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High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers
Journal Pre-proofs Research paper High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers Guanchen Liu, Zhihai Liu, Fanming Zeng, Xinyu Wang, Shuangcui Li, Xiaoyin Xie PII: DOI: Reference:
S0009-2614(20)30101-9 https://doi.org/10.1016/j.cplett.2020.137186 CPLETT 137186
To appear in:
Chemical Physics Letters
Received Date: Revised Date: Accepted Date:
19 December 2019 4 February 2020 5 February 2020
Please cite this article as: G. Liu, Z. Liu, F. Zeng, X. Wang, S. Li, X. Xie, High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers, Chemical Physics Letters (2020), doi: https://doi.org/10.1016/j.cplett.2020.137186
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© 2020 Published by Elsevier B.V.
High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers
Guanchen Liu,a,c Zhihai Liu,b Fanming Zeng,a,* Xinyu Wang,b Shuangcui Li,d Xiaoyin Xiee,**
aSchool
of Materials Science and Engineering, Changchun University of Science and Technology,
Changchun, 130022, China. bSchool
of Opto-Electronic Information Science and Technology, Yantai University, Yantai, Shandong, 264005, China cSchool
of Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022,
China dInstitute
of Advanced Electrical Materials, Qingdao University of Science and Technology, Qingdao 266042, China eDepartment
of Chemical Technology, Jilin Institute of Chemical Technology, Jilin 132022, China
*Corresponding author at: Changchun University of Science and Technology, School of Materials Science and Engineering, Changchun 130022, China. E-mail address: [email protected] (F. Zeng) **Corresponding author at: Jilin Institute of Chemical Technology, Department of Chemical Technology. Jilin 132022, China. E-mail address: [email protected] (X. Xie)
1
Abstract In this work, two-dimensional inverted perovskite solar cells (2D PSCs) were fabricated with dimethylformamide (DMF) and γ-butyrolactone (GBL) as precursor solvent, respectively. The GBL processed 2D perovskite film showed better quality with fewer pinholes and higher crystallinity than the DMF processed case. The GBL processed 2D PSCs showed an average power conversion efficiency (PCE) of 11.17%, which obviously exceeded that (9.81%) of DMF processed devices, with simultaneous improvements in open-circuit voltage, short-circuit current density. The best-performed sample exhibited a PCE of 11.65% with stabilized current output and negligible hysteresis.
Keywords: Solvent, Morphology, Perovskite solar cells, Performance
1. Introduction In the past decade, perovskite solar cells (PSCs) have attracted extensive research interest due to their distinctive advantages, such as high performance, light weight, long carrier diffusing distance and solution processability [1–3]. Since firstly reported by Kojima et al., the power conversion efficiency (PCE) of PSCs have been rapidly improved up to 25.2% [4, 5]. As a result, PSCs are believed as one of the most promising next-generation photovoltaics, which show a great potential for future commercialization [4– 6]. Conventional perovskite materials (such as MAPbX3 and FAPbX3, MA = CH3NH3, FA = CH(NH2)2, X = Cl, Br, or I) usually suffer from the problem of low environmental stability [7–9]. In humid environment, these perovskites can easily convert into hydrated perovskite phases and eventually decompose to PbI2. This phenomenon is mainly due to the hygroscopicity and/or low formation energy of such materials [8, 9]. Although high PCEs have been achieved, the low stability issue of the PSCs needs to be resolved to satisfy the requirement of commercialization [9–11]. As a result, mix-cation perovskites such as CsxFAyMA1-x-yPbIzBr3-z series have been synthesized, improving both the PCE and 2
stability of PSCs [12, 13]. By replacing MA with Cesium (Cs), all-inorganic perovskites (for instance, CsPbBr3 and CsPbI3) can be obtained, which are alternative candidates for fabricating PSCs with high stability [14, 15]. However, the band gaps of these all-inorganic perovskites are about 1.8–2.3 eV, which are much wider than that (about 1.5 eV) of MAPbI3 [9, 15]. The large band gap further limits the light absorption property of the inorganic perovskites, which is a significant restriction to the photovoltaic performance of PSCs [9, 15]. Recently, two-dimensional (2D) perovskite materials, for instance (BA)2(MA)n-1PbnI3n+1 (n is an integer, BA is CH3(CH2)3NH3) series, have been developed, which show a tunable band gap and high environmental stability [16–19]. When n equals to 3, the (BA)2(MA)3Pb4I13 based PSCs exhibited a higher PCE [17, 18]. Although their PCE cannot be compared with the traditional PSCs for the time being, the 2D PSCs exhibit significantly improved long-term stability, which might be more suitable for commercial application [17, 18]. Therefore, further improving the PCE of 2D PSCs is highly desired. Zhang et al. added dimethyl sulfoxide as a co-solvent to control the phase transition of (BA)2(MA)3Pb4I13 perovskite, which resulted in a high PCE of 12.17% [20]. Liu and coworkers doped Cs into (BA)2(MA)3Pb4I13, which effectively controlled the crystallization of 2D perovskite layer. The doped 2D PSCs showed an improved PCE (from 12.3 to 13.7%) with enhanced long-term stability [21]. On the other hand, dimethylformamide (DMF) and γ-butyrolactone (GBL) are most widely used solvents for perovskite preparation [2, 3, 6]. However, due to the high boiling point and low vapor pressure, evaporation speed of GBL is lower than that of DMF [22]. For conventional CH3NH3PbI3 film, retarding perovskite growth is beneficial for improving the the quality of perovskite film [23–26]. Considering the evaporation property of the solvent, it is very necessary to investigate the effect to the performance of 2D perovskite by using DMF and GBL as the processing solvent. In this study, we investigated the effect of using DMF and GBL as the processing solvents for preparation of (BA)2(MA)3Pb4I13 based 2D perovskite. Owning to the low evaporation property, the crystallization process could be retarded during perovskite film growth by using GBL as precursor solvent, which benefits the quality of the 2D perovskite film. We find that, the GBL processed 2D perovskite film 3
showed several advantages such as fewer pinholes, larger grains, higher light absorption and enhanced crystallinity. As a result, a higher PCE (average PCE, 11.17%) was achieved for the PSCs based on GBL processed 2D perovskite, which is 13.9% relatively higher compared with the DMF processed ones (average PCE, 9.81%). The enhanced PCE is mainly induced by the significant improvement with the short-circuit current density and fill factor. (Jsc from 16.3 to 17.6 mA cm−2 and FF from 0.59 to 0.61). The champion device based on GBL processed perovskite exhibited a highest PCE of 11.65% with a stable sustained output and negligible hysteresis. Our work indicates that as the solvent of perovskite precursor, GBL can be an optimized choice to prepare high performance 2D PSCs.
2. Results and discussion The layered structure of the device and the arrangement of the frontier orbital energy levels of each layer is shown in Fig. 1(a). The working mechanism of the inverted 2D PSCs is similar to the conventional inverted perovskite solar cells, in which light is absorbed by the perovskite layer. Then the charge carriers dissociate with electrons transport through PCBM to Ag cathode and holes transport through PTAA to ITO anode. Generally, a proper energy alignment benefits the charge transportation from perovskite layer to charge transport layers (PTAA or PCBM) [15]. As shown in Fig. 1(b), we fabricated a well solid multilayer structure of the 2D PSCs, which conforms to the schematic structure of Fig. 1(a). The thickness of each layer is also shown in Fig. 1(b). For the perovskite and PCBM layers, their thicknesses were about 400 and 50 nm, respectively, which are similar with those of high performance 2D PSCs based on the same structure in previous studies [16–21].
