High-Voltage-Efficiency Inorganic Perovskite Solar Cells in a Wide

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Energy Conversion and Storage; Plasmonics and Optoelectronics

High-Voltage-Efficiency Inorganic Perovskite Solar Cells in Wide Solution-Processing Window Linxing Zhang, Bo Li, Jifeng Yuan, Mengru Wang, Ting Shen, Fei Huang, Wen Wen, Guozhong Cao, and Jianjun Tian J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b01553 • Publication Date (Web): 19 Jun 2018 Downloaded from http://pubs.acs.org on June 19, 2018

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The Journal of Physical Chemistry Letters

High-Voltage-Efficiency Inorganic Perovskite Solar Cells in Wide Solution-Processing Window Linxing Zhang,a Bo Li,a Jifeng Yuan,a Mengru Wang,a Ting Shen,a Fei Huang,a Wen Wen,a Guozhong Cao,a,b Jianjun Tiana,* a

Institute for Advanced Materials and Technology, University of Science and Technology Beijing,

Beijing 100083, China b

Department of Materials and Engineering, University of Washington, Seattle, WA 98195-2120, USA

*E-mail address of corresponding author: [email protected]

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ABSTRACT: Inorganic halide perovskites exhibit significantly photovoltaic performance due to their structural stability and high open-circuit voltage (Voc). Herein a general strategy of solution engineering has been implemented to enable a wide solution-processing window for high Voc (~1.3 V) and power conversion efficiency (PCE, ~12.5 %). We introduce a non-toxic solvent of dimethyl sulfoxide (DMSO) and an assisted heating process in the fabrication of CsPbI2Br (CPI2) to control the improved crystallization. The wide solution-processing window including a wide range of solvent component and solute concentration has been realized. The CPI2-based inorganic perovskite solar cells (IPSCs) exhibit a high PCE up to 12.52 %. More importantly, these devices demonstrate a remarkable Voc of 1.315 V. The performance has possessed such a region with high Voc and PCE in all Cs-based IPSCs, unveiling the wide solution-processing windows with the enhanced solution processability facilitate the potential industrial application especially for tandem solar cells.

TOC Graphic:

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Hybrid organic-inorganic halide perovskites have been considered as the competitive photovoltaic materials for next generation solar cells. These perovskites have the extensively formula of ABX3 (A is an organic cation, such as methylammonium (MA) or formamidinium (FA), B is typically Pb, and X is a halogen element). They exhibit excellent photovoltaic performance, such as appropriate (narrow and direct) band gap, large absorption coefficient, high carrier mobility, and long carrier diffusion, resulting in the rapidly increased PCE from 3.8 % to 22 %.1-10 Recently, another promising halide perovskite system, which is known as purely inorganic version (CsPbX3), has been taken great attention for employing in luminescence and solar cells emerging the PCE higher than 11 %. 11 - 15 These inorganic perovskite systems particularly with the bromine substitute will not generate organic volatile decomposition products and exhibit significantly enhanced structural stability under thermal and environmental stresses, such as oxygen, heat, and ultraviolet (UV) light, comparable to the organic-inorganic hybrid species.13,16 In particular, CPI2 possesses a band gap of 1.91 eV, which is available as a photovoltaic light absorber, and can generate high Voc importantly for the tandem solar cells. The theoretical maximum Voc from the Shockley-Queisser analysis for the given bandgap is as high as 1.615 V. This makes them as suitable candidate for the top cell in the tandem solar cells combining with the relative low Voc of the bottom cells,7-9 such as organic-inorganic perovskite or Si-based cells. The formation process of the perovskite crystal involves crystal nucleation and grain growth. The high nucleation rate leads to high density of uniform nucleation site, which is available to the flat surfaces and complete surface coverage. The controllable fast

