High-Quality (FA)X(MA)1-XPbI3 for Efficient Perovskite Solar Cells Via

Subscriber access provided by BOSTON UNIV

Article

High-Quality (FA)X(MA)1-XPbI3 for Efficient Perovskite Solar Cells Via a Facile Cation-Intermixing Technique Muhammad Mateen, Zulqarnain Arain, Cheng Liu, Yi Yang, Xuepeng Liu, Yong Ding, Pengju Shi, Yingke Ren, Yunzhao Wu, Songyuan Dai, Tasawar Hayat, and Ahmed Alsaedi ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.9b02031 • Publication Date (Web): 04 Jun 2019 Downloaded from http://pubs.acs.org on June 4, 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 25 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 Sustainable Chemistry & Engineering

Table of Contents 146x89mm (220 x 220 DPI)

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

High-Quality (FA)X(MA)1-XPbI3 for Efficient Perovskite Solar Cells Via a Facile Cation-Intermixing Technique Muhammad Mateena,b, Zulqarnain Araina,c, Cheng Liua,b, Yi Yanga,b, Xuepeng Liua,b,*, Yong Dinga,b,*, Pengju Shia,b, Yingke Rena,b, Yunzhao Wua,b, Songyuan Daia,b,*, Tasawar Hayatd, and Ahmed Alsaedid [a]

Key Laboratory of Novel Thin-Film Solar Cells, North China Electric Power University,

2 Beinong road, Beijing, 102206, P. R. China. [b]

State Key Laboratory of Alternate Electrical Power System with Renewable Energy

Sources, North China Electric Power University, 2 Beinong road, Beijing 102206, P. R. China. [c]

Energy Systems Engineering Department, Sukkur IBA University, Sukkur, Pakistan.

[d]

NAAM Research Group, Department of Mathematics, Faculty of Science, King

Abdulaziz University, Jeddah 21589, Saudi Arabia. E-mail: [email protected], [email protected], and [email protected]

Abstract The quality of perovskite light-absorbing materials plays a vital role in the photovoltaic performance of perovskite solar cells. Herein, we present a facile surface engineering technique through post-treating pure MAPbI3 films with formamidinium iodide (FAI) solution, leading to mixed-cation FAxMA1-xPbI3 perovskite with substantial grain dimension, compact and uniform morphology. It is noted that the film post-treated with 20 mg·mL-1 FAI solution produces a highly crystalline and stable lattice structure with the features like the decreased defect density, improved electron transport, and long carrier lifetime. The optimized device based on the FAxMA1-xPbI3 obtained from the cation intermixing technique shows a promising power conversion efficiency of 20.21%, which is even superior than that of the device based on the mixed-cation perovskite from traditional method without post-treatment (19.08%). Moreover, the device based on the developed method also shows a better stability. These findings provide a simple procedure to fabricate high-quality mixed-cation perovskite layers for high-performance devices via controlling the crystallization and reducing defect density states. 1 ACS Paragon Plus Environment

Page 2 of 25

Page 3 of 25 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


Keywords: Perovskite solar cell; post-treatment; mixed-cation; highly crystalline; stability;

Introduction Recently, organo-metallic halide perovskites have come forward as one of the most exceptional materials in the photovoltaic research stream. The remarkable performance of perovskite solar cells (PSCs) takes the benefit of certain exceptional semiconductor properties of perovskite, such as long-range charge transport, tuneable optical band gap, and excellent light absorption.1,2 The swift progress of PSCs has been evidenced by its boosting power conversion efficiency (PCE) from 3.8% to a recently 23.3%,3-5 mainly due to progressive stoichiometric optimization, solvent engineering, controlled growth of seed crystals and enhanced interface engineering.6,7 Traditional perovskite materials, based on methylammonium (MA) with an energy band gap around 1.45-1.55 eV, are commonly used as the light harvesting layer in PSCs.8 Pure MAPbI3 perovskite has a tetragonal phase and it experiences a rescindable phase transition between cubic and tetragonal phase under a low-phase transition temperature.9 The suitable and more effective substitute of MA cation in perovskite structure is formamidinium (FA), which has larger ionic radii than that of MA. FAPbI3 possesses two crystal symmetry, i.e. a hexagonal symmetry (non-perovskite phase, yellow color δ-FAPbI3) and a trigonal symmetry (perovskite phase, black color, α-FAPbI3).10 The earlier studies showed that the large radii of FA cation disrupts the evolution to stronger trigonal α phase and FAPbI3 undergoes phase transition to δ phase.11 The trigonal α-FAPbI3 is quite stable at elevated temperature (around > 160 °C), but it can transform into hexagonal δ-FAPbI3 under a humid environment.12,13 To date, adding more than one supplementary anion or cation into the perovskite matrix is one way to lifting PCE or boosting the phase stability. As a simple notion, a considerable simpler arrangement where one FA is fused with MA as the organic compound leaving integral the inorganic part, have gained a lot of attention.14 The mixedcation perovskite have been proved to be an efficient and flexible approach as it allows fine regulation of the compound band gap with direct influence on tandem solar cell engineering.15 Traditionally, mixed-cation perovskite are always produced by direct 2 ACS Paragon Plus Environment


