.-W. Lee, Overcoming the
[46]
[47]
[48]
[49]
236
electroluminescence efficiency limitations of perovskite light-emitting diodes, Science 350 (2015) 1222–1225. T.A. Berhe, W.-N. Su, C.-H. Chen, C.-J. Pan, J.-H. Cheng, H.-M. Chen, M.-C. Tsai, L.Y. Chen, A.A. Dubale, B.-J. Hwang, Organometal halide perovskite solar cells: degradation and stability, Energy Environ. Sci. 9 (2016) 323–356. C. Liu, W. Ding, X. Zhou, J. Gao, C. Cheng, X. Zhao, B. Xu, Efficient and stable perovskite solar cells prepared in ambient air based on surface-modified perovskite layer, J. Phys. Chem. C 121 (2017) 6546–6553. F. Zhang, W. Shi, J. Luo, N. Pellet, C. Yi, X. Li, X. Zhao, T.J.S. Dennis, Xianggao Li, S. Wang, Y. Xiao, S.M. Zakeeruddin, D. Bi, M. Grätzel, Isomer-pure bis-PCBM-assisted crystal engineering of perovskite solar cells showing excellent efficiency and stability, Adv. Mater. 29 (2017) 1606806. D. Bi, C. Yi, J. Luo, J.-D. Décoppet, F. Zhang, S.M. Zakeeruddin, X. Li, A. Hagfeldt, M. Grätzel, Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%, Nat. Energy 1 (2016) 16142.
Contents lists available at ScienceDirect
Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour
Highly efficient and humidity stable perovskite solar cells achieved by introducing perovskite-like metal formate material as the nanocrystal scaffold
T
Guozhen Liua,b, Liangzheng Zhua,b, Haiying Zhenga,b, Xiaoxiao Xua,b, Ahmed Alsaedic, Tasawar Hayatc,e, Xu Pana,∗, Songyuan Daia,c,d,∗∗ a Key Laboratory of Photovoltaic and Energy Conservation Materials, Institute of Applied Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China b University of Science and Technology of China, Hefei 230026, China c NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia d State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China e Department of Mathematics, Quaid-I-Azam University, Islamabad 44000, Pakistan
H I GH L IG H T S
G R A P H I C A L A B S T R A C T
PLMF was firstly introduced into the • PSCs as a new-type scaffold additive. perovskite films with • High-quality fewer grain boundaries can be achieved.
PCE was boosted from 16.45% to • The PLMF. 19.17% by adding 3 mg ml devices with PLMF showed sig• The nificantly improved humidity stabi−1
lity.
A R T I C LE I N FO
A B S T R A C T
Keywords: Perovskite solar cells Film quality Scaffold additive Photovoltaic performance Humidity stability
Crystallinity and morphology of perovskite absorber layers are important factors for influencing on the performance and stability of perovskite solar cells. Here, a perovskite-like metal formate (PLMF) material is firstly introduced as the scaffold into the perovskite precursor solution to improve the quality of perovskite films by effectively controlling the crystallization process in the course of the perovskite growth. The results show that the perovskite films with PLMF exhibit well-organized crystallinity and compact morphology, and therefore decreased grain boundaries which will notably reduce the electron-hole recombination and the defect points exposed to humidity. Finally, the photoelectricity properties have been significantly improved. The device with 3 mg ml−1 PLMF achieves a power conversion efficiency of 19.17% with less hysteresis under AM 1.5G solar illumination, which shows a 16.53% increase than the pristine one (a power conversion efficiency of 16.45%). Importantly, the device with 3 mg ml−1 PLMF displays excellent stability compared to pristine device under 40 ± 5% and 70 ± 5% relative humidity (RH) in the dark, maintaining about 85% and 60% of the original efficiency after about 1000 h at room temperature, respectively. This work offers a potential way by employing scaffold additive to improve the performance and stability of perovskite solar cells.
∗
Corresponding author. Corresponding author. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China. E-mail addresses: [email protected] (X. Pan), [email protected] (S. Dai). ∗∗
https://doi.org/10.1016/j.jpowsour.2018.07.014 Received 28 February 2018; Received in revised form 24 June 2018; Accepted 2 July 2018 0378-7753/ © 2018 Published by Elsevier B.V.