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crystallization methodologies such as anti-solvent process, air flow, and hot casting, which quickly reach to the supersaturated concentration and then occur the outbreak of nucleation, can be used for preparing high-quality perovskite film. On the other hand, the solvent-engineering process uses the viscosity of solution or the appearance of intermediate phases to retard the rapid reaction during the grain growth, resulting in the dense and uniform perovskite,17-21 especially for organic-inorganic ones such as MAPbI3 or FAPbI3. The all-inorganic perovskites of CsPbI3-xBrx has recently attracted vast research through introducing many methods to stabilize black-phases and improve quality of films, 12,22-38 such as the additive of HI, the employment of Co-evaporation, and the formation of quantum dot and 2D. Nam et al., investigated the crystal formation behavior of CPI2 by precisely controlling the annealing temperature, which revealed the complexity of the crystal formation process of inorganic perovskite and its profound influence on both phase stability and solar cell performance.29 By using Mn2+ ion doping, the nucleation and growth rate could be modulated for different size of grains in CPI2 films. 39 However, such general strategy of solution engineering by controlling the improved crystallization is still lack for high-quality all-inorganic perovskite, due to the high phase transition temperature and low solubility of cesium halide, especially CsBr for CPI2. Herein, coupled with an additional heating process, we introduced DMSO that serves as a capping agent for controlling the uniform growth of crystal to realize the wide solution-processing window, which includes the large range of the solvent component and the solute concentration. These present CPI2 IPSCs feature the high Voc (~1.3 V) and outstanding PCE (~12.5 %) performance.

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In order to control the nucleation and crystallization of all-inorganic perovskite, a heat assisted reaction of hot air flow (HAF) method is used for high-quality perovskite with high PCE (Figure 1a and Figure S1). During the film formation, the wet films first become light brown immediately after HAF and then turn into dark brown by annealing (Figure 1a), as displayed in the absorption spectra (Figure S2). Compared with the solar cells preheating on hot plates, the cells with HAF method feature an enhanced PCE performance (Figure S3a). This indicates that the HAF can exhibit the uniform rapid heating and would form a molecular self-assembly process between the DMSO molecule and precursors molecule.40 The process facilitates the nucleation rate and improved crystallization for high-quality films. In addition, the whole process is proceeded in ambient air under controlled relative humidity (RH 15~25 %), which also demonstrates higher performance than that in the nitrogen or oxygen environments (Figure S3b). This would verify the moderate moisture accumulation at the grain boundaries avails the improved crystallization for high-quality morphology.41,42 For both scientific research and industrial applications, a wide solution-processing window is of great significance to the repeatable preparation of thin films. For the present system of inorganic CPI2, the precursor properties and film thickness are still the restrictive link for preparation of high-quality IPSCs.29,30 Incorporating with the preliminary findings, we introduce a non-toxic solvent of DMSO partially substituting for the toxic N,N-Dimethylformamide (DMF) to realize the wide solution-processing window for high-voltage-efficiency all-inorganic CPI2 solar cells (Figure 1b). The DMSO-based solvents exhibit lower toxicity, which is suitable for industrial manufacturing of perovskite (Table S1). Both the vapor pressure and the solubility are the

