Challenges and modification strategies of air-processed all-inorganic CsPbX3 perovskite films for efficient photovoltaics

All-inorganic perovskites CsPbX3 (X: halogen ions) have gained significant attention for application in next generation photovoltaic technologies due to their superior thermal stability and excellent optoelectronic properties. Compared with fabrication in N2 glove boxes, ambient air processing could simplify the operation and reduce the fabrication cost, which is favorable for boosting the commercialization of perovskite solar cells (PSCs). However, the moisture in ambient air tends to cause the phase transformation of inorganic perovskite from the photoactive black phase to the photo-inactive yellow one, thus deteriorating the photovoltaic performance. Considering the obstacles from both the intrinsic structure instability and the external atmosphere, tremendous efforts have been made for pursuing high-efficiency and stable all-inorganic PSCs that can be processed in ambient air. In this review, we first analyze the challenges for fabricating CsPbX3 in ambient air from both the intrinsic characters and external atmosphere and then overview the progress of the air-fabricated CsPbX3 films for photovoltaic applications. The recently reported various modification strategies, including the compositional/precursor, solvent, additive, and interface engineering, for achieving high-quality and stable CsPbX3 films are comprehensively summarized. Finally, a brief conclusion and outlook is given to inspire more research interest on air-fabricated CsPbX3 photovoltaics. This review provides significant guidance for further optimizing the air-processible CsPbX3 films to boost the large-scale commercialization of cost-effective PSCs in the future.