Fully doctor-bladed planar heterojunction perovskite solar cells under ambient condition

Organic Electronics 58 (2018) 153–158

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Fully doctor-bladed planar heterojunction perovskite solar cells under ambient condition

T

Yongyi Penga, Yudiao Chenga, Chunhua Wanga, Chujun Zhanga, Huayan Xiaa, Keqing Huanga, Sichao Tonga, Xiaotao Haob, Junliang Yanga,∗ a b

Hunan Key Laboratory for Super-microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha, 410083, Hunan, China School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Perovskite solar cell Planar heterojunction Doctor blading Fully printing

It is highly desirable to develop large-scale, low-cost fabrication techniques to process perovskite solar cells (PSCs) under ambient condition for accelerating their potential commercialization. Herein, efficient planar heterojunction (PHJ) PSCs with a simple structure of ITO/NiOx/CH3NH3PbI3 (MAPbI3)/PC61BM/Ag is fabricated via fully doctor blading under ambient condition with the humidity of ∼40%, in which the NiOx layer, MAPbI3 layer, and PC61BM layer are deposited via doctor blading subsequently. The high-quality perovskite CH3NH3PbI3 films are fabricated by one-step doctor-bladed deposition using modified precursors with the co-solvents of dimethylsulphoxide (DMSO) and dimethylformamide (DMF) along with the suitably excess MAI. The well control on solvent recipe retards the crystallization time, leading to the formation of homogeneous and uniform perovskite film with large-size domains. Furthermore, the excess MAI in the modified precursor ink is helpful to form large-size perovskite grains and high crystallinity. With the optimization, the fully doctor-bladed PHJ-PSCs under ambient condition with the power conversion efficiency (PCE) up to 10.92% is achieved, yielding an average PCE of 10.16%. The research suggests that solvent engineering is a good route for fabricating highquality perovskite films via one-step, doctor-blading deposition, and it is feasible to achieve efficient PHJ-PSCs through fully doctor-balding technique under ambient condition.

1. Introduction Methylammonium lead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) have captured researchers' great interest in optoelectronic field due to their excellent optoelectronic properties including wide absorption coefficient, long carrier diffusion length and facile solution-processed ability, resulting in high-efficiency perovskite solar cells [1–6]. Up to now, the power conversion efficiency (PCE) is up to 22.7% [7], and it is comparable to the commercialized polysilicon solar cells, inspiring their potential to be an excellent candidates for the third-generation photovoltaic solar cells. It is very important to develop low-cost, large-scale fabrication process under environment conditions to accelerate their potential commercial production [8]. All kinds of potential large-scale techniques have been developed to fabricate high-quality perovskite layer in laboratory exploration in recent years, such as doctor blading, spray coating, screen printing, inkjet printing and roll-to-roll printing [9–13]. Doctor blading is one of the simple large-scale and cost-effective film deposition techniques, which has been widely used to fabricate solution-processed PSCs with large-

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area uniformity and high crystallinity of perovskite films [14]. However, fully doctor-bladed PSCs, including electron transport layer (ETL), active perovskite layer and hole transport layer (HTL), under ambient condition still remain much challenge because the deposition of functional films would be greatly influenced by device architectures, interface issues and ambient condition factors [15]. It is well believed that the morphology and crystallinity of perovskite films are responsible for the photovoltaic performance of PSCs, which are strongly relied on the formation dynamics of perovskite films and the solvent evaporation process, as well as the interaction between the precursor solution and the substrate surface [16–19]. Solvent engineering and additives are feasible strategies to control the crystallization dynamics for forming uniform and high-quality perovskite films [20–22]. In our previous work, doctor-blading technique was used to fabricate high-quality CH3NH3PbI3 (MAPbI3) perovskite films under ambient condition, and yielded the PCEs of over 11% for PSCs with a simple structure ITO/PEDOT:PSS/MAPbI3/PC61BM/Ag [23]. Herein, planar heterojunction (PHJ) PSCs with a structure of ITO/NiOx/ MAPbI3/PC61BM/Ag were fabricated by fully doctor blading, including

Corresponding author. E-mail address: [email protected] (J. Yang).

https://doi.org/10.1016/j.orgel.2018.04.020 Received 11 February 2018; Received in revised form 27 March 2018; Accepted 10 April 2018 Available online 12 April 2018 1566-1199/ © 2018 Elsevier B.V. All rights reserved.