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key parameters to be controlled for wide solution processing window. The DMSO solvent demonstrates higher boiling point (~189 °C) and lower vapor pressure (~126 Pa at 25 °C) than those (~153 °C, and ~418 Pa at 25 °C) of DMF. The vapor pressure of the mixed solvent decrease with the increasing fraction of DMSO, as shown in the Figure 1b. Hence the solvent evaporation rate associated with the vapor pressure could be effective controlled tuning the ratio of the DMF and DMSO solvents, which is closely associated with the nucleation and crystal growth of the perovskite. On the other hand, the introduced DMSO facilitates the dissolution of the precursors such as CsBr. The maximum solubility of CPI2 in the mixed solvent increases with the increasing fraction of DMSO (Figure 1b). The high solubility of precursors with the introduced DMSO (~35 %) could be up to more than 1 M, while the solubility is only ~0.4 M in the pure DMF solvent. The solubility of precursors is important to control the thickness of films, as discussed below. Hence the introduced DMSO permit the optimized suitable thickness for light absorption. Here, the large range of the fraction of DMSO from 15 % to 55 % and the solute concentration from 0.7 M to 1.2 M are carried out to verify the feasibility of the wide solution-processing window. As shown in Figure 1c and 1d, the Voc and PCE near the maximum solubility line demonstrate higher value. This is because the high initial solution concentration is easier to reach to the supersaturated concentration, which is one of the key conditions for promoting nucleation and crystallization. Hence, both the initial solution concentration and the precursor properties such as vapor pressure are the significant factors for controlled crystallization films. Furthermore, the PCE is higher than ~11 % and the Voc is also higher than ~1.2 V in such wide solution range. This strategy with wide solution-processing window shows the excellent tolerance of the

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precursor solution composition so that is very well suited to large scale manufacture.

Figure 1. (a) The heat assisted process of the hot air flow (HAF), and the optical images of the initial wet film, the processed film after HAF, the annealed film, respectively. (b) The vapor pressure for mixed solvent and the solubility for CPI2 as a function of DMSO content. (c) The PCE and (d) Voc of the wide solution-processing window dependence on the DMSO content and CPI2 solubility.

In order to further explore the window range, we designed the comparison experiment with different DMSO contents at fixed CPI2 concentration of 0.7 M. We classified the representative three systems in present work as D25, D50, and D75, corresponding to the volume percentage of DMSO of 25%, 50%, and 75%, respectively, in the mixture solvents of DMF and DMSO (Figure 2). Figure 2a features the crystal structures of the general X-ray diffraction (XRD) patterns, which are indexed to the cubic perovskite-phase with an apparent (100) orientation for all three inorganic CPI2

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perovskite films, indicating high-quality perovskite. The intensities of (100) and (200) peaks display a weakening trend with the increasing DMSO contents. Simultaneously the full width at half maximum (FWHM) of (200) peaks show an enhanced trend especially for obvious increase of D75 (Figure S4), revealing the poor crystallinity with excess DMSO. The UV-Vis absorption spectrum of CPI2 with the accepted 650 nm of absorption cutoff show a decreasing absorbance value dependent on the DMSO content, also especially for obvious decrease of D75 (Figure 2b), which is consistent with the photographs for the samples colors (insets of Figure 2b). As shown in Figure 2c, the time-resolved photoluminescence (PL) decay profiles were measured for all three films, to understand the kinetics of excitons and free carriers (Figure 2c). The D25 and D50-based films possess a similar A2 of τ2, which is a long lifetime corresponding to the radiative recombination, while that of D75 film shows strong decrease, indicating that excess DMSO contents would cause strong nonradiative recombination (Table S2). Scanning electron microscopy (SEM) images of the films unveil that the introduction of appropriate DMSO contents can significantly increase the grain size of CPI2 perovskites (Figure 2d-2f). The D50-based films achieve larger grain sizes of about 700 nm than that of 500 nm for D25-based films, while excess DMSO (D75) causes the small grain size (~400 nm). The D75-based films also exhibit some pinholes from surface to the FTO substrate. These pinholes would result in the low orientation, poor crystallinity, and weak absorbance, as shown in the XRD and absorption spectrum (Figure 2a and 2b). This variation on morphology could be attributed to the strong bonding ability of DMSO, which can serve as a capping agent and/or facilitate a molecular self-assembly process between the precursor molecules.40,42,43

