Ligand-modified FAPbI3 perovskite quantum dots for efficient near-infrared light-emitting diodes

Perovskite quantum dots (PQDs) have shown great promise for light-emitting diode, benefiting from high defect tolerance, facile bandgap tunability, narrow emission spectra and high photoluminescence quantum yield (PLQY). However, the inherent structural instability remains a key challenge for impeding their commercial application, which is closely associated with the intrinsically ionic and dynamic surface of PQDs. What’s more, in contrast with green-emissive PQDs, it’s more difficult to obtain bright near-infrared PL from PQDs. Among the narrow bandgap PQDs, FAPbI₃ PQDs show higher robustness than the Cs- and MA-only based PQDs with similar sizes, but the issues of structural stability, charge transfer and optical properties still need to be solved. Thus, we analyzed to adopt the non-conjugated organic radical polymers, poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) and the X-type ligand, 1,3-bisbenzyl-2- oxoimidazolidine-4,5-dicarboxylic acid (cycle acid, CA) to replace the oleylamine and oleate for surface treatment. We adopted this treatment on CsPbI₃ QDs and successfully enhanced the optoelectronic properties of QDs. The successfully implement of ligand exchange mainly depend on the strong coordination effect between PTEO or CA and Pb²⁺. Taking advantage of the high affinity and well-matched energy level between PTEO and PQDs can effectively achieve a stable PQDs system with excellent charge transfer characteristics. Furthermore, the etching effect and passivation of CA could effectively homogenize the morphology and sizes, improve the stability and PLQY of PQDs which result from the decrease of the surface defects. Ligand-modified FAPbI₃ PQDs were finally used in the near-infrared light-emitting diodes to solve the problem of film forming properties of PQDs. The performance of the devices based on the ligand-modified FAPbI₃ PQDs could be enhanced.