Pathways toward high-performance inorganic perovskite solar cells: challenges and strategies

High-efficiency and low-cost perovskite solar cells (PSCs) are desirable candidates for addressing the scalability challenge of renewable solar energy. The dynamically evolving research field of cesium-based inorganic PSCs has achieved immense progress in the power conversion efficiency (PCE) of over 17% within just a few years. Compared with thermally vulnerable organic-inorganic perovskites, inorganic perovskites exhibit greater stability advantages for commercial applications. However, there are still a large number of issues and challenges for inorganic perovskites such as unstable phase structures, serious defect traps and limited absorption range, obstructing further development of inorganic PSCs. In this review, we present a unique outlook on the current progress of inorganic PSCs along with their structure-property-synthesis-performance traits. Importantly, we analyse comprehensively the challenges on the paths towards inorganic PSC commercialization, followed by highlighting the state-ofthe- art materials engineering strategies, including phase-structure and composition regulation, surfaceinterfacial modification, ion-doping engineering and lead-free perovskite material design. Combined with the in-depth analyses of advanced materials characterization technologies and theoretical calculations, we present detailed exciton/ charge-carrier dynamics and the physical mechanism of defects in inorganic PSCs. Finally, potential research directions to further improve the photovoltaic performance of inorganic PSCs are proposed, with an aim to gain insight into inorganic perovskites and their future research prospects.