Intralayer A-Site Compositional Engineering of Ruddlesden-Popper

Subscriber access provided by UNIV AUTONOMA DE COAHUILA UADEC

Letter

Intralayer A-Site Compositional Engineering of RuddlesdenPopper Perovskites for Thermostable and Efficient Solar Cells Youyu Jiang, Xinyi He, Tiefeng Liu, Nan Zhao, Minchao Qin, Junxue Liu, Fangyuan Jiang, Fei Qin, Lulu Sun, Xinhui Lu, Shengye Jin, Zewen Xiao, Toshio Kamiya, and Yinhua Zhou ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.9b00403 • Publication Date (Web): 02 May 2019 Downloaded from http://pubs.acs.org on May 2, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 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

ACS Energy Letters

Intralayer A-Site Compositional Engineering of Ruddlesden-Popper Perovskites for Thermostable and Efficient Solar Cells Youyu Jiang,

†

Xinyi He,

‡# Tiefeng

Liu,

†

Nan Zhao,† Minchao Qin,§ Junxue Liu, Fangyuan

Jiang,† Fei Qin,† Lulu Sun,† Xinhui Lu,§ Shengye Jin, Zewen Xiao,*† Toshio Kamiya,‡# and Yinhua Zhou*† †Wuhan

National Laboratory for Optoelectronics, Huazhong University of Science and

Technology, Wuhan, 430074, China ‡Laboratory

for Materials and Structures, Institute of Innovative Research, Tokyo Institute of

Technology, Yokohama 226-8503, Japan #Materials

Research Center for Element Strategy, Tokyo Institute of Technology, Yokohama

226-8503, Japan §Department 6State

of Physics, the Chinese University of Hong Kong, Hong Kong, China

Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation Center of

Chemistry for Energy Materials (iChEM), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China

ACS Paragon Plus Environment

1

ACS Energy Letters 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

Page 2 of 30

Abstract Layered Ruddlesden-Popper (RP) perovskites have good moisture- and photo-stability. But, thermal stability of the RP perovskites is still a challenge. In this work, through a joint theoretical and experimental study, we report an intralayer A-site compositional engineering strategy to enhance the thermal stability of the RP perovskite solar cells. The triple-A-site-cation BA2(MA0.76FA0.19Cs0.05)3Pb4I13 (labeled as T-RP) cells remain 80% of the initial efficiency after stressed at a constant temperature of 85 oC for over 1,400 h in the dark, which is a significant enhancement as compared to the FA-free or Cs-free double-A-site-cation reference devices. Enhanced stability is attributed to improved structural stability, film quality with larger and more compact micrometer grains, and lower trap densities of the T-RP, as compared to the double-Asite-cation RP perovskites. By introducing appropriate excess PbI2 in the T-RP layer, a power conversion efficiency of 15.58% is obtained for RP perovskite solar cells with high thermal stability.


2

Page 3 of 30 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

ACS Energy Letters



Page 4 of 30

Organic-inorganic hybrid lead (Pb) halide perovskites APbX3, where “A” is a relatively large monovalent inorganic or organic cation (e.g., Cs+, CH3NH3+ (MA+), HC(NH2)2+ (FA+)) and X represents a halogen, have emerged as revolutionary solar absorbers with power conversion efficiencies (PCEs) rapidly increasing from 3.8% in 2009 to 23.7%.1 However, the Pb halide perovskite solar cells suffer from poor long-term stability, e.g., against moisture. Efforts have been made to mitigate moisture-induced instability. For example, hydrophobic cations such as aliphatic alkylammonium and aromatic alkylammonium (both denoted as RNH3+) have been used to improve the resistivity to moisture, leading to the formation of the layered RuddlesdenPopper Pb halide perovskites (RNH3)2AnG PbnX3n+1 (n is the number of inorganic [PbX6] octahedral layers).2-6 These layered RP Pb halide perovskites show much improved air/moisture stability as compared to their 3D counterparts.7-11 However, the reduced structural dimensionality of the layered RP perovskites leads to reduced electronic dimensionality, showing larger bandgaps, inferior carrier transport properties and thus lower potential PCEs.12-15 Nevertheless, over the past several years, the record PCE of the low-n (n < 5) RP lead halide perovskite solar cells has reached over 15% through a series of techniques,16-27 e.g., growing the RP perovskite films with the inorganic perovskite layers parallel to the carrier transport direction. These impressive results trigger intense exploration of RP perovskites as solar cell absorbers for high performance as well as long-term stability. Despite the much improved air/moisture stability,3, 7, 10, 28-29 thermal stability of the RP lead halide perovskites remains a major challenge. For example, Tsai et al. showed that the BA2MA3Pb4I13 (BA = CH3(CH2)3NH3+) thin films would completely decompose into PbI2 after 30 h thermal aging at 80 oC in the dark.3 As a result, the corresponding devices rapidly degraded and remain about ca. 40-60% of their initial PCE after about 20 h continuous heating at ca. 70-80


4

Page 5 of 30 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

ACS Energy Letters

oC.10, 19

By partially replacing the intralayer A-site MA cations by Cs cations, Liu et al. found the

resulted BA2(MA0.95Cs0.05)3Pb4I13 solar cells could sustain 85% of their initial PCE for approximately 20 h after stressing at a constant temperature of 80 oC in the dark.10 Very recently, Lee et al. presented a shorter propane-1,3-diammonium (PDA) cations to replace BA R-cations also improved the device thermal stability that can sustain their initial efficiency at 70 °C for over 100 h.19 The improved stability is explained by stronger interaction between neighboring layers in the PDAMA3Pb4I13 Q-2D perovskite structure due to the reduced interlayer distance compared to the BA based perovskite structure. These observations suggest that tailoring cations is possible to further improve thermal stability of the layered RP lead halide perovskites. Previously, in 3D perovskites, it has been reported that mixed triple cations would improve the thermostability of perovskite solar cells. But, the triple-A-cation 2D perovskites have not been reported in the literature. In this work, we report the intralayer A-site compositional engineering of the RP lead halide perovskites, where highly thermostable and efficient perovskite solar cells are designed by introducing three cations, MA/FA/Cs cations, to the intralayer A-sites. Although many studies have been reported on mixed A-cation approaches,10, 30-31 there has been no report of perovskite solar cells that can pass the fundermantal thermal endurance tests (e.g., thermal-cycling test and damp heat test) for industrial commercialization.32-33 Density functional theory (DFT) calculations qualitatively indicate that triple-A-site-cation mixing can attain higher decomposition energies compared with the single-A-site and double-A-site-cation RP perovskites as well as their 3D counterparts. Thus, we fabricated thin films of a triple-A-sitecation mixed RP lead iodide perovskite, BA2(MA0.76FA0.19Cs0.05)3Pb4I13, (hereafter labeled as TRP). The as-fabricated T-RP films exhibited significantly improved thermostability after a harsh