Apart from the lower vapor pressure and higher

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viscosity than DMF associated with the crystal reaction rate as discussed above, DMSO might also coordinate precursor to form intermediates of colloid cluster, resulting in the variational grain size dependence on DMSO contents. However, the solution with excess DMSO contents exhibits too low vapor pressure, which is detrimental to the crystallization, as shown in D75-based films. Similar phenomenon has been verified in Sn-based organic-inorganic perovskite by using DMSO as additive solvent.43 To underpin the above basic performance characterization, the photocurrent density-voltage (J-V) measurements with difference DMSO were carried out on the solar cells structure of FTO/c-TiO2/mp-TiO2/CPI2/spiro-OMeTAD/Ag (Figure 2g). The D25 and D50-based IPSCs exhibit a similar relative high PCE of 10.6 % and 10.4 %, respectively, while the D75-based IPSCs show a smaller one of 8.78 %. The detail photovoltaic parameters are listed in the inset Table of Figure 2g. The incident photon-to-electron conversion efficiency (IPCE) spectra and integrated short-current densities (Jsc) over an AM 1.5G spectrum for IPSCs were displayed in Figure 2h. The integrated Jsc from IPCE spectrum are calculated to be 12.1 mA cm-2, 11.7 mA cm-2, and 10.7 mA cm-2 for D25, D50, and D75-based IPSCs, respectively, which match well with the value derived from the corresponding J-V measurement (inset of Figure 2g). Throughout the above results, we can obtain that the IPSCs performance can be stable at relative high value when the DMSO contents up to 50 %, indicating a wide processing window of DMSO. Furthermore, apart from the factors of vapor pressure and viscosity properties of solvents, the D25-based IPSCs featuring best performance as compared to D50 and D75 can be ascribed to one fact that the control concentration (~0.7 M) is closed to the maximum solubility in D25 precursor (~0.8 M) (Figure 1). This relative high

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concentration of the D25 precursor is easy to reach to the supersaturated concentration, promoting the nucleation and improving the crystallization. These results facilitate exploring the optimized solute concentration and solvent ratio for improved PCE and increased Voc in this wide solution-processing window.

Figure 2. (a) XRD patterns, (b) UV-Vis absorption spectra, (c) PL decay profiles, (d), (e), (f) SEM images of 0.7 M D25, D50, D75-based films, respectively. The insets of (b) exhibit the optical images. (g) J-V characteristics and (h) IPCE spectra and integrated current densities for 0.7 M D25, D50, D75-based IPSCs, respectively. The inset Table of (g) show the detailed photovoltaic parameters. 10


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The formation of high-quality and sufficiently thick inorganic perovskite films is indispensable to achieve superior efficiency. To obtain the optimal thickness for light absorption, the solubility can be controlled up to 1.2 M in D50 precursor. The total thickness of both CPI2 (~175 nm) and mesoporous TiO2 (~50 nm) layers are ~225 nm for 0.7 M D50-based solar cells, while that of 0.4 M DMF-based film is only about 100 nm.29,30 When the solute concentration is up to ~1 M for D50 precursor, the total thickness could reach ~300 nm (including ~250 nm of CP2 and ~50 nm of mp-TiO2). This is consistent with that the 1 M-D50-based films exhibit stronger intensity of XRD and absorption than 0.7 M-D50-based films (Figure S5). This thickness would be enough to guarantee full light harvesting around 650 nm for CPI2, compared with that (~400 nm) of a typical hybrid perovskite layer with an absorption cutoff ~800 nm. The control concentration of ~1 M in D50 precursor avail to improve crystallization due to the fact that it is closed to the maximum solubility (~1.2 M) as discussed above. The representative cross-sectional SEM image of the present solar cell has been fabricated to unveil the uniform stack of functional layers, as shown in Figure 3a, which consists of FTO/c-TiO2/mp-TiO2/CPI2/spiro-OMeTAD/Ag

(Figure

3b).

