Encapsulation of perovskite solar cells for enhanced stability: Structures, materials and characterization

Perovskite solar cells (PSCs) have rapidly reached a certified efficiency of 25.5% within a decade. However, the relatively poor long-term device stability, representing one of the urgent obstacles for PSCs on the path of commercialization, has been widely criticized. On this account, the encapsulation technique is employed to improve the stability of PSCs operating under the ambient conditions. Due to the unique properties of PSCs, especially the organic-inorganic hybrid nature of perovskite absorbers, the encapsulation method learned from the mature commercial photovoltaics is required to be further modified. Herein, we thoroughly introduce the commonly applied optimizing architecture, materials, and manufacturing process for PSCs encapsulation. Significant improvements in the stability are demonstrated, and the corresponding sealing effects under various aging conditions are evaluated. The standard test procedures for PSCs, which should be commonly recognized by the community to directly compare results from different labs around the world without barriers, are also summarized and highlighted. In addition, the characterizations analyzing the failure model, including films and devices, are discussed. Finally, this review concludes with suggestions on how to accelerate the exploration of suitable encapsulation structures and materials, which may shed the light on the future commercialization of PSCs with solved stability issues.