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
1. Introduction
2. Experimental
In the last few years, organometal trihalide perovskites have attracted unprecedented attention owing to their low defect density, wide absorption band, long diffusion length and high charge carrier mobility [1–4]. Since 2009, the power conversion efficiency (PCE) of perovskite solar cells has rapidly increased from 3.81% to more than 22% [5,6]. Furthermore, perovskite solar cells have become the fastest-advancing photovoltaic devices, due to the advantages of high efficiency, simple manufacturing process and low-cost advantages [7–9]. Despite perovskite solar cells have displayed many outstanding properties in the field of photovoltaic application, the instability especially at the condition of moisture prevents them from the further practical development [10–13]. To further improve the performance and stability of perovskite solar cells, many efforts, such as optimizing the preparation methods, replacing the materials of charge transport layer and promoting the contact of different layers, have been made [14–16]. Meanwhile, it has been proved that the defects which are easily formed at the grain boundaries and on the surfaces of the inferior films can not only cause more nonradiative recombination centers but also deleteriously impact charge carrier lifetime [17,18]. Therefore, high-quality perovskite films with dense connected grains, including proper stoichiometry, low surface roughness and less grain boundaries play important roles to fabricate outstanding performance and stable solar cells [19,20]. Generally, high-quality perovskite light absorption layers are gained by changing the compositions of precursor solution suitably, controlling the experiment conditions accurately and employing solvent-engineering skillfully [21–24]. It has been reported that controlling the crystallization process in the course of the perovskite growth is one of the important issues for improving the quality of films and achieving highly efficient and stable perovskite solar cells [25,26]. Alternatively, using an appropriate additive can fabricate excellent crystallinity perovskite films with large grain size and full surface coverage. The superior perovskite films with low bulk defect density and reducing carrier recombination are beneficial for the PCE and stability of devices [27–30]. Wang and co-workers [29] found the 2-Pyridylthiourea additive added into the precursor solution can promote the transform of 2-D PbI2 to tetragonal perovskite crystals and improve the quality of the perovskite films. Finally, a CH3NH3PbI3-based device with the highest PCE of 18.2% and better stability were obtained. Besides, other additives, such as 1,8-diiodooctane [31], terephthalic acid [32], lithium iodide [33] and polyethyleneimine [34], have been introduced into the perovskite films to improve the photovoltaic performance. However, the reported PCE and stability by the method of adding additives are not very satisfactory, it remains an apparent challenge to develop a simple and effective additive to control the crystallinity and morphology of perovskite and improve the PCE and stability distinctly. In this work, to control the crystallization during the growth of the perovskite, a new-type scaffold additive, perovskite-like metal formate (PLMF), is introducing into the perovskite light absorption layer. PLMF, which owns a three-dimensional perovskite-like structure, is used to promote the crystallization of perovskite films. It can be found that the morphology of perovskite film with PLMF additive can be obviously improved and the surface becomes more uniform and compact. With fewer grain boundaries, the rate of electron-hole recombination and the defect points exposed to humidity can be significantly reduced, and therefore the improved photoelectricity properties. Eventually, the device with 3 mg ml−1 PLMF has a PCE of 19.17% with less hysteresis under AM 1.5G solar illumination. Moreover, the humidity stability of the devices under 40 ± 5 and 70 ± 5% RH is significantly increased.
2.1. Materials and preparation Formamidine iodide (FAI): FAI was prepared by stoichiometrically reacting formamidine acetate with hydroiodic acid (57 wt% in H2O) and then were stirred in the ice bath for 2 h. The solution was evaporated at 55 °C using rotary evaporation under reduced pressure for 1 h. Then the powder was washed with anhydrous ether and purified by dissolving in ethanol. After filtration and drying at 60 °C, the pure FAI powder was obtained. Synthesis of perovskite-like metal formate (PLMF): The PLMF (Ni (CHOO)3 [NH2(CH3)2]) was synthesized by the mixture of NiCl2*6H2O (1 mmol), DMA*HCl (DMA*HCl = dimethylamine hydrochloride, 1 mmol), NaCHOO*2H2O (3 mmol), H2O (8 mL) and DMF (8 mL), which was heated in a Teflon lined autoclave (20 mL) at 140 °C for 3 days. Some green precipitation was separated out the solution after slow cooling to room temperature. The product was filtered from the solution and washed by ethanol. Preparation of the PLMF/perovskite precursors: The 1.3 M Pb2+ of (FAPbI3)0.85 (MAPbBr3)0.15 precursor solution was prepared from dissolving the corresponding lead iodide (PbI2), lead bromine (PbBr2), formamidinium iodide (FAI) and methylammonium bromine (MABr) powders in DMSO and DMF mixed solvent (DMSO: DMF = 1:4 by volume). The PLMF/perovskite precursor solutions were obtained by mixing the PLMF suspension (20 mg mL−1) and the precursor solution of perovskite with different volume ratios. All the solutions were stirred at 70 °C for 6 h and filtered with 0.45 μm PVDF filters before using. PbI2 was purchased from TCI. Other materials were purchased from Alfa without further purification. 