After

the

above

optimization, we obtained the best PCE performance of 12.52 % for CPI2 at 1 M-D50-based solar cells (Figure 3c), which is comparable with the recent reported value of 12.39 %.37 The key parameters were summarized in the inset of Figure 3c, including high Voc (1.243 V), Jsc (13.56 mA cm-2), and fill factor (FF, 0.743). The PCE performance dependence on the thickness of mp-TiO2 layers also be optimized (Figure S6), which indicates that a very thin layer (~50 nm) of mesoporous can improve the

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efficiency and maintain a high Voc. The J-V curves of the CPI2 based IPSCs were measured by using both the reverse and forward scan directions (Figure S7), revealing a little hysteresis. The J-t plots measured at the fixed voltage of 0.92 V exhibit the stable Jsc (12.10 mA cm-2) and the stable high PCE with 11.13 %, verified the well output stability (Inset of Figure 3c). Figure 3d demonstrates the IPCE spectrum and integrated Jsc of the present IPSCs. The IPCE from 400 nm to 500 nm is higher than ~80 %, indicating high-quality perovskite films. The integrated Jsc are calculated to be 13.29 mA cm-2, which is higher than that (11.7 mA cm-2) of 0.7 M-D50-based IPSCs as shown above, revealing the suitable thick and high-quality perovskite for superior efficiency.

Figure 3. (a) The representative cross-sectional SEM image and (b) schematic view of the IPSC with the configuration of FTO/c-TiO2/mp-TiO2/CPI2/spiro-OMeTAD/Ag. (c) The J-V characteristic and (d) IPCE spectra and integrated current densities of the optimal CPI2-based IPSCs. The inset of (c) shows the J-t plots measured at the fixed

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voltage of 0.92 V for the optimal steady-state output.

To ensure the repeatability of fabrication with high Voc and excellent PCE, the photovoltaic performance of 34 individual CPI2 based IPSCs on FTO/c-TiO2 (mp-TiO2) substrates have been drawn to the histograms, which exhibits a high average Voc of 1.234 V and an excellent average PCE of 11.05 % (Figure 4a and 4b, Table S3). It is noted that the highest Voc for present CPI2 can be up to 1.315 V (Figure S8a), higher than that of all reported CPI2-based solar cells, which is ~81.4% of the maximum voltage (1.615 V) from the Shockley-Queisser analysis for the given bandgap. We also replaced the c-TiO2/mp-TiO2 layers with the compact SnO2 nano-layers as the electron transfer layer (Figure S8b). These SnO2-based solar cells also show a high Voc of 1.275 V and good PCE of 12.0 %. Furthermore, the low-cost Carbon layer have been used to replace both the organic hole transport layer (HTL) of spiro-OMeTAD and metal electrodes of Ag (Figure S8c), which also display a high Voc of 1.283 V. We compared the Voc and PCE of present 10 individual CPI2-based IPSCs to those of both the reported CPI2-based and the other CsPb-based IPSCs in Figure 4c (Table S4).44 Apparently, the performance of our present fabricated devices distributes the region with high both voltage and efficiency for all Cs-based IPSCs. Hence, the present high-quality perovskite films with high Voc and PCE performance fabricated in the wide solution-processing windows provide possibility for application of tandem solar cells in simple planar heterojunction or stable all-inorganic. The long-term stability of present CPI2-based IPSCs were evaluated under dark storage conditions at ambient atmosphere (~25 °C and RH ≤ ~25 %), as shown in Figure 4d and Figure S9. Both PCE and Voc feature no detectable degradation for more

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than 500 hours, unveiling the excellent air long-term stability.

Figure 4. Statistical histogram of (a) Voc and (b) PCEs obtained from 34 individual CPI2-based IPSCs. (c) Voc and PCE distributions of different IPSCs based on this works and the reported ones. (d) Long-term stability for Voc and PCEs of the IPSC device stored without encapsulation (25 °C and RH < 25 %).

