Trap-State Passivation by Nonvolatile Small Molecules with

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C: Energy Conversion and Storage; Energy and Charge Transport

Trap-State Passivation by Nonvolatile Small Molecules with Carboxylic Acid Groups for Efficient Planar Perovskite Solar Cells Lin Guan, Nan Jiao, and Yiping Guo J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b02621 • Publication Date (Web): 24 May 2019 Downloaded from http://pubs.acs.org on May 24, 2019

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The Journal of Physical Chemistry

Trap-State

Passivation

by

Nonvolatile

Small

Molecules with Carboxylic Acid Groups for Efficient Planar Perovskite Solar Cells Lin Guan,† Nan Jiao,† Yiping Guo,*,† †State

Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering,

Shanghai Jiao Tong University, Material Building D, 800 Dongchuan Road, Minhang District, Shanghai 200240, China

ABSTRACT Trap-state passivation has been validated to efficiently improve the performance of perovskite solar cells. Small volatile molecules and polymers both have the ability to reduce the trap states in perovskite. Here in, we demonstrate the feasibility of passivation by nonvolatile small molecules with carboxylic acid groups such as benzoic acid, p-phthalic acid and trimesic acid. They can obviously increase the fill factor of the photocurrent density-voltage curves. Furthermore, the relationship between molecular structure and passivation effect is proposed by fixing the concentration of carboxylic acid groups. Trimesic acid doped perovskite solar cells significantly increase the power conversion efficiency from 12.52 ± 0.67 to 14.51 ± 0.81 (champion efficiency, 15.81%) under standard AM 1.5-G illumination. Our work expands the chemical additives in perovskite and further demonstrates how the additive molecular structure influences the performance of solar cells.

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INTRODUCTION

Owing to suitable band gaps, facile film deposition methods and excellent optical properties, hybrid organometal halide perovskites have been extensively investigated for optoelectronic applications, especially perovskite solar cells (PSCs). During recent years, certificated power conversion efficiency (PCE) of 24.2% has been realized after continuously rapid improvement on the quality of perovskite film and structural optimization1-5. It is well known that grain boundaries and under-coordinated ions substantially exist in the polycrystalline perovskite film, like other semi-conductor (e.g., Si) films6-8. Therefore, defect states at grain boundaries in perovskite films would unavoidably lead to higher nonradiative recombination rates and energy loss. The difference of electrical potentials and ion migration rates between grain boundaries and bulks has been investigated by Yun et al.9 and Shao et al.10 Such difference would exert harmful microcosmic effects on electrical properties, which finally result in macroscopically worse performance of PSCs, such as lower open circuit voltage (VOC), fill factor (FF), and long-term stability, etc. Thus, defect passivation of the perovskite films is a wise strategy for boosting PCE, especially in planar PSCs. Small volatile molecules, such as chloroform and pyridine, have been applied to passivate defect states effectively by coordinating with Pb atoms11-15. Zuo et al.16 demonstrated the passivation effect of long-chain polymers with different functional groups (amino, Lewis base pyridine and carboxylic acid groups). These polymers can be stably localized at grain boundaries and strongly coordinated with the perovskite. However, it is hard to form high quality films for polymer doped perovskite via conversional anti-solvent methods. On the other hand, nonvolatile small molecules are rarely reported for passivation as effective additive in perovskite layer17. Additionally, benzoic acid (BA) has been widely used as


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a ‘template’ to form self-assembled monolayers (SAMs) to modify the charge transfer layers18-20. Considering its carboxylic acid groups, BA and its derivatives may also be potential to passivate defects in perovskite layers. On the other hand, the PSCs by using mesoporous TiO2 as electron transfer layer (ETL) can be achieved PCE over 20% nearly without hysteresis21,22. However, the stability of perovskite can be negatively affected by compact TiO2 under ultraviolet illumination23,24 due to light-induced desorption of surface-adsorbed oxygen25. Researches show that SnO2 based PSCs exhibit better stability26,27. Besides, SnO2 layer can be sintered at a lower temperature than mesoporous TiO2 (>450°C). Therefore, SnO2 or SnOx is widely considered to replace TiO2 in order to improve the stability27-29 of planar PSCs. In this work, we obtained effective defect passivation results by doping BA, p-phthalic acid (PTA) and trimesic acid (TA) in perovskite films using SnOx as ETL. Firstly, we optimized the doping concentration of carboxylic acid groups (c(-OOH)) by adding different amount of BA. Secondly, BA, PTA and TA were doped separately at the same c(-OOH) to discuss whether the concentration of molecules and relative position of -OOH can affect the passivation. Interestingly, we find that BA doped samples statistically exhibited lower VOC than that of reference samples (Ref for short), while doping PTA or TA successfully enhanced the VOC. By doping 0.067% TA, the PCE can be increased to 14.51 ± 0.81 (champion efficiency, 15.81%) versus Ref (12.52 ± 0.67). EXPERIMENTAL SECTION Materials. PbI2 (99.9%), 4-tert-butylpyridine (t-BP) and Spiro-OMeTAD were purchased from Yingkou Optimal Choice Trade CO., Ltd. (China). N, N-Dimethylformamide (DMF, anhydrous,