5


Page 6 of 30

thermal stress test at a high temperature of 150 oC for 10 h, compared to their double-A-sitecation counterparts (BA)2(MA0.8FA0.2)3Pb4I1328 (D-RP1) and (BA)2(MA0.95Cs0.05)3Pb4I1310 (DRP2), which completely decomposed to yellow PbI2 after less than 2 h of the thermal stress. The solar cells based on the T-RP perovskites kept 80% of the initial efficiency after 1,400 h of thermal aging at 85 oC in the dark, showing much improved device stability compared to those based on D-RP1 and D-RP2 perovskites as well as those reported in the literature.10 Finally, a high PCE of 15.58% is simultaneously achieved based on the T-RP perovskite solar cells, which is the highest efficiency for the BA-based RP perovskite solar cells (comparison shown in Table S1). Firstly, we performed DFT calculations for a qualitative understanding of the effects of Asite cation mixing on the thermostability for both 3D and layered RP halide perovskites, with the related structural models shown in Figure S1 and S2, respectively. Figure 1 shows the calculated decomposition free energies (PGD = PHD – TPS, where PHD is the decomposition enthalpy calculated by DFT, and PS is the mixing entropy of the regular solution model) with respect to the binary compounds as a function of the chemical composition. As shown in Figure 1a and Table S2, for 3D lead iodide perovskites MAPbI3, FAPbI3, and CsPbI3, the calculated PGD values are -65, -39, and -33 meV/f.u., respectively. The negative values reflect the poor thermostability for these pure A-cation perovskites, as observed in experiments. The increasing trend of PGD from MAPbI3, to FAPbI3, and to CsPbI3 is consistent with experimental observation that the CsPbI3 shows better thermostability as compared to FAPbI3 and MAPbI3. Mixing any two of the three cations MA, FA, Cs to form Cs

GxMAxPbI3,

MA

GyFAyPbI3,

and

FA GzCszPbI3 solid solutions leads to significant stabilization with respect to the pure MAPbI3, FAPbI3, and CsPbI3, e.g., with positive calculated PGD values of 121, 98, and 137 meV/f.u. for


6

Page 7 of 30 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

ACS Energy Letters

Cs0.48MA0.52PbI3, MA0.48FA0.52PbI3, and FA0.52Cs0.48PbI3, respectively. Partially incorporating FA into the Cs

GxMAxPbI3

system or partially incorporating Cs into the MA

GyFAyPbI3

to form

triple-A-cation MAxFAyCszPbI3 (where x + y + z = 1) solid solution further increases the PGD values and thus the thermostability. For layered RP halide perovskites, the effects of A-cation mixing are similar to those for 3D halide perovskites (Figure 1b and Table S3). For simplification, we take hypothetical singlelayer A2PbI4 (A = MA, FA, Cs) RP perovskites as models. In contrast to the 3D counterpart perovskites with negative PGD values, the hypothetical 2D layered RP perovskites MA2PbI4, FA2PbI4, and Cs2PbI4 show positive PGD values of 21, 29, and 67 meV/f.u., respectively, indicating that the reduction of structural dimensionality helps to enhance the thermostability. Doubly or triply mixing MA, FA, and Cs cations leads to further enhancement of thermostability of the layered RP lead iodide perovskites, with calculated PGD values of 152, 110, 149, and 161 meV/f.u. for (Cs0.5MA0.5)2PbI4, (MA0.5FA0.5)2PbI4, (FA0.5Cs0.5)2PbI4, and (MA1/3FA1/3Cs1/3)2PbI4, respectively. As shown in Figure 1 and Tables S2 and S3, the enthalpic contribution 7PHD) to the PGD is several times larger than the entropic contribution (–TPS), even at an enhanced temperature of 600 K, which is high enough to initiate the decomposition of hybrid halide perovskites. This indicates that the stabilization is mainly of enthalpy-driven. All these calculation results imply that triple-A-site-cation engineering of RP halide perovskites would enable highly thermostable halide perovskites. Guided by this insight, we fabricated triple-A-site-cation RP perovskite T-RP (i.e., BA2(MA0.76FA0.19Cs0.05)3Pb4I13 along with the double-A-site-cation RP perovskites D-RP1 and D-RP2 (i.e., (BA)2(MA0.8FA0.2)3Pb4I13 and (BA)2(MA0.95Cs0.05)3Pb4I13, respectively) from the precursors