2.2. Device fabrication Fluorine-doped tin oxide (FTO) glass substrates were cleaned sequentially by sonication in detergent, ultrapure water and ethanol for three times. By spray pyrolysis at 460 °C, the TiO2 compact layer was coated on the FTO. The precursor solution for spray pyrolysis is including 0.4 mL bis(acetylacetonate), 0.6 mL titanium diisopropoxide and 7 mL isopropanol. Then, TiO2 mesoporous layer was spin-coated on the substrate with a speed of 4000 r.p.m. for 20 s TiO2 paste for mesoporous layer with 30 nm is diluted via ethanol (ethanol: TiO2 = 5.5: 1). After the spin coating, TiO2 mesoporous layer was sintered at 510 °C for 30 min. Next, the perovskite and PLMF/perovskite precursor solutions were spin-coated with firstly speed 1100 r.p.m. for 15 s, secondly 4500 r.p.m. for 38 s in an air flowing glovebox. A small amount of chlorobenzene (about 120 μL) was fast drop-casted on the perovskite layer during15 s before finishing the spin coating procedure. The substrate was heated at 105 °C for 60 min on a heating platform. The HTL was spin-coated on the substrate with 3000 r.p.m for 20 s, the HTM solution is composed of spiro-OMeTAD (73 mg), 4-tert-butylpyridine (29 μL), Li+ salt (LiTFSI, 17 μL) and cobalt (III) salt (8 μL) in chlorobenzene solvent (1 mL). Finally, Au electrode (about 60 nm) were deposited on top of the HTL via thermal evaporating. 2.3. Characterization EDX and films morphology was measured by a field-emission scanning electron microscope (SEM) with a Schottky Field Emission gun. The X-ray diffraction measurements of the perovskite films were obtained by an X'Pert MPD PRO (PANalytical) and the 2θ range were from 10° to 40°. The absorption spectra were collected by an
230
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
pristine perovskite and PLMF/perovskite films exhibit typical characteristic peaks of (FAPbI3)0.85 (MAPbBr3)0.15 mixed perovskite crystal (β-phase) including three strong diffraction peaks at about 14.2°, 28.4° and 31.9°, which can be validly indexed as (110), (220) and (310) crystal face, respectively [36]. Furthermore, the films with PLMF have the notably increased characteristic peaks. Especially, when the additive amount is 3 mg ml−1, the intensities of peaks at 14.2°, 28.4° and 31.9° are stronger. In addition, the FWHM values of the characteristic (110) peak are shown in Fig. 2 (c). As can be seen, the PLMF-3 perovskite film owns the smallest FWHM value, implying its superior crystallinity with preferred orientation at the (110) direction [37]. The results demonstrate that PLMF additive can enhance the crystallinity of perovskite which will have a beneficial influence on the optoelectronic properties. Presented in Fig. 2 (d) are the UV–vis spectra. As the additive amount increasing from 0 to 3 mg mL−1, the absorption of perovskite shows an obvious enhancement which potentially attributes to the impact of PLMF additive on the uniform surface morphology and preferred orientation crystal structure. However, when the additive amount continues to increase to 5 mg mL−1, there is a certain extent decline of absorption compared to PLMF-3 which can correspond to the decrease of crystallinity [38]. As shown in Fig. 2 (e), steady-state fluorescence (PL) spectra were utilized to study and characterize the light-generated electrons and holes properties of pristine and PLMF perovskite films. To eliminate the influence of electron transport layer and FTO on charge injection, the films were prepared on the glass. Under an excitation wavelength of 473 nm, the fluorescence peaks of the two kinds of films all appear at about 775 nm, which are consistent with the related literature. Besides, in comparison to the pristine film, the PLMF-3 film presents a higher fluorescence peak, suggesting high quality with enhanced crystallization and fewer trap sites [39]. A uniform and compact perovskite film suggests less defects on the surface which is beneficial to the efficient transport of charges in devices [40]. Fig. 3 (a) and (d) show the cross-sectional SEM images of pristine and PLMF-3 devices. Compared with the pristine, PLMF-3 perovskite film is much smoother and owns fewer grain boundaries, which will effectively reduce the centers of carrier recombination and improve the photoelectricity properties [41]. The top view SEM images of pristine and PLMF-3 films at different magnifications are presented in Fig. 3 (b), (e) and (c), (f). The film with 3 mg mL−1 PLMF exhibits enlarged and well-organized grain. By introduced PLMF, the morphology of perovskite film can be remarkably improved and the surface becomes more uniform and compact. As a structure template additive, PLMF is a kind of porous material with regular channel and clear direction of organic ligands and metal ions. During the initial phase of crystallization, the perovskite crystal will arrange in order around organic ligand and metal ions of PLMF template. Hence, the perovskite crystals can grow orderly and the films will become more compact with fewer grain boundaries. Nevertheless, when the content reaches 5 mg mL−1, the excessively high concentration of PLMF trapped in the
Ultraviolet–Vis spectrophotometer (UV–vis, U-3900H, HITACHI, Japan). The steady-state PL spectra measurements were carried out on a spectrofluorometer (photon technology international) and studied by the software Fluorescence. The exciting wavelength of 473 nm was excited by a standard 450 W xenon CW lamp. The transient absorption spectra (TAS) were tested on LKS (Applied photophysics) with repetition rate of 5 Hz and the laser device energy of 150 μJ/cm2. The excitation light and probe light wavelength were 500 nm and 760 nm, respectively. Electrochemical impedance spectroscopy (EIS) was performed at −0.9 V under dark by using an Autolab analyzer (Metrohm, PGSTAT 302N, Switzerland) with a frequency range from 1 Hz to 1 MHz. J–V curves were measured on a solar simulator (Newport, Oriel Class A, 91195 A) with a source meter (Keithley 2420) at 100 mW/cm2 illumination AM 1.5G. By masking a black mask, the active area for each device was controlled at 0.09 cm2. The setup was calibrated with a certified silicon solar cell (Fraunhofer ISE) prior to measurements. The incident photon to current efficiency (IPCE) were recorded on an IPCE measurement