Stability Of Polymer Solar Cells Research Articles

Advancing stability in inverted polymer solar cells through accelerated xenon curing of the ZnO layer

This study delves into the profound implications of employing an intensive xenon lamp treatment with a rapid curing method completed within 4 min, to fabricate a ZnO layer. Subsequently, we applied a coating of PM6:Y6 as the active layer and utilized MoO3/Ag as the contact electrode, aiming to advance the efficiency of polymer solar cells (PSCs) through entirely room-temperature processes. Our investigation juxtaposes this xenon lamp treatment with the conventional hot plate method for annealing the ZnO layer, conducted at 180 °C for both 20 min and 4 min. Remarkably, our proposed xenon lamp treatment process not only promotes charge transfer but also exhibits enhancements of the lattice oxygen in the Zn-O layer. This innovative methodology of xenon treatment yields a notable increase in power conversion efficiency (PCE), achieving 14.55 %, compared to 13.71 % and 12.44 % for the ZnO layers annealed with a hot plate for 20 min and 4 min, respectively. Moreover, devices subjected to the 4-min xenon lamp treatment maintained 85 % (T85) of their original Power Conversion Efficiency (PCE) after enduring 500 h of one-sun aging measurement. These findings evoke optimism regarding the xenon treatment's potential to streamline the fabrication process, and provide a promising avenue for mitigating interface degradation while enhancing the stability of PSCs.

Development of cross-linked donor polymers for polymer solar cells with improved efficiency and thermal stability

Due to low glass-transition temperature and high diffusion coefficient of small molecule acceptors (SMAs), the bi-continuous interpenetrating morphology of SMA-based polymer solar cells (PSCs) are metastable and therefore most SMA-based PSCs exhibit poor operational and thermal stability. Cross-linked donor polymers have been proposed because the cross-linked behavior can “freeze” the initial morphology and avoid its further evolution. In this work, two new cross-linked donor polymers P1 and P2 were designed for application in PSCs with a non-fullerene acceptor Y6, in which the photovoltaic performance and thermal stability of PSCs were significantly improved. The P1-based PSCs achieved a superior power conversion efficiency (PCE) of 17.29 % with a Jsc of 25.99 mA cm−2, a Voc of 0.860 V and a FF of 77.35 %, which surpassed 9 % for PM6-based PSCs (15.86 %). Furthermore, the P1-based PSCs exhibited better thermal stability with a 17 % efficiency loss under continuous 60 °C for 210 h due to the fixation of active layer morphology, while PM6-based PSCs suffered from a serve PCE reduction of over 26 %. These results demonstrate that cross-linked donor polymer has a great application prospect to improve the PCE and thermal stability of PSCs.

In Situ Electrochemical Cobalt Doping in Perovskite-Structured Lanthanum Nickelate Thin Film Toward Energy Conversion Enhancement of Polymer Solar Cells.

This study demonstrates that the electrochemical doping of lanthanum nickelate (LNO) with cobalt ions is a promising strategy for enhancing its physical and electrochemical properties, which are critical for energy storage and conversion devices. LNO emerges as a promising hole transport layer (HTL) in solar cells due to its stability, large band gap, and high transparency. Nevertheless, its low conductivity and improperly aligned band positions are persistent problems. Here, in a pioneering endeavor, Co-doped LNO thin films were synthesized electrochemically and applied as the HTL in polymer solar cells (PSCs). Characterization revealed the impact of Co doping on the electrochemical, structural, morphological, and optical properties of LNO thin films. Depending on the Co doping level, PSCs based on 10 mol % Co-doped LNO outperformed pure LNO, achieving a champion efficiency of 6.11% with enhanced short-circuit current density (12.84 mA cm-2), fill factor (68%), open-circuit voltage (0.70 V), and external quantum efficiency (82.6%). This enhancement resulted from decreased series resistance, refined surface morphology, minimized trap-assisted recombination, enhanced conductivity, increased charge carrier production, favorable energy level alignment, and improved current extraction facilitated by LNC0.10O HTL. Moreover, the unencapsulated PSC-LNC0.10O long-term stability notably improved and retained 86% of its initial PCE after 450 h storage in ambient air, 82% after being continuously heated to 85 °C for 300 h, and 80% after operating at maximum power point for 300 h. These findings offer a straightforward approach to enhancing PSC performance through Co doping of LNO, supported by density functional theory (DFT) calculations that validate the experimental results and confirm the improvement in optical properties and stability of PSCs as an HTL.

