Interfacial modification strategies to secure phase-stability for inorganic perovskite solar cells

The rapid success achieved from perovskite solar cell has drawn great expectations for commercialization of next-generation photovoltaics. Among the various perovskite materials, the inorganic perovskite derivatives have been of particular interest, ascribed to its superior thermal and chemical stability, which is a crucial criterion for reliable long-term operation. Nonetheless, the development of the efficient inorganic perovskite solar cells has been lagged from its organic-inorganic hybrid counterparts owing to the notorious phase-stability challenges associated with the formation of non-photoactive phases. The early progress of the inorganic perovskite solar cells has been centered on the stable perovskite phase-preparation and leads to the effective bulk management through intermediate engineering and compositional engineering strategies. Yet, challenges remain in securing the as-formed perovskite phase throughout the long-term operation. Accordingly, recent studies find interfacial modification strategies successful by constricting the phase-transformation channels in various perspectives such as defect propagation, strain, component segregation, charge accumulation, and external stresses. In this review, we start with the brief description on the inorganic perovskite solar cells and the associated advantages including chemical and optoelectronic properties. We then provide a review on the challenges of inorganic perovskite solar cells associated with the phase instabilities. We elaborate on the origins of the phase instabilities in terms of thermodynamics and the recently proposed channels including intrinsic factors and extrinsic factors that facilitate the detrimental phase transformation. Finally, we survey the recent successful approaches to stabilize the inorganic perovskite solar cells through interface managements and provide outlook on further progress.