Enhancing broadband blue luminescence efficiency and stability in Bi3+-doped Cs2ZnCl4 nanocrystals from STEs and advancing energy applications

Lead-halide perovskites exhibit excellent photovoltaic properties. However, lead's toxicity and limited stability under ambient conditions limit its further commercialization. This paper reports a Bi3+-doped lead-free metal halide, Cs2ZnCl4:Bi3+ nanocrystals (NCs). After doping with Bi3+, the pristine weakly luminescent nanocrystals showed highly efficient broadband blue emission with a peak position of 445 nm, a full width at half-maximum (FWHM) of 92 nm, and a significant increase in the photoluminescence quantum yield (PLQY) to 57.71%. The formation of a water-induced protective layer of BiOCl ensures good water stability. The luminescence mechanism of Cs2ZnCl4:Bi3+ NCs has been investigated by optical characterization and density-functional theory (DFT) calculations, and it has been concluded that the emission of triple-state self-trapped excitons (STEs) induced by Bi3+ doping is the source of broadband blue light emission. Combining nanocrystals as a luminescence down-shifting (LDS) layer with commercial GaAs solar cell devices has solved the problem of the solar cell's weak absorption of short waves, augmenting the photovoltaic conversion efficiency (PCE) by approximately 1%. Additionally, the integration of Cs2ZnCl4:Bi3+ NCs with 365 nm commercial LED chips enables the creation of broadband blue-emitting LED devices. Therefore, we believe that Cs2ZnCl4:Bi3+ NCs have great potential for future optoelectronic applications.