Suppression of Charge Carrier Recombination in Lead-Free Tin

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Energy Conversion and Storage; Plasmonics and Optoelectronics

Suppression of Charge Carrier Recombination in LeadFree Tin Halide Perovskite via Lewis Base Post-Treatment Muhammad Akmal Kamarudin, Daisuke Hirotani, Zhen Wang, Kengo Hamada, Kohei Nishimura, Qing Shen, Taro Toyoda, Satoshi Iikubo, Takashi Minemoto, Kenji Yoshino, and Shuzi Hayase J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b02024 • Publication Date (Web): 18 Aug 2019 Downloaded from pubs.acs.org on August 18, 2019

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The Journal of Physical Chemistry Letters

Suppression of Charge Carrier Recombination in Lead-free Tin Halide Perovskite via Lewis Base Post-treatment Muhammad Akmal Kamarudina‡*, Daisuke Hirotanib‡, Zhen Wangb, Kengo Hamadab, Kohei Nishimuraa, Qing Shenc, Taro Toyodac, Satoshi Iikubob, Takashi Minemotod, Kenji Yoshinoe, Shuzi Hayasea* aInfo-Powered

Energy System Research Center (i-PERC), The University of Electro-

Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585 Japan aGraduate

School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4

Hibikino, Wakamatsu-ku, Kitakyushu-shi, Fukuoka-ken, 808-0196 Japan cFaculty

of Informatics and Engineering, The University of Electro-Communications, 1-5-1

Chofugaoka, Chofu, Tokyo, 182-8585 Japan dDepartment

of Electrical and Electronic Engineering, Faculty of Science and Engineering,

Ritsumeikan University, 1-1-1, Nojihigashi, Kusatsu, Shiga, 525-8577 Japan eDepartment

of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuen

Kibanadai Nishi, Miyazaki, 889-2192 Japan *E-mail: [email protected] (M.A.K), [email protected] (S.H.)

ACS Paragon Plus Environment

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Abstract

Lead-free tin perovskite solar cells (PSCs) showed the most promise to replace the more toxic lead-based perovskite solar cells. However, the efficiency is significantly than that of lead-based PSCs as a result of low open-circuit voltage. This is due to the tendency of Sn2+ to oxidize into Sn4+ in the presence of air together with the formation of defects and traps caused by the fast crystallization of tin perovskite materials. Here, post-treatment of tin perovskite layer with edamine Lewis base to suppress the recombination reaction in tin halide PSCs resulting in efficiencies more than 10 %, which is the highest reported efficiency to date for pure tin-halide PSCs. The X-ray photoelectron spectroscopy data suggest that the recombination reaction is originated from the nonstoichiometric Sn:I ratio rather than Sn4+:Sn2+ ratio. Amine-group in edamine bonded the under-coordinated tin, passivating the dangling bonds and defects resulting in suppressed charge carrier recombination.

TOC


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Tin halide perovskites show the most promise among other alternative lead-free perovskite materials.1 Among the advantages of tin-based perovskites are the ideal bandgap which is closer to the Shockley-Queisser limit, the ability to capture hot electrons and have high charge carrier mobilities.2–5 However, the highest reported power conversion efficiency based on tin halide perovskites is still lower than 10% which is significantly lower than lead-based perovskites.6 This low efficiency is mainly contributed by the tendency of Sn2+ to oxidize into Sn4+ resulting p-type doping and hence high background carrier density.7 Another reason is due to the tin and iodide vacancies as a result of weak bonding energy of these elements.8 Fast crystallization of tin halide perovskite promotes the formation of pinholes and rough surface finally leading to higher charge carrier recombination rate.9,10 All these results in large open-circuit voltage loss of more than 0.8 eV.11 In order to overcome these problems, several techniques have been explored. One technique uses tin powder as a reducing agent and a compensator which improves the Sn2+ content within the perovskite precursor solution.12 Exposing tin perovskite layer to vapor of reducing agent during annealing process has also been shown to suppress tin oxidation and thus reduce the defect density.13 Ran et al. reported surface passivation of tin perovskite using a type of 2D perovskite precursor, phenethylammonium iodide (PEAI), forming quasi 2D-3D structure at the PEDOT:PSS/perovskite interface.14 PEAI helped to decrease the surface roughness and increase the device stability of the solar cell due to the lower acidity. Another method to improve the perovskite stability and reduce the defects is by using additives.15,16 These additives have been reported to passivate the grain boundaries and improve the perovskite crysallinity. However, VOC loss is still large which limit the performance of tin-based PSCs to below 10 %.


