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Significant Stability Enhancement of Perovskite Solar Cells by Facile Adhesive Encapsulation Bo Li, Mengru Wang, Riyas Subair, Guozhong Cao, and Jianjun Tian J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b09595 • Publication Date (Web): 17 Oct 2018 Downloaded from http://pubs.acs.org on October 17, 2018

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The Journal of Physical Chemistry

Significant Stability Enhancement of Perovskite Solar Cells by Facile Adhesive Encapsulation Bo Li1, Mengru Wang1,Riyas Subair2, Guozhong Cao3, Jianjun Tian1*

1 Institute of Advanced Materials and Technology, University of Science and Technology Beijing, 100083, China.

2 Institute of Physics, Slovak Academy of Sciences, Bratislava, 84511, Slovakia.

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

Corresponding Author

*Jianjun Tian. Email: [email protected]; telephone number: 010-82377502

ACS Paragon Plus Environment

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ABSTRACT. The long-term stability of organic-inorganic hybrid halide perovskite solar cells (PSCs) is one of the major concern for the future commercial applications. This study demonstrated that an adhesive encapsulation by employing the commercial polyimide tape, which significantly and simultaneously improved the water resistance and thermal stability of CH3NH3PbI3 based perovskite films and PSCs. The stable operation of encapsulated PSCs in water with a power conversion efficiency (PCE) of 19.1% was achieved, which was slightly higher than that of the device in air (18.2%). The stable power output of device could retain 96.3% of its initial efficiency in water for 1620 s under continuous illumination. In addition, the encapsulated MAPbI3 based films could retain its tetragonal perovskite crystal structure after heated at 240°C for 180 min in an ambient environment. This adhesive encapsulation offers an avenue to improve the stability of halide perovskite devices for future commercialization.

INTRODUCTION


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Organic-inorganic hybrid metal halide perovskite materials, most commonly CH3NH3PbI3 (MAPbI3), have been rediscovered in the past few years due to their well suited physical properties for the applications in photoelectric devices,1-3 such as tunable direct bandgap, large absorption coefficient, high tolerance of defects, low trap-state density and long carrier diffusion length.4-8 The perovskite solar cells (PSCs) have shown the certified power conversion efficiency (PCE) of 23.3%, indicating great potential for next-generation low-cost thin film photovoltaic production.9 The typical organic-inorganic hybrid perovskite crystal structure consists of a network of corner-sharing inorganic lead halide octahedral with the organic methylammonium cation (MA+) occupying the voids between them.10-11 Owing to the low ionic migration activation energy (~0.6 eV for vacancy-assisted migration of I- and ~0.8 eV for vacancy-assisted migration of MA+),11 the organic component can easily escape from the inorganic octahedral cage to induce vacancy defects. As a result, those perovskite materials are very susceptible to the exposure of humidity, light, heat, and oxygen.12-16 The photovoltaic performance of devices would undergo fast deterioration under normal operating conditions,17-18 even under an inert atmosphere.19 For the common architectures of PSCs device, including conventional “n-i-p” and inverted


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“p-i-n” structures, it has been found that the water molecules could infiltrate into perovskite layer to induce the degradation of perovskite active layer.17,

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Recent studies also

demonstrated the presence of relatively rapid oxygen diffusion within the PSCs, leading to the degradation of perovskite from the grain boundaries.15, 23-25 Despite the origins of perovskite degradation have been widely studied, the lacks of the effective strategies to achieve long-term stability of PSCs remain one of the major barriers for the further commercialization of PSCs and other perovskite-based devices.

To address this challenge, the general strategy towards improving the intrinsic stability of perovskite materials is to achieve chemical modification by introducing additives with function groups of –NH2, -O, -P, etc.26-28 For example, the incorporation of polyethylene glycol (PEG) in perovskite film could interact with MA+ by the formation of N-H…O hydrogen bond, so MAI molecules were anchored by PEG molecules in perovskite crystal structure which increased the stability of perovskite films.27 In our previous work, we used 2-aminoethanethiol (2-AET) as a ligand to bridge the organic compound (MAI) and inorganic compound (PbI2) to obtain the water-resistance MAPbI3 film, which could keep


