Defect and stress co-management via bifunctional molecular engineering for high-efficiency and stable CsPbI ₃ perovskite solar cells

Abstract Inorganic cesium lead iodide (CsPbI 3 ) perovskites are promising photovoltaic materials owing to their excellent thermal stability and optoelectronic properties. However, CsPbI 3 film fabricated via solution processing typically suffers from high defect densities and detrimental residual tensile stress due to uncontrolled crystallization and thermal expansion mismatch with the substrate, which impedes its practical application. Herein, we introduce ammonium benzenesulfonate (ABS) as a bifunctional additive to modulate crystallization, thereby passivating defects and regulating residual stress. The sulfonate group of ABS coordinates with undercoordinated Pb 2+ ions, while its ammonium group forms hydrogen bonds with iodide ions. The molecular structure of ABS bridges adjacent [PbI 6 ] 4− octahedra at grain boundaries. This dual interaction effectively enhanced crystallinity, suppressed non-radiative recombination, and improved structural stability. As a result, ABS-modified CsPbI 3 -based perovskite solar cells achieve an impressive power conversion efficiency (PCE) of 21.21% under standard illumination. Remarkably, they deliver a PCE of 40.85% under indoor lighting conditions. Moreover, unencapsulated devices retains 91% of their initial PCE after 800 h of storage in ambient air at a relative humidity of 5%.