system (Newport Corporation, CA) with dual Xenon/ quartz halogen light source and measured in DC mode with no bias light used with the wavelength from 300 to 900 nm. The humidity aging tests were performed in two containers with the relative humidity of 40 ± 5% and 70 ± 5%. The containers remained at ambient temperature under dark. 3. Results and discussion Fig. 1 (a) and (b) show the structure of the perovskite-like metal formate (PLMF), Ni(CHOO)3 [NH2(CH3)2], which has a network threedimensional structure. It has been synthesized by a solvothermal method [35]. In the compound, each asymmetric unit includes a nickel ion, bonding to a formate group (CHOO−), and an unordered dimethylamine (DMA) cation. In addition, the nickel ions are bridged by a three-atom group CHOO−, a three-dimensional tortile perovskite-like structure is forming, and the DMA cations exist in the center of each cage. The scanning electron microscope (SEM) image of the PLMF sample is shown in Fig. S1. In Fig. S2, the energy dispersive X-ray (EDX) spectroscopy is employed to evaluate the chemical compositions of PLMF sample. The schematic diagram, which illustrates the films preparation process from the perovskite precursor solution with PLMF, is shown in Fig. 2 (a). Before one-step deposition method, the precursor solution was firstly sonicated for 15 min and then stirred continuously for 6 h at 70 °C. After spin-coated on the m-TiO2 layer, the films were annealed at 105 °C for 60 min. To study the influence of PLMF additive on the morphology of perovskite films and the performance of solar cells, three different additive amounts 1, 3 and 5 mg mL−1 were selected. For simplicity, they were named as PLMF-1, PLMF-3 and PLMF-5, respectively. In this study, we employed (FAPbI3)0.85 (MAPbBr3)0.15 mixed perovskite as the pristine, which has been reported achieving excellent PCE. The XRD patterns, as shown in Fig. 2 (b), were utilized to reveal the effect of PLMF additive on the crystallinity of perovskite films. All the
Fig. 1. (a) The perovskite-like structure and (b) three-dimensional structure of perovskite-like metal formate (Ni(CHOO)3 [NH2(CH3)2]).
231
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
Fig. 2. (a) Schematic diagram of the fabrication process for perovskite films with PLMF. (b) The XRD patterns of perovskite films with different amounts of PLMF and the magnified XRD patterns of the (110) peak. (c) The dependence of full width at half maximum (FWHM) for the (110) peak. (d) UV–vis spectra and (e) PL spectra of perovskite films with different amounts of PLMF.
Fig. 3. (a, d) Cross-sectional scanning electron microscope (SEM) images of pristine and PLMF-3 devices. (b, c, e, f) Top view SEM images of pristine and PLMF-3 perovskite films.
232
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
Fig. 4. (a) Normalized TA responses of TiO2/perovskite films with 0 and 3 mg mL−1 PLMF. (b) Nyquist plots of PSCs with 0 and 3 mg mL−1 PLMF at V = −0.9 V in the dark. Fig. 5. (a) J–V curves of PSCs with different amounts of PLMF. (b) J–V curves of PSCs with 0 and 3 mg mL−1 PLMF under reverse and forward scan directions. (c) Incident photo to current conversion efficiency (IPCE) spectra of PSCs with 0 and 3 mg mL−1 PLMF. (d) The PCE histogram fitted with a Gaussian distribution of the devices with 0 and 3 mg mL−1 PLMF over 30 measured devices.
recombination occurring in perovskite layer will be slower [43]. After fitted at single exponential decays, the carrier lifetime of PLMF-3 film with 193 ns is longer than the one of pristine (142 ns), which indicates higher quality of PLMF-3 film. Furthermore, electrochemical impedance spectra (EIS) were employed to analyze the charge recombination and charge transfer behavior in the devices, Fig. 4 (b) shows the Nyquist plots of the pristine and PLMF-3 devices measured at voltage of −0.9 V in the dark. According to the Nyquist plots, the low frequency featured resistance is attributed to the recombination resistance (Rrec) and the high frequency should be assigned to the charge transport resistance (Rct) [44]. Clearly, compared with pristine, the PLMF-3 device owns a higher Rrec and a lower Rct, indicating the properties of decreased carrier recombination between electron transporting layer and perovskite layer and enhanced carrier transfer. As testified above, the PLMF additive is advantageous to obtain the perovskite films with more uniform and preferred orientation crystal structure. The current–voltage (J–V) curves of PSCs with different amounts of PLMF additive under AM 1.5G illumination are presented in Fig. 5 (a) and the corresponding parameters are presented in Table 1. The device without PLMF additive shows an optimal PCE of 16.45%, a short-circuit current (Jsc) of 21.59 mA cm−2, an open-circuit voltage
Table 1 Photovoltaic parameters of perovskite solar cells with different amounts of PLMF. Device
Jsc (mA cm−2)
Voc (V)
FF (%)
PCE (%)
Pristine PLMF-1 PLMF-3 PLMF-5
21.59 21.67 22.17 21.75
1.04 1.07 1.08 1.05
73.56 77.45 79.79 74.93
16.45 18.00 19.17 17.15
films will make a negative impact on the photoelectric properties of device and even cause the phase separation between the PLFM nanocrystals and perovskite. The film turns to be coarse and the redundant PLMF appears and distinctly disperses on the surface (Fig S3), which is the reason for resulting from the decreased absorption. To make further study of the quality of the films with and without PLMF, as shown in Fig. 4 (a), transient absorption (TA) spectra was carried out to investigate the electron and hole recombination behavior in the perovskite layer, which can affect the photovoltaic performance of the devices [42]. It is universally acknowledged that a longer carrier lifetime means a longer decay lifetime, and the speed of charge 233
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
Fig. 6. (a) Normalized efficiency variation curves of unsealed perovskite solar cells with different amounts of PLMF (a) under 40 ± 5% RH and (b) 70 ± 5% RH.