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Fig. 1. (a) Schematic structure (associate with energy level alignment of each layer ) of the 2D PSCs fabricated in this work; (b) Cross-sectional SEM image of a 2D PSC fabricated in this work.
We took some measurements to characterize the prepared (BA)2(MA)3Pb4I13 perovskite film with scanning electronic microscopy SEM), UV–vis absorption and X-Ray diffraction (XRD) respectively. The SEM image in Fig. 2(a) shows the surface of DMF processed (BA)2(MA)3Pb4I13 perovskite film, in which several perovskite planes can be observed. However, there are a lot of pinholes existed on the surface, indicating a poor coverage. For the GBL processed case, the perovskite exhibits a condensed and uniform morphology with a full surface coverage. Moreover, the perovskite planes (about 0.6–1.5 μm) of GBL processed film become larger than those (about 1.2–2.3 μm) of DMF processed case, indicating an improved quality of using GBL. The UV–vis absorption spectra in Fig. 2(c) shows a typical light absorption property for (BA)2(MA)3Pb4I13 perovskite processed from DMF and GBL which covers a broad absorption spectrum from 400 nm to 800 nm. The peak of GBL processed perovskite is 612 nm, which shows lightly red shift comparing to that of DMF processed one (609 nm). Moreover, the light absorption of the perovskite becomes higher when using GBL, which ascribe to the optimized perovskite crystallinity. To prove this hypothesis, we analyzed the XRD patterns and Raman spectroscopy spectra of the perovskite films processed with DMF and GBL respectively. As shown in Fig. 2(d), two dominate peaks at 14.3° and 28.4° can be observed from both spectra, which refer to the (111) and (202) crystallographic planes of (BA)2(MA)3Pb4I13 crystal film, respectively [20]. As can be seen, the GBL 5
processed perovskite shows higher and sharper characteristic peaks than the DMF processed case. A small peak at 12.5° was significantly reduced, which stands for the (001) lattice planes of hexagonal (2H polytype) PbI2 [25]. The enhancement in perovskite characteristic peaks and reduction in PbI2 characteristic peak confirms the improved crystallinity of (BA)2(MA)3Pb4I13 perovskite processed by GBL [12, 25]. From the Raman spectra in Fig. S1, the intensity of the characteristic peaks of the GBL processed 2D perovskite is higher than that of the DMF processed case. A right shift of the 3 peaks can be observed, which also indicates the enhanced crystallinity of the 2D perovskite by using GBL [27]. The SEM, UV–vis absorption, XRD and Raman spectroscopy analysis demonstrate that using GBL could improve crystallization of the 2D perovskite films, which would have positive effect on the performance of PSCs.
Fig. 2. SEM images of the (BA)2(MA)3Pb4I13 perovskite films processed from (a) DMF and (b) GBL; UV–vis spectra (c) and XRD patterns (d) of the (BA)2(MA)3Pb4I13 perovskite films processed from DMF and GBL.
The J–V characteristics of the DMF and GBL processed 2D PSCs are shown in Fig. 3(a), and the 6
average/best device parameters are listed in Table 1. The PSCs based on DMF processed perovskite show an average PCE of 9.81%, with a low Jsc of 16.3 mA cm-2, Voc of 1.02 V and FF of 0.59, respectively. The performance of the PSCs is consistent with those existing in previous studies using (BA)2(MA)3Pb4I13 perovskite as absorber, indicating the good optimization of our experiment [16–21]. When using GBL as the processing solvent, the PCE was significantly improved to 11.17%, which was mainly caused by the improved Jsc (17.6 mA cm−2) and FF (0.61). The PCE values of 36 individual PSCs with perovskite films processed with DMF and GBL are collected in Fig. S2, in which indicating a clear difference in PCE by using different solvents. The best sample in the GBL processed group showed a highest PCE of 11.65% under forward scan. As shown in Fig. 3(c), by reverse scan, the best sample exhibited a slightly higher PCE (11.85%), which was induced by the slightly larger FF (0.62). As shown in Fig. S3, the DMF processed PSC showed a significantly higher PCE (11.01%) under forward scan, indicating a larger hysteresis. The reduced hysteresis might be caused by the reduced charge traps in the PSCs, which will be discussed later. In Fig. 3(d), the best PSC exhibited a stabilized Jsc of 15.1 mA cm−2 with PCE of 11.32% for 300 s, indicating a stable power output.
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Fig. 3. (a) J–V characteristics curve (forward scan) for the devices with perovskite films processed with DMF and GBL respectively; (b) IPCE curve of the PSCs of perovskite films processed with DMF and GBL respectively; (c) J–V characteristics curve of the highest performing PSC with perovskite film processed with GBL (forward and reverse scan); (d)Time related Current density and PCE test for the best PSC (forward bias of 0.75 V).
Table 1. Device parameters for PSCs with (BA)2(MA)3Pb4I13 perovskite films processed from DMF and GBL respectively (36 samples for each group). Solvent Voc (V) Jsc (mA cm-2) FF Average PCE (%) Champion PCE (%) DMF 1.02 16.3 0.59 9.81 10.27 GBL 1.04 17.6 0.61 11.17 11.65
The boiling point (BP) and vapor pressure (VP) parameters of DMF and GBL are summarizes in Table 2. Due to the higher BP and lower VP, GBL exhibits a lower evaporation speed than DMF. The schematic in Fig. 4 shows the 2D perovskite crystallization and film formation during the processes of spin coating and thermal annealing. Due to the evaporation characteristic, GBL slowly evaporated from the precursor on the substrate, which limited the speed of perovskite crystallization. This hypothesis can be proved by observing the color variation during the annealing process, which related to the crystallization transversion of the 2D perovskite films. As shown in Fig. S4, after spin coating the perovskite precursor, the sample processed with DMF turned into a light-yellow thin film, whereas the GBL processed one was transparent. When the thermal annealing is carried out to the 10th seconds, the DMF processed sample became brown which is darker than the GBL processed one. Then the DMF processed sample turned into dark black at the 20th second, indicating the typical phase transition for the perovskite thin film [8, 9]. However, the same phase transition of the GBL processed sample didn’t take place until the 30th seconds, indicating a slower crystallization procedure [22]. The retarded crystallization would be beneficial to the perovskite growth during both spin coating and thermal annealing [23, 25]. As
8
a result, using GBL improved the quality and morphology of perovskite film, and the above conclusion is consistent with the analysis based on SEM, UV-vis and XRD data.
Fig. 4. Schematic of the processes of 2D perovskite film formation using precursors solvents of DMF and GBL respectively.
Table 2. Boiling point vapor pressure of DMF and GBL [28, 29]. Solvent Boiling point (°C) Vapor pressure (mm Hg) DMF
153
2.7
GBL
204
1.5
9
Fig. 5. (a) Nyquist plots for PSCs based on (BA)2(MA)3Pb4I13 films processed from DMF and GBL. (b) J–V characteristics curve of the SCLC devices based on (BA)2(MA)3Pb4I13 films processed with DMF and GBL.
