“Sterilizing” the surface of inorganic CsPbI_2.75Br_0.25 perovskite by a bactericide molecule for high-performance carbon-based perovskite solar cells

The carbon-based CsPbI_XBr_3−X all-inorganic perovskite is emerging as one of the most promising photovoltaic materials for single-junction or tandem solar cells, owing to its low fabrication cost and tunable bandgap. Currently, organic passivants in common use usually bind to a single active site and tend to result in dense packing of passivants aligned perpendicular to the surface, which may introduce a transport barrier at the perovskite/carbon electrode interface. In this study, chlorothalonil (TPN), a “bactericide” with multiple reactive sites, was employed to “sterilize” the surface of CsPbI_2.75Br_0.25 perovskite. TPN, featuring two symmetrically arranged cyano groups and four chlorine atoms, can simultaneously anchor two uncoordinated Pb²⁺ ions through Lewis acid-base interactions while passivating halogen vacancy defects, thereby effectively suppressing non-radiative recombination. Theoretical calculations and experimental results reveal that multiple reactive sites enable TPN to adopt a planar arrangement on perovskite surfaces, forming ultrathin passivation layer that mitigates charge transport barriers. Concurrently, this planar configuration exposes benzene rings outward, which establishes gradient energy-level alignment, thereby enhancing hole extraction efficiency and improving perovskite hydrophobicity. As a result, the PCE of the HTL-free CsPbI_2.75Br_0.25 C-PSCs increased from 16.94 % for the control device to 18.23 % after TPN “sterilization”, with an impressive FF of 81.06 %.