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perovskite crystal structure in DI water for 10 minutes.26 However, due to the electrical insulation of polymer or organic ligands, the migration of charge carriers would be retarded, in turn results in a significant decrease in device performance, particularly the PCE.29-31 To protect PSCs devices without compromising efficiency, post-encapsulation is recognized as an effective strategy to simultaneously combine long-term stability and high performance.32 The previous study showed that the shelf-life of PSCs devices extended to more than 500 h under ambient conditions using commercial plastic barrier encapsulation.33 With soft ethylene vinyl acetate encapsulation, the PCE of PSCs retained 90% of their initial performance after 200 temperature cycles between -40 and 80 °C.34 Therefore, the design and development of encapsulation techniques for PSCs are promising for reaching the level of long-term stability and high performance required for the industrial standard. Despite the significant attention has aimed to improve humidity stability, the systematic investigations of the effects of encapsulation on both humidity stability and thermal stability are still required.


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Herein, we reported a facile adhesive encapsulation strategy to improve the stability of perovskite films and PSC devices by employing the commercial Kapton polyimide (PI) tape. We investigated the perovskite films and PSCs in extreme conditions (in DI water or under thermal treatment at 85C or 240C). The possible mechanism for improved stability was also discussed. The results revealed that the encapsulated MAPbI3 based films could retain tetragonal perovskite crystal structure at 240°C for more than 180 mins in the ambient environment. The stable operation of encapsulated PSCs in DI water with a power conversion efficiency (PCE) of 19.1% was achieved, which was slightly higher than that of the device in air (18.2%). This study highlights that the stability of perovskite films is correlate with the adhesion force between encapsulation film and perovskite film.

EXPERIMENTAL SECTION

Device Fabrication. The etched FTO glasses were cleaned by ultrasonic bath using deionized water, acetone and ethanol for 15 min, sequentially. Then the substrates were treated with UV ozone for 20 min before spray pyrolysis deposition or spin coating electron transport layer. For mesoscopic TiO2 structure, a compact TiO2 layer was coated


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by spray pyrolysis, followed by annealing at 450°C for 30 min. Then mesoporous TiO2 layer was deposited on the compact TiO2 by spin-coating at 5000 rpm for 30s, follow by annealing at 500°C for 30 min. For planar SnO2 structure, the deposition method of SnO2 layer is reported elsewhere.43 The commercial SnO2 colloidal solution (Alfa Aesar, 15% in water) were diluted in water with a volume ratio of 1:3.5, then spin coated on cleared FTO substrate at 3000 rpm for 30s, followed by drying at 150°C for 30 min.

CH3NH3I (MAI), CH3NH3Br (MABr), PbI2 and PbBr2 were purchased from Yingkou You Xuan Trade CO., LTD. The MAPbI(3-x)Brx perovskite films were spin coated from a precursor solution containing MAI (1 mol), PbI2 (1.05 mol), MABr (0.05 mol) and PbBr2 (0.05 mol) in 0.75 mL N, N-Dimethylformamide (DMF, 99.8%, Sigma-Aldrich), 71μL of Dimethylsulfoxide (DMSO, 99.5%, Sigma-Aldrich) was added as additive. 40 μL of perovskite precursor solution was spin-coated on the electron transport layer at 4000 rpm for 30 s, and 200 μL of anti-solvent ethyl acetate (EA) was dropped on the center of substrate in 8 sec to induce perovskite intermediate phase. Then annealed at 100°C for 30 min on a hotplate. When the substrate was cooled down, 25 μL spiro-MeOTAD solution


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was spin-coated on the perovskite film at 4000 rpm for 30s from 72.3 mg Spiro-MeOTAD in 1 mL chlorobenzene (29 μL of 4-tert-butylpyridine and 17.5 μL of lithium bis(trifluoromethanesulfonyl) imide slat solution in acetonitrile (520 mg/mL) were doped). After oxidation 12 h in a desiccator, 60 nm of Ag electrode was deposited onto the spiroOMeTAD layer through a shadow mask by thermal evaporation. The active area of the device is 0.1 cm2. To encapsulate the perovskite films or devices, the commercial Kapton® PI tape with Silicone adhesive was applied to the surface of the thin films or devices. All perovskite and perovskite/spiro-OMeTAD were formed on the FTO/SnO2 substrate unless otherwise stated.