of

corresponding

binary

iodides,

i.e.,

butylammonium

iodide

(BAI),


7


Page 8 of 30

methylammonium iodide (MAI), formamidinium iodide (FAI), CsI, and PbI2 (see the experimental details in the Supplemental Information). 1H NMR spectra (Figure S3) and X-Ray energy dispersive spectroscopy (EDS) measurements (Figure S4) indicate the composition ratios in the as-prepared T-RP, D-RP1, and D-RP2 perovskite films are similar to the originally designated values in their precursor solutions. Different from their 3D counterparts, the asprepared RP perovskite films are actually a mixture of multiple perovskite phases with different n values.34-35 Ultrafast transient absorption (TA) spectra was then performed to investigate the width distribution of those quantum wells (QWs) as shown in Figure S5. The difference in the TA spectra between back- and front-excitation implies that all these three RP perovskite films show similar inhomogeneous distribution of QWs with a higher concentration of large n (n , -) wells near the surface of the film and low n (n = 3, 4, 5) wells at the bottom. Figure 2a show the images of all the three RP perovskite thin films kept at 150 oC for 10 h in N2 inert atmosphere in the dark. Both the double-A-site-cation D-RP1 and D-RP2 perovskite films rapidly turn to yellow after 1 h, and completely decompose after 2 h. However, the tripleA-site-cation T-RP perovskite films retain the dark brown color for 10 h after the harsh thermal stress test. This much improved thermal stability was further checked by X-ray diffraction (XRD) measurements. As shown in Figure 2b, all these three pristine films exhibit two distinct diffraction peaks at ca. 14o and 28 o, assigned to (111) and (202) crystallographic planes of RP perovskites, respectively. After 150 oC thermal aging for 10 h, both the D-RP1 and D-RP2 perovskite films do not exhibit the RP characteristic peaks, but two clear PbI2 peaks at ca. 12.7o and 38.6

o

that suggests almost entire decomposition of the RP perovskite structure. This is

consistent with the observed color changes. The triple-A-site-cation T-RP perovskite films preserve strong RP characteristic peaks with almost unchanged peak intensities after the 10-h


8

Page 9 of 30 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

ACS Energy Letters

150 oC thermal stress that indicates a better heat tolerance of the perovskite phase structure as compared to Cs-free D-RP1 and FA-free D-RP2 perovskites. Zhou et al. reported the yellow, non-photoactive S

of FAPbI3 appears when the FA ratio is larger than 0.4 (x > 0.4) in the

double-A-site-cation (BA)2(FAxMA1-x)3Pb4I13 RP perovskite film.28 When herein incorporating Cs cations, the as-fabricated BA2(MA0.19FA0.76Cs0.05)3Pb4I13 film with a high FA ratio in contrast doesn’t show existence of the yellow-phase FAPbI3 (Figure S6). This further confirms the improved structural stability of T-RP perovskites via Cs incorporation. Given the effectiveness of the triple-A-site-cation strategy to enhance the thermal stability of the RP perovskite film, we further performed the heat stress test on the solar cells based on these three types of RP perovskites with a configuration of ITO/MoO3/PEDOT:PSS/RP perovskite/PC61BM/BCP/Ag. Figure 2c shows the normalized PCE as a function of testing time under thermal aging at 85 oC in N2 atmosphere in the dark. The double-A-site-cation D-RP1 devices undergo a fastest degradation and maintain 80% of the initial efficiency after about 40 hours. The D-RP2 samples also show obvious degradation that is consistent with the previous reports.10 Instead, the triple-A-site-cation T-RP based devices exhibit remarkable thermal stability with 80% of their initial efficiencies for 1,400 h. We further conducted the thermal test (85 °C) of the unsealed devices in air (humidity of ca. 10%). The T-RP devices also showed improved thermal stability as compared to the D-RP reference devices (Figure S7a). The improved cell stability is mainly ascribed to the excellent structural stability of the T-RP perovskites. For outdoor practical applications, solar cells (modules) are required to pass initial endurance test such as thermal stress tests at 85 oC run for 1,000 h.32, 36 The triple-A-site-cation strategy here shows promise to fulfill the requirement of 1,000 h stability under 85 oC for the RP perovskite solar cells.


9


Page 10 of 30

In addition, humidity stability test under ambient condition (25 oC, 65% relative humidity) and light stress test under xenon-lamp simulated full-spectrum AM1.5 100 mW cm-2 irradiance in air (humidity of ca. 40%-50%) on the encapsulated T-RP cells were also performed. The cells sustained 90% of their initial PCE for about 1,500 h (Figure S7b-c). After storing at 40%-50% humidity for 200 h, the unsealed devices retained about 60% of their initial PCEs (Figure S7b). These results indicate excellent humidity- and photo-stability of our T-RP recipes, which is comparable to those in RP perovskites as reported previously.3 The main superiority of the T-RP perovskite cells here is the excellent thermal stability. To shed more light on the much improved thermal stability of triple-A-site-cation T-RP perovskites, the film quality including film surface morphology and the grain size, as well as trap densities are studied. These three RP perovskite films were first studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). As shown in Figures 3a-b, the doubleA-site-cation D-RP1 and D-RP2 perovskite films, as well as triple-A-site-cation T-RP perovskite films all exhibit flat surface texture with low root-mean-square (RMS) roughness of 9.8 nm and 11.5 nm, and 7.7 nm, respectively. From the AFM images, T-RP films show uniform and large micrometer-scale grains with dimensions of ca. 2 W : Similar micrometer-sized crystal grains also exist in both D-RP1 and D-RP2 films; however, plenty of small crystal grains with several hundred nanometer-sizes (ca. +:2 W 8 dominate in both films. The growth of larger crystals in the T-RP films is also confirmed from the narrowest full width of half maximum (FWHM) of 0.089o (0.115o for D-RP1 and 0.231o for D-RP2) for the (202) diffraction peak (Figure 2b). The larger crystals in T-RP is likely to arise from the synergistic effect on crystallization behavior of the Cs doping and FA incorporation. The former has been proven to enable prolonged crystallization to help the Q-2D perovskite grains grow larger,10 and the latter


10

Page 11 of 30 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

ACS Energy Letters

influences the phase formation sequence and renders micrometer-size crystal grains.28 This presumed mechanism is also supported by the fact that (BA)2(FA0.95Cs0.05)3Pb4I13 (labeled as DRP3) films contain larger crystals of ca. 1.5 W

