Fundamental understanding in the performance-limiting factors of Cs₂AgBiBr₆-based perovskite photovoltaics

The Lead-free all-inorganic double perovskite Cs₂AgBiBr₆ is regarded as an attractive alternative to lead-based organic-inorganic counterparts in perovskite solar cells (PSCs) because of the superb durability, nontoxicity and distinct optical properties. Nevertheless, the power conversion efficiencies (PCEs) of Cs₂AgBiBr₆-based cells are significantly limited by both inherent and external defects in Cs₂AgBiBr₆ films caused by structural/optical features and fabrication processes, respectively. Thus, it is necessary to conduct a review to enhance fundamental knowledge regarding the decisive performance-limiting factors and relevant performance improvement strategies of Cs₂AgBiBr₆-based PSCs. Herein, fundamental knowledge of the decisive performance-limiting factors and relevant origins of Cs₂AgBiBr₆-based PSCs is presented, including inferior sunlight absorption capability, inferior film quality, high defect amount and unsuitable energy level alignment. On this basis, some distinct strategies to improve the PCEs of Cs₂AgBiBr₆-based cells are proposed such as dye sensitization, band gap regulation, interface control, additive engineering and (anti-)solvent design. Finally, the remaining key problems and future research directions of Cs₂AgBiBr₆-based PSCs are provided. Our review aims to present important guidance for future research on Cs₂AgBiBr₆-based PSCs to break the efficiency record.