Characterization. The atomic force microscopy (AFM) images were measured using an MFP-3D Infinity AFM (Asylum research, Oxford instruments). The UV-vis absorption spectra were performed by T-10 double beams UV-vis spectrophotometer (Persee, China).The Scanning electron microscopy (SEM) measurements were performed using a cold field emission scanning electron microscope (SU4800, Hitachi). The XRD patterns were recorded using X-ray diffractometer (PANalytical, Netherlands) with monochromatic


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Cu Kα radiation source (λ=1.54056 Å).The photoluminescence (PL) mapping were recorded using a HORIBA/LabRAM HR Evolution spectroscopy (Horiba LabRAM HR Evolution), the excitation wavelength was 532 nm. The current-voltage characteristics were recorded using a digital source meter (2400, Keithley Instruments Inc.) under 3A grade AM1.5G simulated sunlight (100 mW cm-2) (7-SS1503A, 7 Star Optical Instruments Co., Beijing, China). The incident light intensity was calibrated with an NRELcalibrated Si solar cell (Newport, Stratford Inc., 91150V). The incident photon conversion efficiency (IPCE) was measured by 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.).

RESULTS AND DISCUSSION

The perovskite films used in this work were based on MAPbI3 composition with the incorporation of 5 mol% MAPbBr3. Figure S1 (a-b) show SEM images of MAPbI(3-x)Brx perovskite films, indicating the typical perovskite morphology with an average grain size


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of ~200 nm. Figure 1 (a-d) show the topography and three-dimensional atomic force microscopy (AFM) images of MAPbI(3-x)Brx perovskite and MAPbI(3-x)Brx/spiro-OMeTAD films. The root mean square roughness values are 10.3 and 2.1 nm, respectively. As shown in Figure 1 (e), the PI tape is used to encapsulate the perovskite films on account of the adhesion force between hydrophobic PI film and the smooth surface of perovskite or spiro-OMeTAD film. It would eliminate the potential diffusion path of ambient water or oxygen towards perovskite films. To verify the water resistance of the perovskite films with adhesive encapsulation, we performed UV-vis absorption measurements for the perovskite films immersed in DI water. In Figure 1 (g-j), we show the ex situ UV-Vis absorption spectra of MAPbI(3-x)Brx perovskite and MAPbI(3-x)Brx/spiro-OMeTAD films without and with encapsulation for different immersion period of time. In the absorption spectrum taken after immersing in water for unencapsulated perovskite films, the characteristic absorption edge of MAPbI(3x)Brx

perovskite around 775 nm is disappeared and while the characteristic absorption

edge around 539 nm is corresponding to the decomposition products of PbI2.26 For the unencapsulated MAPbI3/spiro-OMeTAD films, the water degradation kinetics is slowed


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down due to the protective effect of spiro-OMeTAD. However, the PbI2 absorption feature is also observed after immersion for 30 s. The reduced absorbance at short wavelength region and obvious light scattering at long wavelength region indicate the deterioration of perovskite morphology,35 which implies that the H2O molecule will infiltrate through the spiro-OMeTAD layer to degrade perovskite. Excitingly, the UV-vis absorption spectra show no visible changes for the encapsulated MAPbI(3-x)Brx perovskite films after immersion in water for 1.5 h, and it further prolongs to 3h for the encapsulated MAPbI(3x)Brx/spiro-OMeTAD

films. Besides, we note that the characteristic absorption edge of

perovskite for encapsulated MAPbI(3-x)Brx/spiro-OMeTAD films changes little during the measurement. These results confirm that the excellent water resistance of perovskite films is achieved by the adhesion encapsulation. Further prolonging the immersion period of time leading to the loss of absorbance at short wavelength region. There are visible holes appear on the films after immersion for 3~6 h as shown in Figure 1 (f). Considering that the water vapor transmission rate of commercial Kapton PI tape is ~11 g/m2/day (~60% RH),36 H2O molecules may still infiltrate into perovskite film to induce undesired degradation. Figure S2 (a-d) show the SEM images of encapsulated perovskite films after


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immersion in water for 3 h. It is clear to identify the degradation region on the perovskite films with the decomposition products PbI2 as the shape of hexagonal plates with a width of 2.4~7.2 μm. The microscopic morphology of the undecomposed region is shown in Figure S2(d), it shows no visible changes referring to Figure S1. As shown in Figure S3 (a), the UV-vis absorption curves of the perovskite films encapsulated by two layers of PI tap show negligible change after immersion for 6 h. In Figure S3(b), the encapsulated perovskite films using a single layer of PI tape and two layers of PI tape retain the initial absorbance of 40% and 60% at 475 nm wavelength after immersed in water for 24 h, respectively. Besides, we noticed that after storing the decomposed films under ambient condition, the recovery of perovskite is triggered by the removal of H2O in the films with a timescale of several hours (it depends on the temperature). The color of perovskite films showed a partial recovery to dark brown even for the fully decomposed sample as shown in Figure 1(f), as well as the characteristic absorption edge of perovskite showed in Figure 1 (i-j). Such reversible changes imply that the adhesive encapsulation strategy could also eliminate the potential diffusion path of the escape of gaseous products, such as CH3NH2,


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HI, CH3I, and NH3. As a result, the gaseous product of CH3NH2 can react with HI to form MAI, and then react with nearby PbI2 to regenerate the perovskite.

