Molecular engineering with CuanCl for effective optimization of a defective interface for wide-bandgap perovskite solar cells

In wide-bandgap (WBG) perovskite solar cells (PSCs), the energy level misalignment between the hole transport layer (HTL) and the perovskite layer, coupled with the high-density defects at their buried interface, causes severe non-radiative recombination within PSCs. Herein, CuanCl (carbamoyl-guanidine amidino urea salt, hydrochloride salt) with multifunctional molecular groups is introduced to optimize the WBG perovskite/HTL interface. This strategic introduction aims to suppress non-radiative recombination, consequently mitigating open-circuit voltage loss (Vloss). The findings demonstrate the bifunctional chemical passivation effect of the carbonyl (C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 O) and imine cations (NH+-) within CuanCl molecules on surface defects of perovskite, effectively suppressing diverse defect-assisted non-radiative recombination. Furthermore, the surface-bound CuanCl on the perovskite provides supplementary electronic states at the valence band maximum, achieving a more harmonized energy level alignment and effectively inhibiting charge recombination at the interface. The resultant CuanCl-treated WBG PSCs produce a high open-circuit voltage of 1.27 V, and a decent fill factor of 77.28%, which leads to a power conversion efficiency of 19.36%. Furthermore, the devices exhibit superior stability, maintaining 84% of their initial efficiency after 1000 hours in air with a humidity of 40%. This work provides new insight for optimizing a defective interface with the molecular engineering approach for fabricating efficient and stable WBG PSCs. Molecular engineering with CuanCl forms a coordination bond with under-coordinated Pb2+ and an ionic bond with negatively charged defects, resulting in effcient defect reduction for stable wide-bandgap perovskite solar cells.