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The report by Jokar et al. showed that the addition of ethylenediammonium diiodide which is an organic salt helped to slow down the crystallization of tin halide perovskite. However, the PSC devices still showed a large VOC loss of more than 0.8 eV. This suggests that apart from bulk effect, the surface recombination might also affect the device performance. Hence, surface passivation is one way to solve this problem. Here, we introduced a simple post-treatment of tin perovskite using bidentate amine, ethane-1,2-diamine (edamine) to passivate the surface defects in order to increase the VOC. The increased of the VOC by up to 0.1 V is contributed by the suppression of tin oxidation and stabilization of under-coordinated Sn as suggested by the X-ray Photoelectron Spectroscopy (XPS) measurements. In addition, the presence of unreacted SnI2 has been removed and bigger grain sizes has been obtained with edamine passivation. By optimizing the edamine concentration, we managed to improve the performance of tin perovskite solar cell from 8.09 % up to 9.37 % and reaching a high efficiency of 10.18% after 1 week. We first investigated the X-ray diffraction pattern (XRD) of the perovskite with and without edamine treatment prepared on PEDOT:PSS-coated FTO substrates to resemble the solar cell structure. Figure 1a shows the XRD pattern with typical peaks corresponding to [100], [120] [200], and [211] facets at 14.0o, 24.4o ,26.4o and 33.7o, respectively, of FA0.98EDA0.01SnI3 can be observed similar to what has been reported previously.17 No new peaks appeared upon edamine passivation, suggesting that the perovskite layers still retain their cubic phase. Additionally, the peak at 2θ = 12.60° which corresponds to the unreacted SnI2, noticeably decreased as a result of chemical interaction between SnI2 and edamine (Figure S1a). Edamine passivation clearly helped to improve preferred orientation. The effect of edamine post-treatment on the optical property of the perovskite is investigated using UV-Vis spectroscopy. From the UV-Vis spectra, the absorption onset can be seen slightly


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shifted to lower wavelength (Figure 1b). We calculated the bandgap of the perovskite materials using Tauc plot, giving the values of 1.370 eV, 1.381 eV, 1.385 eV, 1.381 eV and 1.382 eV for 0 mM, 0.01 mM, 0.05 mM, 0.1 mM and 0.5 mM edamine passivation, respectively. Using Photoelectron Yield Spectroscopy (PYS), we determined the value of valence band for each material. The valence band value becomes shallower upon treatment with edamine despite the insulating nature of edamine (Figure S1b). One plausible explanation for this is that the amine which has free electron pair act as an electron donating group to the perovskite layer filling the valence band states. From the Eg values determined from UV-Vis and the valence band values obtained from PYS measurements, we estimated the conduction band values and constructed the energy band diagram as shown in Figure 1c. The presence of edamine on the surface of is also confirmed from the Fourier-transform infrared spectroscopy (FTIR) measurements. Figure 1d shows the FTIR spectra comparing the samples before and after edamine passivation. The peaks around 1500-1550 cm-1, 1580-1650 cm1,

and 1640-1690 cm-1corresponding to the N-O stretching, N=H stretching and N-H stretching,

respectively, increased with higher concentration of edamine, suggesting that edamine is indeed passivating the perovskite surface (Figure S2a). Interestingly, the peak around 2300-2400 cm-1 corresponding to CO2 appeared upon edamine passivation despite prior to the measurements we have performed background CO2 correction (Figure S2b). This is not surprising as there are extensive studies on the reversible reaction of amine with gaseous CO2.18,19 Although the effect of this phenomena on the long term device stability is yet to be seen and further study needed to be performed.