mixing of diverse perovskite ingredients, however, which causes phase transitional stress and a lower order crystallinity, leading to the instability of PSCs.16 In addition, traditional mixed-cation compositional engineering route brings severe nature of alterations in the crystal lattice, morphology related phase isolation and light/field-prompted ion movement changing the cell function.17 These reported complexities of the crystal structure and the problems to reproduce the stable cation intercalation in lattice structure cast the doubts on the easiness of reproducibility and scaling-up of this method.18-22 The orthodox mixedcation-based perovskites fabrication methods are very complex composition engineering for PSCs.11,20 In recent times, the fabrication of mixed-cation-based perovskites via unorthodox techniques emerged as a more attractive route to tune the perovskite crystallinity and phase stability. As a significant milestone, Seok and co-workers prepared the mixed cation perovskite through incorporating the MAPbBr3 into FAPbI3 and produced the α-phase perovskites at low temperature.12 Later, Xu et al. described the preparation of highlycrystalline (FAPbI3)1-x(MAPbBr3)x thin layers via dual ion exchange process.16 Whereas, these above composition engineering methods showed some residual MA ion in the perovskite layer, which could narrow down the range of absorbance.21 Bein et al. witnessed that the substitution of about 15% FA by MA could stabilize the perovskite phase by improving the interaction among MA cation and inorganic Pb-I vacancies.22 Zhang et al. developed the defect-less MAPbI3 thin film treated with FAI.23 Zhao et al. revealed that the MAPbI3 perovskite film treated by a diluted FABr would can effectively increase the crystal quality of the final perovskite film.24 The crystallinity of perovskite film can also be improved by post-treating of grown film with the polar solvents, organic halides vapor, or pyridine vapor.25-27 Unfortunately, many of the reported fabrication techniques are not appropriate for FA-rich perovskite and still lacks phase stability, leading to a drop in performance of the final device.28-30 Therefore, it is necessary to develop a novel route for producing phase-stable highly crystalline mixed-cation perovskite.31,32 Herein, we introduced a facile and highly reproducible method for preparing highly crystalline phase-stable FA-rich mixed-cation perovskite. The developed technique involves the formamidinium iodide (FAI) post-treatment of one-step deposited MAPbI3 film, and followed by brief annealing. The main notion behind this technique comprises of 3 ACS Paragon Plus Environment

Page 4 of 25

Page 5 of 25 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


post-treatment of MAPbI3 layer with FAI solution to obtain FA-rich perovskites with highly-crystalline and large grains for efficient PSCs. We found that the deposition of small ammount of FAI solution onto the surface of MAPbI3 film through spin-coating method supports intermixing of cations and anion with more suitable lattice arrangement. Due to the developed post-treatment technique, MAPbI3 films with comparatively small grain dimensions is transformed into superior quality FA-rich perovskites with large grain dimensions and highly crystalline orientation, which improve the optoelectronic properties. By analytically regulating the FAI concentrations, the obvious grain expansion of the MAPbI3 film was successfully produced, increasing the average PCE from 17.25% to 19.05% for planar perovskite devices. Promisingly, the highest efficiency of 20.21% was obtained with a resilient stability by retaining ~75% of the original efficiency for over 1000 h.

Experimental Section The detailed device fabrication and characterizations are illustrated in supporting information. Briefly, perovskite MAPbI3 precursor solution was prepared by mixing lead iodide (1.2 mol) and methylammonium iodide (1.2 mol) in anhydrous dimethylsulfoxide: dimethylformamide (4:1 volume ratio) solvent system and solution were stirred at 65 °C for one hour. The resulting solution was sequentially spin-coated on the substrate (blocking bi-TiO2-compact) at 1000 rpm for 10 seconds at 3500 rpm for 30 seconds. During second stage of spin-coating 100 μL of anhydrous chlorobenzene (CBZ) were slowly dripped on the centre of the rotating film at last 10th seconds of the process. The prepared films were annealed at 60 °C for 2 min, and 100 °C for 30 min. For FAI post-treatment, 40 μL FAI in 2-isopropanol (IPA) solution with different concentrations (10 mg·mL-1, 20 mg·mL-1, and 30 mg·mL-1), were dripped on the surface of the prepared MAPbI3 film for 5 seconds and spun at 4000 rpm for 20 seconds. FAI post-treated films were then thermally annealed at 100 °C for 2 min and 140 °C for 30 min.

Results and Discussion Schematic in Figure 1 illustrates the step-wise process for preparing large grain, highly crystalline perovskite via FAI post-treatment method. For FAI post-treatment, 40 μL of isopropyl alcohol (IPA) solution involves varied masses of FAI (0, 10, 20 and 30 4 ACS Paragon Plus Environment


mg·mL-1). For the convenience in expression of results, the as-obtained films are labelled as FAI-0, FAI-10, FAI-20 and FAI-30, respectively. Whereas, number 0, 10, 20 and 30 represent different masses of FAI in the IPA.

Figure 1. Schematic illustration of the fabrication process for large grain, highly crystalline perovskite via FAI post-treatment method.

The surface texture and morphology of the films were inspected by scanning electron microscopy (SEM, Figure 2). The FAI-0 exhibits branch crystals and small grain distribution on the surface, indicating a non-uniform growth of grains. The FAI-10 shows an expansion in grain size as compared to the former but lacks uniformity. This could be the result of non-homogeneous cation inter-mixing, which causes sudden surge in grain dimensions. Large grain size and smooth coverage are observed for the FAI-20. In particular, uniform grains are closely packed without any pin-hole or irregularity33. While, the FAI-30 exhibits loosely packed grains with voids between grain boundaries. This is perhaps due to the structural stress caused by the high concentration of FAI, which leads to the shrinkage of the perovskite grains, leaving a gap between them. Therefore, this morphological transformation confirms that the concentration of FAI has a strong effect on the crystal growth of post-treated MAPbI3 film.34

5 ACS Paragon Plus Environment

Page 6 of 25

Page 7 of 25 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


Figure 2. Top Scanning electron microscopy (SEM) images of the films post-treated with varied concentration of FAI in solution.

It is widely accepted that the compact and uniform perovskite film with large grain size is constructive for improving the opto-electronic properties. To ponder into the grain distribution, the mean grain sizes of the post-treated films were calculated (Figure S1). Results confirms an obvious expansion in grain sizes, which increased from ~180 nm of the FAI-0 to ~660 nm of FAI-20, then slightly dropped in FAI-30. As shown in Figure S2, atomic force microscopy (AFM) verifies that the FAI post-treated films show a better uniformity than the pristine MAPbI3 film, while the FAI-20 has a high-quality and smooth film among all. The root mean-square-roughness of the prepared films is 27.5 nm, 17.2 nm, 13.0 nm and 17.8 nm, respectively.35 Crystal stability and phase properties of the prepared films were investigated through X-ray diffraction (XRD, Figure 3a). In Figure S3 the observed diffraction peaks of pure MAPbI3 film is at and 28.4°, corresponding to (110) and (220) plane, respectively. The crystal geometry of FAI post-treated films is commendably improved and developed as compared to the FAI-0 followed by a decrease with higher FAI content (FAI-30), which is possible to be occurred by the deteriortion of the grain size due to the excess FAI mass. Peak intensity of the FAI-20 film increased about five times than that of pristion MAPbI3, 6 ACS Paragon Plus Environment


and the peak postion were shifted from MAPbI3 to FAPbI3 dominated phase with increasing FAI concentration.36 Figure 3b suggests a blue shift to lower wavelength for all the FAI treated films, indicating the mixed-cation of (FA)x(MA)1-xPbI3 is formed. The significant change in the perovskite crystal lattice after the FAI post-treatment is constant with the changes in grain morphology as discussed earlier.