To identify the distinction in J–V characteristic performance of the PSCs, we characterized the property of charge transfer for the PSCs based on (BA)2(MA)3Pb4I13 2D perovskite processed with DMF and GBL using EIS measurement. As can be seen in Fig. 5(a), series resistance (Rs), charge transfer resistance (Rct) and chemical capacitance (C) can be defined in the equivalent circuit [30–32]. The high frequency region (left quarter of the semicircles) of the EIS spectra represent Rs, and the low frequency region (right quarter of the semicircles) represent Rct [25, 26]. Usually Rs is related the inter-facial connections of different functional layers (PTAA/perovskite and perovskite/PCBM) and Rct indicates the charge transfer process through different layers [25, 26]. By fitting the spectra to the equivalent circuit, the Rs and Rct of the DMF processed PSC are 21.7 and 723.5 Ω, respectively. Whereas the GBL processed PSC shows a lower Rs and Rct of 18.3 and 631.6 Ω, which indicates the improved inter-facial connection and charge transfer [25]. From the SEM images in Figs. 2(a) and (b), the rougher surface of DMF processed perovskite would cause larger contact resistance between PTAA/perovskite and perovskite/PCBM [12, 25]. A better inter-facial connection further facilitates the charges transfer from perovskite to electrodes, which is in consistent with lower Rct. Moreover, the pinholes in the perovskite film may trap the charge carriers. For GBL processed perovskite, the number of pinholes was dramatically reduced, which enhance the charge transfer characteristic of the PSCs. To characterize the charge trapping in perovskite, we measured the space charge limited current density (SCLC) plot for the electron only devices with a structure of glass/Ag/perovskite/PCBM/Ag [12, 32]. As shown in Fig. 5(b), the J–V characteristics for the electron only devices can be divided into three parts. An ohmic response can be observed in the low-voltage region, in which the current density slowly increased with the voltage. In the intermediate-voltage region (0.4–0.8 V), the current non-linearly and rapidly increased with the voltage, 10
indicating the limitation of the trap-filled state, which indicates all trap states are occupied by carriers [32, 33]. The voltage between the ohmic contact and trap-filled region is defined as the trap-filled-limit-voltage (VTFL), which can be determined by the trap density. The trap density (ntrap) can be calculated using the following equation:
𝑉TFL =
𝑒𝑛trap𝐿2 2Ɛ0Ɛ
(1)
where L represents the thickness of the perovskite film, Ɛ stand for the dielectric constant of perovskite, Ɛ0 is the permittivity of vacuum, and e is the elementary charge. The VTFL values of the devices with DMF and GBL processed perovskite are 0.62 and 0.42 V respectively, corresponding to ntrap of 6.8 ×1015 and 4.5 ×1015 cm-3, respectively. The electron trap density of the DMF processed device is 51% higher than that of the DMF processed one, which might be induced by the poor morphology the DMF processed perovskite film. The reduction of defect induced electron trap density can also explain the lower hysteresis of GBL processed PSCs [16, 36]. As can be seen from Fig. 2(a), the pinholes of the DMF processed perovskite may act as charge trappers which play a negative role in charge transportation [36]. In the highvoltage region, the current varies quadratically with the voltage [12, 25, 36]. The electron mobility is calculated according to the Mott–Gurney law with the following equation (2) [31, 33,35]: 9
𝑉2
𝐽 = 8𝜀𝜀0µ 𝐿3
(2)
the calculated µelectron of the devices using DMF and GBL processed perovskite are 5.6×10-4 and 7.2×10-4 cm2 V-1 s-1, respectively. The improved µelectron can be explicated by the increased electron transportation from perovskite to PCBM layer, as indicated from the EIS result. The EIS and SCLC analysis corroborate the enhanced charge transfer of PSCs based on GBL processed perovskite, which is in well agreement with the raised Jsc and FF.
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Fig. 6. PL (a) and TRPL (b) spectra of the (BA)2(MA)3Pb4I13 perovskite film (on glass) processed with DMF/GBL.
To analyze the photon to exciton process of the PSCs, we measured the photoluminescence spectroscopy (PL) and time-resolution photoluminescence (TRPL) spectra of the perovskite films processed with DMF and GBL. As can be seen in Fig. 6(a), the steady-state PL intensity of GBL processed perovskite is 33% higher than that of the DMF processed case, which indicated the enhanced photoelectric property of perovskite by using GBL [20, 25]. Moreover, compared to DMF processed perovskite, the PL peak exhibited a 5 nm red shift in GBL processed one. This result was similar with the light absorption spectra, which is also caused by the optimized crystallization of the perovskite film [22, 25]. Fig. 6(b) shows the TRPL spectra of the prepared 2D perovskite, it can be observed a significantly improved PL lifetime for GBL processed perovskite. With bi-exponential fitting for the spectra, the photoluminescence lifetimes of DMF and GBL processed perovskite are calculated to be 175 to 298 ns, respectively. The TRPL data indicated a longer surviving time of excitons in GBL processed perovskite, which benefit achieving higher Jsc of the device [37]. Above results can be explained by the charge-carrier dynamics that the charge trapping processes were dominated by ultrafast intrinsic self-trapping and trapping at surface defects coursed by the processing solvents [38]. Both the PL and TRPL data demonstrate the improved exciton generation process of the GBL processed perovskite film. The increased exciton further dissociate into more free charge carriers by using GBL, which is in consistent with the performance 12
improvement. In addition, we compared the stability performance of the DMF and GBL processed PSCs. As shown in Fig. S5, after 144 hours storage in ambient condition (at 25 °C and 35-45% humidity), the GBL processed PSC still has a PCE of 9.88%, corresponding to a PCE degradation of 11.9%. The PCE degradation of DMF processed PSC was 14.5%, which is lower than that of GBL processed case. A compact perovskite film with high crystallinity usually shows better environmental stability, which can explain the improved stability of PSCs using GBL [12].
3. Conclusions In this work, we studied the effect of DMF and GBL as the processing solvents for preparation of (BA)2(MA)3Pb4I13 based 2D perovskite. Using GBL can boost the quality of the perovskite film by retarding the crystallization during perovskite growth. The SEM, UV–vis, Raman spectra and XRD results indicate the improved crystallinity and light harvesting property of GBL processed perovskite. The PL and TRPL results indicate the enhanced exciton generation property of GBL processed perovskite. The EIS and SCLC analysis demonstrate the increased charge transfer of the devices based on GBL processed perovskite precursor. As a result, the GBL processed PSCs showed an average PCE of 11.17%, which was 13.9% relatively higher than that of DMF processed ones (average PCE 9.81%), with obvious improvements in both Jsc and FF. The best 2D PSC processed from GBL exhibited a highest PCE of 11.65% with a stable power output and negligible hysteresis. The results of our work demonstrate that GBL based precursor solvent is beneficial for 2D perovskite processing, which resulted in higher performance 2D devices.
