Efficient and Stable CFPEAI-Passivated CsPbI QDs toward Red LEDs.

Oleylamine and oleic acid are common organic capping ligands used in the hot injection preparation of perovskite quantum dots (QDs). Their labile nature is responsible for the poor colloidal stability and conductivity that affect the performance of perovskite QD light-emitting diodes (LEDs). We introduced 4-trifluoro phenethylammonium iodide (CFPEAI) directly in the synthesis and found that CFPEAI efficiently modified the I vacancy defects on the QD surface and partially substituted the surface capping ligand oleylamine. The strong electron pulling ability of F in CFPEAI results in a more positive -NH terminal compared to that of PEAI, which promotes tight bonding of CFPEAI on the surface of CsPbI QDs. As a result, we achieved bright QDs with a photoluminescence quantum yield of 92% and efficient red LEDs. The maximal luminance was improved to 4550 cd m for 685 nm red light, which was nearly 4.6-fold of the LEDs with plain CsPbI QDs. Additionally, the peak external quantum efficiency reached 12.5%.