Ultra-flexible and waterproof perovskite photovoltaics for washable power source applications

Strain Effects on Flexible Perovskite Solar Cells

Flexible perovskite solar cells (f-PSCs) as a promising power source have grabbed surging attention from academia and industry specialists by integrating with different wearable and portable electronics. With the development of low-temperature solution preparation technology and the application of different engineering strategies, the power conversion efficiency of f-PSCs has approached 24%. Due to the inherent properties and application scenarios of f-PSCs, the study of strain in these devices is recognized as one of the key factors in obtaining ideal devices and promoting commercialization. The strains mainly from the change of bond and lattice volume can promote phase transformation, induce decomposition of perovskite film, decrease mechanical stability, etc. However, the effect of strain on the performance of f-PSCs has not been systematically summarized yet. Herein, the sources of strain, evaluation methods, impacts on f-PSCs, and the engineering strategies to modulate strain are summarized. Furthermore, the problems and future challenges in this regard are raised, and solutions and outlooks are offered. This review is dedicated to summarizing and enhancing the research into the strain of f-PSCs to provide some new insights that can further improve the optoelectronic performance and stability of flexible devices.

Self-encapsulated wearable perovskite photovoltaics via lamination process and its biomedical application

Flexible perovskite solar cells (PSCs) are highly promising photovoltaic technologies due to the prospect of integration with wearable devices. However, conventional encapsulation strategies for flexible devices often cause secondary damage to the perovskite crystals, which affects device performance. Here, we present self-encapsulated flexible PSCs realized by lamination technology. The conversion of perovskite crystals is achieved by the diffusion of lead iodide and ammonium halide under the effect of temperature and pressure. In addition, the hydrogen bonding of the introduced polyacrylamide enhances the connections of the integral device while improving the crystal quality. The self-encapsulated flexible PSCs achieve an outstanding photovoltaic conversion efficiency of 22.33%, and comprehensive stability tests are conducted based on wearable device application scenarios to verify the feasibility. Finally, 25 cm² wearable perovskite modules are successfully applied into the neuro-assisted wearable devices.

Adjusted Bulk and Interfacial Properties in Highly Stable Semitransparent Perovskite Solar Cells Fabricated by Thermocompression Bonding between Perovskite Layers

In order to shield perovskite solar cells (PSCs) from extrinsic degradation factors and ensure long-term stability, effective encapsulation technology is indispensable. Here, a facile process is developed to create a glass-glass encapsulated semitransparent PSC using thermocompression bonding. From quantifying the interfacial adhesion energy and considering the power conversion efficiency of devices, it is confirmed that bonding between perovskite layers formed on a hole transport layer (HTL)/indium-doped tin oxide (ITO) glass and an electron transport layer (ETL)/ITO glass can offer an excellent lamination method. The PSCs fabricated through this process have only buried interfaces between the perovskite layer and both charge transport layers as the perovskite surface is transformed into bulk. The thermocompression process leads the perovskite to have larger grains and smoother, denser interfaces, thereby not only reducing defect and trap density but also suppressing ion migration and phase segregation under illumination. In addition, the laminated perovskite demonstrates enhanced stability against water. The self-encapsulated semitransparent PSCs with a wide-band-gap perovskite (Eg ∼ 1.67 eV) demonstrate a power conversion efficiency of 17.24% and maintain long-term stability with PCE > ∼90% in the 85 °C shelf test for over 3000 h and with PCE > ∼95% under AM 1.5 G, 1-sun illumination in an ambient atmosphere for over 600 h.

Encapsulation and Stability Testing of Perovskite Solar Cells for Real Life Applications

With the progress in the development of perovskite solar cells, increased efforts have been devoted to enhancing their stability. With more devices being able to survive harsher stability testing conditions, such as damp heat or outdoor testing, there is increased interest in encapsulation techniques suitable for this type of tests, since both device architecture compatible with increased stability and effective encapsulation are necessary for those testing conditions. A variety of encapsulation techniques and materials have been reported to date for devices with different architectures and tested under different conditions. In this Perspective, we will discuss important factors affecting the encapsulation effectiveness and focus on the devices, which have been subjected to outdoor testing or damp heat testing. In addition to encapsulation requirements for these testing conditions, we will also discuss device requirements. Finally, we discuss possible methods for accelerating the testing of encapsulation and device stability and discuss the future outlook and important issues, which need to be addressed for further advancement of the stability of perovskite solar cells.