Acknowledgments Our investigation accepted the financial support of the Department of Science and Technology, Jilin Province (Funding No.: 20160414043GH). Appendix A. Supplementary material 13
References [1] M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, H.J. Snaith, Science 338 (2012) 643–647. [2] W.S. Yang, J.H. Noh, N.J. Jeon, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Science 348 (2015) 1234–1237. [3] 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, Science 356 (2017) 1376–1379. [4] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc. 131 (2009) 6050–6051. [5] National Renewable Energy Laboratory chart, https://www.nrel.gov/pv/assets/pdfs/best-research-cellefficiencies.20190802.pdf. [6] H. Kim, K.-G. Lim, T.-W. Lee, Energy Environ. Sci. 9, (2016) 12–30. [7] L. Chen, X. Xie, Z. Liu, E.-C. Lee, J. Mater. Chem. A 5 (2017) 6974–6980. [8] J. A. Christians, P. A. Miranda Herrera, P. V. Kamat, J. Am. Chem. Soc. 137 (2015) 1530–1538. [9] Y. Hu, T. Qiu, F. Bai, X. Miao, S. Zhang, J. Mater. Chem. A 5 (2017) 25258–25265. [10] Y. Bai, S. Xiao, C. Hu, T. Zhang, X. Meng, H. Lin, Y. Yang, S. Yang, Adv. Energy Mater. 7 (2017) 1701038. [11] R. Lan, F. Zhang, Z. Wang, W. Xiong, H. Yuan, T. Feng, Opt. Eng. 56 (2017) 096112. [12] Y. Liu, Z. Liu, E.-C. Lee, ACS Appl. Energy Mater. 2 (2019) 1932–1942. [13] M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa-Baena, M. K. Nazeeruddin, S. M. Zakeeruddin W. Tress, A. Abate, A. Hagfeldt, M. Grätzel, Energy Environ. Sci. 9 (2016) 1989–1997. [14] C. Li, Z. Zang, C. Han, Z. Hu, X. Tang, J. Du, Y. Leng, K. Sun, Nano Energy 40 (2017) 195–202. [15] J. Zhang, G. Hodes, Z. Jin, S. Liu, Angew. Chem. Int. Ed. 58, 2019, 15596–15618. [16] G. Liu, X. Xie, X. Xu, Y. Wei, F. Zeng, Z. Liu, Org. Electron. 62 (2018) 189–194. [17] H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos, R. Asadpour, B. Harutyunyan, A. J. Neukirch, R. Verduzco, J. J. Crochet, S. Tretiak, L. Pedesseau, J. Even, M. A. Alam, G. Gupta, J. Lou, P. M. Ajayan, M. J. Bedzyk, M. G. Kanatzidis, A. D. Mohite, Nature 536 (2016) 312–316. 14
[18] D. H. Cao, C. C. Stoumpos, O. K. Farha, J. T. Hupp, M. G. Kanatzidis, J. Am. Chem. Soc. 137 (2015) 7843–7850. [19] C. Ma, D. Shen, T.-W. Ng, M.-F. Lo, C. S. Lee, Adv. Mater. 30 (2018) 1800710. [20] X. Zhang, R. Munir, Z. Xu, Y. Liu, H. Tsai, W. Nie, J. Li, T. Niu, D. Smilgies, M. G. Kanatzidis, A. D. Mohite, K. Zhao, A. Amassian, S. Liu, Adv. Mater. 30 (2018) 1707166. [21] X. Zhang, X. Ren, B. Liu, R. Munir, X. Zhu, D. Yang, J. Li, Y. Liu, D. Smilgies, R. Li, Z. Yang, T. Niu, X. Wang, A. Amassian, K. Zhao and S. Liu, Energy Environ. Sci. 10 (2017) 2095–2102. [22] Z. Liu, L. Wang, J. Han, F. Zeng, G. Liu X. Xie, Org. Electron. 78 (2020) 105552. [23] W. Zhang, S. Pathak, N. Sakai, T. Stergiopoulos, P.K. Nayak, N.K. Noel, A.A. Haghighirad, V.M. Burlakov, D.W. deQuilettes, A. Sadhanala, W. Li, L. Wang, D.S. Ginger, R.H. Friend, H.J. Snaith, Nat. Commun. 6 (2015) 10030. [24] J. Qing, H.-T. Chandran, Y.-H. Cheng, X.-K. Liu, H.-W. Li, S.-W. Tsang, M.-F. Lo, C.-S. Lee, ACS Appl. Mater. Interfaces 7 (2015) 23110–23116. [25] Y. Liu, Z. Liu, E.-C. Lee, J. Mater. Chem. C 6 (2018) 6705–6713. [26] H. Wei, J. Xiao, Y. Yang, S. Lv, J. Shi, X. Xu, J. Dong, Y. Luo, D. Li, Q. Meng, Carbon 93 (2015) 861–868 [27] F. Thouin, S. Neutzner, D. Cortecchia, V. A. Dragomir, C. Soci, T. Salim, Y. M. Lam, R. Leonelli, A. Petrozza, A. R. S. Kandada, C. Silva, Phys. Rev. Mater. 2 (2018) 034001 [28] https://www.sigmaaldrich.com/catalog/product/aldrich/l910000hh?lang=ko®ion=KR. [29] https://www.sigmaaldrich.com/catalog/product/sigma/h7629?lang=ko®ion=KR. [30] M. Baga1, L. A. Rennaa, S. P. Jeonga, X. Han, C. L. Cutting, D. Maroudas, D. Venkataraman, Chem. Phys. Lett. 662 (2016) 35–41. [31] C. Xu, Z. Liu, E.-C. Lee, J. Mater. Chem. C 7 (2019) 6956–6963. [32] Z. Liu, J. Hu, H. Jiao, L. Li, G. Zheng, Y. Chen, Y. Huang, Q. Zhang, C. Shen, Q. Chen, H. Zhou, Adv. Mater. 29 (2017) 1606774. 15
[33] M. Li, B. Li, G. Cao, J. Tian, J. Mater. Chem. A 5 (2017) 21313–21319. [34] A. Usami, Chem. Phys. Lett. 292 (1998) 223–228 [35] W. Chandra, L. K. Anga, K. L. Pey, Appl. Phys. Lett. 90 (2007) 153505. [36] G. Liu, X. Xie, F. Zeng, Z. Liu, Energy Technol. 6 (2018) 1283–1289. [37] Q. Dong, Y. Fang, Y. Shao, P. Mulligan, J. Qiu, L. Cao, J. Huang, Science 347 (2015) 967–970. [38] B. Yang, K. Han, Acc. Chem. Res. 52 (2019) 3188–3198.
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·DMF and GBL were respectively used to fabricate quasi 2D PSCs. ·A high PCE of 11.65% was achieved for 2D PSCs processed from GBL. ·Higher quality 2D perovskite was prepared by using GBL with reduced pinholes. ·Crystallinity and light absorption of 2D perovskite were improved by using GBL.
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Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers”. Guanchen Liu, Zhihai Liu, Fanming Zeng, Xinyu Wang, Shuangcui Li, Xiaoyin Xie 2020-2-5
Statement of Author contributions The authors of “High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers” Published in Chemical Physics Letters, declare that our contributions for this paper are as follow: Guanchen Liu: Methodology, Investigation,Writing - Original Draft. Zhihai Liu: Formal analysis,Writing: Review & Editing, Fanming Zeng: Resources, Writing-Review & Editing, Supervision. Xiaoyin Xie: Resources, Writing-Review & Editing, Supervision. Shaungcui Li: Review & Editing Xinyu Wang: Testing, Review & Editing
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S0009-2614(20)30101-9 https://doi.org/10.1016/j.cplett.2020.137186 CPLETT 137186
To appear in:
Chemical Physics Letters
Received Date: Revised Date: Accepted Date:
19 December 2019 4 February 2020 5 February 2020
Please cite this article as: G. Liu, Z. Liu, F. Zeng, X. Wang, S. Li, X. Xie, High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers, Chemical Physics Letters (2020), doi: https://doi.org/10.1016/j.cplett.2020.137186
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© 2020 Published by Elsevier B.V.
