Ammonium Thiocyanate-Passivated CsPbI3 Perovskite Nanocrystals for Efficient Red Light-Emitting Diodes

Lead halide perovskite nanocrystals (NCs) as a promising material have been widely applied in optoelectronic devices, but the massive defects reduces their optical properties and consequently limits the device performance. In this work, we developed a method to reduce the surface defects caused by unbonded lead on the surface of NCs by introducing ammonium thiocyanate (NH4SCN) in the synthesis of CsPbI3 NCs. The thiocyanate ions (SCN-) can link to the unbonded lead on the surface of perovskite NCs, resulting in a prolonged lifetime and enhanced photoluminescence quantum yield. At the same time, the whole energy level of passivated CsPbI3 NC films goes down compared to the pristine CsPbI3 NC films, which contributes to better electron injection. As a result, the passivated NCs based light-emitting diodes (LEDs) realized 10.3% external quantum efficiency (EQE) and 823 cd/m2 luminance, higher than the LEDs made from the non-passivated NCs.