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films. Crystallographic property of perovskite films was characterized by X-ray diffraction (XRD, Rigaku D, Max 2500, Japan). Typical current density-voltage (J-V) curve of perovskite devices was achieved by employing digital Source Meter (Keithley, model 2420, USA) with a solar simulator (Newport 91160s, AM 1.5G, USA) and the light intensity was 100 mW/cm2 calibrated by a standard silicon solar cell. In the process of testing, the scan speed was located at 300 mV/s and the scan direction was from +1.5 V to −1.5 V if without specified note.

HTL NiOx, active perovskite layer MAPbI3 and ETL PC61BM, under ambient condition with the humidity of ∼40%. The results indicate that the precursor ink containing co-solvents of dimethylsulphoxide (DMSO) and dimethylformamide (DMF) are beneficial to produce highquality perovskite films. The proper DMSO manipulated in the DMFbased precursor ink not only retards the crystallization time of the precursor ink, it also enhances the domain sizes of perovskite film with better homogeneity and uniformity. Moreover, the excess MAI additive embedded within the precursor film can further increase grain size and film crystallinity, resulting in smoother and denser perovskite film. Based on the optimization of doctor-bladed NiOx, MAPbI3 and PC61BM layers, the PHJ-PSC devices with a PCE up to 10.92% and an average PCE of 10.16% are achieved. The study provides a large-scale, fully printable method to produce efficient PHJ-PSCs under ambient conditions, which may accelerate their practical application.

3. Results and discussion PHJ-PSCs with a simple architecture of ITO/NiOx/MAPbI3/ PC61BM/Ag were fabricated by fully doctor blading process except for the electrodes under the environment condition with the humidity of ∼40%. The first step is to doctor blade high-quality HTL NiOx on ITOcoated glass substrate. There are three important aspects for achieving compact and uniform NiOx layer via doctor blading. The Ni(AC)2·4H2O colloidal solution is unfavorable to be doctor bladed onto ITO glass directly under ambient condition. Thus, the colloidal solution is heated to 90 °C for increasing its solubility in the mixture of 2-methoxyethanol and ethanolamine to avoid the precipitating at room temperature. Meanwhile, the ITO-coated glass is treated via suitable UV ozone for improving the wettability of doctor-bladed hot colloidal solution. Furthermore, the temperature of ITO-coated glass substrate is held at 120 °C during doctor blading process for promoting solvent volatilization and forming homogenous nickel acetate thin film. At last, a compact and uniform NiOx layer is formed after thermal annealing the doctor-bladed film at 300 °C for 1 h to remove the organic group (CH3COO-). Fig. S1 in the supporting information shows the AFM morphology images of NiOx thin films deposited using doctor blading and spin coating, respectively. Both of NiOx layers fabricated by spincoating and doctor-blading are homogeneous and uniform after the thermal annealing. The root mean square (RMS) values are about 1.05 nm and 0.98 nm for doctor-bladed and spin-coated NiOx thin films, respectively, with the scan area of 10 × 10 μm2, implying that the doctor-bladed NiOx thin film is comparable to the spin-coated one and should be suitable to subsequent deposition of perovskite layer for PSCs. Then, one-step, doctor blading process is used to fabricate highquality perovskite MAPbI3 layer onto the NiOx layer, of which the perovskite precursor is composed of PbI2 and MAI in DMF at a molar ratio of 1:1, and the optical images of doctor-bladed MAPbI3 films at the different substrate temperatures are shown in Fig. S2. The statistical size distribution of perovskite crystal domains grown at the substrate temperature of 110 °C, 130 °C and 150 °C, respectively, is exhibited in Fig. S3. As the substrate temperature increases, the average size raises accordingly. But the higher temperature at 150 °C would accelerate the degradation of perovskite MAPbI3 film, and it definitely influences the performance of PSCs. Through controlling the in-situ doctor blading temperature at the optimized temperature of 130 °C, the homogeneous and crystalline perovskite films could form in just a few seconds without post thermal annealing (Fig. 1a). However, there is large gaps between the neighbouring domains (Fig. 1b), which would influence the device performance. It is well known that the surface morphology of perovskite film can be modified by forming DMSO-PbI2 complexes, which retards the rapid reaction between the PbI2 and MAI [24]. It may allow a more uniform and better crystalline perovskite film to be formed upon doctor blading. Thus, the DMSO additives with the different proportions are added into the original precursor, and the film morphology is shown in Fig. S4. As mentioned above, if using only DMF solvent, the domain size in MAPbI3 film is greatly different with the substrate temperature increasing from 110 °C to 150 °C, resulting in the domain size gradually enhances from about 5.8 μm to 11.6 μm (Fig. S3), and the optimized perovskite film is formed substrate temperature of 130 °C with an average domain size of about 7.1 μm. The addition of co-solvent DMSO can greatly further