Figure 1. Topography and three-dimensional AFM images of MAPbI(3-x)Brx perovskite film (a, b) and MAPbI(3-x)Brx/spiro-OMeTAD film (c, d); (e) schematic illustrations of the elimination of the potential diffusion path of ambient water molecule into perovskite structure; (f) optical images of MAPbI(3-x)Brx perovskite films and MAPbI(3-x)Brx/spiroOMeTAD films with encapsulation after immersion in water for different period of time; ex


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situ UV-vis absorption spectra of perovskite film (g), perovskite/spiro-OMeTAD film (h), perovskite/PI tape film (i) and perovskite/spiro-OMeTAD/PI tape film (j) after immersion in DI water for different time.

We further studied the diffusion behavior of decomposition product PbI2 at the boundary of PI tape on perovskite film. Figure 2(a) shows the width of PbI2 diffusion layer as a function of immersion time in DI water, the nonlinear diffusion rate based on the fitting curve was observed. It suggests that the formed adhesion force between encapsulation film and the surface of perovskite film (or spiro-OMeTAD) retards the diffusion kinetics of water molecule towards perovskite. Figure 2(b) shows the SEM images of the boundary between PbI2 and MAPbI(3-x)Brx. It can be clearly seen that the perovskite grains are surrounded by the micro sized PbI2 tightly. Considering the extremely low solubility of PbI2 in water (~1.65 × 10-3mol Kg-1 at 298.15 K),37 the outside decomposition products of PbI2 crystals would serve as H2O molecule diffusion barrier layer to protect the inside perovskite crystals. The photoluminescence (PL) intensity mapping has been carried out to verify the protection effect of the diffusion barrier layer. Figure 2(c) shows the optical


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images of the selected region in a range of 40 μm × 30 μm. The jagged boundary can be clearly identified in the middle of the selected region. The left section is the region of branch-like PbI2/spiro-OMeTAD which expose to water, while the right section is the region of MAPbI(3-x)Brx/spiro-OMeTAD encapsulated by PI tape. As shown in Figure 2(d), the PL is nearly completely quenched in the left section due to the degradation of perovskite, while the uniform PL signal in the right section can be observed. The PL intensity mapping is well consistent with the optical morphology. The random distribution of PL intensity indicates that H2O molecule cannot go across the boundary. So, it is safe to make the conclusion that the main degradation path of encapsulated perovskite films couldn’t be initiated from the edge of PI tape in air condition, which significantly simplifies the perovskite encapsulation process.


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Figure 2. (a) The width of PbI2 diffusion layer as a function of immersion time in DI water, the inset is the optical image of encapsulated perovskite film immersed in water for 6 hours; (b) SEM images of boundary between decomposition product PbI2 and MAPbI(3x)Brx;

(c) the optical images of the selected region for PL intensity mapping measurement

in a range of 40 μm × 30 μm; (d) PL intensity mapping of MAPbI(3-x)Brx/spiro-OMeTAD film in the selected region in a range of 40 μm × 30 μm.


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We also carried out UV-vis absorption measurements to assess the thermal stability of the encapsulated perovskite films. The perovskite films were heated at 85°C in an ambient atmosphere with humidity in a range of 30~70%. Figure 3(a-d) show the ex situ UV-vis absorption spectra of MAPbI(3-x)Brx perovskite and MAPbI(3-x)Brx perovskite/spiroOMeTAD films without and with encapsulation for different thermal treatment time, respectively. The characteristic absorption edge of MAPbI(3-x)Brx around 775 nm disappears after heating 24 h for unencapsulated perovskite film and 101 h for unencapsulated perovskite/spiro-OMeTAD film, respectively. While the absorption curves of both encapsulated perovskite films change little after heating 1000 h as shown in Figure 3(c-d). Figure 3(e) shows the absorbance at 475 nm as a function of heating time for the perovskite films and perovskite/spiro-OMeTAD films without and with encapsulation. The unencapsulated samples show rapid bleaching behavior on a timescale of a few days during thermal aging. In the case of encapsulated films, the absorbance retains its initial value of 86.1% during thermal aging for 1000 h. We further increased the temperature to 240°C, as shown in Figure S4(a-b), the characteristic absorption of perovskite disappeared within 5 minutes for unencapsulated perovskite films. Surprisingly, the