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Figure 1. a) XRD patterns of FA0.98EDA0.01SnI3 with different concentration of edamine. b) Normalized UV-Vis absorption spectra of the perovskite samples. c) Schematic band energy diagram constructed from UV-Vis and PYS measurements. d) FTIR spectra of tin perovskites coated with concentration of edamine. We investigate the effect of edamine passivation on the perovskite morphology using Scanning Electron Microscopy (SEM) as shown in Figure 2. For the reference sample (Figure 2a), we could see the formation of white flakes on the surface which could be unreacted SnI2 and the surface seems rough. Upon 0.01 mM edamine (Figure 2b) passivation, the white flakes dissappeared either as a result of interaction with edamine molecules leading to more smooth morphology. Increasing the edamine concentration up to 0.05 mM (Figure 2c) removes the


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white flakes completely while still maintaining the smooth surface. However, with 0.1 mM (Figure 2d) and 0.5 mM edamine (Figure 2e) passivation, the surface morphology changed drastically where the surface became rough and decreased in the grain sizes. This is to be expected due to the basicity of edamine which could dissolve the perovskite layer. Figure S3 shows the SEM images at x10000 magnification. The increased in the grain size from ~100 nm up to ~300 nm after edamine post-treament can be attributed to the edamine molecules reacting with the unreacted SnI2 forming cubic phase perovskite especially near the grain boundaries. Additionally, recent report also suggest that bialkyl amine could bridge neighbouring perovskite grains, resulting in compact and pin-hole less films.20 Although it has been suggested that the addition of edamine could form a mesoporous tin perovskite structure as suggested by Ke et al., we could not observe this phenomena in this work. 21


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Figure 2. Top view of SEM images of a) 0 mM, b) 0.01 mM, c) 0.05 mM, d) 0.1 mM and e) 0.5 mM edamine -passivated tin perovskite samples prepared on PEDOT:PSS-coated FTO substrates at x20000 magnification. Formation of white flakes are circled in red. To investigate the effect of edamine passivation on the solar cell performance, we fabricated inverted (p-i-n) structure solar cells. Champion J-V plot for each condition is given in Figure 3a and the photovoltaic parameters are tabulated in Table 1. The best performing reference device showed a short-circuit current density (JSC) of , VOC of V, fill factor (FF) of and efficiency (η) of 8.09 %. Upon 0.01 mM edamine post-treatment, the device performance improved to 8.90 %. This improvement is due to the higher JSC and VOC which can be explained from removal of unreacted SnI2 or complete conversion of SnI2 into perovskite at the surface as seen from SEM images. At an optimal concentration of 0.05 mM edamine, the solar cell reached the highest efficiency of 9.37 %, mainly contributed by the higher VOC. However, this came with lower JSC due to the insulating nature of edamine which reduces charge injection from the perovskite into the ETL. Trap passivation by edamine molecules is manifested by the enhanced VOC and this phenomena has been observed previously with Lewis bases.20,22 Further discussion on the origin of traps/defects will be given later in this report. For higher concentration of edamine posttreatment, although the VOC still improve, deterioration of the perovskite surface significantly affect the JSC and thus the efficiency is reduced compared to other devices. After 7 days storage in N2 atmosphere, both 0.05 mM and 0.1 mM edamine passivated device showed higher performance reaching 10.18 % and 10.05 %, respectively, which is the highest reported efficiency for pure tin perovskite solar cells (Figure 3b). The photovoltaic parameters of the devices after 7 days are tabulated in Table S1. The parameter distribution of fresh samples is given in Figure S4 with similar trend can be observed with 0.05 mM edamine passivated showed


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the best peformance, followed by 0.1 mM edamine passivated devices. The increased in the efficiency is mainly contributed by the improvement in the VOC which increased by as much as 0.1 V. Figure S5 shows the External Quantum Efficiency (EQE) plot for the champion cells after 1 week storage in the glove box. For all samples the absorption is up to 900 nm which agrees with our UV-Vis absorption spectra. The calculated JSC shows a decreasing trend similar to what have been observed from the J-V plot. Clearly the improvement in the efficiency is due to the enhanced VOC. Despite the extremely low JSC, 0.1 mM edamine-passivated sample still showed a VOC of 0.63 V. We

performed

Intensity‑Modulated

Photocurrent

Spectroscopy

(IMPS)

and

Intensity‑Modulated Photovoltage Spectroscopy (IMVS) to evaluate the understand the underlying electron transport and recombination mechanism (Figure S6).23,24 From these measurements, we can evaluate the electron recombination lifetime (τrec) and electron transport lifetime (τtr) using the following equations (1)

