Organic photovoltaics (OPVs) evolve in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) has in the last decade been increased by almost a factor of ten approaching 10%. A main concern has been the stability that was previously measured in minutes, but can now, in favorable circumstances, exceed many thousands of hours. This astonishing achievement is the subject of this article, which reviews the developments in stability/degradation of OPVs in the last five years. This progress has been gained by several developments, such as inverted device structures of the bulk heterojunction geometry device, which allows for more stable metal electrodes, the choice of more photostable active materials, the introduction of interfacial layers, and roll-to-roll fabrication, which promises fast and cheap production methods while creating its own challenges in terms of stability.

Stability of polymer solar cells.

This review article examines the current state of understanding in how metal halide perovskite solar cells can degrade when exposed to moisture, oxygen, heat, light, mechanical stress, and reverse bias. It also highlights strategies for improving stability, such as tuning the composition of the perovskite, introducing hydrophobic coatings, replacing metal electrodes with carbon or transparent conducting oxides, and packaging. The article concludes with recommendations on how accelerated testing should be performed to rapidly develop solar cells that are both extraordinarily efficient and stable.

Understanding Degradation Mechanisms and Improving Stability of Perovskite Photovoltaics.

Degradations of silicon photovoltaic modules: A literature review

The performance of perovskite solar cells has rapidly increased above 22%, and their environmental stability is also progressing. However, the mismatch in thermal expansion coefficients and low fracture energy of layers in perovskite solar cells raise a concern as to whether devices can withstand mechanical stresses from temperature fluctuations. We measured the fracture energy of a perovskite film stack, which was shown to produce 23.6% efficiency when incorporated in a monolithic perovskite-silicon tandem. We found that the fracture energy increased by a factor of two after 250 standardized temperature cycles between −40 °C and 85 °C and a factor of four after laminating an encapsulant on top of the stack. In order to observe how the increased mechanical stability translated from film stacks to device performance and reliability, we carried out a comparative study of perovskite solar cells packaged between glass and two commonly used encapsulants with different elastic moduli. We demonstrated that solar cells encapsulated with a stiffer ionomer, Surlyn, severely decreased in performance with temperature cycling and delaminated. However, the solar cells encapsulated in softer ethylene vinyl acetate withstood temperature cycling and retained over 90% of their initial performance after 200 temperature cycles. This work demonstrates a need for an encapsulant with a low elastic modulus to enable mechanical stability and progress toward 25 year operating lifetime.

Design and understanding of encapsulated perovskite solar cells to withstand temperature cycling

Photovoltaic (PV) modules are subject to climate-induced degradation that can affect their efficiency, stability, and operating lifetime. Among the weather and environment related mechanisms, the degradation mechanisms of the prominent polymer encapsulant, ethylene-vinyl-acetate copolymer (EVA), and the relationships of the stability of this material to the overall reliability of Si-based PV modules were addressed. The EVA function and properties correlated to its deterioration factors as temperature, moisture, and ultraviolet radiation (UV) were discussed in this work. The main objective of this study is to review the literature on EVA encapsulation and its degradation, which promotes the loss in performance of the PV module. The deleterious effects on EVA such as photodegradation, moisture, delamination, bubble formation and potential induced degradation (PID), their relationship with the polymer structure, chemical, mechanical, optical and electrical properties are approaches carried out in this review. This paper also provides a brief review of the developing field of EVA composites technology aiming at higher performance materials.

Tom J. McMahon

Papers

Acetic acid production and glass transition concerns with ethylene-vinyl acetate used in photovoltaic devices