(Figure S8). To characterize the crystal

orientation with respect to the substrate in these RP perovskite films we then performed grazingincidence wide-angle scattering (GIWAXS) analysis using synchrotron radiation (Figure 3c). All these three samples showed sharp and discrete (111) Bragg spots along qz and (202) spots along qx, indicating well-aligned 2D perovskite structure with (101) planes parallel to the substrate surface, which is similar to previous reports.3, 10, 28 Besides, the diffraction spots of TRP perovskite films exhibit similar intensity as comparted to the double-A-site-cation samples, confirming comparable orientation ordering. The cross-section SEM images (Figure 3d) of all three RP perovskite films exhibit vertically oriented crystallites, indicating highly-ordered preferential orientation growth. We also found that the T-RP samples showed more denselypacked and larger grains, which is consistent well with the observations from plan-view SEM and AFM images. These results suggest the T-RP perovskites with increased complexity of the cations still retain excellent crystal vertical orientation (Figure S9). Space charge limited current (SCLC) technique with a hole-only device with a glass/ITO/MoO3/PEDOT:PSS/perovskite/Au

structure

and

an

electron-only

device

glass/FTO/TiO2/perovskite/PC61BM/Ag was employed to assess trap densities of the RP perovskites. As shown in Figures 4a-b, the plotted dark current-density versus voltage (J-V) curves of all the devices shows three characteristic regimes; (i) a linear ohmic regime in the low bias region, (ii) a trap-filled regime to estimate the trap density at a middle bias in the intermediate bias, and (iii) a trap-free SCLC regime in the high bias. The trap-state density can be determined from the following equation:37


11


2 =

Page 12 of 30

0 2

Where Nt is the trap-density, L is the thickness of the perovskite films, 30 is the vacuum permittivity, 3r is the relative dielectric constant of the perovskite (taken as a value of 2510), and VTFL is trap-filling limit voltage. The hole and electron trap density in the triple-A-site-cation TRP perovskites are calculated to be 0.87 ± 0.17 × 1016 cm-3 and 2.78 ± 0.10 × 1015 cm-3, respectively. These defect-density values are lower than those of the double-A-site-cation based analogs (ca. 1.38-1.58 × 1016 cm-3 for hole traps and ca. 4.90-6.04 × 1015 cm-3 for electron traps as summarized in Table S4) prepared under the same experimental conditions. These results demonstrate that the triple-A-site-cation T-RP perovskites deliver larger and denser micrometer-sized crystals, as well as lower trap densities as compared to the double-Asite-cation reference films. The grain boundaries and defects are commonly considered as the main path/channel of the degradation.36, 38 Perovskite single crystals with fewer numbers of grain boundaries and lower structural disorders and defects exhibit much higher thermal stability than polycrystalline perovskite thin films.39 Therefore, besides the higher structural stability of the perovskites, the improved film quality with larger grains and less defects may also contribute to the observed excellent thermal stability of our triple-A-site-cation T-RP perovskite cells. Further, to probe the cation-engineering effects on optical properties, we compared both the UV-vis absorption and steady-state photoluminescence (PL) spectra of the three different RP perovskite films. As shown in Figure 4c, the partial replacement of MA with FA cations in RP perovskite structure shifts the absorption onset to longer wavelength, whereas a small portion of Cs doping leads to a slightly reduced optical band gap (Eg). The Eg values of the D-RP1, D-RP2, and T-RP films are estimated by Tauc plots of the absorption coefficients (inset of the Figure 4c) to be 1.58 eV, 1.63 eV, and 1.59 eV, respectively. The reduced Eg in D-RP1 and T-RP


12

Page 13 of 30 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

ACS Energy Letters

compared to D-RP2 sample is mainly due to the incorporation of FA.28 The absorption profiles of all these films display similar high-energy excitonic peaks in the 550-700 nm regions. These excitonic peaks are commonly assigned to single-phase of low-n 2D RP perovskites.25, 40 The triple-A-site-cation T-RP films show red-shift and blue-shift of the dominant emission peak when compared to D-RP2 and D-RP1, respectively (Figure 4d). These distinct shifts are mainly attributed to the change of the Eg. Furthermore, T-RP films show a highest PL intensity, which is associated to the improved grain sizes and fewer defects. In addition, the triple-A-site-cation TRP film shows increased carrier lifetime from ~ 50 ns to ~100 ns determined by time-resolved photoluminescence

(TRPL)

spectroscopy

(Figure

S10a).

When

coated

with

the

ITO/MoO3/PEDOT:PSS substrate, the T-RP samples have shorter quenching lifetime that indicates improved charge transfer at the T-RP/PEDOT:PSS surface (Figure S10b). To evaluate the photovoltaic performance of this novel triple-A-site-cation T-RP, we fabricate

devices

with

a

planar

configuration

of

ITO/PEDOT:PSS/RP

perovskite/PC61BM/BCP/Ag (Figure 5a). The current-voltage (J-V) curves under simulated AM1.5G irradiation (100 mW cm-2) and the corresponding photovoltaic parameters of the RP perovskite cells are displayed in Figure 5b and Table 1, respectively. The double-A-site-cation D-RP1 and D-RP2 based control devices deliver PCEs of 12.74% and 12.08% with similar open-circuit voltage (VOC) and fill factor (FF), which are comparable to those in reported literature.10, 28 For the triple-A-site-cation T-RP cells, the PCE reaches 14.58%. This efficiency enhancement is attributed to the overall increase in VOC (1.06 V), short-circuit current (JSC = 18.56 mA cm-2) and FF (0.741). Considering similar absorption spectra with D-RP1, the main contribution to the improved JSC for T-RP is the improved charge extraction and reduced carrier recombination because of the improved film quality with larger grains and less defects. The


13


Page 14 of 30

reduced recombination losses are also responsible for the higher VOC and FF. Figure 5c shows the external quantum efficiency (EQE) of the devices based on the aforementioned RP perovskites. The integrated photocurrent density based on EQE is 16.99 mA cm-2, 16.00 mA cm2,

and 17.71 mA cm-2 for D-RP1, D-RP2, and T-RP based devices, which are consistent with