(2)

where fIMPS and fIMVS are the frequencies at which the imaginary part is minimum. τrec is evidently longer in the case of edamine passivated device than the reference device. Edamine passivated device exhibited slightly lower τtr which could be attributed to the higher energy barrier between the perovskite layer and ETL (Figure 3c). τrec is evidently longer in the case of edamine passivated device than the reference device. This suggests that the recombination rate is suppressed upon edamine passivation (Figure 3d). Both these results agree well with the solar


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cell trend where VOC is improved while JSC is slightly reduced. Using τrec and τtr values, we can calculate the charge collection efficiency according to the equation (3)

Overall, higher charge collection efficiency is observed upon edamine post treatment reaching 80 % at 100 % light intensity whereas at the same intensity, the reference cell only showed ηcc = 40 % (Figure 3e). This proves that edamine passivation not only suppresses recombination reaction but simultaneously improves charge collection through better energy alignment. Figure 3f shows the change of electron diffusion length as a function of light intensity. 0.05 mM edamine passivated device displayed longer diffusion length as compared to the reference device as a result of subdued charge recombination. From these measurements, it is evident that the low efficiencies of tin halide PSCs is limited by τrec rather than τrec. This is to be expected considering the p-type carrier density is high in the case of tin perovskites compared to lead-based perovskites. We have also calculated the electron diffusion length using IMPS and IMPV data by applying the following equation

where

is the diffusion coefficient.25 The diffusion length markedly increased with edamine

surface passivation which could be attributed by the passivation of the surface traps. At 100% light intensity, the diffusion length for edamine passivated device is almost 300 nm compared to 200 nm for the reference device. It is interesting to note that the diffusion length decreased with higher light intensity which is different in nature compared to that of MAPbI3 perovskite which showed almost constant diffusion length irrespective of light intensity.26


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Figure 3. Light J-V plot of champion FA0.98EDA0.01SnI3 with different concentration of edamine for a) fresh samples and b) after 7 days storage in the glovebox. a) Plot of transport lifetime as a function of light intensity between 0 mM and 0.05 mM edamine-passivated devices obtained from IMPS measurements. b) Plot of recombination lifetime as a function of light intensity of 0


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mM and 0.05 mM edamine-passivated devices obtained from IMVS measurements. c) Charge collection efficiency plot against light intensity comparing the reference tin perovskite solar cell device and edamine-passivated device. d) Plot of diffusion length as a function of light intensity of 0 mM and 0.05 mM edamine-passivated devices. Table 1. Photovoltaic parameters of fresh perovskite solar cells measured in the glovebox filled with Nitrogen. The values in parentheses are the average values based on 12 devices for each condition. Device

0 mM

0.01 mM

0.05 mM

0.1 mM

JSC

VOC

FF

η

(mA cm-2)

(V)

23.70

0.47

0.73

8.09

(23.13)

(0.48)

(0.65)

(7.21)

24.08

0.49

0.75

8.90

(23.24)

(0.49)

(0.68)

(7.82)

22.80

0.56

0.74

9.37

(21.74)

(0.55)

(0.72)

(8.68)

21.11

0.59

0.73

9.04

(16.89)

(0.59)

(0.70)

(7.02)

(%)


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0.5 mM

0.90

0.56

0.52

0.26

(0.62)

(0.43)

(0.42)

(0.13)

