How far are we from attaining 10-year lifetime for metal halide perovskite solar cells?

Metal halide perovskite solar cells (PSCs) have attracted considerable attention from both academia and industry as a promising next-generation technology to harvest solar energy with high power conversion efficiencies (PCEs) at low-cost. At the current stage, efficiencies of these cells have been improved to an impressive level, but the instability issue remains as a major obstacle impeding further commercialization of this technology. In this review, we start with examining the status about the technological aspects of PSC stability research, e.g., stability measurement protocols, their relevance to the realistic operational lifetime, and where we are from the viewpoint of 10-year lifetime. These pressing challenges are correlated with the investigations on the fundamental aspects emphasizing the comprehensive physicochemical understanding of degradation mechanisms in perovskite materials. We examine the various extrinsic and intrinsic factors influencing stability of perovskite materials with different compositions (mixed cations and / or mixed anions, double perovskites, etc.), dimensionality (3D perovskites, 2D perovskites, 2D/3D mixed dimensional perovskites), instability induced by functional layers other than the perovskite layer, and the interactions at various interfaces. On the basis of the analyses of these multiple degradation factors with an emphasis on the holistic microscopic views acquired above, we discuss strategies to improve PSC stability. We finish the review by outlining future research directions that can help achieve long-term stability of PSCs.