Recent progress in encapsulation strategies to enhance the stability of organometal halide perovskite solar cells

Organometal halide perovskite solar cells (PSCs) have emerged as promising candidates for next-generation thin-film solar cells. Over the past ten years, the efficiency of PSCs has increased from 3.8% to over 25% through the optimization of the perovskite film formulation and the engineering of suitable fabrication strategies and device architectures. However, the relatively poor long-term device stability, which has not been able to exceed some hundreds of hours until now, represents one of the key aspects still hampering their widespread diffusion to commercial contexts. After briefly introducing the origin and basic mechanisms behind PSC degradation and performance decline, a systematic outline and classification of the available strategies to improve the long-term stability of this class of photovoltaic devices will be presented, mainly focusing on encapsulation procedures. Indeed, the aim of this review is to offer an in-depth and updated account of the existing encapsulation methods for PSCs according to the present understanding of reliability issues. More specifically, an analysis of currently available encapsulation materials and on their role in limiting the penetration of UV light and external agents, such as water vapour and oxygen, will be proposed. In addition, a thorough discussion on various encapsulation techniques and configurations will be presented, highlighting specific strengths and limitations of the different approaches. Finally, possible routes for future research to enhance the effectiveness of the most performing encapsulation procedures will be suggested and new paths to be explored for further improvements in the field will be proposed.