Chemical Decoration of Perovskites by Nickel Oxide Doping for

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Chemical Decoration of Perovskite by Nickel Oxide Doping for Efficient and Stable Perovskite Solar Cells Fayin Zhang, Shanyi Guang, Meidan Ye, Kaibing Xu, Wenxi Guo, Xiang Yang Liu, and Hongyao Xu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b08658 • Publication Date (Web): 09 Oct 2018 Downloaded from http://pubs.acs.org on October 9, 2018

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ACS Applied Materials & Interfaces

Chemical Decoration of Perovskite by Nickel Oxide Doping for Efficient and Stable Perovskite Solar Cells Fayin Zhang†, Shanyi Guang†, Meidan Ye❈, Kaibing Xu§*, Wenxi Guo❈,Xiangyang Liu‡❈*,Hongyao Xu†§* † The State Key Laboratory for Modication of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China. § Research Center for Analysis and Measurement, Donghua University, Shanghai 201620, China ❈

Research Institute for Soft Matter and Biomimetics, Fujian Provincial Key Laboratory for Soft

Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China. ‡Department of Physics, Faculty of Science, National University of Singapore, Singapore, 117542, Singapore.

ABSTRACT Crystal engineering of CH3NH3PbI3-xClx perovskite film through p-type semiconductor materials modification-directed was proposed as an efficient method for dominating crystallization process. Then a simple method is demonstrated to perfect the quality of perovskite film by uniting nickel oxide (NiOx) nanoparticles into the precursor solution. The combination of NiOx brings about high-crystallized crystals, and convenient photo-generated charge transport with reduced defect density owing to efficient control of the preferred nucleation and crystal growth. The sufficient contact between CH3NH3PbI3-xClx-NiOx and electron transport layer can contribute to photo-generated carrier lifetime and transport through the optimized interface. Moreover, it is demonstrated that a strong chemical bonding decoration between MAPbI3-xClx

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and NiOx could protect perovskite materials from the oxygen and humidity corrosion, which shows remarkable stability holding ~81% of its incipient PCE after 50 days. The device with best PCE of 19.34 % is achieved because of the improved short-circuit current from 22.23 to 23.01 mA cm-2 and fill factor from 68.97 to 75.06%. The results certify that this p-type charge transport material-decorated method for the optimization of perovskite film was demonstrated as an efficient way to optimize the performance. KEYWORDS：： Chemical decoration, nickel oxide, perovskite solar cell, chemical bonding, stability INTRODUCTION In recent years, perovskite solar cell (PSC) is becoming an attractive field compared with commercial silicon-based cells due to their excellent optoelectronic performance, charge carrier mobility, and simple machining process.1-4 The efficiency of photovoltaic has already exceeded 22%,5 what is more, extensive efforts have been made to develop materials and technologies for improving the PSC performance, including the mechanism investigation of crystal formation,6,7 solvent8-10 and interface engineering.11-16 Normally the high quality film with favorable structure is urgent for making better PSC.17-20 Meanwhile the existence of trap states in perovskite film lead to carrier recombination and adverse current hysteresis effect.21-23 The intrinsic property of perovskite material is susceptible to humidity- and air-induced degradation severely limiting their practical applications in ambient environment.24-27 Therefore, it is highly imperative to optimize the morphology and quality of crystallization to reduce the defects and decrease the defect-induced performance loss. Perovskite crystallization is a complicated process, which starts from nucleation of crystal and then fast growth.28 Several works have been reported at present, which emphasize the