We performed Hall effect measurements comparing reference sample and 0.05 mM edamine passivated sample to investigate the electronic property of the bulk perovskite material (Table 2). The carrier density of the reference sample is 1.53 x 1016 cm-3 compared to -4.11 x 1015 cm-3 for 0.05 mM edamine passivated sample, 1 magnitude lower than the reference sample. Interestingly, the reference sample showed holes as the major charge carriers whereas upon 0.05 mM edamine passivation, the major charge carriers are electrons. Due to this, the conductivity of the 0.05 mM edamine passivated sample (1.14 x 10-3 S cm-1) is lower than that of the reference thin film (7.90 x 10-3 S cm-1). The carrier mobility also improved significantly upon edamine passivation, from 21.51 cm2 V-1 s-1 (reference) up to 74.10 cm2 V-1 s-1 (0.05 mM edamine). This could be explained from the reduced number of intrinsic traps within the perovskite and thus we could observe higher carrier mobility. The suppression of tin oxidation and iodide vacancies by edamine molecules is also one of the reasons for the reduced carrier density. Table 2. Electronic properties of the reference sample and 0.05 mM edamine-passivated sample obtained Hall effect measurements performed in the glovebox with N2 atmosphere. The values are average values for 4 different samples for each condition. Parameter

NHall

σ

μ

(cm-3)

(S cm-2)

(cm2 V-1 s-1)


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0 mM

1.53 x 1016

7.90 x 10-3

21.51

0.05 mM

-4.11 x 1016

1.14 x 10-3

74.10

To further understand the effect of edamine passivation on the perovskite layer, we performed XPS measurements. Figure 4 shows the narrow spectra of Sn which have been fitted with Gaussian fit to differentiate between Sn0, Sn2+ and Sn4+. The Sn peak for the reference (Figure 4a) and 0.05 mM edamine (Figure 4c) are broad. Typically, we would expect post treatment of tin perovskite will reduce the Sn4+:Sn2+ ratio which has always been the reason for low VOC and hence low efficiency. However, this is not the case in this work, although the Sn4+:Sn2+ ratio decreased upon edamine passivation, the decreased is not enough to explain the large improvement of VOC. We also performed Argon etching on the perovskite layer to investigate the change within the perovskite bulk where the Sn peaks for the reference (Figure 4b) and 0.05 mM (Figure 4d) samples became sharp. Here, the ratio of Sn4+ and Sn0 has been reduced significantly for both samples regardless of with or without edamine passivation although the Sn4+ and Sn0 content is much higher without edamine passivation. We could expect that edamine passivation mainly affect the surface rather than deep into the perovskite bulk. Additionally, the peak position of Sn2+ remain the same even after edamine passivation whereas the peak positions of Sn4+ and Sn0 shifted towards higher binding energy. This shift in the binding energy is a prove that there is a reaction occured between the Sn species with edamine molecules. Edamine is electron-rich which could donate two pairs of electrons to the under-coordinated Sn4+ species (dangling bonds) as shown in Figure S7.27 Dangling bonds have been known to act as recombination centers and in the case of silicon semiconductors where the amount of dangling bond is large, hydrogen is introduced to passivate these defects.28,29 These phenomena are not


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limited to tin-based perovskites but has also been studied in lead-based perovskites previously30,31. Table S1 shows the percentages of Sn species before and after Argon etching for the 2 samples. We also evaluated the ratio between Sn and I where we found that the perovskite suffers from a severe loss of I- which could explain the large VOC loss (Figure S8a).32 The Sn:I ratio for the reference sample is 1:1.08 compared to 1:1.19 for 0.05 mM edamine passivated sample. Upon Argon etching several nm into the perovskite bulk, the Sn:I ratio increased up to 1:1.85. This suggests that most of the recombination reaction is induced by the nonstoichiometric Sn:I ratio. Additionally, we also evaluated the Sn:O ratio with the highest ratio obtained for the reference sample (1:1.05) and 1:0.83 for the 0.05 mM edamine passivated sample (Figure S8b). Interestingly, the value of Sn:O ratio dropped to zero upon 10 s of Argon etching. These phenomena agrees well with previous report by Lee et al. explaining the instability of tin-based halide perovskites originate from the breaking of Sn-I bonds and degradation of the A site cations even at room temperature.33 Table S3 summarises the atomic percentage and ratio of different elements.