those from J-V measurements. We have also attempted to further increase the FA ratio in our triple-A-site-cation RP perovskites because of its advantage for improving the light harvesting. However, devices based on BA2(MA0.19FA0.76Cs0.05)3Pb4I13 with a high FA ratio yielded a lower PCE of 11.25% (Table S5). The decreased efficiency is due to the low JSC (15.30 mA cm-2), which is mainly ascribed to the decreased out-of-plane charge transport resulting from the reduced crystal vertical orientation in perovskite films as shown in Figure S6. Increasing the Cs ratio is also found to deteriorate the device efficiencies (Table S5). These observations support the optimum ratio of triple-A-sitecation in the BA2(MA0.76FA0.19Cs0.05)3Pb4I13 films for high-efficiency and stable RP perovskite solar cells. To further increase the efficiency of the RP perovskite solar cells, we introduce an appropriate excess PbI2 in the precursors. As shown in Figure 5d, an optimum PCE of 15.58% (JSC = 19.67 mA cm-2, VOC = 1.08 V, FF = 0.733) is achieved with negligible hysteresis (Figure S11a) for the quadruple-cation Q-2D perovskite devices when 8.6 mol% excess PbI2 is added. The integrated photocurrent density based on EQE is 18.84 cm-2 for PbI2-excess T-RP based devices (Figure S11b), which is comparable to that from the J-V measurements. A stable steady output PCE of 15.39% is obtained based on the steady-state photocurrent measured at the maximum power point of J-V curve (Figure 5e). The PbI2-excess T-RP cells also showed superior reproducibility with narrower PCE distributions (Figure S11c). When the amount of


14

Page 15 of 30 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

ACS Energy Letters

PbI2 further increases, efficiency of the cells decreases due to poor film morphology and crystallites observed from the SEM images and GIWAXS patterns (Figure S12). An appropriate excess addition of PbI2 has been demonstrated to effectively passivate the defects at the grain boundaries (GBs) in 3D perovskites41-44 and reduce the charge carrier recombination. The residual PbI2 in the as-fabricated films is confirmed by the visible diffraction peak at ca. 12.7o from the XRD patterns (Figure S13). To elucidate the effect of PbI2 excess in RP perovskites, first, the absorbance spectra of the RP perovskites with different ratios of PbI2 excess is compared. The addition of the PbI2 doesn’t change the absorbance feature of the RP perovskites with a similar excitonic absorbance peak (Figure S11d). Then, we used Kelvin probe force microscope (KPFM) to measure the surface potential at the grain boundaries (GBs). Two-dimensional topography spatial maps (Figure S14a and c) and the corresponding surface potentials (Figure S14b and d) of the RP perovskite films reveal a clear correlation between the GBs and the potential variation. In an illustrative black line crossing the GBs, the control T-RP films exhibit surface potential difference of around 20-40 mV between two grains (Inset in Figures S14b and d). In contrast, the surface potential difference for PbI2-excess sample is as low as 10\mV. This result is consistent with the previous observations of PbI2 defect-passivation in 3D MAPbI3,45 in which a surface potential difference change reduces from 50 mV to 30 mV. The passivated GBs in T-RP films with excess PbI2 result in lower hole and electron trap-state densities of 2.88 ± 0.15 × 1015 cm-3 and 1.35 ± 0.12 × 1015 cm-3, and higher carrier mobilities of 0.13 ± 0.01 cm2 V-1 S-1 and 0.75 ± 0.02 cm2 V-1 S-1 for holes and electrons determined by the SCLC method (Figure S15). Therefore, in RP perovskite films, a moderate excess PbI2 enables efficient GBs passivation for reducing defects and improving charge extraction, thus rendering improved VOC and JSC of the T-RP perovskite cells. The further reduction in defects in RP


15


Page 16 of 30

perovskite films can also contribute to improvement in environment stability.38, 46-48 The PbI2excess T-RP perovskite cells yield even slightly better thermal stability than the pristine T-RP cells (Figure S16). In conclusion, we report a triple-A-site-cation strategy that effectively enhances the thermal stability of the RP perovskite solar cells. The triple-A-site-cation RP perovskite-based solar cells display excellent thermal stability, remaining 80% of the initial efficiency after stressed at a constant temperature of 85 oC for over 1,400 hours, which is much more stable than the doubleA-site-cation reference devices in our study as well as reported in the literature (less than 100 h). We also find that the triple-A-site-cation strategy yields larger and more compact micro-meter grains and the lower trap densities, as compared to the double-A-site-cation RP perovskites. With combining an appropriate excess of PbI2, we could obtain a high power conversion efficiency of 15.58% for the triple-A-site-cation RP perovskite solar cells. Therefore, the tripleA-site-cation strategy simultaneously enhances the thermal stability and improves the efficiency of the RP perovskite solar cells. It should be noted that the triple A site cations could lead to the complexity of crystal structure compared to the pure phase. Performance might be different for the case of the mixed cations with fully random occupation and local segregation/ordering of certain cations. However, it is still challenging to characterize the precise local structure for RP perovskites. The RP perovskites typically are mixture of multiple perovskite phases in the RP perovskite films.15, 34 Further work will be needed for this challenging topic. This work would trigger the study of tailoring multiple cations (including organic and alkali metal cations) in the perovskites to optimize the thermal stability, crystalline structure and performance of the RP perovskite optoelectronic devices.


16

Page 17 of 30 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

ACS Energy Letters

ASSOCIATED CONTENT Supporting Information. Details of DFT calculations, and other results including 1H NMR spectra, TA spectra, and J-V curves of the RP solar cells. AUTHOR INFORMATION Corresponding Author [email protected] [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT Y. Y. J., X. Y. H. and T. F. L., contributed equally to this work. The work is supported by the National Natural Science Foundation of China (Grant No. 51773072, 61804060), by the Recruitment Program of Global Youth Experts, the HUST Innovation Research Fund (Grant No. 2016JCTD111, 2017KFKJXX012), the Science and Technology Program of Hubei Province (2017AHB040) and China Postdoctoral Science Foundation funded project (2016M602289). The authors also would like to thank the Analytical and Testing Center of Huazhong University of Science and Technology for providing the facilities to conduct the characterization.


17


Page 18 of 30

REFERENCES (1) Chart,

N.