In conclusion, we introduce the solvent of dimethyl sulfoxide accompanied by an additional heating process of hot air flow for all-inorganic perovskite CPI2. It realizes the wide solution-processing window for excellent performance along with the highest Voc (~1.315 V) and the optimal PCE (~12.52 %). The controlled crystallization can be implemented by the incorporation of the solution properties, the control solute

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concentration, and the HAF. We need to stress some functions of the present additional solvent, which could create a distinct pathway for repeatable extensive preparation: (i) It could coordinate precursor to form a molecular self-assembly process for intermediates of colloid cluster and serve as a capping agent due to its strong bonding ability, which is related to the grain size of perovskite films; (ii) The low vapor pressure and high viscosity of DMSO facilitate the effective control of the solvent evaporation rate, which is associated with the improved crystallization and growth for high-quality films; (iii) The good solubility for precursors permit control of suitable thickness for guaranteeing full light harvesting. The present wide solution-processing window with high-voltage performance will promote the research and industrial application of inorganic perovskite such as tandem solar cells and large scale manufacture.

EXPERIMENTAL METHODS

Device fabrication. The etched FTO glasses were cleaned in sequence with deionized water, acetone, and ethanol then further treated under ultraviolet ozone for 10 min. A compact TiO2 layer (c-TiO2) was deposited at 450 °C on the FTO glass by spray pyrolysis deposition using a solution diluting titanium diisopropoxide bis(acetylacetonate) (75 wt % in isopropanol) in ethanol with a volume ratio of 1/25, and annealed at the same temperature for 30 min. After cooling, a mesoporous TiO2 (mp-TiO2) layer was deposited by spin coating for 30 s for 4000 rpm, using a Dyesol 18NRT paste diluting in ethanol with a weight ratio of 1/14, and annealed at 450 °C for 30 min. Afterward, the substrate was immersed in a 20 mM TiCl4 (99.0 %, Aladdin) aqueous solution at 80 °C for 30 min, and washed with distilled water and ethanol, then followed by annealing again at 450 °C for 30 min. CsPbI2Br precursor solution at different concentration was prepared through 15



dissolving the equimolar PbI2 (99.9 %, Yingkou, You Xuan Trade Co., Ltd) and CsBr (99.9 %, Aladdin) in the mixed solvents of DMF (N,N-Dimethylformamide, 99.8 %, Sigma-Aldrich) and DMSO (Dimethyl sulfoxide, Sigma-Aldrich) and stirred at 120 °C for 30 min. The wet perovskite film was formed by spin-coating the perovskite precursor solution at 5000 rpm for 30 second on glass /FTO/c-TiO2/mp-TiO2. Then the wet transparent film was blew into the semitransparent light brown film by the hot air flow (HAF), as shown in Figure S1. Right after that, the film was annealed at 280 °C for 6 min. To prepare the hole-transporting layer precursor solution, 72.3 mg spiro-MeOTAD (Yingkou, You Xuan Trade Co., Ltd) was dissolved in 1 mL chlorobenzene (99.8 %, Sigma-Aldrich) and mixed with 29 µL 4-tert-butylpyridine (Yingkou, You Xuan Trade Co., Ltd) and 17.5 µL Li-TFSI solution (lithium bis(trifluoromethanesulfonyl)imide salt solution in acetonitrile (520 mg mL-1), both You Xuan). The spiro-OMeTAD solution was spin-coated on perovskite film at 4000 rpm for 30 s. Finally, the Ag electrode was deposited by thermal evaporation. The active area of the device is 0.12 cm-2. All the fabrication steps were performed in the dry atmosphere (~25 °C, RH < 25%) except that of spiro-OMeTAD layer. Characterizations. The crystal structure of the perovskite film was determined by the X-ray diffraction (XRD), which was performed on the diffractometer (PW3040/60, PANalytical, Holland) with Cu Kα radiation. The morphologies were investigated by the scanning electron microscopy (SEM) measurement, which was performed using a cold field emission scanning electron microscope (SU4800, Hitachi). The absorption spectra were measured using an ultraviolet-visible (UV-vis) spectrophotometer (T10, Persee). The photoluminescence (PL) decay spectra were measured using a time-resolved