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importance to control the quality of perovskite film towards larger grains.29-32 Yang et al. report a cross-link interface between nickel oxide (NiO) hole extraction layer and CH3NH3PbI3-xClx through chemical bonds by ethanolamine monomolecular. The modified interface endows the perovskite film with better crystallization, hole extraction efficiency and reduced defect densities.33 Jen and co-workers show an efficient approach to fabricate Cu-doped NiOx hole transport layer, which renders the PSC with decent environment stability and high performance.34 In addition to this under-layer abduction strategy, additive addition and doping technologies have also been reported to perfect the perovskite film. Hagfeldt et al. firstly add nitrogen-doped reduced grapheme oxide into the perovskite precursor to slow down the crystallization process with better crystal morphology and large grain size.35 Liao and coworkers incorporates a inorganic of C3N4 into the perovskite precursor, which also show improved crystals with high crystallinity, even with an enhanced conductivity of perovskite film.36 However, the trap states is strongly dependent on the disorder of crystals resulted from lattice vacancies, ionized impurities and interstices within perovskite film. Though the abovementioned methods obtained the perovskite film still exist some trap states near the grain boundary. What’s more, the control of crystallization process is confronted with huge challenge for spin-coating method owing to the complicated dynamic process. Among those additives, NiOx has great potential because of its simple solution processability, good chemical stability and optimal energy level alignment with perovskite, so it has been widely investigated as HTL in the PSC with different device architectures.37-39 In addition, NiOx can dispersed well in perovskite precursor and keep good dispersibility for a long time. Here, a crystal engineering is introduced for NiOx incorporated into perovskite solution, which brings about some significant results about performance. First of all, the suitable amount


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of doping increases the grain size and crystallization quality along with better light-absorption capability. Secondly, the reduced defect density inside the perovskite layer could retard the charge recombination around the grain boundaries. Most of all, the generated chemical bonds between CH3NH3PbI3-xClx and NiOx endow the PSC excellent stability under air condition. The PSC photovoltaic containing such chemical decoration demonstrates an exciting PCE of 19.34 % against 16.56 % for the original one. RESULTS AND DISCUSSION The device structure and fabrication process of perovskite film with NiOx doping compared with the pristine precursor is illustrated in Figure 1. Figure 1a shows common device structure, which is made up of NiOx HTL, CH3NH3PbI3-xClx-NiOx composite perovskite, phenyl-C61butyric acid methyl ester (PCBM) and 2,9-dimethyl-4,7- diphenyl-1,10-phenanthroline (BCP) electron transport layer (ETL), capped with Ag electrode. The various energy level of functional layers in the PSC are presented in Figure 1b, where the values of them are cited from previous literature.40, 41 Figure 1c shows a cross section of the as-fabricated PSC, the thicknesses of the NiOx, perovskite layer, PCBM, BCP were about 30, 350, 48 and 8 nm, respectively. Figure. 1d shows the fabrication process of perovskite film. PbI2, MAI and PbCl2 were dissolved in the solvent of dimethylformamide (DMF) with varied NiOx concentration. The composited solution was then spun coated on the NiOx-covered glass followed with a calcination process, and obtained a high quality of perovskite film than the pristine one. In our work, the NiOx NPs were fabricated via hydrolysis reaction of nickle (II) nitrate hexahydrate in alkaline solution. The SEM and TEM images in Figure S1 show that the as-prepared NiOx NPs has uniform structure with diameter of ~10 nm, and five characteristic diffraction peaks attributed to cubic NiO phase in


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Figure S2 from the X-ray diffraction (XRD) pattern (JCPDS card No. 65-2901). No other impurity peaks were detected, which indicate the high purity of NiOx samples.

Figure 1 (a) A schematic illustration of PSC structure. (b) The energy levels in PSC. (c) The cross section SEM of PSC. (d) The fabrication process of perovskite film. The SEM images of perovskite film have been performed to research the influence of varying NiOx content on the film morphology. Figure 2a-d show the morphologies of these films in the with (a, c) and without (b, d) of NiOx NPs (0.1 mg mL-1 precursor solution) in the perovskite precursor. Both of them were homogenous and formed with better grains. The NiOx NP-combined perovskite film was composed of larger crystal size than the original film, and the grain size for the MAPbI3-xClx and MAPbI3-xClx-NiOx (0.1 mg mL-1) perovskite film are 350 nm (Figure 2g) and 450 nm (Figure 2h), respectively. Figure S3 shows the morphology of MAPbI3xClx-NiOx

with varying NiOx concentration from 0 to 0.5 mg mL-1, which clearly shows the

biggest crystal size for MAPbI3-xClx-NiOx (0.1 mg mL-1), and gradually decreases when NiOx concentration reaches to 0.1 mg mL-1. It is probable that excess NiOx will inhibit the crystal growth significantly due to the restricted space. In addition, the crystal boundaries obviously