Figure 3.(a) XRD patterns of the films post-treated with varied concentration of FAI. (b) Extended XRD region for 110 peak peak. (c) Schematic illustration of the formation mechanism of FAXMA1-XPbI3 via FAI post-treatment method.

Figure S4 shows the effect of FAI concentration on the pseudo cubic lattice parameters calculated from the XRD peaks at 6.30 Å, 6.32 Å and 6.33 Å of FAI-10, FAI20 and FAI-30, respectively. The lattice parameters can be assigned as X=0.25, X=0.50, and X=0.62, and are summarized in Table S1. The ratio of the FA/MA composition in the FAxMA1-xPbI3 films is FA0.25MA0.75, FA0.50MA0.50 and FA0.62MA0.38, respectively.37 This suggests that the FAI cations have a strong interaction toward MAPbI3 structure into perovskite crystal lattice. It is reported that the traditional mixed cation solution methods need a large quantity of FAI cation to stabilize the mixed-cation lattice phase, while in this


Page 8 of 25

Page 9 of 25 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


case only 50% composition of each cation were needed.36-38 The formation mechanism of post-treatment method was proposed in Figure 3c.14 X-rays photoelectron spectra (XPS) were measured since the expansion of cubicoctahedral volume could possibly lead to the change in chemical bonding between Pb and I (Figure S5). The bonding energies of Pb 4f and I 3d shift along with the increased FAI content in the post-treated films. It is witnessed that the Pb 4f peak of FAI-20 film shifts to lower bonding energy by 1.24 eV, and I 3d peak shifts to lower binding energy by 1.25 eV. Shifting of Pb 4f and I 3d peaks toward lower binding energies is indicative of reduced cationic charge over Pb and I ions, which could be responsible for the expansion of lattice structure as observed in the diffraction parameters and grain morphology.38 UV-vis absorption spectra were used to study the impact of FAI post-treatment on the optical properties of the prepared films (Figure 4a). The results show a reasonable improvement in absorption spectrum of each prepared films after FAI post-treatment compared with pristine MAPbI3 film. Absorption co-efficient becomes stronger with the increase of FAI concentration, while the FAI-20 film stands the strongest among them. As expected, it is noticed that the absorption onset experiences a red-shift in the absorption edge along with the increased concentration of FAI (Figure 4b). When the FAI concentration increases to 20 mg·mL-1, the absorption edge gradually shifted from ~780 nm (FAI-0) to ~820 nm (FAI-20).39 This postive change in absorption edge could be ascribed to the different ionic radius of cations. Due to the larger FAI ionic radius, the bandgap of mixed-cation perovskites becomes smaller, indicating the film with the ability to absorb low energy photons for electron excitation. The energy bandgap (Eg) of pure MAPbI3 perovskite is ~1.59 eV, while for FAPbI3 ~1.49 eV. The significant red-shift in absorption edge is the perk of cation intermixing which not only improves absorption ability but also enhances the absorption edge for a broader spectral conversion.35



Page 10 of 25

Figure 4. (a) UV-vis absorption spectra of the film post-treatment with different concentration of FAI. (b) The magnified UV-vis absorption region for FAI-0 and FAI-20, (c) TRPL spectra, and (d) PL spectra of the FAI-0 and FAI-20 films.

Time-resolved photoluminescence (TRPL) and steady-state photoluminescence (PL) spectroscopy were conducted to dig deep into the opto-electronic changes of the posttreated films. TRPL results of FAI-0 and best performing FAI-20 films are shown in Figure 4c. Both kinds of films were prepared on the bare glass so as to avoid the charge injection between the active layer and FTO.29 The TRPL decay curve was fitted by double exponential to calculate the carrier lifetime (τave)5, as follows： 𝑡

𝑓(𝑡) = ∑𝑖 𝐴𝑖 𝑒𝑥𝑝 (− 𝜏 )+𝑓0 𝑖

(1)

Where 𝐴𝑖 is the relative decay amplitude, 𝜏𝑖 is the decay time, and 𝑓0 is the constant. The related parameters are summarized in Table 1. The decay process can be attributed mainly to trap assisted non-radiative recombination at the interface and defects. The non-treated film (FAI-0) exhibits decay time of 𝜏1 =21.76 ns (fraction 𝐴1 = 40.50 %) and 𝜏2 =81.31 ns (fraction 𝐴2 =59.95%). In contrast, the FAI-20 sample gives 𝜏1 =25.46 (fraction 9 ACS Paragon Plus Environment

Page 11 of 25 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


𝐴1 =19.39%) and 𝜏2 = 201.43 ns (fraction 𝐴2 = 80.61%). The average PL decay time (τave) was calculated by the following equation: 40 ∑ 𝐴 𝜏𝑖2 𝑖 𝜏𝑖

𝜏𝑎𝑣𝑒 = ∑ 𝐴𝑖

(2)

As expected, the τave value of the non-treated MAPbI3 film is 72.19 ns, however, the τave value significantly increases to 196 ns for FAI-20 film, indicating a higher crystallinity due to cation intermixing associated to lower energetic disorder with respect to the pure MAPbI3.41 This surge in carrier lifetime shows an improved carrier dynamic of the film in terms of reduced trap states.35,37 PL spectra shows a significant red-shift of the emission peak for FAI-20 post-treated film (Figure 4d). The gradual shift derives from the intermixing of FA and MA in the perovskite lattice, exhibiting stronger PL spectra than pristine MAPbI3 film. It is generally believed that less non-radioactive recombination, long-term carrier lifetime and effective charge transport are essential for high-performance devices. Particularly, the defects between the grain boundaries provide charge quenching sites to affect the opto-electronic performance.42 The FAI-20 film reflects a better uniformity and less traps states witnessed by sharp and narrowed PL spectra. The observed red-shift in peak position from 780 nm to 820 nm for FAI-20 film compared to FAI-0 film is in line with the absorption onset. This visible narrowing of the peak indicates that the film has less surface defect and enhanced crystallite than the former one.29