2. Experimental section 2.1. Material and solution The 141 mg MAI (99%, Jingge, Wuhan) and 409 mg lead (II) iodide (PbI2, 99.99%, Polymer, Xian) were dissolved in 1 ml of DMF (J&K Seal) for making 550 mg/ml original precursor ink with stirring at 60 °C over night. The nickel (II) acetate tetrahydrate (Ni(AC)2·4H2O, 99%, Alfa Aesar) solution including 125 mg Ni(AC)2·4H2O crystalline in 1 ml of 2- methoxyethanol (99.3%, Alfa Aesar) and 60 μl of ethanolamine (99%, Alfa Aesar) liquid was stirred at 90 °C for 3 h before doctor blading. The PC61BM (Polymer, Xi'an) dissolved in anhydrous chlorobenzene (CB, J&K Seal) with 8 mg/ml was stirred at 60 °C over night. 2.2. Device fabrication The indium tin oxide (ITO) glass (∼5 Ω sq−1, 1.5 × 1.5 cm2)was ultrasonically cleaned in detergent, deionized water, acetone, and isopropyl alcohol for 20 min, respectively. The clean glass was dried by N2 and then dealt with ultraviolet-ozone for 20 min. In order to prepare high-quality uniform perovskite films, the perovskite precursor was optimized with two steps. Firstly, the DMF-based precursor solution was modified by adding different volume ratio (v/v) of DMSO to DMF in the precursor ink (5%, 10% and 20%, respectively). Secondly, the modified precursor ink (DMSO/DMF, 10%, v/v) with the different molar ratio of excess MAI additive (3.2%, 6.3% and 9.4%, respectively) were used. The typical formula for 550 mg/ml precursor with 6.3% excess MAI is 151 mg MAI, 409 mg PbI2, 100 μl of DMSO in 1 ml of DMF. In order to form the compact NiOx HTL, 30 μl of Ni(AC)2·4H2O solution was doctor-bladed on the ITO glass at humidity of ∼40% and the gap between blade and substrate surface was fixed at 80 μm and then annealed at 300 °C for 1 h. Afterwards, 30 μl perovskite precursor ink was deposited on the NiOx layer with a blade speed of 15 cm/s to form high-quality perovskite film at the substrate temperature of 130 °C. Furthermore, the PC61BM layer was fabricated via doctor blading by dropping 20 μl solution on the perovskite layer at room temperature. Finally, an Ag electrode of ∼80 nm was evaporated at a constant evaporation rate of 0.5 Å/s under a vacuum of 8 × 10−4 Pa. The relative humidity of ∼40% was controlled by an air conditioner and two dehumidifiers together in a closed room. The effective area of fully doctor blading devices is 0.09 cm2 defined by a mask. 2.3. Characterization The surface morphology of NiOx layer was characterized by atomic force microscopy (Agilent Technologies 5500 AFM/SPM System, USA) with tapping-mode. Scanning electron microscopy (SEM, FEI Helios Nanolab 600i, USA) was employed to characterized the morphology of perovskite films. Ultraviolet–visible spectrophotometer (UV–vis, Puxi, T9, China) was used to obtain the absorption spectra of perovskite 154