Recent progress and prospects of dimer and multimer acceptors for efficient and stable polymer solar cells.

High power conversion efficiency (PCE) and long-term stability are essential prerequisites for the commercialization of polymer solar cells (PSCs). Small-molecule acceptors (SMAs) are core materials that have led to recent, rapid increases in the PCEs of the PSCs. However, a critical limitation of the resulting PSCs is their poor long-term stability. Blend morphology degradation from rapid diffusion of SMAs with low glass transition temperatures (Tgs) is considered the main cause of the poor long-term stability of the PSCs. The recent emergence of oligomerized SMAs (OSMAs), composed of two or more repeating SMA units (i.e., dimerized and trimerized SMAs), has shown great promise in overcoming these challenges. This innovation in material design has enabled OSMA-based PSCs to reach impressive PCEs near 19% and exceptional long-term stability. In this review, we summarize the evolution of OSMAs, including their research background and recent progress in molecular design. In particular, we discuss the mechanisms for high PCE and stability of OSMA-based PSCs and suggest useful design guidelines for high-performance OSMAs. Furthermore, we reflect on the existing hurdles and future directions for OSMA materials towards achieving commercially viable PSCs with high PCEs and operational stabilities.

Tethered Small-Molecule Acceptor Refines Hierarchical Morphology in Ternary Polymer Solar Cells: Enhanced Stability and 19% Efficiency.

Polymer solar cells (PSCs) are promising for efficient solar energy conversion, but achieving high efficiency and device longevity within a bulk-heterojunction (BHJ) structure remains a challenge. Traditional small-molecule acceptors (SMAs) in the BHJ blend show thermodynamic instability affecting the morphology. In contrast, tethered SMAs exhibit higher glass transition temperatures, mitigating these concerns. Yet, they might not integrate well with polymer donors, causing pronounced phase separation and overpurification of mixed domains. Herein, a novel ternary device is introduced that uses DY-P2EH, a tethered dimeric SMA with conjugated side-chains as host acceptor, and BTP-ec9, a monomeric SMA as secondary acceptor, which respectively possess hypomiscibility and hypermiscibility with the polymer donor PM6. This unique combination affords a parallel-connected ternary BHJ blend, leading to a hierarchical and stable morphology. The ternary device achieves a remarkable fill factor of 80.61% and an impressive power conversion efficiency of 19.09%. Furthermore, the ternary device exhibits exceptional stability, retaining over 85% of its initial efficiency even after enduring 1100 h of thermal stress at 85°C. These findings highlight the potential advantage of tethered SMAs in the design of ternary devices with a refined hierarchical structure for more efficient and durable solar energy conversion technologies.

Modular-Approach Synthesis of Giant Molecule Acceptors via Lewis-Acid-Catalyzed Knoevenagel Condensation for Stable Polymer Solar Cells.

The operational stability of polymer solar cells is a critical concern with respect to the thermodynamic relaxation of acceptor-donor-acceptor (A-D-A) or A-DA'D-A structured small molecule acceptors (SMAs) within their blends with polymer donors. Giant molecule acceptors (GMAs) bearing SMAs as subunits offer a solution to this issue, while their classical synthesis via the Stille coupling suffers from low reaction efficiency and difficulty in obtaining mono-brominated SMA, rendering the approach impractical for their large-scale and low-cost preparation. In this study, we present a simple and cost-effective solution to this challenge through Lewis acid-catalyzed Knoevenagel condensation with boron trifluoride etherate (BF3∙OEt2) as catalyst. We demonstrated that the coupling of the monoaldehyde-terminated A-D-CHO unit and the methylene-based A-link-A (or its silyl enol ether counterpart) substrates can be quantitatively achieved within 30 minutes in the presence of acetic anhydride, affording a variety of GMAs connected via the flexible and conjugated linkers. The photophysical properties was fully studied, yielding a high device efficiency of over 18%. Our findings offer a promising alternative for the modular synthesis of GMAs with high yields, easier work up, and the widespread application of such methodology will undoubtedly accelerate the progress of stable polymer solar cells.