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99.8%), gamm-Butyrolactone (GBL, anhydrous, 99.9%) and Dimethylsulphoxide (DMSO, anhydrous) were purchased from Aladdin reagent. Chlorobenzene (CB, anhydrous, 99.8%) and Li-bis (trifluoromethanesulfonyl) imide (Li-TFSI) were purchased from Sigma-Aldrich. SnCl2·2H2O (SP) came from MACKLIN reagent. MAI came from Shanghai MaterWin New Materials Co, Ltd (China). Solar cell fabrication. Patterned FTO glass was soaked in piranha solution for 10 min and ultrasonically cleaned with deionized water and ethanol for 30 min, respectively. SnCl2·2H2O (0.08 M) was dissolved in ethanol and then the solution was stirred under oxygen atmosphere for about one day. The precursor was spin-coated on FTO substrates at 3000 rpm for 30s, followed by annealing at 190°C for 1h. PbI2 and MAI (1:1 / n:n) were dissolved in the mixture of DMF, DMSO and GBL (4:3:3 / v:v) for 1.0M perovskite precursor solution under constant stirring at 50°C. BA, TMA and TA (0.036 M) were dissolved respectively in DMSO for further doping in MAPbI3 solution. The perovskite layer was deposited on SnOx film at 1000 rpm for 15s and 5000 rpm for 25s. Then, 200 μL CB was dropped at about 14s before the end of the second step. Spiro-OMeTAD solution was prepared by dissolving 72.3 mg Spiro-OMeTAD, 28.8 μL t-BP and 17.5 μL Li-TFSI solution (520 mg / mL in acetonitrile) in 1 mL CB. It was spin-coated on the perovskite layer at 4000 rpm for 30s. Finally, an 80 nm Ag counter electrode was thermal evaporated on the SpiroOMeTAD layer to complete the fabrication of devices. Characterization. X-ray diffraction (XRD) patterns were measured by Rigaku D/MAX 2400 diffractomete (Cu Kα). UV−vis spectra were measured by Agilent UV−vis spectrophotometer. Morphologies of perovskite films and cross section of PSCs were characterized by Hitachi S-4800 field-emission scanning electron microscopy (SEM). The Keithley 2400 source meter was applied to record the J-V curves of PSCs under AM 1.5G illumination. The external quantum efficiency


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(EQE) spectra and integrated current density were measured by SM-250 Hyper Monolight system. Perovskite films covered by PMMA were used to characterize the steady-state photoluminescence (PL) spectra and time-resolved PL (TRPL) decay by steady-state and time-resolved fluorescence spectrofluoromete. The electrochemical impedance spectroscopy (EIS) was measured at dark by impedance/gain-phase analyzer (Solartron SI 1260) from 100 kHz to 10 Hz at different bias voltages. Fourier Transform infrared (FTIR) spectrum was measured by PerkinElmer Spectrum 100. The perovskite films were prepared on the NaCl substrates.