Table 1. The decay time and the relative decay amplitude time parameters derived from the TRPL decay curves. Samples

𝜏1 (ns)

𝐴1 (%)

𝜏2 (ns)

𝐴2 (%)

τave (ns)

FAI-0

21.76

40.50

81.31

59.95

72.19

FAI-20

25.46

19.39

201.43

80.61

196.23

As illustrated in Figure 5a, perovskite solar cells were fabricated with the structure of fluorine-doped tin oxide (FTO)/compact titanium dioxide (C-TiO2)/MAPbI3 absorber with or

without

FAI-post-treatment/2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-

9,9′spirobifluorene (spiro-OMeTAD)/Gold. The photovoltaic performance of each device 10 ACS Paragon Plus Environment


was tested under simulated illumination of AM 1.5 G solar simulator (100 mW cm-2). The photovoltaic parameters of each sample are summarized in Table 2. The PCE of the best performing device (FAI-20) reached 20.21%, with a short-circuit current density (Jsc) of 23.58 mA.cm-2, open-circuit voltage (Voc) of 1.10 V, and fill factor (FF) of 77.77%, which is higher than that of FAI-0-based device (17.25%). The surge in FF, Jsc and Voc is probably due to the stronger light absorption, reduced defects and less carrier recombination.43 The relationship between Voc and the energy levels of perovskite in table S2. It can be seen that the variation in Voc was observed as compared to the other performance indicators of the dvice based on FA post-treated film. A noticeable lift in Voc was observed as compared to the other performance indicators of the post-treated devices. This could be due to the introduction of larger FAI cation into the lattice structure, which is not only improved film crystallinity and morphology, but also improved absorption edge and the resultant optimized energy level of the film.44,45 It can be seen that the Eg value varies along with the different contraction of FAI. Normally, the onset bandgap of mixed FAxMA1-XPbI3 perovskite locates at an intermediate value from 1.56 eV of MAPbI3 to 1.48 eV of FAPbI3, indicating that the energy band gap is a function of varying composition of the FA/MA. In this context, calculated the energy bandgaps of the as prepared perovskite layers from the UV-Vis absorption spectra as mentioned in Table S2. The analysis shows that the different concentrations of FA in the MAPbI3 influenced the energy bandgap, there by affecting the Voc of the devices. At optimized concertation (FA-20) the Eg value of 1.51 eV yields the highest value of Voc.11,46,47Moreover, statistical box plots of Voc, FF, Jsc and PCE without and with different concentration of FAI post-treatment films are shown in Figure S6. It is worth noting that the post-treated devices have much higher FF, Voc and Jsc, probably due to larger crystallite and better photo-physical properties ascribed to better cation inter-mixing.


Page 12 of 25

Page 13 of 25 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


Figure 5. (a) Schematic device configuration, (b) cross-sectional SEM image of the prepared device, (c) J-V curves, and (d) the corresponding IPCE spectra of the bestperforming devices without and with FAI post-treatment.

Table 2. Performance parameters of the best-performing devices without and with FAI post-treatment. FAI (mg·mL-1)

Jsc (mA.cm-2)

Voc (V)

FF (%)

PCE (%)

FAI-0

22.96

1.01

74.03

17.25

FAI-10

23.42

1.09

76.15

19.33

FAI-20

23.58

1.10

77.77

20.21

FAI-30

23.09

1.04

75.34

18.09

To further ponder into the photo-physical spectral response of the prepared devices, incident photon-to-current conversion efficiency (IPCE) were measured, and results of the best PSCs are shown in Figure 5d. The risen IPCE curves of post-treated devices, particularly of FAI-20, are great due to the strong and high absorptions of the high-quality FAxMA1-xPbI3 film and effective charge separation in respective layer.48 The stronger IPCE spectra of the FAI treated PSCs could be credited to the few important things. Firstly, the mix-cation films always show the better photo-physical response than pure MAPbI3, as 12 ACS Paragon Plus Environment


larger radii cation (FAI) boosts opto-electronic properties by improving band gap. Secondly, the adopted FAI post-treatment method helps to reduce grain boundary by growing larger grain in size without losing surface uniformity, compactness and coverage. These morphological aspects are always requisite conditions for effective electron-hole separation and collection, leading to the enhanced Jsc, Voc and FF.

Figure 6. Statistical PCEs of (a) traditional and FAI-20 based 30 devices. (b) J-V curves and performance parameters of the best performing Trade-PSC and FAI-20-based PSC.

To prove the application potential of the developed cation intermixing technique for high-performance PSCs, we further fabricated mixed-cation-based PSCs using traditional one-step method without post-treament.11,20 The statistical distribution of PCEs for 30 individual devices based on traditional mixed-cation and FAI-20 based devices are compared in Figure 6a. Apparently, the statistical parameters of FAI-20-based devices show a much narrower distribution in the higher efficiency compared with the traditional mixed-cation based devices. Despite of same ingredients, the performance superiority of FAI-20-based device advocates the FAI post-treatment technique as a more effective route to fabricate scalable and efficient mixed perovskite devices. As shown in Figure 6b, the mixed-cation devices from traditional one-step method without post-treament shows a PCE of 19.08% under the same conditions of developed post-treatment method. It can be noted that the PSCs fabricated from developed cation intermixing technique show an obvious better performance than traditional mixed-cation devices. On the other hand, Figure S7 compares the hysteresis profile of FAI-0, FAI-20 and traditional mixed-cation devices by measuring under reverse and forward scan. As expected, the FAI-20 post-treated device experienced minor hysteresis (4%) than its both 13 ACS Paragon Plus Environment