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Fig. 1. SEM morphology images of MAIPbI3 films fabricated at 130 °C via doctor blading on the NiOx layer with typical formulas of precursor ink in (a–b) DMF, (c–d) DMF + DMSO and (e–f) DMF + DMSO + MAI, respectively. They are 550 mg/ml precursor in DMF solvent in (a–b), mixed solvent DMSO/DMF (10:90, v/v) in (c–d) and mixed solvent DMSO/DMF (10:90, v/v) with 6.3% excess MAI in (e–f), respectively.

crystalline grains are obtained, indicating that 6.3% excess MAI in DMF + DMSO further promotes the growth of perovskite along preferred orientation and improves its surface morphology with better homogeneity and uniformity. In addition, the excess MAI layer can also form at the grain boundaries and suppresses non-radiative recombination and improves hole and electron extraction at the grain boundaries by forming ionic-conducting pathways [27]. Therefore, more photogenerated carriers can be effectively extracted by the interface layer. If further increasing the more excess MAI, e. g, 9.4% excess MAI, the perovskite film becomes worse. It is composed of smaller domain and larger boundaries, as show in Fig. S6e-f. Thereby, the high-quality perovskite films with large-size grains and better film crystallinity are fabricated by in-situ thermal-treatment doctor blading using 550 mg/ml precursor with 6.3% excess MAI in mixed solvent DMSO/DMF (10:90, v/v). As compared to the optimized CH3NH3PbI3 films via doctor blading, the optical morphology of spin-coating ones fabricated under the same conditions is shown in Fig. S9. It is obvious that spin-coated CH3NH3PbI3 films are consisted of widespread voids and textile due to the slow nucleation and growth, which are not suitable for further fabricating PHJ-PSC devices. The light absorption of these perovskite films via doctor blading using the different precursor inks, i.e., DMF, DMF + DMSO and DMF + DMSO + MAI is characterized as well. As shown in Fig. 2a, with 10% DMSO and 6.3% excess MAI added, respectively, the absorption of perovskite films gradually increases. The raised absorption is ascribed to the enhancement of the perovskite grains and domain size and the quality improvement of perovskite film (Fig. 1c–d). Meanwhile, the addition of 6.3% excess MAI to the optimized precursor ink can further enhance the absorption intensity. These results are consistent to the morphology evolution. XRD is used to characterize the crystal structure of doctor-bladed perovskite films using various precursors, as shown in Fig. 2b. It can be seen that all the perovskite films show strong diffraction peaks at 14.15°, 20.17°and 40.75°, representing the (110), (112) and (224) crystal planes of perovskite films, respectively, and indicating the typical tetragonal structure [20]. But the impurity PbI2 peak can also be observed in perovskite film from the precursor with only DMF, which can be attributed to the incomplete evolution in perovskite film during the nucleation and crystallization [28]. It is obvious that the diffraction peaks are strengthened after adding 10% DMSO in the original precursor ink, and the diffraction peak from PbI2 disappears, indicating that the PbI2 can be fully transformed into perovskite. Furthermore,

