Interfacial engineering strategy based on polymer modification to regulate the residual stress in CsPbI2Br based perovskite solar cells

All-inorganic perovskite solar cells have been developed rapidly in the field of photovoltaics due to their excellent photothermal stability. Whereas, the phase stability issues of the inorganic perovskite, caused by the significant residual stress in the film, severely limits the practical applications of inorganic perovskite solar cells (PSCs). Herein, we propose the utilization of organic polymer J71 with N- and S-atoms to release the internal stress in the CsPbI2Br film. It is uncovered that the coordination between J71 and perovskite could effectively regulate the strain from tensile- to compressive-type, among which the strain-free film could be realized at an optimal J71 concentration. Moreover, we revealed that the covalent bond between J71 and perovskite could induce the secondary crystal growth of CsPbI2Br during thermal annealing, which leads to refined film morphology in terms of larger and compact perovskite grains. Additionally, J71 molecule with strong hydrophobicity serves as a barrier to block the moisture evasion, which prevents the lattice distortion of [PbI6]4− triggered by water molecules. Owing to the synergistic effects of J71 treatment, the CsPbI2Br based PSCs achieved an excellent PCE of 16.15%, with outstanding stability by retaining over 80% of the initial PCEs under both N2 and humid environment.