NREL

Chart,

https://www.nrel.gov/pv/assets/pdfs/pv-efficiency-

chart.20190103.pdf (asscesssed: January 2019 ). (2) Smith, I. C.; Hoke, E. T.; Solis-Ibarra, D.; McGehee, M. D.; Karunadasa, H. I. A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability. Angew. Chem. Int. Ed. 2014, 126, 11414-11417. (3) Tsai, H.; Nie, W.; Blancon, J.-C.; Stoumpos, C. C.; Asadpour, R.; Harutyunyan, B.; Neukirch, A. J.; Verduzco, R.; Crochet, J. J.; Tretiak, S.; Pedesseau, L.; Even, J.; Alam, M. A.; Gupta, G.; Lou, J.; Ajayan, P. M.; Bedzyk, M. J.; Kanatzidis, M. G.; Mohite, A. D. High-efficiency two-dimensional Ruddlesden–Popper perovskite solar cells. Nature. 2016, 536, 312. (4) Wang, N.; Cheng, L.; Ge, R.; Zhang, S.; Miao, Y.; Zou, W.; Yi, C.; Sun, Y.; Cao, Y.; Yang, R.; Wei, Y.; Guo, Q.; Ke, Y.; Yu, M.; Jin, Y.; Liu, Y.; Ding, Q.; Di, D.; Yang, L.; Xing, G.; Tian, H.; Jin, C.; Gao, F.; Friend, R. H.; Wang, J.; Huang, W. Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells. Nat. Photonics. 2016, 10, 699. (5) Etgar, L. The merit of perovskite's dimensionality; can this replace the 3D halide perovskite? Energy Environ. Sci. 2018, 11, 234-242. (6) Blancon, J.-C.; Tsai, H.; Nie, W.; Stoumpos, C. C.; Pedesseau, L.; Katan, C.; Kepenekian, M.; Soe, C. M. M.; Appavoo, K.; Sfeir, M. Y.; Tretiak, S.; Ajayan, P. M.; Kanatzidis, M. G.; Even, J.; Crochet, J. J.; Mohite, A. D. Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites. Science. 2017, 355, 1288.


18

Page 19 of 30 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

ACS Energy Letters

(7) Quan, L. N.; Yuan, M.; Comin, R.; Voznyy, O.; Beauregard, E. M.; Hoogland, S.; Buin, A.; Kirmani, A. R.; Zhao, K.; Amassian, A.; Kim, D. H.; Sargent, E. H. Ligand-Stabilized Reduced-Dimensionality Perovskites. J. Am. Chem. Soc. 2016, 138, 2649-2655. (8) Yao, K.; Wang, X.; Xu, Y.-x.; Li, F.; Zhou, L. Multilayered Perovskite Materials Based on Polymeric-Ammonium Cations for Stable Large-Area Solar Cell. Chem. Mater. 2016, 28, 3131-3138. (9) Chen, Y.; Sun, Y.; Peng, J.; Tang, J.; Zheng, K.; Liang, Z. 2D Ruddlesden–Popper Perovskites for Optoelectronics. Adv. Mater. 2017, 30, 1703487. (10) Zhang, X.; Ren, X.; Liu, B.; Munir, R.; Zhu, X.; Yang, D.; Li, J.; Liu, Y.; Smilgies, D.-M.; Li, R.; Yang, Z.; Niu, T.; Wang, X.; Amassian, A.; Zhao, K.; Liu, S. Stable high efficiency two-dimensional perovskite solar cells via cesium doping. Energy Environ. Sci. 2017, 10, 2095-2102. (11) Jiang, Y.; Luo, B.; Jiang, F.; Jiang, F.; Fuentes-Hernandez, C.; Liu, T.; Mao, L.; Xiong, S.; Li, Z.; Wang, T.; Kippelen, B.; Zhou, Y. Efficient Colorful Perovskite Solar Cells Using a Top Polymer Electrode Simultaneously as Spectrally Selective Antireflection Coating. Nano Lett. 2016, 16, 7829-7835. (12) Xiao, Z.; Meng, W.; Wang, J.; Mitzi, D. B.; Yan, Y. Searching for promising new perovskite-based photovoltaic absorbers: the importance of electronic dimensionality. Mater. Horiz. 2017, 4, 206-216. (13) Xiao, Z.; Meng, W.; Saparov, B.; Duan, H.-S.; Wang, C.; Feng, C.; Liao, W.; Ke, W.; Zhao, D.; Wang, J.; Mitzi, D. B.; Yan, Y. Photovoltaic Properties of Two-Dimensional (CH3NH3)2Pb(SCN)2I2 Perovskite: A Combined Experimental and Density Functional Theory Study. J. Phys. Chem. Lett. 2016, 7, 1213-1218.


19


Page 20 of 30

(14) Xiao, Z.; Song, Z.; Yan, Y. From Lead Halide Perovskites to Lead-Free Metal Halide Perovskites

and

Perovskite

Derivatives.

Adv.

Mater.

2019,

doi.org/10.1002/adma.201803792. (15) Liu, T.; Jiang, Y.; Qin, M.; Liu, J.; Sun, L.; Qin, F.; Hu, L.; Xiong, S.; Jiang, X.; Jiang, F.; Peng, P.; Jin, S.; Lu, X.; Zhou, Y. Tailoring vertical phase distribution of quasi-twodimensional perovskite films via surface modification of hole-transporting layer. Nat. Commun. 2019, 10, 878. (16) Lai, H.; Kan, B.; Liu, T.; Zheng, N.; Xie, Z.; Zhou, T.; Wan, X.; Zhang, X.; Liu, Y.; Chen, Y. Two-Dimensional Ruddlesden-Popper Perovskite with Nanorod-like Morphology for Solar Cells with Efficiency Exceeding 15%. J. Am. Chem. Soc. 2018, 140, 11639-11646. (17) Zhu, X.; Xu, Z.; Zuo, S.; Feng, J.; Wang, Z.; Zhang, X.; Zhao, K.; Zhang, J.; Liu, H.; Priya, S.; Liu, S. F.; Yang, D. Vapor-fumigation for record efficiency two-dimensional perovskite solar cells with superior stability. Energy Environ. Sci. 2018, 11, 3349. (18) Yang, R.; Li, R.; Cao, Y.; Wei, Y.; Miao, Y.; Tan, W. L.; Jiao, X.; Chen, H.; Zhang, L.; Chen, Q.; Zhang, H.; Zou, W.; Wang, Y.; Yang, M.; Yi, C.; Wang, N.; Gao, F.; McNeill, C. R.; Qin, T.; Wang, J.; Huang, W. Oriented Quasi-2D Perovskites for High Performance Optoelectronic Devices. Adv. Mater. 2018, 30, 1804771. (19) Ma, C.; Shen, D.; Ng, T.; Lo, M.; Lee, C. 2D Perovskites with Short Interlayer Distance for High-Performance Solar Cell Application. Adv. Mater. 2018, 30, 1800710. (20) Mao, L.; Ke, W.; Pedesseau, L.; Wu, Y.; Katan, C.; Even, J.; Wasielewski, M. R.; Stoumpos, C. C.; Kanatzidis, M. G. Hybrid Dion–Jacobson 2D Lead Iodide Perovskites. J. Am. Chem. Soc. 2018, 140, 3775-3783.