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present in the reference film (Figure 2c), while it becomes continuous when the suitable amount of NiOx incorporated into the precursor (Figure 2d). In order to research the distribution of NiOx NPs through the perovskite film, elemental energy spectrum (EDS) analysis is performed from cross-sectional perovskite film in Figure S4. It shows that the NiOx NPs are mainly concentrated in the bottom of perovskite film, as clearly shown with small NiOx NPs from SEM. Accordingly, the EDS of nickel element is also adjacent to the ITO glass for the most part. It is likely that NiOx NPs gradually subside in the process of precursor spin coating because of its gravitational effects.


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Figure 2 The corresponding SEM of perovskite film: (a, c) pristine MAPbI3-xClx film. (b, d) NiOx-CH3NH3PbI3-xClx film. AFM images of (e) MAPbI3-xClx film, (f) NiOx-CH3NH3PbI3-xClx film. (g, h) The histograms below are the grain size statistics. Figure 2e-f show the atomic force microscope (AFM) images of MAPbI3-xClx and NiOxCH3NH3PbI3-xClx film, the root-mean-square (RMS) of perovskite film with 0.1 mg mL-1 NiOx was higher (11.09 nm) than the pristine one (9.76 nm). The smaller increase in roughness may enhance the contact area with PCBM at the micro scale, which can boost the charge transportation efficiency from perovskite film to PCBM layer. These results indicate that the growth of perovskite crystal is impressionable to the suitable additive. The existence of NiOx not only brings about changes in the morphology, but also plays a stabilizer role to connect with unstable perovskite via chemical bonding. Figure 3a schematically illustrates the change of chemical bonding within the perovskite crystals after NiOx doping, and the strong binding energy of chemical bonds could prevent perovskite degradation to a certain extent under air condition, as clearly shown in the PSC stability test subsequently. Fourier transform infrared spectroscopy (FTIR) spectrum provides further evidence for chemical bonds between NiOx and CH3NH3PbI3-xClx (Figure 3b). In detail, the characteristic peaks for pristine CH3NH3PbI3-xClx at 3112 cm−1, 1652 cm−1, 2724 cm−1 and 1386 cm−1, corresponds to N-H, C-H, C-N stretching vibrations and C-H or N-H bending vibrations, respectively. The NiOxCH3NH3PbI3-xClx composite film with a C-O stretching vibration peak at 1059 cm−1, 42, 43 where C and O atoms belong to CH3NH3PbI3-xClx and NiOx, Pb-O vibration peak at 689 cm−1, Ni-N in the region 400-500 cm−1 (Figure 3c) 44, demonstrating that the chemical interaction was existed between NiOx and CH3NH3PbI3-xClx, it can improve charge transport efficiency and provides the function of stabilizing PSC. Figure 3e reveals the difference in their optical properties of pristine


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and NiOx-doped perovskite film deposited on NiOx/ITO substrate. With NiOx NPs incorporation, the light-harvesting capacity has a slight improvement in the whole visible spectra, which certifies the enhanced grain size facilitating the strong light absorption.45 When it is further increased to 0.5 mg mL-1, the absorbance decreases compared with optimal doping content, which may be ascribe to the growth limitation of perovskite crystal owing to the excess NiOx NPs (Figure S5). Figure 3f shows the XRD patterns of control and NiOx-combined perovskite film. The characteristic peaks at 14.51° and 28.44° are belonged to crystal planes in (110) and (220) of MAPbI3-xClx, and the diffraction peaks at 15.59° and 31.41° are attributed to (100) and (200) planes belonging to pristine MAPbCl3 which is clearly demonstrated that additional Clonly form the MAPbCl3 crystal lattice rather than MAPbI3-xClx (Figure 3e and Figure 3f).46 From these characteristic peaks, the relative intensities are nearby with almost the same curve (Figure S6), indicating that the combination with NiOx has not damage for the perovskite crystal. But the absolute intensity of these characteristic peaks has different trends with varying the NiOx content, which has increased first and then reduced slightly with NiOx content increasing from 0 mg mL-1 to 0.5 mg mL-1, and reach the highest value at 0.1 mg mL-1. The results certify that the optimal NiOx additive is beneficial to crystal growth and film formation with high crystallinity. And the EDS images (Figure S7) show a uniform distribution of Cl. It also can be seen clearly that chlorine and iodine element are emerged in the white regions, which corresponds to very few of residual lead salt component. It is almost negligible for lead salt diffraction peaks, such as PbI2.