enlarges the domain size at the optimized temperature of 130 °C, and the statistical size distribution of perovskite crystal domains resulted from the different DMSO proportions is shown in Fig. S5. With the volume ratio of DMSO increasing from 5% (Fig. S4a-b) to 10% (Fig. S4c-d), the domain size dramatically enlarges from about 20.0 μm to 45.2 μm (Fig. S5). If further increasing DMSO up to 20%, the perovskite may generate discernible defects such as pinhole or voids (Fig. S4e-f) due to the effect of residual co-solvent on the film morphology during solution convection or escape of a small amount of methylamine gas from perovskite microstructure upon in-situ thermal-treatment doctor blading. Meanwhile, the average domain size dramatically decreases to about 17.4 μm (Fig. S5). The incorporation of DMSO enables to facilitate strong interaction of organic-inorganic hybrid cations and inorganic anion for improving the microstructure [20]. Thus, the optimized 10% DMSO manipulated in DMF solvent not only retards the crystallized time of perovskite grain, it also raises the domain size, leading to form homogeneous and uniform perovskite film (Fig. 1c–d). It possible to inhabit the photonic carrier recombination via improving the quality of doctor-bladed MAPbI3 film [25]. Thereby, it obviously suggests that manipulating 10% DMSO in DMF is able to assure the more compact and uniform perovskite film. Although the film is homogenous at a small area with adding DMSO, the gaps between the domains are still very large, which is about several micrometers and comparable to the ones without the DMSO, as shown in Fig. 1b and d. It will result in the carrier recombination and greatly influence the device performance [26]. It is reported that the excess MAI plays a significant role upon air-annealing and can greatly promote the grain growth along with preferred orientation [25]. Herein, the excess MAI is embedded within the precursor film because it might be beneficial for in-situ thermal annealing doctor blading, improving the perovskite morphology and film crystallinity. As exhibited in Fig. S6, the optical morphology of perovskite films grown on the NiOx layer fabricated by doctor blading via using 550 mg/ml precursor in mixed solvent DMSO/DMF (10:90, v/v) with the different molar ratio of excess MAI about 3.2%, 6.3%, 9.4%, respectively. With the molar ratio of excess MAI increasing from 3.2% to 6.3%, the domain size has significantly increased (Fig. S7). The average domain size boosts from about 18.9 μm (Fig. S6a-b) to 53.4 μm (Fig. S6 c-d). The suitable MAI additive not only enhances grain size of perovskite, it also improves film crystallinity (Fig. 1e), in which the average grain size is up to about 456 nm (Fig. S8) from about 262 nm (Fig. 1a). Moreover, the smaller domain boundaries and larger polygon domains with large 155

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Fig. 2. (A) UV–vis absorption spectra and (b) XRD spectra of doctor-bladed perovskite films using the precursors with DMF, DMF + DMSO and DMF + DMSO + MAI, respectively.