RESULTS AND DISCUSSION PSCs were fabricated with the structure of FTO / SnOx / perovskite / Spiro-OMeTAD / Ag. Three additives were doped in perovskite (e.g., TA). A suitable c(-OOH) was firstly investigated by doping BA with different contents (0, 0.08%, 0.2% and 0.5% vs MAPbI3). Figure S1 presents the photocurrent density-voltage (J-V) curves of different devices. It is found that the PSC based on 0.2% BA shows the best performance of 14.74% (13.57% of Ref), which confirms the passivation effect of –OOH. However, when the content of BA is over 0.5%, the PCE of devices begins to gradually attenuate. Therefore, c(-OOH) was controlled at 0.2% to demonstrate how molecular structure affects the passivation. Then BA, PTA and TA were chosen to compare the passivation effect for further study. According to the different amount of carboxylic acid groups on BA, PTA and TA, their doping concentration was set as 0.2%, 0.1% and 0.067%, respectively. The J-V curves of champion devices of Ref or doping samples are presented in figure 1a. All doped samples exhibit better PCE than Ref. It is worth noting that the 0.067% TA doped PSC (0.067% TA for short) shows obviously better performance with a VOC of 1.07V, a JSC of 20.9 mA/cm2, a


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FF of 0.704 and a PCE of 15.81%, in comparison with the Ref (a VOC of 1.01V, a JSC of 20.5 mA/cm2, a FF of 0.656 and a PCE of 13.57%). Both Ref and 0.0067% TA have negligible hysteresis as shown in figure 1b, which reveals a relative judiciously evaluation of PCE. Furthermore, in figure 1c, steady-state JSC and output power are applied to simulate the real working condition of PSCs. The decay of voltage was 0.17s. The 0.067% TA at a bias voltage of 0.7734V exhibits a higher output PCE around 15.5% than Ref at 0.7133V (a PCE about 12.9%). A steady-state output at longer time was demonstrated in figure S2. The decay was adjusted to 1s to prolong the test time. Interestingly, a more obvious fluctuation is found at longer decay time. The unencapsulated sample of 0.067% TA shows a bit better stability than Ref. For demonstrating the different effect of defect passivation, the statistical results of VOC, JSC, FF and PCE are listed in figure 2a-d. Remarkably, the VOC of 0.1% PTA doped PSCs (0.1% PTA for short) and 0.067% TA is statistically higher than that of Ref, while 0.2% BA doped PSCs (0.2% BA for short) seems lower as shown in figure 2a. Zuo et al.16 has reported the higher VOC after defect passivation by polyacrylic acid (PAA). Moreover, in accordance to the previous report19,20, no significant increase on VOC was found after ETL or hole transfer layer (HTL) decorated by BA SAM. The planar perovskite film was deposited on SnOx as shown in figure 3a. Thus, the loss of VOC in 0.2% BA can be attributed to the weak contract between BA and perovskite (SnOx) when the -OOH is coordinated with SnOx (perovskite). In contrast to BA, PTA and TA can coordinate with both SnOx and perovskite as illustrated in figure 3b. Their good contact at interface, as well as coordination with Pb, makes 0.1% PTA and 0.067% TA show higher VOC than Ref. In figure 2b and 2c, JSC and especially FF of all doped samples are statistically higher than that of Ref. The increase of JSC and FF results from the reduction of the defects and carrier recombination at grain boundaries by additive coordination. Therefore, an obvious promotion of PCE is obtained as


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shown in figure 2d. Additionally, the higher FF but lower VOC of 0.2% BA results in the similar PCE in average of 0.2% BA and 0.1% PTA. Comparing with 0.1% PTA, the lower concentration of TA seems to be beneficial to further increase of VOC and FF, which finally lead to the better performance of 0.067% TA. Thus, it can be concluded that the better contact at interface and lower concentration of matrix (functional groups with no effect of passivation) can decrease the defects more effectively. Figure S3 shows the XRD patterns of perovskite layers with three additives (BA, PTA and TA). They all exhibit the pure perovskite phase without PbI2 and similar full width at half maxima (FWHM) around 0.16 of (110) peaks. No obvious phase change can be seen in the XRD patterns. The cross-section SEM images in figure S4 exhibits the PSCs fabricated on FTO glasses. The SnOx layer spin-coated on FTO seems negligible under the perovskite layer. For identifying the existence of SnOx layer, Top-view images of bare FTO and SnOx layer are shown in figure S5. The thickness of perovskite doped or not is similar around 250 nm, which is independent of the additives. Taking the uv-vis spectrum in figure S6 and SEM images in figure S7 into consideration, our doping in perovskite has almost no significant influence on the crystalline, morphologies or thickness of perovskite films. BA, PTA and TA doped in perovskite cannot affect the crystallization progress of perovskite. Their main distribution at the grain boundary finally results in the weak relation between addition of BA, PTA or TA and morphologies of perovskite. Therefore, the performance promoted by doping BA, PTA or TA can be attributed to the grain boundary passivation because of the coordination between Pb and -COOH. Further characterization revealing the difference after doping was carried out to certify the effect of reducing the trap states.