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Figure 3 (a) The chemical bonding generation after NiOx doping. FTIR spectra of samples: (b) 400-3600 cm-1. (c) 400-490 cm-1 (d) 680-800 cm-1. (e) The absorbance spectra of two perovskite samples. (f) The XRD spectrums of two perovskite samples. Williamson-Hall analysis of (g) MAPbI3−xClx-NiOx film. (h) MAPbI3−xClx film. In order to verify the variation trend of crystal size whether or not consistent with the XRD spectrum, Williamson-Hall was applied to estimated crystal grain size and the corresponding formula is given by


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βcosθ =

௄ఒ ஽

+ 4ߝ‫ߠ݊݅ݏ‬

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(1)

where β corresponds to the full width at half maximum (FWHM), θ is the bragg angle, K is the shape factor, λ is the of X-ray wavelength, ε is the strain in crystal. The above Eq. (1) is usually based on independent of grain size and strain within crystal, and where it is supposed that strain in both crystallographic direction is uniform. When the plot is plotted with 4sinθ used as x-axis and βcosθ used as y-axis, the reciprocal of crystal size value is obtained from the intercept of yaxis in fitted line. According to the fitted formula, it can be concluded that the crystal size for CH3NH3PbI3-xClx-NiOx is larger than that of CH3NH3PbI3-xClx (Figure 3 (g-h)). In addition to the above-mentioned improvement, the efficiency of electron transmission was also significantly improved with slightly higher roughness interface, reduced defect density and charge recombination, as illustrated in Figure 4a and b. In order to demonstrate the influence of NiOx on the electronic properties, the steady-state photo-luminescence (PL) spectra of perovskite films on ITO substrate is performed (Figure 4c). The perovskite film is excited with light source along with certain wavelength containing larger energy than the band gap of perovskite, the electrons and holes are formed in the energy bands. After their stability towards the ground state, the electrons and holes will recombine along with the release of photons, where the trap states act as the recombination centers. The intensity of PL peak has significantly improved after incorporating with NiOx due to the better crystallinity and reduced trap states of CH3NH3PbI3-xClx- NiOx films. And it approaches to the highest intensity for 0.1 mg mL-1 NiOx content (Figure 4c), and then decrease for 0.5 mg mL-1 (Figure S8), which is consistent with XRD patterns aforementioned. In addition, the peak of CH3NH3PbI3-xClx-NiOx shows a small red-shift due to its reduced band-gap compared with pristine CH3NH3PbI3-xClx, as confirmed in Figure 3e. To further understand the electrical characteristic of NiOx-CH3NH3PbI3-xClx based