45.69%, accordingly) that stems from the larger grain size and a fewer grain boundary in the perovskite film thus reduce the charge recombination [31]. Furthermore, more uniform perovskite films by using 6.3% excess MAI additive in precursor enable the carriers easily extracted by transporting layer. By choosing the optimized morphology of the perovskite layer and the well-controlled interface, we could prepare efficient solar cells with the PCE over 10% under AM 1.5 illumination with negligible hysteresis of the J-V curve for forward and reverse scan directions (Fig. S12). The PHJ-PSC device shows a maximum PCE up to 10.92% with a Voc of 1.024 V, a Jsc of 17.60 mA/cm2 and a FF of 60.6%, respectively (Fig. 3b). The external quantum efficiency (EQE) spectrum in Fig. 3c suggest that excellent photon conversion efficiency takes place over the whole wavelength range ranging from 400 nm to 750 nm, and the integrated Jsc is 16.33 mA/cm2, which just a little smaller than the value from J-V curve. It is reasonable because all the measurements are carried out under ambient condition with the humidity of ∼40%. In order to objectively evaluate fully doctor-bladed photovoltaic performance, 8 PHJ-PSC devices were fabricated in the same batch, and the statistic performance parameters for three types of PHJ-PSCs are shown in Fig. 4 and Table 1. The average PCE of PHJ-PSCs employing the optimized DMF + DMSO + MAI precursor show an excellent average value of 10.16%, and the Voc, Jsc and FF are 1.00 V, 17.41 mA/ cm2 and 58.25%, respectively, with small standard deviations, implying the good reproducibility. The absolute enhancements in the average Voc, Jsc and FF are about 0.06 V, 5.93 mA/cm2 and 16.82%, resulting in the impressive improvement in the average PCE from 4.57% to 10.16%. One should note that the increase of performance parameters strongly hinge on two aspects. One is the improvement of surface coverage and crystallinity of the perovskite film, resulting from the DMF/DMSO coexist solvent. Moreover, perovskite domain is modified by the excess MAI due to the stepped edges of grain disappeared and the unreacted MAI can also recrystallized on the perovskite grains so that the boundary between perovskite domains reduced tremendously [15]. The suitable exposure to the moisture could improve the quality of perovskite film and accordingly improve the device performance [8]. However, the degradation of PHJ-PSCs is inevitable when PHJ-PSCs are exposed to the moisture for a long time, for example, over 60 days [32–34]. The results suggest that, on the one hand, it is feasible to fabricate high-quality perovksite film and PHJ-PSC devices under ambition conditions with controllable humidity via printing process. On the other hand, it is necessary to develop suitable encapsulation techniques for prolonging the stability of PHJ-PSCs under ambition conditions, which would directly determine the actual commercialization of PHJ-PSCs.

adding 6.3% excess MAI to the precursor in DMF + DMSO can further enhance the diffraction peaks, indicating the crystallinity of the perovskite film is dramatically improved. As compared with the perovskite film using DMF + DMSO, all peaks are similar expect the intensity, suggesting the excess MAI did not influence the growth direction of perovskite crystal but is beneficial for improving the perovskite film crystallinity and domain size. Finally, the fullerene derivative PC61BM as the ETL was deposited onto the well-controlled uniform surface of the perovskite film using doctor blading under ambient condition. It should be noted that highperformance PC61BM layer is necessary to ensure electrons effectively extracted from the perovskite layer. An 8 mg/ml PC61BM in anhydrous CB was used to prepare the high-grade ETL. There is a hindrance to achieve a homogeneous PC61BM layer with uniform surface on a typical perovskite layer (DMF + DMSO + MAI) by solution processing. Because of the uneven distribution of the fluid surface of the PC61BM solution upon doctor blading, it begins to dry from all sides to the center in some regions under ambient condition. At the same time, a large amount of solute is accumulated as the solution evaporates, forming a circle of marks. Herein, in order to avoid the solution staying in some places on the surface of the perovskite film and leaving unnecessary traces, we immediately tilted the glass to ∼45° after doctor blading, making it gradually evaporate from the top to the down. In addition, a petri dish is used to prevent ambient air flow affecting the natural drying process. It can be found that the PC61BM layer is very homogeneous and uniform, covering the whole perovskite surface completely, as show in Fig. S10. Accordingly, it is reasonable to assume that the thin PC61BM layer is able to prevent leakage because of the direct contact between the electrode and the perovskite layer [29], potentially leading to better photovoltaic performance. With depositing the Ag via thermal evaporation on the PC61BM layer as the top electrode, the PHJ-PSCs with the architecture of ITO/ NiOx/CH3NH3PbI3/PC61BM/Ag were fabricated. The cross-sectional SEM image of optimized fully doctor-bladed PHJ-PSC device is exhibited in Fig. S11, and it illustrates a well-defined stacked arrangement of optimized PHJ-PSCs with a good uniformity for each interlayer. The thicknesses of NiOx, MAPbI3, PC61BM and Ag layer are about 20 nm, 280 nm, 30 nm and 90 nm, respectively. The typical J-V curves with three kinds of perovskite precursors are shown in Fig. 3a, The PHJ-PSC devices prepared from DMF presents much poor photovoltaic performance with an open-circuit voltage (Voc) of 0.947 V, a short-circuit current density (Jsc) of 12.41 mA/cm2, a fill factor (FF) of 42.77%, and yield a PCE of 5.02%. The much lower Jsc and FF mainly result from the poor surface coverage and crystallinity of the perovskite film because the defects and voids cause part of the carrier recombination and shunt to impede carrier transport and collection [30]. With adding 10% DMSO, the photovoltaic device exhibits an enhanced PCE to 8.28%, which is attributed to the increase in the Jsc and FF (15.81 mA/cm2 and 156