High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers
Guanchen Liu,a,c Zhihai Liu,b Fanming Zeng,a,* Xinyu Wang,b Shuangcui Li,d Xiaoyin Xiee,**
aSchool
of Materials Science and Engineering, Changchun University of Science and Technology,
Changchun, 130022, China. bSchool
of Opto-Electronic Information Science and Technology, Yantai University, Yantai, Shandong, 264005, China cSchool
of Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022,
China dInstitute
of Advanced Electrical Materials, Qingdao University of Science and Technology, Qingdao 266042, China eDepartment
of Chemical Technology, Jilin Institute of Chemical Technology, Jilin 132022, China
*Corresponding author at: Changchun University of Science and Technology, School of Materials Science and Engineering, Changchun 130022, China. E-mail address: [email protected] (F. Zeng) **Corresponding author at: Jilin Institute of Chemical Technology, Department of Chemical Technology. Jilin 132022, China. E-mail address: [email protected] (X. Xie)
1
Abstract In this work, two-dimensional inverted perovskite solar cells (2D PSCs) were fabricated with dimethylformamide (DMF) and γ-butyrolactone (GBL) as precursor solvent, respectively. The GBL processed 2D perovskite film showed better quality with fewer pinholes and higher crystallinity than the DMF processed case. The GBL processed 2D PSCs showed an average power conversion efficiency (PCE) of 11.17%, which obviously exceeded that (9.81%) of DMF processed devices, with simultaneous improvements in open-circuit voltage, short-circuit current density. The best-performed sample exhibited a PCE of 11.65% with stabilized current output and negligible hysteresis.
Keywords: Solvent, Morphology, Perovskite solar cells, Performance
1. Introduction In the past decade, perovskite solar cells (PSCs) have attracted extensive research interest due to their distinctive advantages, such as high performance, light weight, long carrier diffusing distance and solution processability [1–3]. Since firstly reported by Kojima et al., the power conversion efficiency (PCE) of PSCs have been rapidly improved up to 25.2% [4, 5]. As a result, PSCs are believed as one of the most promising next-generation photovoltaics, which show a great potential for future commercialization [4– 6]. Conventional perovskite materials (such as MAPbX3 and FAPbX3, MA = CH3NH3, FA = CH(NH2)2, X = Cl, Br, or I) usually suffer from the problem of low environmental stability [7–9]. In humid environment, these perovskites can easily convert into hydrated perovskite phases and eventually decompose to PbI2. This phenomenon is mainly due to the hygroscopicity and/or low formation energy of such materials [8, 9]. Although high PCEs have been achieved, the low stability issue of the PSCs needs to be resolved to satisfy the requirement of commercialization [9–11]. As a result, mix-cation perovskites such as CsxFAyMA1-x-yPbIzBr3-z series have been synthesized, improving both the PCE and 2
stability of PSCs [12, 13]. By replacing MA with Cesium (Cs), all-inorganic perovskites (for instance, CsPbBr3 and CsPbI3) can be obtained, which are alternative candidates for fabricating PSCs with high stability [14, 15]. However, the band gaps of these all-inorganic perovskites are about 1.8–2.3 eV, which are much wider than that (about 1.5 eV) of MAPbI3 [9, 15]. The large band gap further limits the light absorption property of the inorganic perovskites, which is a significant restriction to the photovoltaic performance of PSCs [9, 15]. Recently, two-dimensional (2D) perovskite materials, for instance (BA)2(MA)n-1PbnI3n+1 (n is an integer, BA is CH3(CH2)3NH3) series, have been developed, which show a tunable band gap and high environmental stability [16–19]. When n equals to 3, the (BA)2(MA)3Pb4I13 based PSCs exhibited a higher PCE [17, 18]. Although their PCE cannot be compared with the traditional PSCs for the time being, the 2D PSCs exhibit significantly improved long-term stability, which might be more suitable for commercial application [17, 18]. Therefore, further improving the PCE of 2D PSCs is highly desired. Zhang et al. added dimethyl sulfoxide as a co-solvent to control the phase transition of (BA)2(MA)3Pb4I13 perovskite, which resulted in a high PCE of 12.17% [20]. Liu and coworkers doped Cs into (BA)2(MA)3Pb4I13, which effectively controlled the crystallization of 2D perovskite layer. The doped 2D PSCs showed an improved PCE (from 12.3 to 13.7%) with enhanced long-term stability [21]. On the other hand, dimethylformamide (DMF) and γ-butyrolactone (GBL) are most widely used solvents for perovskite preparation [2, 3, 6]. However, due to the high boiling point and low vapor pressure, evaporation speed of GBL is lower than that of DMF [22]. For conventional CH3NH3PbI3 film, retarding perovskite growth is beneficial for improving the the quality of perovskite film [23–26]. Considering the evaporation property of the solvent, it is very necessary to investigate the effect to the performance of 2D perovskite by using DMF and GBL as the processing solvent. In this study, we investigated the effect of using DMF and GBL as the processing solvents for preparation of (BA)2(MA)3Pb4I13 based 2D perovskite. Owning to the low evaporation property, the crystallization process could be retarded during perovskite film growth by using GBL as precursor solvent, which benefits the quality of the 2D perovskite film. We find that, the GBL processed 2D perovskite film 3
showed several advantages such as fewer pinholes, larger grains, higher light absorption and enhanced crystallinity. As a result, a higher PCE (average PCE, 11.17%) was achieved for the PSCs based on GBL processed 2D perovskite, which is 13.9% relatively higher compared with the DMF processed ones (average PCE, 9.81%). The enhanced PCE is mainly induced by the significant improvement with the short-circuit current density and fill factor. (Jsc from 16.3 to 17.6 mA cm−2 and FF from 0.59 to 0.61). The champion device based on GBL processed perovskite exhibited a highest PCE of 11.65% with a stable sustained output and negligible hysteresis. Our work indicates that as the solvent of perovskite precursor, GBL can be an optimized choice to prepare high performance 2D PSCs.
2. Results and discussion The layered structure of the device and the arrangement of the frontier orbital energy levels of each layer is shown in Fig. 1(a). The working mechanism of the inverted 2D PSCs is similar to the conventional inverted perovskite solar cells, in which light is absorbed by the perovskite layer. Then the charge carriers dissociate with electrons transport through PCBM to Ag cathode and holes transport through PTAA to ITO anode. Generally, a proper energy alignment benefits the charge transportation from perovskite layer to charge transport layers (PTAA or PCBM) [15]. As shown in Fig. 1(b), we fabricated a well solid multilayer structure of the 2D PSCs, which conforms to the schematic structure of Fig. 1(a). The thickness of each layer is also shown in Fig. 1(b). For the perovskite and PCBM layers, their thicknesses were about 400 and 50 nm, respectively, which are similar with those of high performance 2D PSCs based on the same structure in previous studies [16–21].