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absorption curves of encapsulated perovskite films change slightly during the thermal treatment at 240°C within 180 min. The absorbance at 475 nm retains its initial value of 91.2% after heating 180 min as shown in Figure 3(f). Figure S5 (a-b) show the X-ray diffractometer (XRD) patterns of perovskite films after heating at 240°C. The characteristic diffraction peaks of MAPbI(3-x)Brx perovskite disappeared for the unencapsulated perovskite films, and the strong intensity of PbI2 diffraction peaks at 12.6° was identified. However, for the encapsulated perovskite films, the XRD patterns showed no visible changes before and after thermal treatment at 240°C. We observed the sharp MAPbI(3-x)Brx characteristic diffraction peaks at 14.15° and 28.51° after heating at 240°C for 180 min. The negligible enhancement of PbI2 characteristic diffraction peak intensity may be induced by the self-induced passivation effect at grain boundaries during thermal annealing.38 These results confirm that the thermal stability of organic and inorganic hybrid perovskite films could be also significantly improved by the adhesive encapsulation strategy. Based on the previous studies,11, 39 the volatile property and relatively low ion migration activation energy of organic component should be responsible for the lack of thermodynamic stability for the hybrid perovskite materials. Figure 3(g) schematic


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illustrates that the vacancies and grain boundaries in perovskite crystal lattice may be the fast channel for the escape of organic component. The accelerated ion diffusion kinetics in such an open system would be expected during the thermal treatment.21, 40 Inversely, the adhesion force between the PI tape and perovskite film leads to the formation of the closed system as shown in Figure 3 (h), which eliminates the potential diffusion path for the volatilization of the organic component and results in the significant improvement of thermal stability of hybrid perovskite films.


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Figure 3. Ex situ UV-vis absorption spectra of perovskite film (a), perovskite/spiroOMeTAD film (b), perovskite/PI tape film (c) and perovskite/spiro-OMeTAD/PI tape film (d) after heating at 85°C for different period of time; the absorbance at 475 nm as a function of heat time at 85°C (e) and 240°C (f); schematic illustrations that the vacancies and grain boundaries in perovskite crystal lattice may the fast channel for the escape of organic component during thermal treatment at open system (g), the elimination of the potential diffusion path for the volatilization of organic component at close system formed by adhesive encapsulation strategy (h).

To assess the water resistance of the adhesive encapsulation for the conventional PSCs devices, we fabricated the PSCs devices with structure of FTO/compact TiO2/mesoscopic TiO2/ perovskite/Spiro-OMeTAD/Ag architecture. The cross-section SEM image can be found in Figure S6, the device shows smooth perovskite films with a thickness of ~400 nm. Typical J-V curves with different scan directions and scan rates are shown in Figure S7 (a-b). The PSCs shows small forward and reversed scan hysteresis. However, as shown in Figure S7 (b) the open-circuit voltage (Voc) decreased


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obviously when the scan rates were increased from 37 mV/s to 73 mV/s, while only the slight changes were observed when we further increased the scan rates to 109 mV/s and 138 mV/s. The possible reason may be correlated with the charge accumulation at perovskite/TiO2 interface, due to the poor charge extraction efficiency for TiO2.41-43 Figure 4 (a) shows the J-V curves of encapsulated PSCs device measured in air and in water. In the case of air condition, the device showed a Voc of 1.14 V, a short-circuit current density (Jsc) of 21.82 mA/cm2 and a fill fact (FF) of 73.2%, yielding a PCE of 18.2%. Figure S8 shows the incident photon conversion efficiency (IPCE) of the corresponding device, the IPCE reaches 80% at 373~737 nm wavelengths with an integrated current density of 21.28 mA/cm2, which is in agreement with the Jsc measured from J-V curve. Interestingly, we observed obvious enhancement (~5%) of Jsc from J-V curve when testing the devices in water (see Figure 4a inset photo), which may be associated with light refraction effect at air/water interface as shown in Figure 4(b). More light can be concentrated on the device to increase Jsc. As a result, the PCE measured in water was increased from 18.2% to 19.1%. To verify the enhancement of Jsc induced by light refraction effect at air/water interface, we employed a water droplet on the light-exposed surface (glass side) of the