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composite film in the PSC devices, electronic impedance spectroscopy (EIS) has been investigated at 0 V under dark condition in Figure 4d. According to the fitting equivalent circuit, Rs, Rrec and Rctr represent the series resistance, charge recombination and charge transfer resistance, respectively (Table 1). The diameter of semicircle in the Nyquist plot denoting as Rrec relates to current leakage and recombination of charge carriers. It is clearly shown that the diameter of semicircle for NiOx-CH3NH3PbI3-xClx is much larger than CH3NH3PbI3-xClx based device indicating less charge recombination and current leakage at interface.47-49 From Figure S9, the Rrec increase firstly and then decrease when the NiOx content reached to 0.5 mg mL-1, and the highest Rrec is achieved with the 0.1 mg mL-1 NiOx, which demonstrate that perovskite film with 0.1 mg mL-1 NiOx possess lowest defect density, and excess NiOx in the perovskite film serving as trap center capture the photo-charges. As shown in Figure 4e, the Rctr decrease obviously with the bias voltage increasing, and the Rctr of NiOx-CH3NH3PbI3-xClx based device is larger than that of CH3NH3PbI3-xClx at different bias voltage, demonstrating that the NiOx doping can remarkably decrease the charge transfer barrier. For purpose of studying the lifetime of electron (τr) in the two devices, Bode EIS measurement is implemented at 0.6 V under dark condition presented in Figure 4f. The τr was evaluated by the Eq:(1)50

τ

r

1

= 2π

f

(2) max

Consequently, the τr for CH3NH3PbI3-xClx and NiOx-CH3NH3PbI3-xClx device are 1.60 µs and 2.83 µs, respectively. The obviously increased τr for NiOx-CH3NH3PbI3-xClx based device may be attributed to the enhanced electron density with strong light-absorption, and more charges transfer from the NiOx-CH3NH3PbI3-xClx film to the ETL layer.


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Figure 4 (a, b) The schematic illustration effect about NiOx doping on the perovskite solar cell. (c) PL measurements of MAPbI3-xClx and optimal NiOx-CH3NH3PbI3-xClx composite film on glass/ITO substrate. (d) EIS of original and NiOx NP-incorporated PSCs under dark at a bias of 0V. (e) The fitted Rrec at different applied potentials. (f) Bode spectrum of the two devices.


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The PSC devices are fabricated using varying NiOx NPs to research the influence of NiOx content on the device performance. Figure S10 and Table S1 show the key parameters of asfabricated devices, and the NiOx with 0.1 mg mL-1 is chosen to be the optimum content with a PCE of 19.34%, along with Voc (open-circuit voltage) of 1.12 V, Jsc (short-circuit current density) of 23.01 mA cm-2, and FF (fill factor) of 75.06%. The Jsc and Voc increase firstly with the NiOx content increase from 0 to 0.1 mg mL-1, and then decrease when approach to 0.5 mg mL-1, which is accordance with the characterization abovementioned. The comparison of photovoltaic performance for the inverted PSC with optimal NiOx doping and pristine precursorbased device is investigated in detail (Figure. 5). The J-V characteristic under standard AM 1.5 G simulated sunlight is shown in Figure 5a, and the key parameters are displayed in Table 1. The reference solar cell shows a Voc of 1.08 V, Jsc of 22.23 mA cm-2 and FF of 68.97%, yielding PCE of 16.56 %. By introducing NiOx as the additive into the perovskite layer greatly improve the device performance. The improved Jsc can be interpreted as enhanced light absorption owing to larger grain size, as demonstrated in the above absorption spectrum. As aforementioned, NiOx plays a significant role in optimizing crystal quality and passivating the perovskite film with reduced trap states, which result in higher extent of charges separated from the interior, thus along with significant increase in Voc. In addition, the optimized interface along with efficient charge transfer and reduction of series resistance, brings about increase of FF significantly. The as-fabricated devices further confirmed by the dark J-V measurement (Figure 5b), an efficient charge injection in the NiOx-doped devices makes the reverse saturation current density (J0) significantly suppressed. The relation between Voc and J0 was derived from the following equation (2):


13


V

oc

=

kT ln( J sc + 1) q J0

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(2)

