Anchoring Cs₄PbBr₆ Crystals to PbSe Nanocrystals for the Fabrication of UV/VIS/NIR Photodetectors Using Halide Surface Chemistry

Nanocrystal (NC)-in-matrix solids are currently attracting considerable research attention in the fields of materials science and engineering owing to their unique optoelectronic characteristics and high stability. However, the interaction between the NC surface and the matrix has been veiled and induces interface defect states that degrade the performance of photovoltaics. In this study, the effect of halide ligands on the formation of a Cs₄PbBr₆ (CPB) crystal matrix by determining the surfaces of PbSe NCs is investigated. The surface of the PbSe NCs is passivated with halide ions (Cl⁻, Br⁻, or I⁻), and the CPB crystal matrix is formed via PbBr₂/CsBr treatment onto the PbSe NCs. The effects of different halide ions on the nucleation/growth of the CPB matrix are examined by chemical, structural, and optical analyses. It is found that each halide ligand has a distinct effect not only on the anchoring of CPB but also on its carrier transport mechanisms. To characterize the electronic properties of the NC matrix, its carrier mobility, photoresponsivity, and stability are measured using field-effect transistors. Consequently, it is demonstrated that more densely passivated PbSe NCs form a higher-quality CPB matrix. Using a NC matrix, ultraviolet-/visible-/near-infrared-active flexible photodetectors are achieved.