20

Page 21 of 30 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

ACS Energy Letters

(21) Chen, Y.; Sun, Y.; Peng, J.; Zhang, W.; Su, X.; Zheng, K.; Pullerits, T.; Liang, Z. Tailoring Organic Cation of 2D Air-Stable Organometal Halide Perovskites for Highly Efficient Planar Solar Cells. Adv. Energy Mater. 2017, 7, 1700162. (22) Proppe, A. H.; Quintero-Bermudez, R.; Tan, H.; Voznyy, O.; Kelley, S. O.; Sargent, E. H. Synthetic Control over Quantum Well Width Distribution and Carrier Migration in LowDimensional Perovskite Photovoltaics. J. Am. Chem. Soc. 2018, 11, 232-234. (23) Soe, C. M. M.; Nie, W.; Stoumpos, C. C.; Tsai, H.; Blancon, J.-C.; Liu, F.; Even, J.; Marks, T. J.; Mohite, A. D.; Kanatzidis, M. G. Understanding Film Formation Morphology and Orientation in High Member 2D Ruddlesden–Popper Perovskites for High-Efficiency Solar Cells. Adv. Energy Mater. 2017, 8, 1700979. (24) Zhang, X.; Wu, G.; Fu, W.; Qin, M.; Yang, W.; Yan, J.; Zhang, Z.; Lu, X.; Chen, H. Orientation Regulation of Phenylethylammonium Cation Based 2D Perovskite Solar Cell with Efficiency Higher Than 11%. Adv. Energy Mater. 2018, 8, 1702498. (25) Zhang, X.; Munir, R.; Xu, Z.; Liu, Y.; Tsai, H.; Nie, W.; Li, J.; Niu, T.; Smilgies Detlef , M.; Kanatzidis Mercouri, G.; Mohite Aditya, D.; Zhao, K.; Amassian, A.; Liu, S. Phase Transition Control for High Performance Ruddlesden-Popper Perovskite Solar Cells. Adv. Mater. 2018, 30, 1707166. (26) Chen, A. Z.; Shiu, M.; Ma, J. H.; Alpert, M. R.; Zhang, D.; Foley, B. J.; Smilgies, D.-M.; Lee, S.-H.; Choi, J. J. Origin of vertical orientation in two-dimensional metal halide perovskites and its effect on photovoltaic performance. Nat. Commun. 2018, 9, 1336. (27) Tsai, H.; Asadpour, R.; Blancon, J.-C.; Stoumpos, C. C.; Even, J.; Ajayan, P. M.; Kanatzidis, M. G.; Alam, M. A.; Mohite, A. D.; Nie, W. Design principles for electronic


21


Page 22 of 30

charge transport in solution-processed vertically stacked 2D perovskite quantum wells. Nat. Commun. 2018, 9, 2130. (28) Zhou, N.; Shen, Y.; Li, L.; Tan, S.; Liu, N.; Zheng, G.; Chen, Q.; Zhou, H. Exploration of Crystallization Kinetics in Quasi Two-Dimensional Perovskite and High Performance Solar Cells. J. Am. Chem. Soc. 2018, 140, 459-465. (29) Zheng, H.; Liu, G.; Zhu, L.; Ye, J.; Zhang, X.; Alsaedi, A.; Hayat, T.; Pan, X.; Dai, S. The Effect of Hydrophobicity of Ammonium Salts on Stability of Quasi-2D Perovskite Materials in Moist Condition. Adv. Energy Mater. 2018, 1800051. (30) Saliba, M.; Matsui, T.; Seo, J.-Y.; Domanski, K.; Correa-Baena, J.-P.; Nazeeruddin, M. K.; Zakeeruddin, S. M.; Tress, W.; Abate, A.; Hagfeldt, A.; Gratzel, M. Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy Environ. Sci. 2016, 9, 1989-1997. (31) Yi, C.; Luo, J.; Meloni, S.; Boziki, A.; Ashari-Astani, N.; Gratzel, C.; Zakeeruddin, S. M.; Rothlisberger, U.; Gratzel, M. Entropic stabilization of mixed A-cation ABX3 metal halide perovskites for high performance perovskite solar cells. Energy Environ. Sci. 2016, 9, 656662. (32) Rong, Y.; Liu, L.; Mei, A.; Li, X.; Han, H. Beyond Efficiency: the Challenge of Stability in Mesoscopic Perovskite Solar Cells. Adv. Energy Mater. 2015, 5, 1501066. (33) Meng, L.; You, J.; Yang, Y. Addressing the stability issue of perovskite solar cells for commercial applications. Nat. Commun. 2018, 9, 5265. (34) Liu, J.; Leng, J.; Wu, K.; Zhang, J.; Jin, S. Observation of Internal Photoinduced Electron and Hole Separation in Hybrid Two-Dimentional Perovskite Films. J. Am. Chem. Soc. 2017, 139, 1432-1435.