Page 14 of 25

Page 15 of 25 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


counterparts (14% and 8%), probably due to the less trap-states and reduced interfacial ion trapping.21,31 Figure S8 verifies the performance credibility of the devices as stabilized power output was measured by applying a constant bias equal to the voltage at their respective maximum power point. The PCEs rapidly stabilized at 15.80% and 19.31% for the device based on FAI-0 and FAI-20 absorbers, respectively, well matched with J-V measurement. The FAI-20-based device exhibited a stable power output throughout the observed time span (200 s), indicating a credible efficiency stability of the device.5,43, One of the critical challenges in PSCs is the stability of device. To study the impact of FAI post-treatment on the device stability, efficiency evolution of the devices for each case were analysed. Figure 7a shows the long-term efficiency evolution of the FAI-0, FAI20 and traditional mixed-cation based devices. All the devices were stored in the air glove box at room temperature (25 °C) and under relative humidity of ~40%. Promisingly, the devices fabricated from the developed cation intermixing technique show an obviously better stability than traditional and FAI-0 mixed-cation devices. Moreover, the former device retained almost ~75% of the recorded PCE even after 1000 h of exposure.

Figure 7. (a) Normalized efficiency evolution of the device for a period of 1000 hours. (b) Electrochemical impedance spectroscopy (EIS) of the prepared devices at an applied



Page 16 of 25

voltage of 0.90 V. (c) Voc decay curves and (d) correlation function between electron lifetime and Voc of the FAI-0 FAI-20 and traditional mixed-cation device.

To further investigate the dynamics of charge transfer among the layers of devices, electrochemical impedance spectroscopy (EIS) with an applied bias voltage of 0.90 V under 1 sun illumination was carried out (Figure 7b). According to an equivalent circuit, curves are fitted to study the interfacial charge transport and recombination. The recombination resistance (Rrec) of the FAI-0-based and traditional mixed-cation devices are fairly lower than that of the FAI-20-based device, indicating the suppressed recombination rate because of the reduced non-radiative charge recombination at the perovskite layer/cTiO2 layer interface, which ultimately enhances Voc as earlier witnessed in Table 2.49 Besides EIS, one of the widely used effective tool to analyse the charge carrier recombination and their lifetime in the device is the open-circuit voltage decay.50 It reveals the link between interface recombination rate and the charge carrier lifetime. Figure 7c shows the Voc decay curves of FAI-0, FAI-20 and traditional mixed-cation devices. There are three stages in electron transport profile in different voltage regions as elaborated in the decay curves. Firstly, the instantaneous lifetime constant at high voltage region under illumination could be attributed to the free electrons. Secondly, the exponential decrease at mean voltage region can be attributed to the internal trapping and de-trapping of electrons due to the existence of bulk trap-states. At last, the inverted parabola at low photo-voltage region is mainly due to the c-TiO2/perovskite interface, which shows obvious difference in both devices. Moreover, the electron lifetime (τn) is calculated by the following formula:5,37 τn= KB Te-1 (dVoc/dt)-1

(3)

Where kB is the Boltzmann constant, T is the temperature, and e is the elementary charge. As shown in Figure 7d, the τn is the highest for each case at lower voltage region, particularly the device with FAI post-treatment, which is consistent with the Voc decay curve. The τn of all the cases gradually decreases with increasing Voc. However, the τn of FAI-20-based device remains higher than that of FAI-0-based and little better than the traditional one, till they reaches the higher Voc region, suggesting an improved film morphology. In the perovskite films with large grain size, the photo generated carriers can easily be collected without encountering bulk defects at grain boundaries, where the current 15 ACS Paragon Plus Environment

Page 17 of 25 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


leakage and charge recombination could be greatly reduced.43 The FAI post-treated film exhibits the much longer τn than that of non-treated or traditionally produced mixed-cation perovskite film over the same voltage region, demonstrating the suppressed instantaneous non-radiative carrier recombination at the interface. This enhancement could be attributed to the high charge mobility caused by effectively passivation of the perovskite layer and respective interfaces by the FAI-post treatment,32,49,50 which is useful for the efficient transport of photo carriers from perovskite layer into HTL and ETL.

Conclusion We developed a post-treatment method for MAPbI3 layer with FAI solution to obtain the mixed-cation perovskite with high crystal quality and large grains for efficient and stable PSCs. The deposition of 20 mg mL-1 FAI in IPA solution onto the MAPbI3 perovskite film supports uniform intermixing of cations and anions with more suitable lattice arrangement. The MAPbI3 film with comparatively small grain dimensions were completely transformed into superior quality mixed-cation perovskites with large grain and highly crystalline orientation. In addition, surface features and optoelectronic properties were improved by the FAI post-treatment method, which yields a hybrid FAxMA1-xPbI3 film with the enhanced carrier lifetime and reduces non-radiative recombination with resilient nature of stability. Promisingly, the mixed-cation PSCs fabricated from this developed method show higher PCE and better stability than the devices from traditional method.

Acknowledgment This work was supported by the National Key Research and Development Program of China (No. 2016YFA0202400), the 111 Project (No. B16016), the National Natural Science Foundation of China (No. 51702096 and U1705256), and the Fundamental Research Funds for the Central Universities (No. 2018ZD07 and 2019MS027)

Supporting Information Description of the experimental and characterization process of the prepared samples; The grain size from the surface morpohlogy of SEM image; AFM images of the prepared films; 16 ACS Paragon Plus Environment


Page 18 of 25

lattice parameter is calculated from Bragg equation: 2dsinθ =nλ (λ= 1.54056 Å) and Summary of lattice parameters for perovskite films; X-ray photoelectron (XPS) of core spectra; Statistical results for (a) Voc, (b) FF, (c) Jsc and (d) PCE values of the devices without and with FAI post-treatment; Current density-voltage (J-V) Curves of the best performing devices based on FAI-0, FAI-20 and traditional mixed cation films and J-V curves measured by forward and reverse scan of the best-performance devices based on (a) FAI-0, (b) FAI-20 and (c) traditional mixed cation films.

Conflict of interest The authors declare that they have no conflict of interest.

