Lowing surface steric hindrance of strongly-confined perovskite quantum dots enables efficient pure-red light-emitting diodes

Based on strongly quantum confinement, reducing size of single-halide perovskite CsPbI3 quantum dot (QD) can achieve high purity red emission that meets requirement of Rec. 2020 standard. However, the strongly-confined QDs (SQDs) are difficult to achieve efficient light-emitting diodes (LEDs), due to that purification process for the device fabrication results in the surface ligands detachment, inducing incomplete coordination of Pb2+ to increase trap density and decrease stability. In this study, we develop a synthesis strategy of pure-red CsPbI3 SQDs with utilizing novel I− source of octylammonium iodide (OTAI) for rich halogen ions environment. Importantly, the OTAI replaced the high steric hindrance original ligands to form low steric hindrance (LSH-SQDs). The LSH-SQDs were resistant to purification process and maintained photoluminescence quantum yield (PLQY), which is vital for the fabrication of electroluminescence (EL) devices. This is attributed to that the low steric hindrance ligands with a smaller "force-receiving area" are less likely to desorb from the surface of SQDs during purification. As a result, the LEDs based on the LSH-SQD presented high external quantum efficiency (EQE) of 18.3 %, maximum brightness of 3552 cd/m2, and pure-red emission at 639 nm that is accord with Rec.2020 requirement.