Fig. 7. Schematic view of the crystal growth process of pristine and PLMF perovskite thin films.
(Voc) of 1.04 V, and a fill factor (FF) of 73.56%. Fascinatingly, the device with the PLMF presents a significantly increased performance. The PLMF-3 device shows the best performance with an optimal PCE of 19.17%, a Jsc of 22.17 mA cm−2, a Voc of 1.08 V, and FF of 79.79%. The PLMF-3 device has an obvious enhancement of Jsc because of the enhanced absorption which is ascribed to its improvement of the uniform and compact perovskite absorption layer. The Voc increased from 1.04 V to 1.08 V due to the reduced defect-induced recombination and improved charge transport in the PLMF-3 device [38]. However, when the content reaches 5 mg mL−1, the excessively high concentration of PLMF trapped in the films will make a negative impact on the performance of device. The PLMF-5 device displays a declining PCE of 17.15%. Besides, the common hysteresis phenomenon connected with the changes of the defect state in the interface and the ferroelectric effect which can influence the photovoltaic performances of PSCs. The J–V curves and the corresponding parameters of the devices based on pristine and PLMF-3 under different scan directions are shown in Fig. 5 (b) and Table S1, respectively. By adding the PLMF, the hysteresis effect of the J-V curves becomes more negligible due to the reduction of spontaneous radiative recombination among trap states [45]. The IPCE spectra of pristine and PLMF-3 PSCs are summarized in Fig. 5 (c). The PLMF-3 PSC shows higher IPCE than pristine between 350 and 750 nm. The integrated currents of pristine and PLMF-3 are 20.71 and 21.61 mA cm−2, respectively, which are in good agreement with the corresponding values in Fig. 5 (a). To evaluate the reproducibility of photovoltaic performance, Fig. 5 (d) shows the PCE histograms of pristine and PLMF-3 PSCs fitted with a Gaussian distribution. Each histogram consists of 30 measured devices. It displays that the PLMF-3 devices exhibit an impressive average PCE about 17.93%, compared with 15.61% for the pristine devices, demonstrating that PLMF-3 devices have an evident improvement PCE and outstanding reproducibility. At present, stability is a key challenge for PSCs especially the ability of resistance to humidity [46,47]. Therefore, the humidity stability of
unsealed devices with different amounts of PLMF was investigated. All the aging tests were carried out in dark. Fig. 6 (a) shows the normalized efficiency variation curves of the unsealed devices tested under 40 ± 5% RH at room temperature. At the first 250 h, all the devices keep good stability. Whereas, the pristine device begins to degrade and the PCE decreases by 40% after about 1000 h. While, for the device with PLMF, the PCE shows a slower decrease and retains about 80% of the original efficiency after aging for about 1000 h. In addition, when tested under 70 ± 5% RH at room temperature (Fig. 6 b), the device with PLMF presents more significantly stability than pristine one by attributing to its high-crystallinity and fewer defects. After aging for about 1000 h, the PLMF-3 device still retains about 60% of the original efficiency, while, for the pristine device, the value of PCE decreases by 80% under the same conditions. The enhanced performance and stability of PSCs with PLMF may be attributed to the structural property of the scaffold additive. Fig. 7 shows the schematic view of the crystal growth process of pristine and PLMF perovskite thin films. PLMF nanocrystal material, with a periodicity three-dimensional perovskite-like structure, can effectively control the crystallization process in the course of the perovskite growth because of its organized micropores. For nucleation, because of the existence of ordered template with directional arrangement of organic ligand and metal ions in the precursor solution, the dispersal of Pb+ becomes more ordered, leading to evenly distributive nucleation centers. Then, for growth, perovskite crystallites will grow in their preferred direction during the initial phase of crystallization around the organic ligand and metal ions [48,49]. Because of the fewer defects on the surface and at the grain boundaries, the defect points exposed to humidity can be reduced obviously, which can lead to the improved stability of devices under moisture. The existence of steady PLMF, which acts as a regular scaffold, can further improve the stability. As a result, the devices based on the perovskite with PLMF absorber layer present improved humidity stability and photoelectricity properties.