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Fig. 1. (a) Schematic structure (associate with energy level alignment of each layer ) of the 2D PSCs fabricated in this work; (b) Cross-sectional SEM image of a 2D PSC fabricated in this work.
We took some measurements to characterize the prepared (BA)2(MA)3Pb4I13 perovskite film with scanning electronic microscopy SEM), UV–vis absorption and X-Ray diffraction (XRD) respectively. The SEM image in Fig. 2(a) shows the surface of DMF processed (BA)2(MA)3Pb4I13 perovskite film, in which several perovskite planes can be observed. However, there are a lot of pinholes existed on the surface, indicating a poor coverage. For the GBL processed case, the perovskite exhibits a condensed and uniform morphology with a full surface coverage. Moreover, the perovskite planes (about 0.6–1.5 μm) of GBL processed film become larger than those (about 1.2–2.3 μm) of DMF processed case, indicating an improved quality of using GBL. The UV–vis absorption spectra in Fig. 2(c) shows a typical light absorption property for (BA)2(MA)3Pb4I13 perovskite processed from DMF and GBL which covers a broad absorption spectrum from 400 nm to 800 nm. The peak of GBL processed perovskite is 612 nm, which shows lightly red shift comparing to that of DMF processed one (609 nm). Moreover, the light absorption of the perovskite becomes higher when using GBL, which ascribe to the optimized perovskite crystallinity. To prove this hypothesis, we analyzed the XRD patterns and Raman spectroscopy spectra of the perovskite films processed with DMF and GBL respectively. As shown in Fig. 2(d), two dominate peaks at 14.3° and 28.4° can be observed from both spectra, which refer to the (111) and (202) crystallographic planes of (BA)2(MA)3Pb4I13 crystal film, respectively [20]. As can be seen, the GBL 5
processed perovskite shows higher and sharper characteristic peaks than the DMF processed case. A small peak at 12.5° was significantly reduced, which stands for the (001) lattice planes of hexagonal (2H polytype) PbI2 [25]. The enhancement in perovskite characteristic peaks and reduction in PbI2 characteristic peak confirms the improved crystallinity of (BA)2(MA)3Pb4I13 perovskite processed by GBL [12, 25]. From the Raman spectra in Fig. S1, the intensity of the characteristic peaks of the GBL processed 2D perovskite is higher than that of the DMF processed case. A right shift of the 3 peaks can be observed, which also indicates the enhanced crystallinity of the 2D perovskite by using GBL [27]. The SEM, UV–vis absorption, XRD and Raman spectroscopy analysis demonstrate that using GBL could improve crystallization of the 2D perovskite films, which would have positive effect on the performance of PSCs.
Fig. 2. SEM images of the (BA)2(MA)3Pb4I13 perovskite films processed from (a) DMF and (b) GBL; UV–vis spectra (c) and XRD patterns (d) of the (BA)2(MA)3Pb4I13 perovskite films processed from DMF and GBL.
The J–V characteristics of the DMF and GBL processed 2D PSCs are shown in Fig. 3(a), and the 6
average/best device parameters are listed in Table 1. The PSCs based on DMF processed perovskite show an average PCE of 9.81%, with a low Jsc of 16.3 mA cm-2, Voc of 1.02 V and FF of 0.59, respectively. The performance of the PSCs is consistent with those existing in previous studies using (BA)2(MA)3Pb4I13 perovskite as absorber, indicating the good optimization of our experiment [16–21]. When using GBL as the processing solvent, the PCE was significantly improved to 11.17%, which was mainly caused by the improved Jsc (17.6 mA cm−2) and FF (0.61). The PCE values of 36 individual PSCs with perovskite films processed with DMF and GBL are collected in Fig. S2, in which indicating a clear difference in PCE by using different solvents. The best sample in the GBL processed group showed a highest PCE of 11.65% under forward scan. As shown in Fig. 3(c), by reverse scan, the best sample exhibited a slightly higher PCE (11.85%), which was induced by the slightly larger FF (0.62). As shown in Fig. S3, the DMF processed PSC showed a significantly higher PCE (11.01%) under forward scan, indicating a larger hysteresis. The reduced hysteresis might be caused by the reduced charge traps in the PSCs, which will be discussed later. In Fig. 3(d), the best PSC exhibited a stabilized Jsc of 15.1 mA cm−2 with PCE of 11.32% for 300 s, indicating a stable power output.
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Fig. 3. (a) J–V characteristics curve (forward scan) for the devices with perovskite films processed with DMF and GBL respectively; (b) IPCE curve of the PSCs of perovskite films processed with DMF and GBL respectively; (c) J–V characteristics curve of the highest performing PSC with perovskite film processed with GBL (forward and reverse scan); (d)Time related Current density and PCE test for the best PSC (forward bias of 0.75 V).
Table 1. Device parameters for PSCs with (BA)2(MA)3Pb4I13 perovskite films processed from DMF and GBL respectively (36 samples for each group). Solvent Voc (V) Jsc (mA cm-2) FF Average PCE (%) Champion PCE (%) DMF 1.02 16.3 0.59 9.81 10.27 GBL 1.04 17.6 0.61 11.17 11.65
The boiling point (BP) and vapor pressure (VP) parameters of DMF and GBL are summarizes in Table 2. Due to the higher BP and lower VP, GBL exhibits a lower evaporation speed than DMF. The schematic in Fig. 4 shows the 2D perovskite crystallization and film formation during the processes of spin coating and thermal annealing. Due to the evaporation characteristic, GBL slowly evaporated from the precursor on the substrate, which limited the speed of perovskite crystallization. This hypothesis can be proved by observing the color variation during the annealing process, which related to the crystallization transversion of the 2D perovskite films. As shown in Fig. S4, after spin coating the perovskite precursor, the sample processed with DMF turned into a light-yellow thin film, whereas the GBL processed one was transparent. When the thermal annealing is carried out to the 10th seconds, the DMF processed sample became brown which is darker than the GBL processed one. Then the DMF processed sample turned into dark black at the 20th second, indicating the typical phase transition for the perovskite thin film [8, 9]. However, the same phase transition of the GBL processed sample didn’t take place until the 30th seconds, indicating a slower crystallization procedure [22]. The retarded crystallization would be beneficial to the perovskite growth during both spin coating and thermal annealing [23, 25]. As
8
a result, using GBL improved the quality and morphology of perovskite film, and the above conclusion is consistent with the analysis based on SEM, UV-vis and XRD data.
Fig. 4. Schematic of the processes of 2D perovskite film formation using precursors solvents of DMF and GBL respectively.
Table 2. Boiling point vapor pressure of DMF and GBL [28, 29]. Solvent Boiling point (°C) Vapor pressure (mm Hg) DMF
153
2.7
GBL
204
1.5
9
Fig. 5. (a) Nyquist plots for PSCs based on (BA)2(MA)3Pb4I13 films processed from DMF and GBL. (b) J–V characteristics curve of the SCLC devices based on (BA)2(MA)3Pb4I13 films processed with DMF and GBL.