22

Page 23 of 30 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

ACS Energy Letters

(35) Quintero-Bermudez, R.; Gold-Parker, A.; Proppe, A. H.; Munir, R.; Yang, Z.; Kelley, S. O.; Amassian, A.; Toney, M. F.; Sargent, E. H. Compositional and orientational control in metal halide perovskites of reduced dimensionality. Nat. Mater. 2018, 17, 900. (36) Berhe, T. A.; Su, W.-N.; Chen, C.-H.; Pan, C.-J.; Cheng, J.-H.; Chen, H.-M.; Tsai, M.-C.; Chen, L.-Y.; Dubale, A. A.; Hwang, B.-J. Organometal halide perovskite solar cells: degradation and stability. Energy Environ. Sci. 2016, 9, 323-356. (37) Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Electron-hole diffusion lengths > 175 W

in solution-grown CH3NH3PbI3 single crystals. Science. 2015,

347, 967-970. (38) Wu, Y.; Xie, F.; Chen, H.; Yang, X.; Su, H.; Cai, M.; Zhou, Z.; Noda, T.; Han, L. Thermally Stable MAPbI3 Perovskite Solar Cells with Efficiency of 19.19% and Area over 1 cm2 achieved by Additive Engineering. Adv. Mater. 2017, 29, 1701073. (39) Liu, Y.; Yang, Z.; Cui, D.; Ren, X.; Sun, J.; Liu, X.; Zhang, J.; Wei, Q.; Fan, H.; Yu, F.; Zhang, Xu.; Zhao, C.; Liu, S. Two-Inch-Sized Perovskite CH3NH3PbX3 (X = Cl, Br, I) Crystals: Growth and Characterization. Adv. Mater. 2015, 27, 5176-5183. (40) Stoumpos, C. C.; Cao, D. H.; Clark, D. J.; Young, J.; Rondinelli, J. M.; Jang, J. I.; Hupp, J. T.; Kanatzidis, M. G. Ruddlesden–Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductors. Chem. Mater. 2016, 28, 2852-2867. (41) Jacobsson, T. J.; Correa-Baena, J.-P.; Halvani Anaraki, E.; Philippe, B.; Stranks, S. D.; Bouduban, M. E. F.; Tress, W.; Schenk, K.; Teuscher, J.; Moser, J.-E.; Rensmo, H.; Hagfeldt, A. Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells. J. Am. Chem. Soc. 2016, 138, 10331-10343.


23


Page 24 of 30

(42) 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, 1, 16177. (43) Jiang, Y.; Li, J.; Xiong, S.; Jiang, F.; Liu, T.; Qin, F.; Hu, L.; Zhou, Y. Dual functions of interface

passivation

and

n-doping

using

2,6-dimethoxypyridine

for

enhanced

reproducibility and performance of planar perovskite solar cells. J. Mater. Chem. A. 2017, 5, 17632-17639. (44) Jiang, Q.; Chu, Z.; Wang, P.; Yang, X.; Liu, H.; Wang, Y.; Yin, Z.; Wu, J.; Zhang, X.; You, J. Planar-Structure Perovskite Solar Cells with Efficiency beyond 21%. Adv. Mater. 2017, 29, 1703852. (45) Chen, Q.; Zhou, H.; Song, T. B.; Luo, S.; Hong, Z.; Duan, H. S.; Dou, L.; Liu, Y.; Yang, Y. Controllable self-induced passivation of hybrid lead iodide perovskites toward high performance solar cells. Nano Lett. 2014, 14, 4158-4163. (46) Bi, D.; Tress, W.; Dar, M. I.; Gao, P.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Correa Baena, J.-P.; Decoppet, J.-D.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; Grätzel, M.; Hagfeldt, A. Efficient luminescent solar cells based on tailored mixedcation perovskites. Sci. Adv. 2016, 2, e1501170. (47) Roldan-Carmona, C.; Gratia, P.; Zimmermann, I.; Grancini, G.; Gao, P.; Graetzel, M.; Nazeeruddin, M. K. High efficiency methylammonium lead triiodide perovskite solar cells: the relevance of non-stoichiometric precursors. Energy Environ. Sci. 2015, 8, 3550-3556. (48) Jung, M.; Shin, T. J.; Seo, J.; Kim, G.; Seok, S. I. Structural features and their functions in surfactant-armoured methylammonium lead iodide perovskites for highly efficient and stable solar cells. Energy Environ. Sci. 2018, 11, 2188.


24

Page 25 of 30 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

ACS Energy Letters

Table 1. Photovoltaic characteristics of as-fabricated solar cells with mixed cation based BA2(MA,FA,Cs)3Pb4I13 RP perovskites over 50 devices for each geometry. BA2(MA,FA,Cs)3Pb4I13

VOC (V)

JSC (mA/cm2)

FF (%)

PCE (%)

Double-A-site-cation (BA)2(MA0.80FA0.20)3Pb4I13

Average

1.02 ± 0.03

17.23 ± 1.43

69.4 ± 0.8

12.19 ± 1.3

(D-RP1)

Best

1.03

17.75

69.7

12.74

(BA)2(MA0.95Cs0.05)3Pb4I13

Average

1.01 ± 0.04

16.21 ± 1.56

69.6 ± 1.0

11.45 ± 1.2

(D-RP2)

Best

1.02

16.90

70.1

12.08

BA2(MA0.76FA0.19Cs0.05)3Pb4I13

Average

1.05 ± 0.02

17.93 ± 1.38

72.9 ± 1.8

13.72 ± 0.7

(T-RP)

Best

1.06

18.56

74.1

14.58

Average

1.07 ± 0.03

19.00 ± 1.26

72.0 ± 0.4

14.64 ± 0.8

Best

1.08

19.67

73.3

15.58

Triple-A-site-cation

8.6% PbI2 excess


25


Page 26 of 30

Figure 1. Predicted thermostability against decomposition. Calculated decomposition energies of (a) (MAxCsyFAz)PbI3 and (b) (MAxCsyFAz)2PbI4 as a function of chemical composition. Values outside and inside the parentheses show the decomposition free energies 7PGD) in meV/f.u. and the mixing entropy contributions 7GTPS) in meV/f.u., respectively.


26

Page 27 of 30 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

ACS Energy Letters




Page 28 of 30

Page 29 of 30 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

ACS Energy Letters




Page 30 of 30

Intralayer A-Site Compositional Engineering of Ruddlesden-Popper

Recommend Documents