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FTIR spectrum was demonstrated in Figure S8 to testify the existence of TA in perovskite films. To increase the intensity of TA, we use 1% TA doped perovskite to show the characteristic peaks of TA. Comparing with Ref, the transmittance of peak near 1250 nm is lower than the peak around 1100 nm. And the width of the peak near 1250 nm in 1% TA doped perovskite seems larger than Ref, which is in accordance with the doping of TA. Figure 4a shows the EQE spectra of Ref and 0.067%TA. Both curves of Ref and 0.067%TA exhibit a wide photo-response region from 300 nm to 800 nm. The rapid decrease of EQE at 650 nm is possibly related to the thinner perovskite layer by comparing with other researches30. The higher EQE of 0.067%TA than Ref means that more electrons generated by light at wide range are transferred to the electrodes. Integrated JSC calculated by EQE is 19.73 mA/cm2 and 18.57 mA/cm2 of 0.067%TA and Ref, respectively. This result is a bit lower than the statistical average JSC in Figure 2b. The higher Integrated JSC and EQE of 0.067%TA can response the lower density of traps, in which the electrons are easily recombined to result in a lower current density. Therefore, the doping of TA prevents the recombination of electrons to realize the trap passivation. For a better insight of charge properties in perovskite before and after doped by TA, Figure 4b compares the PL spectra of perovskite layer of Ref and 0.067% TA. The doping of TA greatly increase the intensity of PL spectra at about 770nm, which reveals a lower nonradiative decay rate of 0.067% TA doped perovskite than that in Ref. This result strongly proves that the coordination between Pb and –COOH decrease the defects and recombination of charge carriers at grain boundary. Therefore, the better performance of 0.067% TA discussed above are in accord with the higher PL spectra. Additionally, TRPL decay spectra in Figure 4c were operated to characterize the quenching of free carriers. The curves are fitted by the double-exponential function. It is well acknowledged that


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the fast decay lifetime (τ1) and the slow decay lifetime (τ2) accounts for a radiative bimolecular decay and the trap-assisted recombination, respectively. τ1 of the TA doped perovskite layer is 4.2 ns, which is almost the same as that in Ref (3.8 ns). τ2 of perovskite layers in 0.067% TA and Ref are 32.7 ns and 14.5 ns, respectively. A longer lifetime exhibits lower recombination rate of free carriers excited by light. Thus, by doping TA, defects in perovskite have been effectively decreased. The less recombination proved by PL spectra and TRPL decay spectra facilitates the carrier transportation in perovskite and finally decrease the energy loss and enhance the performance in PSCs. EIS was widely carried out to study the kinetic processes in PSCs. Bias voltage from 0.7 V to 0.9 V and amplitude sinusoidal voltage of 10 mV was added on samples to measure the Nyquist plots at dark. The parameters, such as charge recombination resistance (Rrec) and capacitance can be also utilized to investigate the defects in perovskite films. Figure 5a shows the Nyquist plots of Ref and 0.067% TA at a bias voltage of 0.75V. The typical semicircle, similarly demonstrated in some articles16,31, is related to the Rrec at the perovskite films as well as the interfaces of perovskite and charge transfer layers. The series resistance (Rs) of the solar cells is relatively much smaller than Rrec. Thus, RS cannot be observed clearly in the plots. The larger curve of 0.067% TA is associated with higher Rrec than Ref. Moreover, the Rrec of Ref and 0.067% TA is presented and linear fitted as a function of bias voltage (0.7-0.9V) in figure 5b. The Rrec and its difference of the two samples, has negative correlation with bias voltage. The results indicates that the defect passivation by doping TA limits the charge recombination effectively, which facilitates the charge injection to SnOx and Spiro-OMeTAD for increasing VOC and JSC. As illustrated in figure 5c, the capacitance (C) is linear fitted under the logarithmic coordinate. C can reflex the relative amount of charge carriers stored at the traps. According to the previous researches15,32, the density of trap


