Challenges and strategies relating to device function layers and their integration toward high-performance inorganic perovskite solar cells

Parallel to the flourishing of inorganic-organic hybrid perovskite solar cells (PSCs), the development of inorganic cesium-based metal halide PSCs (CsPbX3) is accelerating, with power conversion efficiency (PCE) values of over 20% being obtained. Although CsPbX3 possesses numerous merits, such as superior thermal stability and great potential for use in tandem solar cells, severe challenges remain, such as its phase instability, trap state density, and absorption range limitations, hindering further performance improvements and commercialization. This review summarizes challenges and strategies relating to each device functional layer and their integration for the purposes of performance improvement and commercialization, utilizing the fundamental configuration of a perovskite photo-absorption layer, electron transport layer (ETL), and hole transport layer (HTL ). In detail, we first analyze comprehensively strategies for designing high-quality CsPbX3 perovskite films, including precursor engineering, element doping, and post-treatment, followed by discussing the precise control of the CsPbX3 film fabrication process. Then, we introduce and analyze the carrier dynamics and interfacial modifications of inorganic ETLs, such as TiO2, SnO2, ZnO, and other typical organic ETLs with p-i-n configuration. The pros and cons of inorganic and organic HTLs are then discussed from the viewpoints of stability and band structure. Subsequently, promising candidates,i.e., HTL-free carbon-electrode-based inorganic CsPbX3 PSCs, that meet the "golden triangle" criteria used by the PSC community are reviewed, followed by discussion of other obstacles, such as hysteresis and large-scale fabrication, that lie on the road toward PSC commercialization. Finally, some perspectives relating to solutions to development bottlenecks are proposed, with the attempt to gain insight into CsPbX3 PSCs and inspire future research prospects.