Modular‐Approach Synthesis of Giant Molecule Acceptors via Lewis‐Acid‐Catalyzed Knoevenagel Condensation for Stable Polymer Solar Cells

AbstractThe operational stability of polymer solar cells is a critical concern with respect to the thermodynamic relaxation of acceptor‐donor‐acceptor (A‐D‐A) or A‐DA'D‐A structured small‐molecule acceptors (SMAs) within their blends with polymer donors. Giant molecule acceptors (GMAs) bearing SMAs as subunits offer a solution to this issue, while their classical synthesis via the Stille coupling suffers from low reaction efficiency and difficulty in obtaining mono‐brominated SMA, rendering the approach impractical for their large‐scale and low‐cost preparation. In this study, we present a simple and cost‐effective solution to this challenge through Lewis acid‐catalyzed Knoevenagel condensation with boron trifluoride etherate (BF3 ⋅ OEt2) as catalyst. We demonstrated that the coupling of the monoaldehyde‐terminated A‐D‐CHO unit and the methylene‐based A‐link‐A (or its silyl enol ether counterpart) substrates can be quantitatively achieved within 30 minutes in the presence of acetic anhydride, affording a variety of GMAs connected via the flexible and conjugated linkers. The photophysical properties was fully studied, yielding a high device efficiency of over 18 %. Our findings offer a promising alternative for the modular synthesis of GMAs with high yields, easier work up, and the widespread application of such methodology will undoubtedly accelerate the progress of stable polymer solar cells.

Ionic Ir(III) complex-interfacial layer for efficient carrier collection via induced electric dipole.

The power conversion efficiency (PCE) of polymer solar cells (PSCs) has recently reached >19% through the development of photoactive materials, particularly non-fullerene acceptors. Interfacial layers (ILs) have been another essential factor in optimizing device charge extraction. In this study, we propose a series of ILs, in which ionic iridium(III) (Ir(III)) complexes of different alkali metal cations (Li+, Na+, and K+) enhance the charge collection efficiency between zinc oxide and active layers through an induced internal electric field. The anionic coordinate sphere and counter-cations of the Ir(III) complexes are distributed according to the operating voltage of the PSCs, causing electric dipoles that enhance the internal electric field and charge collection efficiency. Ion species migration in the ILs is confirmed using electrochemical impedance spectroscopy. The PCE of the PM6:Y6-based PSCs was improved from 14.0% to 15.6% by introducing an IL (Ir-K+). Furthermore, the stability of PSCs containing ionic Ir(III) complexes is enhanced significantly under ultraviolet (UV) light and AM 1.5 G one-sun irradiation owing to the intense UV absorption capacity and photo durability of the ILs. A device containing the Ir(III) complex-based ILs retained ∼60% of its initial PCE after UV irradiation, whereas the control device retained only ∼20%.

Tethered Small-Molecule Acceptors Simultaneously Enhance the Efficiency and Stability of Polymer Solar Cells.

For polymer solar cells (PSCs), the mixture of polymer donors and small-molecule acceptors (SMAs) is fine-tuned to realize a favorable kinetically trapped morphology and thus a commercially viable device efficiency. However, the thermodynamic relaxation of the mixed domains within the blend raises concerns related to the long-term operational stability of the devices, especially in the record-holding Y-series SMAs. Here, a new class of dimeric Y6-based SMAs tethered with differential flexible spacers is reported to regulate their aggregation and relaxation behavior. In their polymer blends with PM6, it is found that they favor an improved structural order relative to that of Y6 counterpart. Most importantly, the tethered SMAs show large glass transition temperatures to suppress the thermodynamic relaxation in mixed domains. For the high-performing dimeric blend, an unprecedented open circuit voltage of 0.87V is realized with a conversion efficiency of 17.85%, while those of regular Y6-base devices only reach 0.84V and 16.93%, respectively. Most importantly, the dimer-based device possesses substantially reduced burn-in efficiency loss, retaining more than 80% of the initial efficiency after operating at the maximum power point under continuous illumination for 700h. The tethering approach provides a new direction to develop PSCs with high efficiency and excellent operating stability.