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states (DOS) are proportional to C. Therefore, the fitting curves of DOS versus energy level in figure 5d can be calculated from the linear relationship in figure 5c. The lower CPE and DOS of 0.067% TA at all bias voltages show less defects after TA coordinating with Pb. This result is in agreement with the TRPL decay spectra in analyzing the kinetic properties after doping TA. CONCLUSIONS In summary, the doping of BA, PTA and TA, especially TA, as demonstrated above is efficient to increase the PCE of PSCs. The PCE has been increased from 12.52 ± 0.67 to 14.51 ± 0.81 (champion efficiency, 15.81%) by doping 0.067% TA. The additives does not obviously influence the crystalline or morphologies of perovskite layers. Therefore, the better performance is attributed to the trap passivation of the coordination between the carboxylic acid groups and Pb. Furthermore, by controlling the concentration of –OOH, the different passivation effect of BA, PTA and TA can be explained by their concentration and the contract at the interface between SnOx and perovskite. The various VOC of 0.2% BA and 0.1% PTA seems relative to the change of the interface. The further improvement of 0.067% TA than 0.1% PTA should be attributed to the molecular structure. Less concentration of matrix (benzene ring in this article) can result in better passivation effect. Moreover, as depicted in Figure S1, lower coordinated –OOH (0.08% BA) may lead worse performance than 0.2% BA. Thus, the low concentration of TA and PTA does not greatly decrease the concentration of coordinated –OOH from the discussion above, which partially proved the homogeneous distribution of additives in perovskite layers. The decreased density of trap states in 0.067% TA is successfully evidenced by the investigation of EQE, PL, TRPL spectra and electronic impedance measurements. ASSOCIATED CONTENT


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Supporting Information. J-V curves of Ref, 0.08% BA, 0.2% BA and 0.5% BA, XRD patterns, UV-vis spectra and SEM images of perovskite films with or without additives, cross-section SEM images of Ref, 0.2% BA, 0.1% PTA and 0.067%TA, SEM images of FTO and SnOx deposited on FTO and normalized steady-state output power of Ref and 0.067% TA. (PDF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Y.G.). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by Natural Science Foundation of China (Nos. 11874257 and 11474199). Instrumental Analysis Center of Shanghai Jiao Tong University and National Engineering Research Center for Nanotechnology are sincerely acknowledged for assisting with relevant analyses. REFERENCES (1) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T., Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells. J. Am. Chem. Soc. 2009, 131, 6050-6051.


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(21)Li, X.; Bi, D. Q.; Yi, C. Y.; Decoppet, J. D.; Luo, J. S.; Zakeeruddin, S. M.; Hagfeldt, A.; Gratzel, M., A Vacuum Flash-Assisted Solution Process for High-Efficiency Large-Area Perovskite Solar Cells. Science 2016, 353, 58-62. (22)Saliba, M.; Matsui, T.; Domanski, K.; Seo, J. Y.; Ummadisingu, A.; Zakeeruddin, S. M.; Correa-Baena, J. P.; Tress, W. R.; Abate, A.; Hagfeldt, A. et al., Incorporation of Rubidium Cations into Perovskite Solar Cells Improves Photovoltaic Performance. Science 2016, 354, 206-209. (23)Shin, S. S.; Yeom, E. J.; Yang, W. S.; Hur, S.; Kim, M. G.; Im, J.; Seo, J.; Noh, J. H.; Seok, S. I., Colloidally Prepared La-Doped BaSnO3 Electrodes for Efficient, Photostable Perovskite Solar Cells. Science 2017, 356, 167. (24)Pathak, S. K.; Abate, A.; Ruckdeschel, P.; Roose, B.; Gödel, K. C.; Vaynzof, Y.; Santhala, A.; Watanabe, S.-I.; Hollman, D. J.; Noel, N. et al., Performance and Stability Enhancement of Dye-Sensitized and Perovskite Solar Cells by Al Doping of TiO2. Adv. Funct. Mater. 2014, 24, 6046-6055. (25)Leijtens, T.; Eperon, G. E.; Pathak, S.; Abate, A.; Lee, M. M.; Snaith, H. J., Overcoming Ultraviolet Light Instability of Sensitized TiO2 with Meso-Superstructured Organometal TriHalide Perovskite Solar Cells. Nat. Commun. 2013, 4, 2885. (26)Jiang, Q.; Zhang, L.; Wang, H.; Yang, X.; Meng, J.; Liu, H.; Yin, Z.; Wu, J.; Zhang, X.; You, J., Enhanced Electron Extraction Using SnO2 for High-Efficiency Planar-Structure HC(NH2)2PbI3-Based Perovskite Solar Cells. Nat. Energy 2016, 2, 16177.


