LAUSR

Direct synthesis of APbX3 [A = Cs+, methylammonium (MA+) or formamidinium (FA+) and X = Cl-, Br- or I-] perovskite nanocrystals (NCs) following a generic approach is a challenging task even today. Motivated by our recent success in obtaining directly high-quality red/NIR-emitting APbI3 NCs employing 1,3-diiodo-5,5-dimethylhydantoin (DIDMH) as an iodide precursor, we explore here whether violet/green-emitting APbCl3 and APbBr3 NCs can also be obtained using the chloro- and bromo-analog of DIDMH keeping in mind that a positive outcome will provide the generic protocol for direct synthesis of all APbX3 NCs using similar halide precursors. It is shown that green-emitting APbBr3 NCs with near-unity PLQY and violet-emitting CsPbCl3 NCs with an impressive PLQY of ∼70%, mixed-halide NCs, CsPb(Cl/Br)3 and CsPb(Br/I)3, emitting in the blue and yellow-orange region with PLQYs of 87-95% and 68-98%, respectively can indeed be obtained employing the bromo- and chloro-analog of DIDMH. These NCs exhibit remarkable stability under different conditions including the polar environment. Femtosecond pump-probe studies show no ultrafast carrier trapping in these systems. The key elements of the halide precursors that facilitated the synthesis and the factors contributing to the excellent characteristics of the NCs are determined by careful analysis of the data. The results are of great significance because a direct method of obtaining highly luminescent and stable APbX3 NCs (except violet-emitting hybrid NCs) is eventually identified and the work provides valuable insight into the selection of appropriate halide precursors for the development of superior systems.