234
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
4. Conclusions
[16] J. Jiang, Z. Jin, J. Lei, Q. Wang, X. Zhang, J. Zhang, F. Gao, S. Liu, ITIC surface modification to achieve synergistic electron transport layer enhancement for planar-type perovskite solar cells with efficiency exceeding 20%, J. Mater. Chem. 5 (2017) 9514–9522. [17] C. Besleaga, L.E. Abramiuc, V. Stancu, A.G. Tomulescu, M. Sima, L. Trinca, N. Plugaru, L. Pintilie, G.A. Nemnes, M. Iliescu, H.G. Svavarsson, A. Manolescu, I. Pintilie, Iodine migration and degradation of perovskite solar cells enhanced by metallic electrodes, J. Phys. Chem. Lett. 7 (2016) 5168–5175. [18] W. Nie, H. Tsai, R. Asadpour, J.-C. Blancon, A.J. Neukirch, G. Gupta, J.J. Crochet, M. Chhowalla, S. Tretiak, M.A. Alam, H.-L. Wang, A.D. Mohite, High-efficiency solution-processed perovskite solar cells with millimeter-scale grains, Science 347 (2015) 522–525. [19] G.A. Al-Dainy, S.E. Bourdo, V. Saini, B.C. Berry, A.S. Biris, Hybrid perovskite photovoltaic devices: properties, architecture and fabrication methods, Energy Technol. 5 (2017) 373–401. [20] J. Ye, H. Zheng, L. Zhu, X. Zhang, L. Jiang, W. Chen, G. Liu, X. Pan, S. Dai, Hightemperature shaping perovskite film crystallization for solar cell fast preparation, Sol. Energy Mater. Sol. Cell. 160 (2017) 60–66. [21] D. Bi, W. Tress, M.I. Dar, P. Gao, J. Luo, C. Renevier, K. Schenk, A. Abate, F. Giordano, J.-P.C. Baena, J.-D. Decoppet, S.M. Zakeeruddin, M.K. Nazeeruddin, M. Grätzel, A. Hagfeldt, Efficient luminescent solar cells based on tailored mixedcation perovskites, Sci. Adv 2 (2016) e1501170. [22] H. Wang, J. Lei, F. Gao, Z. Yang, D. Yang, J. Jiang, J. Li, X. Hu, X. Ren, B. Liu, J. Liu, H. Lei, Z. Liu, S. Liu, Magnetic field-assisted perovskite film preparation for enhanced performance of solar cells, ACS Appl. Mater. Interfaces 9 (2017) 21756–21762. [23] W.-T. Wang, S.K. Das, Y. Tai, Fully ambient processed perovskite film for perovskite solar cells: effect of solvent polarity on lead iodide, ACS Appl. Mater. Interfaces 9 (2017) 10743–10751. [24] N.J. Jeon, J.H. Noh, W.S. Yang, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Compositional engineering of perovskite materials for high-performance solar cells, Nature 517 (2015) 476–480. [25] R. Linblad, D. Bi, B.-W. Park, J. Oscarsson, M. Gorgoi, H. Siegbahn, M. Odelius, E.M.J. Johansson, H. Rensmo, The electronic structure of TiO2/CH3NH3PbI3 perovskite solar cell interfaces, J. Phys. Chem. Lett. 5 (2014) 648–653. [26] J.-H. Im, I.-H. Jang, N. Pellet, M. Grätzel, N.-G. Park, Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells, Nat. Nanotechnol. 9 (2014) 927–932. [27] T.-H. Chang, C.-W. Kung, H.-W. Chen, T.-Y. Huang, S.-Y. Kao, H.-C. Lu, M.-H. Lee, K.M. Boopathi, C.-W. Chu, K.-C. Ho, Planar heterojunction perovskite solar cells incorporating metal–organic framework nanocrystals, Adv. Mater. 27 (2015) 7229–7235. [28] Y. Wu, F. Xie, H. Chen, X. Yang, H. Su, M. Cai, Z. Zhou, T. Noda, L. Han, Thermally stable MAPbI3 perovskite solar cells with efficiency of 19.19% and area over 1 cm2 achieved by additive engineering, Adv. Mater. 29 (2017) 1701073. [29] M. Sun, F. Zhang, H. Liu, X. Li, Y. Xiao, S. Wang, Tuning the crystal growth of perovskite thin-films by adding the 2-pyridylthiourea additive for highly efficient and stable solar cells prepared in ambient air, J. Mater. Chem. 5 (2017) 13448–13456. [30] F. Han, J. Luo, H.A. Malik, B. Zhao, Z. Wan, C. Jia, A functional sulfonic additive for high efficiency and low hysteresis perovskite solar cells, J. Power Sources 359 (2017) 577–584. [31] P.-W. Liang, C.-Y. Liao, C.-C. Chueh, F. Zuo, S.T. Williams, X.-K. Xin, J. Lin, A.K.Y. Jen, Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells, Adv. Mater. 26 (2014) 3748–3754. [32] X. Hou, S. Huang, W. Ou-Yang, L. Pan, Z. Sun, X. Chen, Constructing efficient and stable perovskite solar cells via interconnecting perovskite grains, ACS Appl. Mater. Interfaces 9 (2017) 35200–35208. [33] H. Luo, J. Wu, Q. Liu, J. Huang, Y. Tu, J. Lin, M. Huang, Addition of lithium iodide into precursor solution for enhancing the photovoltaic performance of perovskite solar cells, Energy Technol. 