Bidentate Lewis Base\nLigand-Mediated Surface Stabilization\nand Modulation of the Electronic Structure of CsPbBr<sub>3</sub> Perovskite\nNanocrystals

The desorption of conventional ligands from the surface\nof halide\nperovskite nanocrystals (NCs) often causes their structural instability\nand deterioration of the optoelectronic properties. To address this\nchallenge, we present an approach of using a bidentate Lewis base\nligand, namely, 1,4-bis(diphenylphosphino)butane (DBPP), for the synthesis\nof CsPbBr<sub>3</sub> NCs. The phosphine group of DBPP has a strong\ninteraction with the PbBr<sub>2</sub> precursor, forming a highly\ncrystalline intermediate complex during the reaction. In the presence\nof oleic acid, the uncoordinated phosphine group of DBPP is converted\ninto the phosphonium cation, which strongly binds to the surface bromide\nof the formed CsPbBr<sub>3</sub> NCs through hydrogen bonding. Density\nfunctional theory calculations suggest that DBPP can strongly bind\nto the undercoordinated lead and surface bromide ions of CsPbBr<sub>3</sub> NCs through its unprotonated and protonated phosphine groups,\nrespectively. The robust binding of DBPP to the surface of perovskite\nNCs helps to preserve their structural integrity under various environmental\nstresses. Moreover, the electron density and energy levels are regulated\nin DBPP-capped CsPbBr<sub>3</sub> NCs by the donation of electrons\nfrom the ligands to the NCs, resulting in their improved photocatalytic\nCO<sub>2</sub> reduction performance. Our study highlights the potential\nof using bidentate ligands to stabilize the surface of perovskite\nNCs and modulate their optical and electronic properties.