To identify the distinction in J–V characteristic performance of the PSCs, we characterized the property of charge transfer for the PSCs based on (BA)2(MA)3Pb4I13 2D perovskite processed with DMF and GBL using EIS measurement. As can be seen in Fig. 5(a), series resistance (Rs), charge transfer resistance (Rct) and chemical capacitance (C) can be defined in the equivalent circuit [30–32]. The high frequency region (left quarter of the semicircles) of the EIS spectra represent Rs, and the low frequency region (right quarter of the semicircles) represent Rct [25, 26]. Usually Rs is related the inter-facial connections of different functional layers (PTAA/perovskite and perovskite/PCBM) and Rct indicates the charge transfer process through different layers [25, 26]. By fitting the spectra to the equivalent circuit, the Rs and Rct of the DMF processed PSC are 21.7 and 723.5 Ω, respectively. Whereas the GBL processed PSC shows a lower Rs and Rct of 18.3 and 631.6 Ω, which indicates the improved inter-facial connection and charge transfer [25]. From the SEM images in Figs. 2(a) and (b), the rougher surface of DMF processed perovskite would cause larger contact resistance between PTAA/perovskite and perovskite/PCBM [12, 25]. A better inter-facial connection further facilitates the charges transfer from perovskite to electrodes, which is in consistent with lower Rct. Moreover, the pinholes in the perovskite film may trap the charge carriers. For GBL processed perovskite, the number of pinholes was dramatically reduced, which enhance the charge transfer characteristic of the PSCs. To characterize the charge trapping in perovskite, we measured the space charge limited current density (SCLC) plot for the electron only devices with a structure of glass/Ag/perovskite/PCBM/Ag [12, 32]. As shown in Fig. 5(b), the J–V characteristics for the electron only devices can be divided into three parts. An ohmic response can be observed in the low-voltage region, in which the current density slowly increased with the voltage. In the intermediate-voltage region (0.4–0.8 V), the current non-linearly and rapidly increased with the voltage, 10
indicating the limitation of the trap-filled state, which indicates all trap states are occupied by carriers [32, 33]. The voltage between the ohmic contact and trap-filled region is defined as the trap-filled-limit-voltage (VTFL), which can be determined by the trap density. The trap density (ntrap) can be calculated using the following equation:
𝑉TFL =
𝑒𝑛trap𝐿2 2Ɛ0Ɛ
(1)
where L represents the thickness of the perovskite film, Ɛ stand for the dielectric constant of perovskite, Ɛ0 is the permittivity of vacuum, and e is the elementary charge. The VTFL values of the devices with DMF and GBL processed perovskite are 0.62 and 0.42 V respectively, corresponding to ntrap of 6.8 ×1015 and 4.5 ×1015 cm-3, respectively. The electron trap density of the DMF processed device is 51% higher than that of the DMF processed one, which might be induced by the poor morphology the DMF processed perovskite film. The reduction of defect induced electron trap density can also explain the lower hysteresis of GBL processed PSCs [16, 36]. As can be seen from Fig. 2(a), the pinholes of the DMF processed perovskite may act as charge trappers which play a negative role in charge transportation [36]. In the highvoltage region, the current varies quadratically with the voltage [12, 25, 36]. The electron mobility is calculated according to the Mott–Gurney law with the following equation (2) [31, 33,35]: 9
𝑉2
𝐽 = 8𝜀𝜀0µ 𝐿3
(2)
the calculated µelectron of the devices using DMF and GBL processed perovskite are 5.6×10-4 and 7.2×10-4 cm2 V-1 s-1, respectively. The improved µelectron can be explicated by the increased electron transportation from perovskite to PCBM layer, as indicated from the EIS result. The EIS and SCLC analysis corroborate the enhanced charge transfer of PSCs based on GBL processed perovskite, which is in well agreement with the raised Jsc and FF.
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Fig. 6. PL (a) and TRPL (b) spectra of the (BA)2(MA)3Pb4I13 perovskite film (on glass) processed with DMF/GBL.
To analyze the photon to exciton process of the PSCs, we measured the photoluminescence spectroscopy (PL) and time-resolution photoluminescence (TRPL) spectra of the perovskite films processed with DMF and GBL. As can be seen in Fig. 6(a), the steady-state PL intensity of GBL processed perovskite is 33% higher than that of the DMF processed case, which indicated the enhanced photoelectric property of perovskite by using GBL [20, 25]. Moreover, compared to DMF processed perovskite, the PL peak exhibited a 5 nm red shift in GBL processed one. This result was similar with the light absorption spectra, which is also caused by the optimized crystallization of the perovskite film [22, 25]. Fig. 6(b) shows the TRPL spectra of the prepared 2D perovskite, it can be observed a significantly improved PL lifetime for GBL processed perovskite. With bi-exponential fitting for the spectra, the photoluminescence lifetimes of DMF and GBL processed perovskite are calculated to be 175 to 298 ns, respectively. The TRPL data indicated a longer surviving time of excitons in GBL processed perovskite, which benefit achieving higher Jsc of the device [37]. Above results can be explained by the charge-carrier dynamics that the charge trapping processes were dominated by ultrafast intrinsic self-trapping and trapping at surface defects coursed by the processing solvents [38]. Both the PL and TRPL data demonstrate the improved exciton generation process of the GBL processed perovskite film. The increased exciton further dissociate into more free charge carriers by using GBL, which is in consistent with the performance 12
improvement. In addition, we compared the stability performance of the DMF and GBL processed PSCs. As shown in Fig. S5, after 144 hours storage in ambient condition (at 25 °C and 35-45% humidity), the GBL processed PSC still has a PCE of 9.88%, corresponding to a PCE degradation of 11.9%. The PCE degradation of DMF processed PSC was 14.5%, which is lower than that of GBL processed case. A compact perovskite film with high crystallinity usually shows better environmental stability, which can explain the improved stability of PSCs using GBL [12].
3. Conclusions In this work, we studied the effect of DMF and GBL as the processing solvents for preparation of (BA)2(MA)3Pb4I13 based 2D perovskite. Using GBL can boost the quality of the perovskite film by retarding the crystallization during perovskite growth. The SEM, UV–vis, Raman spectra and XRD results indicate the improved crystallinity and light harvesting property of GBL processed perovskite. The PL and TRPL results indicate the enhanced exciton generation property of GBL processed perovskite. The EIS and SCLC analysis demonstrate the increased charge transfer of the devices based on GBL processed perovskite precursor. As a result, the GBL processed PSCs showed an average PCE of 11.17%, which was 13.9% relatively higher than that of DMF processed ones (average PCE 9.81%), with obvious improvements in both Jsc and FF. The best 2D PSC processed from GBL exhibited a highest PCE of 11.65% with a stable power output and negligible hysteresis. The results of our work demonstrate that GBL based precursor solvent is beneficial for 2D perovskite processing, which resulted in higher performance 2D devices.