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fluorescence spectrometer (FLS900, Edinburg), and the excitation wavelength was 450 nm. The photocurrent density-voltage (J-V) characteristics were measured using the digital source meter (2400, Keithley Instruments Inc.) under AM 1.5 G illumination simulated sunlight (100 mW cm-2) (7-SS1503A, 7 Star Optical Instruments Co., Beijing, China). The incident light intensity was calibrated with a standard Si solar cell for 1 sun. The incident photon conversion efficiency (IPCE) as a function of wavelength was measured in the direct current (DC) mode using a custom measurement system consisting of a 150 W xenon lamp (7ILX150A, 7 Star Optical Instruments Co., Beijing, China), a monochromator (7ISW30, 7 Star Optical Instruments Co., Beijing, China) and a digital source meter (2400, Keithley Instruments Inc.).

ASSOCIATED CONTENT AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] ORCID Linxing Zhang: 0000-0002-6767-2771 Guozhong Cao: 0000-0003-1498-4517 Jianjun Tian: 0000-0002-4008-0469 Conflict of Interest Disclosure The authors declare no competing financial interest.

ACKNOWLEDGEMENTS 17



This work was supported by the National Science Foundation of China (51774034, 51772026 and 51611130063), Beijing Natural Science Foundation (2182039), Fundamental Research Funds for the Central Universities (FRF-TP-17-030A1, FRF-TP-17-083A1, FRF-TP-17-082A1, TW2018010), and Project funded by China Postdoctoral Science Foundation (2017M620611, 2018M630068).

Supporting Information Available: Typical physical parameters and chemical properties for the DMF and DMSO solvents. The detailed parameters of the PL decay curves for the D25 and D50-based films fitted. Photovoltaic parameters of 34 individual CPI2 based IPSCs. Photovoltaic performance comparison of CsPb-based IPSCs. The device fabrication details and some properties characterization details are included.

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Figure 1. (a) The heat assisted process of the hot air flow (HAF), and the optical images of the initial wet film, the processed film after HAF, the annealed film, respectively. (b) The vapor pressure for mixed solvent and the solubility for CPI2 as a function of DMSO content. (c) The PCE and (d) Voc of the wide solutionprocessing window dependence on the DMSO content and CPI2 solubility. 180x129mm (300 x 300 DPI)


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Figure 2. (a) XRD patterns, (b) UV-Vis absorption spectra, (c) PL decay profiles, (d), (e), (f) SEM images of 0.7 M D25, D50, D75-based films, respectively. The insets of (b) exhibit the optical images. (g) J-V characteristics and (h) IPCE spectra and integrated current densities for 0.7 M D25, D50, D75-based IPSCs, respectively. The inset Table of (g) show the detailed photovoltaic parameters. 199x167mm (300 x 300 DPI)



Figure 3. (a) The representative cross-sectional SEM image and (b) schematic view of the IPSC with the configuration of FTO/c-TiO2/mp-TiO2/CPI2/spiro-OMeTAD/Ag. (c) The J-V characteristic and (d) IPCE spectra and integrated current densities of the optimal CPI2-based IPSCs. The inset of (c) shows the J-t plots measured at the fixed voltage of 0.92 V for the optimal steady-state output. 180x126mm (300 x 300 DPI)


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Figure 4. Statistical histogram of (a) Voc and (b) PCEs obtained from 34 individual CPI2-based IPSCs. (c) Voc and PCE distributions of different IPSCs based on this works and the reported ones. (d) Long-term stability for Voc and PCEs of the IPSC device stored without encapsulation (25 °C and RH 25 %). 180x136mm (300 x 300 DPI)



TOC graphic 50x49mm (300 x 300 DPI)


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High-Voltage-Efficiency Inorganic Perovskite Solar Cells in a Wide

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