Simultaneously Achieving Highly Efficient and Stable Polymer:Non-Fullerene Solar Cells Enabled By Molecular Structure Optimization and Surface Passivation.

Despite the tremendous efforts in developing non‐fullerene acceptor (NFA) for polymer solar cells (PSCs), only few researches are done on studying the NFA molecular structure dependent stability of PSCs, and long‐term stable PSCs are only reported for the cells with low efficiency. Herein, the authors compare the stability of inverted PM6:NFA solar cells using ITIC, IT‐4F, Y6, and N3 as the NFA, and a decay rate order of IT‐4F > Y6 ≈ N3 > ITIC is measured. Quantum chemical calculations reveal that fluorine substitution weakens the C═C bond and enhances the interaction between NFA and ZnO, whereas the β‐alkyl chains on the thiophene unit next to the C═C linker blocks the attacking of hydroxyl radicals onto the C═C bonds. Knowing this, the authors choose a bulky alkyl side chain containing molecule (named L8‐BO) as the acceptor, which shows slower photo bleaching and performance decay rates. A combination of ZnO surface passivation with phenylethanethiol (PET) yields a high efficiency of 17% and an estimated long T 80 and Ts80 of 5140 and 6170 h, respectively. The results indicate functionalization of the β‐position of the thiophene unit is an effective way to improve device stability of the NFA.

Patterned Sandwich-Type Silver Nanowire-Based Flexible Electrode by Photolithography.

Silver nanowires (AgNWs) are one of the important flexible electrode material candidates that can replace brittle indium tin oxide (ITO). In this work, we demonstrated novel patterned sandwich-type AgNW-based transparent electrodes easily prepared using the photolithography method for application in flexible devices. A cross-linked underlayer was introduced to increase the adhesion properties between a poly(ethylene terephthalate) substrate and AgNWs, and as a result, a uniform AgNW layer was easily deposited. Finally, the AgNW layer could be easily patterned by introducing a photocross-linkable upper layer without lift-off, dry transfer, and removal methods. A mixture of poly(sodium-4-styrene sulfonate) (PSS-Na+) and 2,4-hexadiyne-1,6-diol (HDD), which is a component of the upper layer, exhibited good cross-linking properties as well as excellent adhesion to the AgNW layer. Through the above method, it was possible to easily fabricate a patterned electrode with smooth surface morphology. Moreover, AgNW-based patterned electrodes exhibit good optical and electrical properties (Rs = 29.8 Ω/□, T550 nm = 94.6%), making them suitable for optoelectronic devices. Flexible polymer solar cells (PSCs) using patterned AgNW electrodes showed a high power conversion efficiency of over 10%, which is comparable to that of PSCs using rigid ITO electrodes. In addition, the high mechanical stability of AgNW-based PSCs was confirmed by bending experiments.

Improved Hole Extraction Selectivity of Polymer Solar Cells by Combining PEDOT:PSS with WO3

As the device performance and stability of polymer solar cells strongly depend on the interfacial charge extraction layers, the hole transport layer (HTL) properties are crucial. Furthermore, unfavorable interactions with the electrode or the photoactive layer should be screened and prevented. Organic solar cells of conventional architecture by varying the HTL material and layer stack systematically between PEDOT:PSS and a sol–gel‐derived tungsten oxide (WO3) are investigated. The impact of various HTLs in the solar cells is investigated by optical and electrical characterization. Interestingly, a triple‐layer WO3/PEDOT:PSS/WO3 configuration results in the best device performance specifically compared with the use of pristine WO3 and pristine PEDOT:PSS hole extraction layers. The triple layer also shows an increased reproducibility in the lifetime, which, combined with the improvement in the efficiency, can be the keys for expectable revenue.