Acknowledgments Our investigation accepted the financial support of the Department of Science and Technology, Jilin Province (Funding No.: 20160414043GH). Appendix A. Supplementary material 13
References [1] M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, H.J. Snaith, Science 338 (2012) 643–647. [2] W.S. Yang, J.H. Noh, N.J. Jeon, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Science 348 (2015) 1234–1237. [3] 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, Science 356 (2017) 1376–1379. [4] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc. 131 (2009) 6050–6051. [5] National Renewable Energy Laboratory chart, https://www.nrel.gov/pv/assets/pdfs/best-research-cellefficiencies.20190802.pdf. [6] H. Kim, K.-G. Lim, T.-W. Lee, Energy Environ. Sci. 9, (2016) 12–30. [7] L. Chen, X. Xie, Z. Liu, E.-C. Lee, J. Mater. Chem. A 5 (2017) 6974–6980. [8] J. A. Christians, P. A. Miranda Herrera, P. V. Kamat, J. Am. Chem. Soc. 137 (2015) 1530–1538. [9] Y. Hu, T. Qiu, F. Bai, X. Miao, S. Zhang, J. Mater. Chem. A 5 (2017) 25258–25265. [10] Y. Bai, S. Xiao, C. Hu, T. Zhang, X. Meng, H. Lin, Y. Yang, S. Yang, Adv. Energy Mater. 7 (2017) 1701038. [11] R. Lan, F. Zhang, Z. Wang, W. Xiong, H. Yuan, T. Feng, Opt. Eng. 56 (2017) 096112. [12] Y. Liu, Z. Liu, E.-C. Lee, ACS Appl. Energy Mater. 2 (2019) 1932–1942. [13] M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa-Baena, M. K. Nazeeruddin, S. M. Zakeeruddin W. Tress, A. Abate, A. Hagfeldt, M. Grätzel, Energy Environ. Sci. 9 (2016) 1989–1997. [14] C. Li, Z. Zang, C. Han, Z. Hu, X. Tang, J. Du, Y. Leng, K. Sun, Nano Energy 40 (2017) 195–202. [15] J. Zhang, G. Hodes, Z. Jin, S. Liu, Angew. Chem. Int. Ed. 58, 2019, 15596–15618. [16] G. Liu, X. Xie, X. Xu, Y. Wei, F. Zeng, Z. Liu, Org. Electron. 62 (2018) 189–194. [17] H. Tsai, W. Nie, J.-C. Blancon, C. C. Stoumpos, R. Asadpour, B. Harutyunyan, A. J. Neukirch, R. Verduzco, J. J. Crochet, S. Tretiak, L. Pedesseau, J. Even, M. A. Alam, G. Gupta, J. Lou, P. M. Ajayan, M. J. Bedzyk, M. G. Kanatzidis, A. D. Mohite, Nature 536 (2016) 312–316. 14
[18] D. H. Cao, C. C. Stoumpos, O. K. Farha, J. T. Hupp, M. G. Kanatzidis, J. Am. Chem. Soc. 137 (2015) 7843–7850. [19] C. Ma, D. Shen, T.-W. Ng, M.-F. Lo, C. S. Lee, Adv. Mater. 30 (2018) 1800710. [20] X. Zhang, R. Munir, Z. Xu, Y. Liu, H. Tsai, W. Nie, J. Li, T. Niu, D. Smilgies, M. G. Kanatzidis, A. D. Mohite, K. Zhao, A. Amassian, S. Liu, Adv. Mater. 30 (2018) 1707166. [21] X. Zhang, X. Ren, B. Liu, R. Munir, X. Zhu, D. Yang, J. Li, Y. Liu, D. Smilgies, R. Li, Z. Yang, T. Niu, X. Wang, A. Amassian, K. Zhao and S. Liu, Energy Environ. Sci. 10 (2017) 2095–2102. [22] Z. Liu, L. Wang, J. Han, F. Zeng, G. Liu X. Xie, Org. Electron. 78 (2020) 105552. [23] W. Zhang, S. Pathak, N. Sakai, T. Stergiopoulos, P.K. Nayak, N.K. Noel, A.A. Haghighirad, V.M. Burlakov, D.W. deQuilettes, A. Sadhanala, W. Li, L. Wang, D.S. Ginger, R.H. Friend, H.J. Snaith, Nat. Commun. 6 (2015) 10030. [24] J. Qing, H.-T. Chandran, Y.-H. Cheng, X.-K. Liu, H.-W. Li, S.-W. Tsang, M.-F. Lo, C.-S. Lee, ACS Appl. Mater. Interfaces 7 (2015) 23110–23116. [25] Y. Liu, Z. Liu, E.-C. Lee, J. Mater. Chem. C 6 (2018) 6705–6713. [26] H. Wei, J. Xiao, Y. Yang, S. Lv, J. Shi, X. Xu, J. Dong, Y. Luo, D. Li, Q. Meng, Carbon 93 (2015) 861–868 [27] F. Thouin, S. Neutzner, D. Cortecchia, V. A. Dragomir, C. Soci, T. Salim, Y. M. Lam, R. Leonelli, A. Petrozza, A. R. S. Kandada, C. Silva, Phys. Rev. Mater. 2 (2018) 034001 [28] https://www.sigmaaldrich.com/catalog/product/aldrich/l910000hh?lang=ko®ion=KR. [29] https://www.sigmaaldrich.com/catalog/product/sigma/h7629?lang=ko®ion=KR. [30] M. Baga1, L. A. Rennaa, S. P. Jeonga, X. Han, C. L. Cutting, D. Maroudas, D. Venkataraman, Chem. Phys. Lett. 662 (2016) 35–41. [31] C. Xu, Z. Liu, E.-C. Lee, J. Mater. Chem. C 7 (2019) 6956–6963. [32] Z. Liu, J. Hu, H. Jiao, L. Li, G. Zheng, Y. Chen, Y. Huang, Q. Zhang, C. Shen, Q. Chen, H. Zhou, Adv. Mater. 29 (2017) 1606774. 15
[33] M. Li, B. Li, G. Cao, J. Tian, J. Mater. Chem. A 5 (2017) 21313–21319. [34] A. Usami, Chem. Phys. Lett. 292 (1998) 223–228 [35] W. Chandra, L. K. Anga, K. L. Pey, Appl. Phys. Lett. 90 (2007) 153505. [36] G. Liu, X. Xie, F. Zeng, Z. Liu, Energy Technol. 6 (2018) 1283–1289. [37] Q. Dong, Y. Fang, Y. Shao, P. Mulligan, J. Qiu, L. Cao, J. Huang, Science 347 (2015) 967–970. [38] B. Yang, K. Han, Acc. Chem. Res. 52 (2019) 3188–3198.
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·DMF and GBL were respectively used to fabricate quasi 2D PSCs. ·A high PCE of 11.65% was achieved for 2D PSCs processed from GBL. ·Higher quality 2D perovskite was prepared by using GBL with reduced pinholes. ·Crystallinity and light absorption of 2D perovskite were improved by using GBL.
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Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers”. Guanchen Liu, Zhihai Liu, Fanming Zeng, Xinyu Wang, Shuangcui Li, Xiaoyin Xie 2020-2-5
Statement of Author contributions The authors of “High performance two-dimensional perovskite solar cells based on solvent induced morphology control of perovskite layers” Published in Chemical Physics Letters, declare that our contributions for this paper are as follow: Guanchen Liu: Methodology, Investigation,Writing - Original Draft. Zhihai Liu: Formal analysis,Writing: Review & Editing, Fanming Zeng: Resources, Writing-Review & Editing, Supervision. Xiaoyin Xie: Resources, Writing-Review & Editing, Supervision. Shaungcui Li: Review & Editing Xinyu Wang: Testing, Review & Editing
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