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Fig. 3. (A) Typical J-V curve measured under AM 1.5 illumination for PHJ-PSCs via doctor blading using the optimized precursors of DMF, DMF + DMSO, DMF + DMSO + MAI, respectively. (b) The J-V curve and (c) EQE spectra with the integrated Jsc for PHJ-PSC prepared by a typical formula of DMF + DMSO + MAI.

4. Conclusion

crystallites and small grain boundaries could be achieved. Furthermore, excess MAI embedded within the precursor film not only promotes grain size and film crystallinity of the perovskite film compared to that using DMF/DMSO co-solvent, it also results in the uniform morphology and a compact, well-grained perovskite film. Thereby, with better control over the process of the crystallization and grain-growth by using nonstoichiometric MAPbI3 precursor, the champion device yielded a

In summary, efficient PHJ-PSCs with a simple structure of ITO/ NiOx/CH3NH3PbI3/PC61BM/Ag were fabricated via fully doctorblading technique in ambient condition with humidity of ∼40%. The results demonstrated that by replacing DMF with DMF/DMSO co-exist solvent, homogenous and compact perovskite film with large perovskite

Fig. 4. The statistical plots of photovoltaic parameters of (a) Voc, (b) Jsc, (c) FF and (d) PCE for fully doctor-bladed PHJ-PSCs using the different precursor solutions with DMF, DMF + DMSO, DMF + DMSO + MAI, respectively. The middle dots are the average value, the box edges are the standard error, the whiskers are the maximum and minimum of the distributions and the central horizontal line is the median. The data of 8 PHJ-PSCs are shown adjacently to the boxes. The numbers mean the amount of total measured points.

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Table 1 The photovoltaic performance parameters of fully doctor-bladed PHJ-PSCs with the simple structure of ITO/NiOx/CH3NH3PbI3/PC61BM/Ag and the optimized perovskite precursors. The best photovoltaic parameters are shown in the bracket. Precursor solvent

Voc (V)

Jsc (mA/cm2)

FF (%)

PCE (%)

DMF DMF + DMSO DMF + DMSO + MAI

0.94 ± 0.96 0.98 ± 0.03 1.00 ± 0.02

11.48 ± 0.91 16.72 ± 1.57 17.41 ± 0.87

41.43 ± 4.86 44.89 ± 5.02 58.25 ± 3.49

4.57 ± 0.59 (5.02) 7.30 ± 0.48 (8.28) 10.16 ± 0.51 (10.92)

PCE of 10.92% and an average PCE of 10.16% with good repeatability. The research demonstrated that solvent engineering in the process of doctor blading by modify perovskite precursor is beneficial for fabricating high-quality perovskite films and thus yielding efficient PHJPSCs, which may pave a boulevard for fabricating high-efficiency and low-cost PHJ-PSCs under ambient condition.

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Acknowledgements [17]

This work was supported by the National Natural Science Foundation of China (51673214), the National Key Research and Development Program of China (2017YFA0206600) and the Hunan Provincial Natural Science Foundation of China (2015JJ1015). The SEM technical support from Institute for Materials Microstructure at CSU is appreciated.

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Appendix A. Supplementary data [21]

Supplementary data related to this article can be found at http://dx. doi.org/10.1016/j.orgel.2018.04.020.

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