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Figure 4. Narrow XPS spectra of Sn 3d5/2 for a) 0 mM edamine and b) 0.05 mM edaminepassivated FA0.98EDA0.01SnI3 samples. Narrow XPS spectra after 10 s of Argon etching of c) 0 mM edamine and d) 0.05 mM edamine-passivated FA0.98EDA0.01SnI3 samples. In conclusion, high efficiency pure tin halide PSCs have been demonstrated via Lewis bases post-treatment. An optimal concentration of edamine converted the unreacted SnI2 into cubic phase perovskite and improved the perovskite surface morphology leading to smoother film and bigger grain sizes. In addition, edamine passivation prevented the perovskite layer from being oxidized and at the same time the amine group in edamine molecules helped to stabilize the under-coordinated Sn in the perovskite by donating free electron pairs. Interestingly, rather than tin oxidation, iodide deficiency as a result of nonstoichiometric Sn/I ratio is the main reason for


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charge recombination. These improvements contributed mainly to the enhanced VOC from an average of 0.49 V up to 0.59 V. Moreover, electronic properties such as the Hall effect mobility and carrier density have been enhanced significantly. As a result, an efficiency of 10.18 % has been obtained for a pure tin halide PSC, which is the highest reported value for lead-free PSC. This work suggests that, Sn-based lead-free PSCs can compete with lead PSCs through facile surface passivation technique. ACKNOWLEDGMENT M. A. K. and H. D. contributed equally to this work. The authors acknowledge the support from JST Mirai (JPMJMI17EA). SUPPORTING INFORMATION Experimental methods, XRD, PYS, FTIR, SEM, photovoltaic parameters, IPCE, IMPS, IMVS, XPS intensity. REFERENCES (1)

Ke, W.; Kanatzidis, M. G. Prospects for Low-Toxicity Lead-Free Perovskite Solar Cells. Nat. Commun. 2019, 10 (1), 965.

(2)

Fang, H.-H.; Adjokatse, S.; Shao, S.; Even, J.; Loi, M. A. Long-Lived Hot-Carrier Light Emission and Large Blue Shift in Formamidinium Tin Triiodide Perovskites. Nat. Commun. 2018, 9 (1), 243.

(3)

Mitzi, D. B.; Feild, C. A.; Schlesinger, Z.; Laibowitz, R. B. Transport, Optical, and Magnetic Properties of the Conducting Halide Perovskite CH3NH3SnI3. J. Solid State Chem. 1995, 114 (1), 159–163.


17


(4)

Page 18 of 22

Shockley, W.; Queisser, H. J. Detailed Balance Limit of Efficiency of P-N Junction Solar Cells. J. Appl. Phys. 1961, 32 (3), 510–519.

(5)

Takahashi, Y.; Hasegawa, H.; Takahashi, Y.; Inabe, T. Hall Mobility in Tin Iodide Perovskite CH3NH3SnI3: Evidence for a Doped Semiconductor. J. Solid State Chem. 2013, 205, 39–43.

(6)

Jokar, E.; Chien, C. H.; Tsai, C. M.; Fathi, A.; Diau, E. W. G. Robust Tin-Based Perovskite Solar Cells with Hybrid Organic Cations to Attain Efficiency Approaching 10%. Adv. Mater. 2019, 31 (2), 1–7.

(7)

Leijtens, T.; Prasanna, R.; Gold-Parker, A.; Toney, M. F.; McGehee, M. D. Mechanism of Tin Oxidation and Stabilization by Lead Substitution in Tin Halide Perovskites. ACS Energy Lett. 2017, 2 (9), 2159–2165.

(8)

Rajendra Kumar, G.; Kim, H. J.; Karupannan, S.; Prabakar, K. Interplay between Iodide and Tin Vacancies in CsSnI3 Perovskite Solar Cells. J. Phys. Chem. C 2017, 121 (30), 16447–16453.

(9)

Yokoyama, T.; Cao, D. H.; Stoumpos, C. C.; Song, T. Bin; Sato, Y.; Aramaki, S.; Kanatzidis, M. G. Overcoming Short-Circuit in Lead-Free CH3NH3SnI3 Perovskite Solar Cells via Kinetically Controlled Gas-Solid Reaction Film Fabrication Process. J. Phys. Chem. Lett. 2016, 7 (5), 776–782.

