Directing efficient hole transport: Surface defects in three-dimensional perovskites can decrease performance but can be healed with coatings based on two-dimensional (2D) perovskite such as Ruddlesden-Popper phases. However, the bulky organic groups of these 2D phases can lead to low and anisotropic charge transport. F. Zhang et al . show that a metastable polymorph of a Dion-Jacobson 2D structure based on asymmetric organic molecules reduced the energy barrier for hole transport and their transport through the layer. When used as a top layer for a triple-cation mixed-halide perovskite, a solar cell retained 90% of its initial power conversion efficiency of 24.7% after 1000 hours of operation at approximately 40°C in nitrogen. —PDS

Spray-deposition is a low-cost, roll-to-roll compatible technique that could potentially replace spin-coating for the deposition of highly efficient perovskite solar cells. Here, perovskite active layers were fabricated in air using an ultra- sonic spray system and compared with equivalent spin-coated films. A chlorine containing perovskite ink with a wide processing window coupled with an anti- solvent extraction resulted in perovskite films with relatively rougher surfaces than those spin-coated. A power conversion efficiency (PCE) of 17.3% was achieved with an average of 16.3% from 24 devices. Despite observing differences in film roughness and structure, the performance of sprayed perovskite solar cells was comparable to that of the spin-coated cells processed in an inert atmosphere, showing the versatility of perovskite processing.

Glass/glass (G/G) photovoltaic (PV) module construction is quickly rising in popularity due to increased demand for bifacial PV modules, with additional applications for thin-film and building-integrated PV technologies. G/G modules are expected to withstand harsh environmental conditions and extend the installed module lifespan to greater than 30 years compared to conventional glass/backsheet (G/B) modules. With the rapid growth of G/G deployment, understanding the outdoor performance, degradation, and reliability of this PV module construction becomes highly valuable. In this review, we present the history of G/G modules that have existed in the field for the past 20 years, their subsequent reliability issues under different climates, and methods for accelerated testing and characterization of both cells and packaging materials. We highlight some general trends of G/G modules, such as greater degradation when using poly(ethylene-co-vinyl acetate) encapsulants, causing the industry to move toward polyolefin-based encapsulants. Transparent backsheets have also been introduced as an alternative to the rear glass for decreasing the module weight and aiding the effusion of trapped gaseous degradation products in the laminate. New amendments to IEC 61215 standard protocols for G/G bifacial modules have also been proposed so that the rear side power generation and UV exposure will be standardized. We further summarize a suite of destructive and non-destructive characterization techniques, such as current–voltage scans, module electro-optical imaging, adhesion tests, nanoscale structural/chemical investigation, and forensic analysis, to provide deeper insights into the fundamental properties of the module materials degradation and how it can be monitored in the G/G construction. This will set the groundwork for future research and product development.

The presence of soiling on photovoltaic modules reduces light transmission through the front cover glass to the active absorber, thereby reducing efficiency and performance. Current soiling mitigation techniques are expensive and/or ineffective. However, anti-soiling coatings applied to the solar cover glass have the potential to reduce soiling for long periods of time without continuous maintenance. This paper reports the performance of two transparent hydrophobic coatings (A and B) exposed to the outdoor environment of coastal Denmark for 24 weeks. A comparison was made between the performance of coated and uncoated glass coupons, periodically cleaned coupons, and accelerated laboratory tests. Although initial results were promising, water contact angle and transmittance values were found to decline continuously for all coated and uncoated coupons. Surface blisters, film thickness reduction, changes in surface chemistry (fluorine loss), and abrasion damage following cleaning were observed. Coupons cleaned every 4 weeks showed a restoration in transmittance. Cycles of light rainfall and evaporation combined with a humid and salty environment led to cementation occurring on all coupons. The development of an abrasion-resistant, super-hydrophobic coating with a low roll-off angle and high water contact angle is more likely to provide an anti-soiling solution by reducing the build-up of cementation.

Soiling of solar module cover glass is a serious problem for solar asset managers. It causes a reduction in power output due to attenuation of the incident light, and reduces the return on investment. Regular cleaning is required to mitigate the effect but this is a costly procedure. The application of transparent hydrophobic, anti-soiling coatings to the cover glass is a promising solution. These coatings have low surface energy and contaminants do not adhere well. Even if soiling does remain on the coated surface, it is much more easily removed during cleaning. The performance of the coatings is determined using the water contact angle and roll-off angle measurements. However, although hydrophobic coatings hold out great promise, outdoor testing revealed degradation that occurs surprisingly quickly. In this study, we report on results using laboratory-based damp heat and UV exposure environmental tests. We used SEM surface imaging and XPS surface chemical analysis to study the mechanisms that lead to coating degradation. Loss of surface fluorine from the coatings was observed and this appeared to be a major issue. Loss of nanoparticles was also observed. Blistering of surfaces also occurs, leading to loss of coating material. This was probably due to the movement of retained solvents and was caused by insufficient curing. This mechanism is avoidable if care is taken for providing and carrying out carefully specified curing conditions. All these symptoms correlate well with observations taken from parallel outdoor testing. Identification of the mechanisms involved will inform the development of more durable anti-soiling, hydrophobic coatings for solar application.