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(27)Wang, L.; Zhou, H.; Hu, J.; Huang, B.; Sun, M.; Dong, B.; Zheng, G.; Huang, Y.; Chen, Y.; Li, L. et al., A Eu3+-Eu2+ Ion Redox Shuttle Imparts Operational Durability to Pb-I Perovskite Solar Cells. Science 2019, 363, 265. (28)Park, M.; Kim, J.-Y.; Son, H. J.; Lee, C.-H.; Jang, S. S.; Ko, M. J., Low-Temperature Solution-Processed Li-Doped SnO2 as an Effective Electron Transporting Layer for HighPerformance Flexible and Wearable Perovskite Solar Cells. Nano Energy 2016, 26, 208-215. (29)Ren, X.; Yang, D.; Yang, Z.; Feng, J.; Zhu, X.; Niu, J.; Liu, Y.; Zhao, W.; Liu, S. F., Solution-Processed Nb:SnO2 Electron Transport Layer for Efficient Planar Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2017, 9, 2421-2429. (30)Zhu, X.; Xu, Z.; Zuo, S.; Feng, J.; Wang, Z.; Zhang, X.; Zhao, K.; Zhang, J.; Liu, H.; Priya, S. et al., Vapor-Fumigation for Record Efficiency Two-Dimensional Perovskite Solar Cells with Superior Stability. Energy Environ. Sci. 2018, 11, 3349-3357. (31)Qin, J.; Zhang, Z.; Shi, W.; Liu, Y.; Gao, H.; Mao, Y., Enhanced Performance of Perovskite Solar Cells by Using Ultrathin BaTiO3 Interface Modification. ACS Appl. Mater. Interfaces 2018, 10, 36067-36074. (32)O'Regan, B. C.; Scully, S.; Mayer, A. C.; Palomares, E.; Durrant, J., The Effect of Al2O3 Barrier Layers in TiO2/Dye/CuSCN Photovoltaic Cells Explored by Recombination and DOS Characterization Using Transient Photovoltage Measurements. J. Phys. Chem. B 2005, 109, 4616-4623.


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Table 1. Device parameters of Ref, 0.2% BA, 0.1% PTA and 0.067% TA Sample

VOC (V)

JSC (mA/cm2)

FF

1.018 (0.996

20.56

0.656

(20.05

PCE (%) (0.625

13.57 (12.52

Ref ± 0.016) 0.2% BA 0.1% PTA 0.067% TA

1.015 (0.977 ± 0.020) 1.054 (1.015 ± 0.028) 1.074 (1.029 ± 0.027)

± 0.45) 21.38

± 0.023) (20.66

± 0.67) 21.32

± 0.51)

(0.676

± 0.020) (20.54

± 0.47) 21.54

0.723

± 0.67)

0.695

± 0.70) (0.658

± 0.033) (20.77

0.705

14.74 (13.65

14.57 (13.57 ± 0.73)

(0.679

± 0.024)

15.81 (14.51 ± 0.81)


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TOC Graphic


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Figure 1. (a) J-V curves of Ref, 0.2% BA, 0.1% PTA and 0.067% TA. (b) J-V hysteresis behavior and (c) steady-state JSC and output power of Ref and 0.067% TA.



Figure 2. Statistical results with different additives of (a) VOC, (b) JSC, (c) FF, (d) PCE.


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Figure 3. Schematic diagram of (a) the device architecture and additives (e.g., TA) doped in perovskite and (b) the interface between perovskite and SnOx with BA, PTA and TA.



Figure 4. (a) EQE spectra and the integrated current density of Ref and 0.067% TA. (b) PL spectra and (c) TRPL decay spectra of perovslite and 0.067% TA doped perovskite.


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Figure 5. Electronic impedance measurements of Ref and 0.067% TA. (a) Nyquist plots measured at a bias of 0.75V at dark. (b) Rrec and (C) C at different bias voltages. (d) DOS versus electron energy level.


Trap-State Passivation by Nonvolatile Small Molecules with

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