(10)

Hao, F.; Stoumpos, C. C.; Guo, P.; Zhou, N.; Marks, T. J.; Chang, R. P. H.; Kanatzidis, M. G. Solvent-Mediated Crystallization of CH3NH3SnI3 Films for Heterojunction Depleted Perovskite Solar Cells. J. Am. Chem. Soc. 2015, 137 (35), 11445–11452.


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Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(11)

Do Kim, H.; Miyamoto, Y.; Kubota, H.; Yamanari, T.; Ohkita, H. Open-Circuit Voltage Loss in CH3NH3SnI3 Perovskite Solar Cells. Chem. Lett. 2017, 46 (2), 253–256.

(12)

Gu, F.; Ye, S.; Zhao, Z.; Rao, H.; Liu, Z.; Bian, Z.; Huang, C. Improving Performance of Lead-Free Formamidinium Tin Triiodide Perovskite Solar Cells by Tin Source Purification. Sol. RRL 2018, 2 (10), 1800136.

(13)

Song, T. Bin; Yokoyama, T.; Stoumpos, C. C.; Logsdon, J.; Cao, D. H.; Wasielewski, M. R.; Aramaki, S.; Kanatzidis, M. G. Importance of Reducing Vapor Atmosphere in the Fabrication of Tin-Based Perovskite Solar Cells. J. Am. Chem. Soc. 2017, 139 (2), 836– 842.

(14)

Ran, C.; Xi, J.; Gao, W.; Yuan, F.; Lei, T.; Jiao, B.; Hou, X.; Wu, Z. Bilateral Interface Engineering toward Efficient 2D-3D Bulk Heterojunction Tin Halide Lead-Free Perovskite Solar Cells. ACS Energy Lett. 2018, 3 (3), 713–721.

(15)

Kayesh, M. E.; Matsuishi, K.; Kaneko, R.; Kazaoui, S.; Lee, J. J.; Noda, T.; Islam, A. Coadditive Engineering with 5-Ammonium Valeric Acid Iodide for Efficient and Stable Sn Perovskite Solar Cells. ACS Energy Letters. 2019, pp 278–284.

(16)

Tai, Q.; Guo, X.; Tang, G.; You, P.; Ng, T. W.; Shen, D.; Cao, J.; Liu, C. K.; Wang, N.; Zhu, Y.; et al. Antioxidant Grain Passivation for Air-Stable Tin-Based Perovskite Solar Cells. Angew. Chemie - Int. Ed. 2019, 58 (3), 806–810.

(17)

Jokar, E.; Chien, C. H.; Fathi, A.; Rameez, M.; Chang, Y. H.; Diau, E. W. G. Slow Surface Passivation and Crystal Relaxation with Additives to Improve Device


19


Page 20 of 22

Performance and Durability for Tin-Based Perovskite Solar Cells. Energy Environ. Sci. 2018, 11 (9), 2353–2362. (18)

Dutcher, B.; Fan, M.; Russell, A. G. Amine-Based CO2 Capture Technology Development from the Beginning of 2013-A Review. ACS Appl. Mater. Interfaces 2015, 7 (4), 2137– 2148.

(19)

Zhou, S.; Chen, X.; Nguyen, T.; Voice, A. K.; Rochelle, G. T. Aqueous Ethylenediamine for CO2 Capture. ChemSusChem 2010, 3 (8), 913–918.

(20)

Wu, W. Q.; Yang, Z.; Rudd, P. N.; Shao, Y.; Dai, X.; Wei, H.; Zhao, J.; Fang, Y.; Wang, Q.; Liu, Y.; et al. Bilateral Alkylamine for Suppressing Charge Recombination and Improving Stability in Blade-Coated Perovskite Solar Cells. Sci. Adv. 2019, 5 (3), 1–10.