A universal strategy via polymerizing non-fullerene small molecule acceptors enables efficient all-polymer solar cells with > 1 year excellent thermal stability

Record-holding polymer solar cells (PSCs) composed of polymer donors and Y-series non-fullerene small molecule acceptors have reached the efficiency threshold for commercialization, but this type of PSCs is often difficult to work continuously and stably at high temperatures close to 100 °C, limiting its outdoor application. Therefore, in this work, we tried to boost the thermal stability of PSCs based on Y-series acceptors Y5-F-Br by polymerizing Y5-F-Br obtaining PFA1, and establish a precise correlation between the molecular structure and device thermal stability. Consequently, the excellent film stability based on long-chain acceptor PFA1 effectively suppressed the thermally induced phase separation of PTzBI-oF:PFA1 blend film at high temperatures, resulting in over 98% thermal stability at 100 °C for over 1 year in the nitrogen-filled glovebox. Furthermore, the use of long-chain acceptor for improving thermal stability was also confirmed in other two commonly used PSCs, suggesting that polymerizing non-fullerene small molecule acceptors is an effective and universal strategy to boost the thermal stability of PSCs.

Performance and Stability of Polymer:Nonfullerene Solar Cells with 100 °C-Annealed Electron-Collecting Combination Layers.

Invited for this month's cover is the group of Youngkyoo Kim at the Kyungpook National University. The image shows the improved electron transfer by hybrid combination layers featuring peculiar morphology for better efficiency and stability in polymer solar cells. The Full Paper itself is available at 10.1002/cssc.202100841.

Enhancing Efficiency and Stability of Polymer Solar Cells Based on CuI Nanoparticles as the Hole Transport Layer

Copper(І) iodide (CuI) is a very efficient inorganic p-type material and has a potential application in polymer solar cells (PSCs). However, the solution-processed CuI film tends to be rough surface morphology. Herein, CuI nanoparticles (NPs) were synthesized by water decomposing the CuI N,N-dimethylformamide (DMF) dispersion and used as hole transporting layers (HTLs) of PSCs with the configuration of ITO/CuI/P3HT:PC61BM/Ca/Al. As a result, a smooth and uniform CuI film was formed by spin coating from CuI NP acetonitrile solution. The root-mean-square roughness of the film reduced from 2.25 nm for spin coating from bulk CuI acetonitrile solution to 0.65 nm for CuI NPs. The power conversion efficiency of PSCs increased from 3.10% to 3.47% for CuI NP HTL. Moreover, the CuI NPs-based device demonstrated enhanced stability. The higher efficiency and better stability of CuI NPs-based PSCs should be attributed to uniform surface morphology and reducing exciton quenching of the CuI/the photoactive layer interface. This work indicates that CuI NPs will be a novel promising hole transporting material for highly efficient and stable PSCs.

An alcohol-soluble small molecule as efficient cathode interfacial layer materials for polymer solar cells

Abstract Interface modification makes an important contribution to improving the optoelectronic performance and stability of polymer solar cells (PSCs). Here, the hexamethylenetetramine (C6H12N4) was successfully introduced into PSCs as cathode interface layers (CILs) using environmental-friendly methanol as solvent. Compared to the PSCs without CILs, the open circuit voltage (VOC) and short-circuit current density (JSC) of the device with C6H12N4 CILs was increased from 0.44 V to 12.73 mA cm−2 to 0.77 V and 15.89 mA cm−2, respectively. More importantly, under the same experimental conditions, the optimal power conversion efficiency (PCE) of the device with C6H12N4 CILs was improved to 7.79%, which is 185% higher than that of the device without C6H12N4 CILs (2.73%). We found that the active layer PTB7-Th:PC71BM showed a smoother interface morphology and better hydrophilicity after insertion of CILs, which facilitated enhance the physical contact between active layers and cathode as well as electron extraction and transport. The results show that the introduction of C6H12N4 as CILs provides an effective method for preparing high-performance PSCs.

An N-type Naphthalene Diimide Ionene Polymer as Cathode Interlayer for Organic Solar Cells

Polymer solar cells (PSCs) based on non-fullerene acceptors have the advantages of synthetic versatility, strong absorption ability, and high thermal stability. These characteristics result in impressive power conversion efficiency values, but to further push both the performance and the stability of PSCs, the insertion of appropriate interlayers in the device structure remains mandatory. Herein, a naphthalene diimide-based cathode interlayer (NDI-OH) is synthesized with a facile three-step reaction and used as a cathode interlayer for fullerene and non-fullerene PSCs. This cationic polyelectrolyte exhibited good solubility in alcohol solvents, transparency in the visible range, self-doping behavior, and good film forming ability. All these characteristics allowed the increase in the devices’ power conversion efficiencies (PCE) both for fullerene and non-fullerene-based PSCs. The successful results make NDI-OH a promising cathode interlayer to apply in PSCs.