It can be seen that the smaller J0 leads to higher Voc. According to the Figure S11, the Voc variation tendency with different content of NiOx is consistent with the results in J-V (Table S1). Figure 5c shows the IPCE spectra of the corresponding devices. The NiOx-doped device presents a better photon-to-electron conversion than the control device, which attributes to the better perovskite film and charge extraction efficiency. The integrated Jsc keep the same with that from the J-V curves in Figure 5a. Furthermore, the devices based on NiOx-MAPbI3-xClx composite film show excellent repeatability. Figure S12 and Figure S13 summarize the J-V statistics of 35 devices collected over different batches, where the values of parameters are shown in the Table S2, and the performance of most device are close with distributing in Voc in 1.05 V, Jsc in 22.35 mA cm-2, FF in 73.77 % and PCE in 17.33 %. It is well known that the serious hysteresis effect for the PSC at different scan direction would influence the stable power output, however, such adverse phenomenon can be avoided via solvent and interface engineering. As depicted in Figure 5d, the pristine MAPbI3-xClx and NiOx-MAPbI3-xClx based devices reveal negligible hysteresis regardless of the different scan direction, which confirms that inverted structure PSC can avoid the hysteresis effect effectively.


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Figure 5 (a) J-V characteristics. (b) The semi-logarithmic plots of dark J-V. (c) EQE spectra of the devices. (d) J-V curves of pristine and optimal NiOx doping devices under different scan direction. Table 1 The specific parameters of devices based on pristine and NiOx doped, respectively. Voc

Jsc

FF

PCE

Rs

R1

(V)

(mA cm-2)

(%)

(%)

(Ω cm2)

(Ω cm2)

1.08

22.23

68.97

16.56

12.18

36.81

1.12

23.01

75.06

19.34

8.72

21.05

devices

pristine NiOx doping


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Figure 6 Schematic illustration of perovskite passivation without or with NiOx incorporated into perovskite layer. Based on the above analysis, a probable mechanism of the device with or without NiOx incorporated into perovskite layer is illustrated in Figure 6. For the pristine MAPbI3-xClx, the existence of large number of crystal defects at grain boundaries could act as the center of charge accumulation, which will result in greatly increase recombination of charge carriers at the grain boundaries. In addition, the trap states at grain boundaries have proven to be existed with a deep and broad energetic distribution, causing it very difficult for the trapped charge carriers to escape from the trap states. However, in the device with NiOx incorporated into perovskite layer, the hole transmission efficiency is greatly improved, derived from the accelerated PL intensity in the ITO/MAPbI3-xClx (NiOx), which is probably attributed to the NiOx material with outstanding hole


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collection ability. In addition, the NiOx at the grain boundaries is effective to block electrons from transferring to the cathode because of the high conduction band of NiOx, which will suppress electrons and holes recombination. Moreover, the large amounts of trap states with broad energetic distribution could be passivated efficiently by the NiOx at grain boundaries, due to the better match for valence-band level of NiOx and perovskite. Therefore, the NiOx incorporated into perovskite layer can provide efficient transmission channel and passivate defects in the perovskite film, and finally improve the device performance. Since it is vital to keep long-time performance in commercialization, we investigate two types of PSC based on MAPbI3-xClx-NiOx and MAPbI3-xClx perovskite precursor without encapsulation for 50 day (at temperature of 25°C, humidity of 40 %). Figure 7 a-d reveals the device stability measurements against time in regard to the normalized parameters. The MAPbI3xClx-NiOx

based PSC exhibits remarkable stability with retaining ~94 % of original Voc, ~98 %

of Jsc, ~92 % of FF, ~85 % of PCE for 50 days. However, the performance of pristine device has decreased seriously after 50 days. The detailed J-V curves during 50 days were presented in Figure S14, and the specific values of performance parameter are provided in Table S3. The long-term stability of fabricated device based on NiOx doping is likely to be difficult to decompose, which is most likely to stabilize the organic methylamine counterpart, derived from the strong chemical bonding in the FTIR measurement. Furthermore, the incorporation of NiOx into perovskite not only enhance the film quality with favorable morphology, but also passivate perovskite effectively, which also can stabilize the air stability for devices.


