Controlled synthesis of brightly fluorescent CHNHPbBr perovskite nanocrystals employing Pb(CHCOO) as the sole lead source.

Organometal halide perovskite nanocrystals hold vast potential for application in photovoltaics, light emitting diodes, low-threshold lasers, and photodetectors due to their size-tunable bandgap energies and photoluminescence as well as excellent electron and hole mobilities. However, the synthesis of such nanocrystals typically suffers from poor structural stability in solution and the coexistence of lamellate nanocrystals (nanoplatelets) and spherical nanocrystals (nanoparticles). Here we show that the pure nanoparticle morphology of CHNHPbBr nanocrystals can be realized by employing lead oleate (Pb(CHCOO)) as the sole lead source and controlled using short- and long-chain mixed alkyl ammonium. These nanocrystals are monodispersed (2.2 ± 0.4 nm in diameter), highly fluorescent (with a quantum yield approaching 85%), and highly stable in the solution (for more than 30 days). Comparative studies reveal that the shape of CHNHPbBr nanocrystals is strongly dependent on the lead source, PbBr and Pb(CHCOO), and evolves as a function of the ratio of short- and long-chain alkyl ammoniums in the precursors. At an optimal short to long-chain alkyl ammonium ratio of 4 : 6, the growth of CHNHPbBr nanoplatelets can be selectively suppressed with Pb(CHCOO) as the sole lead source, enhancing the overall photoluminescence quantum yield of the produced CHNHPbBr nanocrystals. This work reveals important new insights for controlled synthesis of perovskite nanocrystals with pure crystal shape and significantly improved photoluminescence properties and stability.