Defect Passivation via a Bifunctional Guanidinium Sulfamate Ligand for High-Efficiency Perovskite Solar Cells

Achieving high crystallinity and low defect density remains a critical bottleneck for maximizing the power conversion efficiency (PCE) and operational stability of perovskite solar cells (PSCs). Herein, we introduce guanidinium sulfamate (GASM) as a bifunctional ligand to modulate the defect chemistry of perovskite films. DFT calculations reveal thermodynamically favorable binding of GASM to defect sites on selected α-FAPbI3 (100) surface models. Separately, the stronger (100) diffraction response observed by XRD is consistent with improved film crystallinity, although a change in out-of-plane texture cannot be excluded. Meanwhile, theoretical and spectroscopic results suggest Pb-O coordination involving the sulfamate moiety and N-H···I hydrogen bonding involving the guanidinium moiety, consistent with the observed defect-passivation effect. The GASM-treated perovskite films show a stronger (100) diffraction response, larger grains, and a longer photoluminescence lifetime. The resulting n-i-p structured PSCs deliver a champion PCE of 24.43%, alongside environmental stability. These results highlight the potential of GASM as an additive for improving perovskite film quality and suppressing defect-assisted nonradiative recombination, contributing to enhanced photovoltaic performance.