Synthesis, Optical Properties,\nand Exciton Dynamics\nof Organolead Bromide Perovskite Nanocrystals

Abstract

Organolead\nbromide CH₃NH₃PbBr₃ perovskite nanocrystals\n(PNCs) with green photoluminescence (PL)\nhave been synthesized using two different aliphatic ammonium capping\nligands, octylammonium bromide (OABr) and octadecylammonium bromide\n(ODABr), resulting in PNC–OABr and PNC–ODABr, respectively.\nStructural studies by X-ray diffraction (XRD) and transmission electron\nmicroscopy (TEM) determined that the PNCs exhibit cubic phase crystal\nstructure with average particle size dependent on capping ligand (3.9\n± 1.0 nm for PNC–OABr and 6.5 ± 1.4 nm for PNC–ODABr).\nThe exciton dynamics of PNCs were investigated using femtosecond transient\nabsorption (TA) techniques and singular value decomposition global\nfitting (SVD-GF), which revealed nonradiative recombination on the\npicosecond time scale mediated by surface trap states for both types\nof PNCs. The PL lifetime of the PNCs was measured by time-resolved\nphotoluminescence (TRPL) spectroscopy and fit with integrated SVD-GF\nto determine the radiative as well as nonradiative lifetimes on the\nnanosecond time scale. Finally, a simple model is proposed to explain\nthe optical and dynamic properties of the PNCs with emphasis on major\nexciton relaxation or electron–hole recombination processes.\nThe results indicate that the use of capping ligand OABr resulted\nin PNCs with a high PL quantum yield (QY) of ∼20% (vs fluorescein,\n95%), which have interesting optical properties and are promising\nfor potential applications including photovoltaics, detectors, and\nlight-emitting diodes (LEDs).