5 (2017) 1–7. [34] Q. Dong, Z. Wang, K. Zhang, H. Yu, P. Huang, X. Liu, Y. Zhou, N. Chen, B. Song, Easily accessible polymer additives for tuning the crystal-growth of perovskite thinfilms for highly efficient solar cells, Nanoscale 8 (2016) 5552–5558. [35] X.-Y. Wang, L. Gan, S.-W. Zhang, S. Gao, Perovskite-like metal formates with weak ferromagnetism and as precursors to amorphous materials, Inorg. Chem. 43 (2004) 4615–4625. [36] H. Zheng, G. Liu, L. Zhu, J. Ye, X. Zhang, A. Alsaedi, T. Hayat, X. Pan, S. Dai, Enhanced performance and stability of perovskite solar cells using NH4I interfacial modifier, ACS Appl. Mater. Interfaces 9 (2017) 41006–41013. [37] X. Li, D. Bi, C. Yi, J.-D. Décoppet, J. Luo, S.M. Zakeeruddin, A. Hagfeldt, M. Grätzel, A vacuum flash–assisted solution process for high-efficiency large-area perovskite solar cells, Science 353 (2016) 58–62. [38] G. Xing, N. Mathews, S.S. Lim, N. Yantara, X. Liu, D. Sabba, M. Grätzel, S. Mhaisalkar, T.C. Sum, Low-temperature solution-processed wavelength-tunable perovskites for lasing, Nat. Mater. 13 (2014) 476–480. [39] M. Yang, T. Zhang, P. Schulz, Z. Li, G. Li, D.H. Kim, N. Guo, J.J. Berry, K. Zhu, Y. Zhao, Facile fabrication of large-grain CH3NH3PbI3-xBrx films for high-efficiency solar cells via CH3NH3Br-selective ostwald ripening, Nat. Commun. 7 (2016) 12305. [40] J.S. Yun, A. Ho-Baillie, S. Huang, S.H. Woo, Y. Heo, J. Seidel, F. Huang, Y.B. Cheng, M.A. Green, Benefit of grain boundaries in organic–inorganic halide planar perovskite solar cells, J. Phys. Chem. Lett. 6 (2015) 875–880. [41] R. Long, J. Liu, O.V. Prezhdo, Unravelling the effects of grain boundary and chemical doping on electron-hole recombination in CH3NH3PbI3 perovskite by timedomain atomistic simulation, J. Am. Chem. Soc. 138 (2016) 3884–3890. [42] Q. Shen, Y. Ogomi, J. Chang, S. Tsukamoto, K. Kukihara, T. Oshima, N. Osada,
In summary, a significative method is adopted to enhance the crystallinity and morphology of perovskite films via employing a perovskite-like metal formate (PLMF) material, Ni(CHOO)3 [NH2(CH3)2], as a scaffold additive. It is found that PLMF, acting as an ordered scaffold, is beneficial for the crystallinity of perovskite and can promote to form a uniform and compact absorber layer with fewer grain boundaries. As a result, photoelectricity properties are improved due to the improvement of quality of the perovskite films and the decreased electron-hole recombination. Compared to the pristine device (a PCE of 16.45%), the device with 3 mg ml−1 PLMF additive exhibits a PCE of 19.17% with less hysteresis under AM 1.5G solar illumination. Moreover, the device with 3 mg ml−1 PLMF shows excellent stability compared to pristine device under 40 ± 5 and 70 ± 5% RH after about 1000 h. Thus, the PLMF additive provides an easy strategy for improving the performance and stability of PSCs. Acknowledgements This work was financially supported by the National High Technology Research and Development Program of China under Grant No.2015AA050602, STS project of Chinese Academy of Sciences (KFJSW-STS-152). Appendix A. Supplementary data Supplementary data related to this article can be found at https:// doi.org/10.1016/j.jpowsour.2018.07.014. References [1] M. Liu, M.B. Johnston, H.J. Snaith, Efficient planar heterojunction perovskite solar cells by vapour deposition, Nature 501 (2013) 395–398. [2] H.-S. Kim, C.-R. Lee, J.-H. Im, K.-B. Lee, T. Moehl, A. Marchioro, S.-J. Moon, R. Humphry-Baker, J.-H. Yum, J.E. Moser, M. Grätzel, N.-G. Park, Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%, Sci. Rep. 2 (2012) 591. [3] L. Zhu, Z. Shao, J. Ye, X. Zhang, X. Pan, S. Dai, Mesoporous BaSnO3 layer based perovskite solar cells, Chem. Commun. 52 (2016) 970–973. [4] Q. Chen, H. Zhou, Z. Hong, S. Luo, H.-S. Duan, H.-H. Wang, Y. Liu, G. Li, Y. Yang, Planar heterojunction perovskite solar cells via vapor assisted solution process, J. Am. Chem. Soc. 136 (2014) 622–625. [5] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskites as visible-light sensitizers for photovoltaic cells, J. Am. Chem. Soc. 131 (2009) 6050–6051. [6] W.S. Yang, B.-W. Park, E.H. Jung, N.J. Jeon, Y.C. Kim, D.U. Lee, S.S. Shin, J. Seo, E.K. Kim, J.H. Noh, S.I. Seok, Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells, Science 356 (2017) 1376–1379. [7] J. You, L. Meng, T.