Simultaneous Performance and Stability Improvement of Ternary Polymer Solar Cells Enabled by Modulating the Molecular Packing of Acceptors

Nanoscale morphology of the active layer plays a crucial role in the power conversion efficiency (PCE) and stability of polymer solar cells (PSCs). Blending the photoactive layer with a third component to produce a ternary system is considered a reliable approach to tune the nanomorphology, thereby improving the device performance. Herein, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]‐dithiophene)‐co‐(1,3‐di(5‐thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4,5‐c′]dithiophene‐4,8‐dione))] (PBDB‐T): 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) solar cells doped with a third small molecule are systematically investigated, namely, (5Z,5′Z)‐5,5′‐((7,7′‐(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl)bis(benzo[c]1,2,5]thiadiazole‐7,4‐diyl))‐bis(methanylyl‐idene))bis(3‐ethyl‐2‐thioxothiazolidin‐4‐one) (FBR). Owing to the wide optical bandgap of FBR, blending PBDB‐T:ITIC with FBR increases the device's light‐harvesting capability in the short wavelength range (400–550 nm), which improves the short circuit current. Differential scanning calorimetry and grazing incidence wide angle X‐ray scattering analyses reveal that the FBR exhibits impressive miscibility with ITIC, leading to the formation of ITIC:FBR alloys. Optimum performance is achieved with a PBDB‐T:ITIC:FBR (1:0.8:0.2) cell, which yields a PCE of 11.17%, demonstrating a 10% improvement relative to the PBDB‐T:ITIC binary cell. Crucially, the ternary solar cells also show improved device stability, which is attributed to the formation of ITIC:FBR alloys suppressing the crystallization of ITIC. This study provides deep insights into the performance‐ and stability‐related improvements available to PSCs devices that incorporate a third conjugated small molecule.

An Optimized Fibril Network Morphology Enables High-Efficiency and Ambient-Stable Polymer Solar Cells.

Morphological stability is crucially important for the long‐term stability of polymer solar cells (PSCs). Many high‐efficiency PSCs suffer from metastable morphology, resulting in severe device degradation. Here, a series of copolymers is developed by manipulating the content of chlorinated benzodithiophene‐4,8‐dione (T1‐Cl) via a random copolymerization approach. It is found that all the copolymers can self‐assemble into a fibril nanostructure in films. By altering the T1‐Cl content, the polymer crystallinity and fibril width can be effectively controlled. When blended with several nonfullerene acceptors, such as TTPTT‐4F, O‐INIC3, EH‐INIC3, and Y6, the optimized fibril interpenetrating morphology can not only favor charge transport, but also inhibit the unfavorable molecular diffusion and aggregation in active layers, leading to excellent morphological stability. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable PSCs, and also provides new insights into the effect of chemical structure on the fibril network morphology and photovoltaic performance of PSCs.

The influence of UV filter and Al/Ag moisture barrier layer on the outdoor stability of polymer solar cells

The degradation of the polymer solar cells in the outdoor condition was studied. It was found that the devices with normal structure (ITO/PEDOT:PSS/PBDTTT-EFT:PC71BM/ZrOx/Al) show better stability than those with inverted device structure (ITO/ZnO/PBDTTT-EFT:PC71BM/MoO3/Ag). PBDTTT-EFT is poly[4, 8-bis(5-(2-ethylhexyl) thiophen-2-yl) benzo [1,2-b;4,5-b'] dithiophene-2, 6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno [3,4-b]thiophene-) −2-carboxylate-2-6-diyl)] and PC71BM is [6,6]-phenyl-C71-butyric acid methyl ester. The major cause of degradation was attributed to the ultraviolet (UV) part of the sunlight. When the UV filter with cut-off wavelength of 400 nm was used to protect the device, the decay rate was improved by 50 times and the protected device retains 95% of their initial power conversion efficiency after 13 days outside. In the meanwhile, the decay of device fabricated by toluene was found 8 times faster than device by chlorobenzene. Thin 20 nm of Ag capping layer can further improve the stability. Degradation under water immersion indicates that the major effect of Ag is to protect against the residual moisture inside the encapsulation.