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Figure 7 Stability test of the solar cell without encapsulation for 50 days: (a) Voc, (b) Jsc, (c) FF, (d) PCE. CONCLUSION Totally, we have investigated a new way to decorate and optimize the perovskite layer. The incorporation of NiOx into the perovskite film can provides better crystal quality, and generate with strong chemical bonds to stabilize the air stability of perovskite devices. Consequently, the photovoltaic performance of as-fabricated PSC is improved remarkably from 16.56% to 19.34% resulting from the significant increase in Jsc and FF. More importantly, the existence of chemical bonds not only can contribute to charge carriers transport within the grain boundaries, but also improve the device stability significantly, which shows remarkable stability after 50 days


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retaining ~81% of its initial PCE. These results indicate that the p-type metal oxide doping is a simple and effective way to construct high-performance and stability PSC. EXPERIMENTAL SECTION Materials: The materials are purchased from Alfa-Aesar. PbI2, CH3NH3I and PbCl2 were obtained from Xi’an Polymer Light Technology Corp. NiOx fabrication: NiOx particles were fabricated depending on the previously reported method[1]. First, nickel nitrate hexahydrate (0.1 mol) was dissolved in 40 mL of deionized water. Then sodium hydroxide solution (10mol/L) was dropped into the solution slowly. After stirring，the precipitation was thoroughly centrifuged to wash off the impurities and dried. The resultant was calcined at 270°C for 2 h. Then the NiOx solution was made in anhydrous dimethylamine to ca. 0.05mg/ml, 0.1mg/ml, 0.5mg/ml concentration. Solar cell fabrication: First, the ITO glass was washed with toluene and water, respectively. The HTL was fabricated by spin coating with NiOx solution (20 mg/mL) (3000 rpm). The perovskite solution was composed of 989.2 mg of PbI2, 59.7 mg of PbCl2, and 375.7 mg of CH3NH3I in 2 mL of N, N- dimethyl formamide (DMF) in the paper,26 For comparison, the perovskite solution was doped with NiOx with different concentration (0.05 mg mL-1, 0.1 mg mL-1, 0.5 mg mL-1). For the NiOx NP additive, the morphology and particle size have an important influence on the crystallization process. The size of NiOx NP has taken process with strict optimization via controlling the reaction rate. Before the spin coating procedure, the mixed precursor solution was treated with ultrasonic process and sealed it tightly, then coated onto the ITO/NiOx substrates at 4,000 r.p.m for 30 s in the glovebox. When the time reach to 8 s, the perovskite film was deal with 200 µL chlorobenzene solvent. Then the film was treated at 80 °C with 10 min. When it was cooled, PC61BM (20 mg/mL, 3000 r.p.m) was covered on the perovskite film, and dried in the vacuum oven. Finally, the devices were transferred to a vacuum chamber, BCP (7 nm) and Ag (100 nm) were thermally evaporated. Device characterizations: The light absorption of the samples was measured by Shimadzu UV3600. The phase characterization was measured by PAN alytical diffractometer. The materials


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morphology was tested by Hitachi SU-70 and JEM 2100. The EIS was carried out on the solar cells to measure charge transfer resistance (Rct) using a CHI 660E electrochemical workstation. The photovoltaic J-V measurement was performed under a solar simulator and the EQE was measured by QEX10 with a 300 W steady-state xenon lamp. ASSOCIATED CONTENT Supporting information The supporting information is composed of SEM images about the NiOx nanoparticle, perovskite film with different variation of NiOx, and solar cell photovoltaic performance. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] *E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This research was financially supported by the National Natural Science Fund of China (Grant No. 21671037, 21471030, 21771036, and 51602049, 51502253, U140526), Guangdong Natural Science Foundation (2016A030310369), Fujian Natural Science Foundation (No. 2017J01104), China Postdoctoral Science Foundation (2017M610217, 2018T110322), the Fundamental Research Funds for the Central Universities (No. 20720160127, No. 20720180013, No.2232017D-15). REFERENCE 1. Arora, N.; Dar, M. I.; Hinderhofer, A.; Pellet, N.; Schreiber, F.; Zakeeruddin, S. M.; Grätzel, M., Perovskite Solar Cells with CuSCN Hole Extraction Layers Yield Stabilized Efficiencies Greater than 20%. Science 2017, 358 (6364), 768-771.


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Chemical Decoration of Perovskites by Nickel Oxide Doping for

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