-B. Song, T.-F. Guo, Y. Yang, W.-H. Chang, Z. Hong, H. Chen, H. Zhou, Q. Chen, Y. Liu, N.D. Marco, Y. Yang, Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers, Nat. Nanotechnol. 11 (2016) 75–81. [8] J. Liu, J. Lin, Q. Xue, Q. Ye, X. He, L. Ouyang, D. Zhuang, C. Liao, H.-L. Yip, J. Mei, W.-M. Lau, J. Power Sources 301 (2016) 242–250. [9] Y. Wu, X. Yang, W. Chen, Y. Yue, M. Cai, F. Xie, E. Bi, A. Islam, L. Han, Perovskite solar cells with 18.21% efficiency and area over 1 cm2 fabricated by heterojunction engineering, Nat. Energy 1 (2016) 16148. [10] J.H. Kim, S.T. Williams, N. Cho, C.-C. Chueh, A.K.-Y. Jen, Enhanced environmental stability of planar heterojunction perovskite solar cells based on blade-coating, Adv. Energy Mater 5 (2015) 1401229. [11] H. Back, G. Kim, J. Kim, J. Kong, T.K. Kim, H. Kang, H. Kim, J. Lee, S. Lee, K. Lee, Achieving long-term stable perovskite solar cells via ion neutralization, Energy Environ. Sci. 9 (2016) 1258–1263. [12] Y. Rong, L. Liu, A. Mei, X. Li, H. Han, Beyond efficiency: the challenge of stability in mesoscopic perovskite solar cells, Adv. Energy Mater 5 (2015) 1501066. [13] B. Conings, J. Drijkoningen, N. Gauquelin, A. Babayigit, J. D'Haen, L. D'Olieslaeger, A. Ethirajan, J. Verbeeck, J. Manca, E. Mosconi, F.D. Angelis, H.-G. Boyen, Intrinsic thermal instability of methylammonium lead trihalide perovskite, Adv. Energy Mater 5 (2015) 1–8. [14] F. Xie, C.-C. Chen, Y. Wu, X. Li, M. Cai, X. Liu, X. Yang, L. Han, Vertical recrystallization for highly efficient and stable formamidinium based inverted structure perovskite solar cells, Energy Environ. Sci. 10 (2017) 1942–1949. [15] Q. Jiang, L. Zhang, H. Wang, X. Yang, J. Meng, H. Liu, Z. Yin, J. Wu, X. Zhang, J. You, Enhanced electron extraction using SnO2 for high-efficiency planar-structure HC(NH2)2PbI3-based perovskite solar cells, Nat. Energy 2 (2016) 16177.
235
Journal of Power Sources 402 (2018) 229–236
G. Liu et al.
K. Yoshino, K. Katayama, T. Toyoda, S. Hayase, Charge transfer and recombination at the metal oxide/CH3NH3PbClI2/spiro-OMeTAD interfaces: uncovering the detailed mechanism behind high efficiency solar cells, Phys. Chem. Chem. Phys. 16 (2014) 19984–19992. [43] Q. Shen, Y. Ogomi, J. Chang, T. Toyoda, K. Fujiwara, K. Yoshino, K. Sato, K. Yamazaki, M. Akimoto, Y. Kuga, K. Katayama, S. Hayase, Optical absorption, charge separation and recombination dynamics in Sn/Pb cocktail perovskite solar cells and their relationships to photovoltaic performances, J. Mater. Chem. 3 (2015) 9308–9316. [44] H. Zhang, J. Mao, H. He, D. Zhang, H.L. Zhu, F. Xie, K.S. Wong, M. Grätzel, W.H. Choy, A smooth CH3NH3PbI3 film via a new approach for forming the PbI2 nanostructure together with strategically high CH3NH3I concentration for high efficient planar-heterojunction solar cells, Adv. Energy Mater 5 (2015) 1501354. [45] H. Cho, S.-H. Jeong, M.-H. Park, Y.-H. Kim, C. Wolf, C.-L. Lee, J.H. Heo, A. Sadhanala, N. Myoung, S. Yoo, S.H. Im, R.H. Friend, T.-W. Lee, Overcoming the
[46]
[47]
[48]
[49]
236
electroluminescence efficiency limitations of perovskite light-emitting diodes, Science 350 (2015) 1222–1225. T.A. Berhe, W.-N. Su, C.-H. Chen, C.-J. Pan, J.-H. Cheng, H.-M. Chen, M.-C. Tsai, L.Y. Chen, A.A. Dubale, B.-J. Hwang, Organometal halide perovskite solar cells: degradation and stability, Energy Environ. Sci. 9 (2016) 323–356. C. Liu, W. Ding, X. Zhou, J. Gao, C. Cheng, X. Zhao, B. Xu, Efficient and stable perovskite solar cells prepared in ambient air based on surface-modified perovskite layer, J. Phys. Chem. C 121 (2017) 6546–6553. F. Zhang, W. Shi, J. Luo, N. Pellet, C. Yi, X. Li, X. Zhao, T.J.S. Dennis, Xianggao Li, S. Wang, Y. Xiao, S.M. Zakeeruddin, D. Bi, M. Grätzel, Isomer-pure bis-PCBM-assisted crystal engineering of perovskite solar cells showing excellent efficiency and stability, Adv. Mater. 29 (2017) 1606806. D. Bi, C. Yi, J. Luo, J.-D. Décoppet, F. Zhang, S.M. Zakeeruddin, X. Li, A. Hagfeldt, M. Grätzel, Polymer-templated nucleation and crystal growth of perovskite films for solar cells with efficiency greater than 21%, Nat. Energy 1 (2016) 16142.