Minimizing defect states through multidentate coordination and morphology regulation for enhancing the performance of inverted perovskite solar cells

The diversity of the defects present in perovskite materials negatively impacts both the power conversion efficiency (PCE) and the long-term stability of perovskite solar cells (PSCs). The chemical passivation of these defects has been addressed through a multifunctional molecule, 4-((trifluoromethyl)thio)benzoic acid, that contains the carbonyl (CO) group, which exhibits a strong passivation effect by interacting with both the organic cation (FA⁺) and uncoordinated Pb²⁺ ionic defects while the sulfur (S) heteroatom passivates Pb²⁺ defects at the grain boundary and on the surfaces of the perovskite layer. Additionally, the CF₃ group protects the perovskite film from ambient degradation as well as stabilizing the perovskite framework by forming hydrogen and coordination bonds with the FA⁺ cation and Pb²⁺ ions, respectively. The interaction between CO and Pb²⁺ forms a Lewis acid-base adduct that regulates grain growth during crystallization, enhancing the perovskite film's surface morphology as confirmed by SEM, AFM, and PL mapping. This reduces trap-assisted recombination of charged carriers, thereby enhancing their lifetime and transport, as observed from TRPL, KPFM, and c-AFM analyses. As a result of the combined effect of the additive molecule, the optimized device showed a marked improvement in efficiency rising from 16.54% in the pristine device to 20.87% with a reduction in hysteresis. Moreover, the optimized device shows enhancement of stability by retaining ∼86% normalized PCE after 40 days of storage under ambient conditions at 25 ± 3 °C and a relative humidity of ∼45-55%.