References (1) Akihiro, K.; Kenjiro, T.; Yasuo, S.; Tsutomu, M. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J. Am. Chem. Soc. 2009, 131, 60506051, DOI: 10.1021/ja809598r. (2) Wu, Y.; Yang, X.; Chen, W.; Yue, Y.; Cai, M.; Xie, F.; Bi, E.; Islam, A.; Han, L. Perovskite solar cells with 18.21% efficiency and area over 1 cm2 fabricated by heterojunction

engineering.

Nat.

Energy.

2016,

1,

16148,

DOI:

10.1038/nenergy.2016.148. (3) Im, J. H.; Lee, C. R.; Lee, J. W.; Park, S. W.; Park, N. G. 6.5% efficient perovskite quantum-dot-sensitized solar cell. Nanoscale. 2011, 3, 4088-4093, DOI: 10:1039/clnr10867k. (4) Arain, Z.; Liu, C.; Yang, Y.; Mateen, M.; Ren, Y.; Ding, Y.; Liu, X.; Ali, Z.; Kumar, M.; Dai, S. Elucidating the dynamics of solvent engineering for perovskite solar cells. Sci. China Mater. 2019, 62, 2095-8226, DOI: 10.1007/s40843-018-9336-1. (5) Liu, C.; Yang, Y.; Ding, Y.; Xu, J.; Liu, X.; Zhang, B.; Yao, J.; Hayat, T.; Alsaedi, A.; Dai, S. High-efficiency and UV-stable planar perovskite solar cells using lowtemperature solution-processed Li-TFSI doping C60 as electron transport layers. ChemSusChem 2018, 11, 1232-1237, DOI: 10.1002/cssc.201702248.


Page 19 of 25 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


(6) Correabaena, J. P.; Abate, A.; Saliba, M.; Tress, W.; Jacobsson, T. J.; Grätzel, M.; Hagfeldt, A. The rapid evolution of highly efficient perovskite solar cells. Energy Environ. Sci. 2017, 10, 710-727, DOI: 10.1039/c6ee03397k. (7) Zhongmin, Z.; Zaiwei, W.; Yuanyuan, Z.; Shuping, P.; Dong, W.; Hongxia, X.; Zhihong, L.; Padture, N. P.; Guanglei, C. Methylamine-gas-induced defect-healing behavior of CH3NH3PbI3 thin films for perovskite solar cells. Angew. Chem. Int. Ed. 2015, 54, 9705-9709, DOI: 10.1002/anie.201504379. (8) Liu, D.; Gangishetty, M.; Kelly, T. Effect of CH3NH3PbI3 thickness on device efficiency in planar heterojunction perovskite solar cells. J. Mater. Chem. A. 2014, 2, 19873-19881, DOI: 10.1039/c4ta02637c. (9) Baikie, T.; Fang, Y.; Kadro, J. M.; Schreyer, M.; Wei, F.; Mhaisalkar, S. G.; Graetzel, M.; White, T. Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for solid-state sensitised solar cell applications. J. Mater. Chem. A. 2013, 1, 56285641, DOI: 10.1039/c3ta10518k. (10) Koh, T. M.; Fu, K.; Fang, Y.; Chen, S.; Sum, T. C.; Mathews, N.; Mhaisalkar, S.G.;Boix, P. P.; Baikie, T. Formamidinium-containing metal-halide: An alternative material for near-IR absorption perovskite solar cells. J. Phys. Chem. C. 2014, 118, 16458-16462, DOI: 10.1021/jp411112k. (11) Yi, Z.; Grancini, G.; Feng, Y.; Asiri, A. M.; Nazeeruddin, M. K. Optimization of stable quasi-cubic FAxMA1–xPbI3 perovskite structure for solar cells with efficience beyond

20%.

ACS

Energy

Lett.,

2017,

2,

802–806,

DOI:

10.1021/acsenergylett.700112. (12) Nam Joong, J.; Jun Hong, N.; Woon Seok, Y.; Young Chan, K.; Seungchan, R.; Jangwon, S. Compositional engineering of perovskite materials for high-performance solar cells. Nature 2015, 517, 476-480, DOI: 10.1038/nature14133. (13) Wang, Z.; Zhou, Y.; Pang, S.; Xiao, Z.; Zhang, J.; Chai, W.; Xu, H.; Liu, Z.; Padture, N. P.; Cui, G. J. Additive-modulated evolution of HC(NH2)2PbI3 black polymorph for mesoscopic perovskite solar cells. Chem. Mater. 2015, 27, 7149-7155, DOI: 10.1021/acs.chemmater.5b03169. (14) Li, G.; Zhang, T.; Guo, N.; Xu, F.; Qian, X.; Zhao, Y. Ion-exchange-induced 2D–3D conversion of HMA1−xFAxPbI3Cl perovskite into a high-quality MA1-xFAxPbI3 18 ACS Paragon Plus Environment


perovskite.

Angew.

Chem.

Int.

Ed.

2016,

55,

Page 20 of 25

13460–13464,

DOI:

10.1002/anie.201606801. (15) Mc Meekin, D. P.; Sadoughi, G.; Rehman, W.; Eperon, G. E.; Saliba, M.; Horantner, M.T.; Haghighirad, A.; Sakai, N.; Korte, L.; Rech, B.; et al. A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells. Science 2016, 3, 151–155, DOI: 10.1126/science.aad5845. (16) Zhang, T.; Long, M.; Yan, K.; Qin, M.; Lu, X.; Zeng, X.; Cheng, C. M.; Wong, K. S.; Liu, P.; Xie, W.; Xu, J. Crystallinity preservation and ion migration suppression through dual ion exchange strategy for stable mixed perovskite solar cells. Adv. Energy Mater. 2017, 7, 1700118, DOI: 10.1002/aenm.201700118. (17) Rehman, W.; McMeekin, D. P.; Patel, J. B.; Milot, R. L.; Johnston, M. B.; Snaith, H. J. Photovoltaic mixed-cation lead mixed-halide perovskites: links between crystallinity, photo-stability and electronic properties. Energy Environ. Sci. 2017, 10, 361–369, DOI: 10.1039/c6ee03014a. (18) Ji, F.; Wang, L.; Pang, S.; Gao, P.; Xu, H.; Xie, G.; Zhang, J.; Cui, G. A balanced cation exchange reaction toward highly uniform and pure phase FA1−xMAxPbI3 perovskit films. J. Mater. Chem. A. 2016, 4, 14437–14443, DOI:10.1039/c6ta05727f. (19)

Cho, K. T.; Paek, S.; Grancini, G.; Roldán-Carmona, C.; Gao, P.; Lee, Y.; Nazeeruddin, M. K. Highly efficient perovskite solar cells with a compositionally engineered perovskite/hole transporting material interface. Energy Environ. Sci. 2017, 10, 621-627, DOI: 10.1039/c6ee03182j.