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device. As shown in the inset to Figure S9, it is expected that the arc interface of water drop would work as a focusing lens, more parallel light can be concentrated onto the device to deliver a higher power output. As a result, the significant Jsc enhancement of 43.4% was observed, while the Voc and FF changed slightly, which demonstrated that the light refraction effect at air/water interface should be responsible for the enhancement of

Jsc. We further investigated the stable power output at the maximum power point (MPP) of PSCs devices immersed in water under continuous AM 1.5 irradiation. Figure 4(c) shows the normalized stable power output of PSCs devices. The loss of stabilized PCE is comparable for both the unencapsulated and encapsulated PSCs devices measured in air condition within 150 s (from 30 s to 180 s). Then we poured the DI water to immerse the devices during the measurements. We also observed 5~6% improvement of stabilized efficiency in DI water due to the light refraction effect as discussed above. The stabilized PCE of unencapsulated device rapidly drops to 0% in water for 293 s, while it prolongs to 1522 s for the device encapsulated by one layer of PI tape. Surprisingly, the PSCs device encapsulated by two layers PI tape maintains 89.3% of its initial efficiency after immersion in water for 1620 s (from 180 s to 1800 s), which is close to that of samples measured in


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air as shown in Figure S10 (89.3% for unencapsulated device, 92.1% for encapsulated device). Employing SnO2 as electron transport layer can further improve the stability of PSCs device during continues illumination.44-45 We also fabricated devices based on planar SnO2 architecture, the cross-section SEM images can be found in Figure S11 (a, c), the device also shows smooth perovskite films with a thickness of ~400 nm. The integrated current density (20.01 mA/cm2) calculated from IPCE showed in Figure S11(b) is lower than that of the device based on mesoscopic TiO2 architecture. As shown in Figure S12 (a-b), there is not visible hysteresis when operating the devices from forward and reversed scans and the results are no longer depending on the scan rates in a range of 37~138 mV/s. The stabilized efficiency (see Figure 4(d)) of PSCs device based on planar SnO2 architecture retains 96.3% of its initial efficiency in water under the same test conditions as Figure 4(c), which also shows comparable loss of stabilized efficiency measured in ambient conditions (retains 98.9% of its initial efficiency, see Figure S12(c)). These results confirm that the stability of PSCs devices, including mesoscopic and planar structures, is significantly improved by the adhesive encapsulation strategy.


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Figure 4. J-V curves (a) of PSCs device measured in air and in DI water, the inset is optical image of device immersed in DI water in the testing process; (b) schematic illustration of more light can be concentrated on the device to increase Jsc due to light refraction effect at air/water interface; the normalized stabilized efficiency of PSCs device based on mesoscopic TiO2 architecture (c) and planar SnO2 architecture (d) measured in air for 150 s and in water for 1620 s at MPP. CONCLUSIONS


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In summary, we have demonstrated that the stability of organic and inorganic hybrid perovskite MAPbI3 films in extreme conditions (in DI water or heating at 240 C) can be significantly improved by the adhesive encapsulation. The formed adhesion force between PI film and perovskite films leads to the formation of the closed system, which not only retard the diffusion kinetics of water molecule into perovskite structure from the boundaries of PI film, but also eliminate the potential diffusion path for the volatilization of the organic component to enhance the thermal stability of perovskite. This is a simple and effective strategy to combine the long-term stability and high performance for the devices including solar cells, light-emitting diodes, and photodetectors with both flexible and rigid structures.

ASSOCIATED CONTENT

The Supporting Information is available free of charge on the ACS Publications website.


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Including: Detailed experimental methods, SEM images, UV-vis absorption spectra, and XRD patterns of perovskite films; J-V curves, IPCE, and stable power output at MPP measurements of perovskite solar cells.

AUTHOR INFORMATION Corresponding Author * Jianjun Tian. Email: [email protected]; telephone number: 010-82377502

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT 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-TP17-083A1, FRF-TP-17-082A1 and TW2018010), and Project funded by China Postdoctoral Science Foundation (2017M620611, 2018M630068).


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