3D Lead-Organoselenide-Halide Perovskites and Their Mixed-Chalcogenide and -Halide Alloys

Following our previous report of organosulfide-halide perovskites (RS)PbX₂ (X = Cl, Br; RS = organosulfide ligand), we present the first examples of organoselenide-halide perovskites (RSe)PbX₂ (RSe = organoselenide ligand) using organoselenide zwitterionic ligands, occupying both the X and A sites in the prototypical ABX₃ perovskite lattice. We applied X-ray diffraction/scattering measurements to study the average structures of the organochalcogenide-halide perovskites, with disordered organic components and anion sites. Considering the heteroanionic nature of these materials, we collected solid-state ⁷⁷Se and ²⁰⁷Pb NMR to probe the local coordination environments at Pb centers and anion (X/Se) distributions, complemented by theoretical simulations. The experimental results support the fully disorder distribution of organochalcogenide in (L)PbX₂. The band structures calculated by density functional theory (DFT) of (SeCYS)PbX₂ closely resemble those of (CYS)PbX₂ with chalcogenide dominating the valence band maximum (VBM). Due to the higher energy of Se 4p orbitals compared to the S 3p orbitals, (SeCYS)PbX₂ exhibit considerable bandgap (<i>E</i>_g) decrease, with <i>E</i>_gs = 2.07 and 1.86 eV for X = Cl and Br, respectively. We further demonstrate different methods to alloy the halides (Cl/Br) and chalcogenides (S/Se) to obtain a continuous bandgap tuning. Overall, the expansion of this novel family of organochalcogenide-halide perovskites can provide new handles to tune the band structures of halide perovskites, and the comprehensive understanding of both average and local structures sets the foundation to further optimize the optoelectronic properties.