(20) Li, C.; Zhou, Y.; Wang, L.; Chang, Y.; Zong, Y.; Etgar, L.; Cui, G.; Padture, N. P.; Pang, S. Methylammonium-mediated evolution of mixed-organic-cation perovskite thin films: A dynamic composition-tuning process. Angew. Chem. Int. Ed. 2017, 129, 7782-7786, DOI: 10.1002/ange.201704188. (21) Eperon, G. E.; Stranks, S. D.; Menelaou, C.; Johnston, M. B.; Herz, L. M.; Snaith,H. J. Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells. Energy Environ. Sci. 2014, 7, 982988, 10.1039/c3ee43822h.


DOI:

Page 21 of 25 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


(22) Binek, A.; Hanusch, F. C.; Docampo, P.; Bein, T. Stabilization of the trigonal hightemperature phase of formamidinium lead iodide. J. Phys. Chem. Lett. 2015, 6, 12491253, DOI: 10.1021/acs.jpclett.5b00380. (23) Zou, Y.; Wang, H.-Y.; Qin, Y.; Mu, C.; Li, Q.; Xu, D.; Zhang, J.-P. Reduced defects of MAPbI3 thin films treated by FAI for high-performance planar perovskite solar cells. Adv. Funct. Mater. 2018, 10, 1805810, DOI: 10.1002/adfm.201805810. (24) Yang, M.; Zhang, T.; Schulz, P.; Li, Z.; Li, G.; Dong, H. K.; Guo, N.; Berry, J. J.; Zhu, K.; Zhao, Y. Facile fabrication of large-grain CH3NH3PbI3−xBrx films for highefficiency solar cells via CH3NH3Br-selective Ostwald ripening. Nat. Commun. 2016, 7, 12305, DOI: 10.1038/ncomms12305 (25) Luo, P.; Zhou, S.; Zhou, Y.; Xia, W.; Sun, L.; Cheng, J.; Xu, C.;Lu, Y. Fabrication of CsxFA1-xPbI3 mixed-cation perovskites Via gas phase-assisted compositional modulation for efficient and stable photovoltaic devices. ACS Appl. Mater. Interfaces, 2017, 9, 42708-42716, DOI: 10.1021/acsami.7b12939. (26) Luo, P.; Liu, Z.; Xia, W.; Yuan, C.; Cheng, J.; Lu, Y. Uniform, stable, and efficient planar-heterojunction perovskite solar cells by facile low-pressure chemical vapor deposition under fully open-air conditions. ACS Appl. Mater. Interfaces 2015, 7, 2708-2714, DOI: 10.1021/am5077588. (27) Li, F.; Bao, C.; Zhu, W.; Lv, B.; Tu, W.; Yu, T.; Yang, J.; Zhou, X.; Wang, Y.; Wang, X.; Zhou, Y.; Zou, Z. Microstructure modulation of the CH3NH3PbI3 layer in perovskite solar cells by 2-propanol pre-wetting and annealing in a spray-assisted solution process. J. Mater. Chem. A 2016, 4, 11372-11380, DOI:10.1039/c6ta04600b. (28) Pellet, N.; Gao, P.; Gregori, G.; Yang, T. Y.; Nazeeruddin, M. K.; Maier, J.; Grätzel, M. Mixed-organic-cation perovskite photovoltaics for enhanced solar-light harvesting. Angew. Chem. Int. Ed. 2014, 53, 3151-3157, DOI: 10.1002/anie.201309361. (29) Liu, J.; Shirai, Y.; Yang, X.; Yue, Y.; Chen, W.; Wu, Y.; Islam, A.; Han, L. Highquality mixed-organic-cation perovskites from a phase-pure non-stoichiometric intermediate (FAI)1−xPbI2 for solar cells. Adv. Mater. 2015, 27, 4918-4923, DOI: 10.1002/adma.201501489.



Page 22 of 25

(30) Du, T.; Wang, N.; Chen, H.; Lin, H.; He, H. Comparative study of vapor-and solutioncrystallized perovskite for planar heterojunction solar cells. ACS Appl. Mater. Interfaces, 2015, 7, 3382-3388, DOI: 10.1021/am508495r. (31) Chen, J.; Xu, J.; Zhao, C.; Zhang, B.; Liu, X.; Dai, S.; Yao, J. Enhanced open-circuit voltage of cs-containing FAPbI3 perovskite solar cells by the formation of a seed layer through a vapor-assisted solution process. ACS Sustain. Chem. Eng. 2019, 7, 34043413, DOI: 10.1021/acssuschemeng.8b05610. (32) Isikgor, F. H.; Li, B.; Zhu, H.; Xu, Q.; Ouyang, J. High performance planar perovskite solar cells with a perovskite of mixed organic cations and mixed halides, MA1−xFAxPbI3−yCly.

J.

Mater.

Chem.

A

2016,

4,

12543–12553,

DOI:

10.1039/c6ta03381d. (33) Zhang, P.; Yang, F.; Kapil, G.; Ng, C. H.; Ma, T.; Hayase, S. Preparation of perovskite films under liquid nitrogen atmosphere for high efficiency perovskite solar cells. ACS Sustain. Chem. Eng. 2019, 7, 3956-3961, DOI: 10.1021/acssuschemeng.8b05139. (34) Arain, Z.; Liu, C.; Ren, Y.; Yang, Y.; Mateen, M.; Liu, X.; Ding, Y.; Ali, Z.; Liu, X.; Dai, S.; Hayat, T.; Alsaedi, A. Low Temperature annealed perovskite films: a tradeoff between fast and retarded crystallization via solvent engineering. ACS Appl. Mater. Interfaces, 2019, 11, 16704-16712, DOI: 10.1021/acsami.9b02297. (35)

Chen, J.; Xu, J.; Xiao, L.; Zhang, B.; Dai, S.; Yao, J. Mixed-organic-cation (FA)x(MA)1–xPbI3 planar perovskite solar cells with 16.48% efficiency via a lowpressure vapor-assisted solution process. ACS Appl. Mater. Interfaces 2017, 9, 24492458, DOI: 10.1021/acsami.6b13410.