(21)

Ke, W.; Stoumpos, C. C.; Zhu, M.; Mao, L.; Spanopoulos, I.; Liu, J.; Kontsevoi, O. Y.; Chen, M.; Sarma, D.; Zhang, Y.; et al. Enhanced Photovoltaic Performance and Stability with a New Type of Hollow 3D Perovskite {en}FASnI 3. Sci. Adv. 2017, 3 (8), e1701293.

(22)

Lee, S.; Park, J. H.; Lee, B. R.; Jung, E. D.; Yu, J. C.; Di Nuzzo, D.; Friend, R. H.; Song, M. H. Amine-Based Passivating Materials for Enhanced Optical Properties and Performance of Organic-Inorganic Perovskites in Light-Emitting Diodes. Journal of Physical Chemistry Letters. 2017, pp 1784–1792.

(23)

Pockett, A.; Eperon, G. E.; Peltola, T.; Snaith, H. J.; Walker, A.; Peter, L. M.; Cameron, P. J. Characterization of Planar Lead Halide Perovskite Solar Cells by Impedance Spectroscopy, Open-Circuit Photovoltage Decay, and Intensity-Modulated Photovoltage/Photocurrent Spectroscopy. J. Phys. Chem. C 2015, 119 (7), 3456–3465.


20

Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24)

Albadri, A.; Yadav, P.; Alotaibi, M.; Arora, N.; Alyamani, A.; Albrithen, H.; Dar, M. I.; Zakeeruddin, S. M.; Grätzel, M. Unraveling the Impact of Rubidium Incorporation on the Transport-Recombination Mechanisms in Highly Efficient Perovskite Solar Cells by Small-Perturbation Techniques. J. Phys. Chem. C 2017, 121 (45), 24903–24908.

(25)

Aharon, S.; Dymshits, A.; Rotem, A.; Etgar, L. Temperature Dependence of Hole Conductor Free Formamidinium Lead Iodide Perovskite Based Solar Cells. J. Mater. Chem. A 2015, 3 (17), 9171–9178.

(26)

Cohen, B. El; Li, Y.; Meng, Q.; Etgar, L. Dion-Jacobson Two-Dimensional Perovskite Solar Cells Based on Benzene Dimethanammonium Cation. Nano Lett. 2019, 19 (4), 2588–2597.

(27)

Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith, H. J. Enhanced Photoluminescence and Solar Cell Performance via Lewis Base Passivation of Organic-Inorganic Lead Halide Perovskites. ACS Nano 2014, 8 (10), 9815– 9821.

(28)

Yates, J. T. Surface Chemistry of Silicon - The Behaviour of Dangling Bonds. J. Phys. Condens. Matter 1991, 3 (S), S143.

(29)

Cartier, E.; Stathis, J. H.; Buchanan, D. A. Passivation and Depassivation of Silicon Dangling Bonds at the Si/SiO2 interface by Atomic Hydrogen. Appl. Phys. Lett. 1993, 63 (11), 1510–1512.

(30)

Wang, F.; Bai, S.; Tress, W.; Hagfeldt, A.; Gao, F. Defects Engineering for HighPerformance Perovskite Solar Cells. npj Flex. Electron. 2018, 2 (1).


21


(31)

Page 22 of 22

Barboni, D.; De Souza, R. A. The Thermodynamics and Kinetics of Iodine Vacancies in the Hybrid Perovskite Methylammonium Lead Iodide. Energy Environ. Sci. 2018, 11 (11), 3266–3274.

(32)

Li, W.; Sun, Y. Y.; Li, L.; Zhou, Z.; Tang, J.; Prezhdo, O. V. Control of Charge Recombination in Perovskites by Oxidation State of Halide Vacancy. J. Am. Chem. Soc. 2018, 140 (46), 15753–15763.

(33)

Lee, Y. M.; Park, J.; Yu, B. D.; Hong, S.; Jung, M. C.; Nakamura, M. Surface Instability of Sn-Based Hybrid Perovskite Thin Film, CH3NH3SnI3: The Origin of Its Material Instability. J. Phys. Chem. Lett. 2018, 9 (9), 2293–2297.


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Suppression of Charge Carrier Recombination in Lead-Free Tin

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