(36) Noh, J. H.; Sang, H. I.; Jin, H. H.; Mandal, T. N.; Sang, I. Chemical management for colorful, efficient, and stable inorganic–organic hybrid nanostructured solar cells. Nano. Lett. 2013, 13, 1764-1769, DOI: 10.1021/nl400349b. (37) Xie, F.; Chen, C. C.; Wu, Y.; Xing, L.; Cai, M.; Xiao, L.; Yang, X.; Han, L. Vertical recrystallization for highly efficient and stable formamidinium-based invertedstructure perovskite solar cells. Energy Environ. Sci. 2017, 10, 1942-1949, DOI: 10.1039/c7ee01675a.


Page 23 of 25 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


(38)

Lee, J. W.; Kim, D. H.; Kim, H. S.; Seo, S. W.; Cho, S. M.; Park, N. G. Formamidinium and cesium hybridization for photo- and moisture-stable perovskite solar cell. Adv. Energy Mater. 2015, 5, 1501310, DOI: 10.1002/aenm.201501310.

(39) Gonzalez-Carrero, S.; Espallargas, G. M.; Galian, R. E.; Pérez-Prieto, J. Blueluminescent organic lead bromide perovskites: highly dispersible and photostable materials. J . Mater.Chem. A. 2015, 3, 14039-14045, DO: 10.1039/c5ta01765c. (40) Fei, C.; Li, B.; Zhang, R.; Fu, H.; Tian, J.; Cao, G. Highly efficient and stable perovskite solar cells based on monolithically grained CH3NH3PbI3 film. Adv. Energy Mater. 2017, 7, 160201, DOI: 10.1002/aenm.201602017. (41) Wang, F.; Geng, W.; Zhou, Y. Phenylalkylamine passivation of organolead halide perovskites enabling high-efficiency and air-stable photovoltaic cells. Adv. Mater. 2016, 28, 9986, DOI: 10.1002/adma.201603062. (42) Zhou, Z.; Xu, J.; Xiao, L.; Chen, J.; Tan, Z. a.; Yao, J.; Dai, S. Efficient planar perovskite solar cells prepared via a low-pressure vapor-assisted solution process with fullerene/TiO2 as an electron collection bilayer. RSC Adv. 2016, 6, 78585-78594, DOI: 10.1039/c6ra14372e. (43) Yang, Y.; Peng, H.; Liu, C.; Arain, Z.; Ding, Y.; Ma, S.; Liu, X.; Hayat, T.; Alsaedi, A.; Dai, S. Bi-functional additive engineering for high-performance perovskite solar cells with reduced trap density. J. Mat. Chem. A 2019, 7, 6450-6458, DOI: 10.1039/c8ta11925b. (44) Zhang, W.; Saliba, M.; Moore, D. T.; Pathak, S. K.; Stergiopoulos, T.; Stranks, S. D.; Eperon, G. E.; Alexanderwebber, J. A.; Abate, A.; Sadhanala, A. Ultrasmooth organic-inorganic perovskite thin-film formation and crystallization for efficient planar heterojunction solar cells. Nat. Commun. 2015, 6, 6142, DOI: 10.1038/ncomms7142. (45) Zhang, X.; Liu, H.; Wang, W.; Zhang, J.; Xu, B.; Karen, K. L.; Zheng, Y.; Liu, S.; Chen, S.; Wang, K. Hybrid perovskite light-emitting diodes based on perovskite nanocrystals with organic-inorganic mixed cations. Adv. Mater. 2017, 29 , 1606405, DOI: 10.1002/adma.201606405. (46) Elseman, A. M.; Shalan, A. E.; Sajid, S.; Rashad, M. M.; Hassan, A. M.; Li, M., Copper-substituted lead perovskite materials constructed with different halides for 22 ACS Paragon Plus Environment


working (CH3NH3)2CuX4-based perovskite solar cells from experimental and theoretical view. ACS Appl. Mater. Interfaces, 2018, 10, 11699-11707, DOI: 10.1021/acsami.8b00495. (47) Slimi, B.; Mollar, M.; Assaker, I. B.; Kriaa, I.; Chtourou, R.; Marí B. Perovskite FA1xMAxPbI3

for solar cells: films formation and properties, Energy Procedia 2016, 102

87-95, DOI: 10.1016/j.egypro.2016.11.322. (48) Jing, C.; Jia, X.; Zhang, S.; Zhou, S.; Zhou, K.; Bing, Z.; Xin, X.; Yang, L.; Dai, S.; Yao, J. Halogen versus pseudo-halogen induced perovskite for planar heterojunction solar cells: some new physical insights. J. Phys. Chem. C. 2017, 121, 28443-2853, DOI: 10.1021/acs.jpcc.7b10018. (49) Saidaminov, M. I.; Abdelhady, A. L.; Murali, B.; Alarousu, E.; Burlakov, V. M.; Peng, W.; Dursun, I.; Wang, L.; He, Y.; Maculan, G.; et al High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization. Nat. Commun. 2015, 6, 7586, DOI: 10.1038/ncomms8586. (50) Liang, Z.; Zhang, S.; Xu, X.; Wang, N.; Wang, J.; Wang, X.; Bi, Z.; Xu, G.; Yuan, N.; Ding, J. A large grain size perovskite thin film with a dense structure for planar heterojunction solar cells via spray deposition under ambient conditions. RSC Adv. 2015, 5, 60562-60569, DOI: 10.1039/c5ra09110a.


Page 24 of 25

Page 25 of 25 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


Table of Contents

The developed method can produce large grain and highly crystalline (FA)x(MA)1-xPbI3 for efficient and stable perovskite solar cells


High-Quality (FA)X(MA)1-XPbI3 for Efficient Perovskite Solar Cells Via

Recommend Documents