查看文章

All-inorganic perovskite QDs (APQDs), such as CsPbX3 (X= Cl, Br, and I), exhibit superior thermal stability compared to their hybrid analogues. They have the potential to be integrated into various optoelectronic devices that can exploit quantum confinement effects. Kovalenko and co-workers fabricated CsPbX3 QDs with exceptionally tunable optical properties and high photoluminescence (PL) quantum yield, suggesting a major opportunity to employ this family of materials for LEDs.[20] Unfortunately, the highest EQE reported so far is 0.19%,[21] which is partly since the QDs are capped with relatively insulating long ligands that are required for the processing and stability of the QDs.[22, 23] Replacing these long ligands (usually oleylamine (OAm) and oleic acid (OA)) with shorter ligands without degrading or destabilizing the APQD films remains the key challenge preventing the fabrication of efficient LEDs from APQDs.

Here, we realize highly stable films of CsPbX3 QDs capped with a halide ion pair (eg, di-dodecyl dimethyl ammonium bromide (DDAB)), a relatively short ligand that facilitates carrier transport in the QD film and ultimately enables us to fabricate efficient PeLEDs. The synthesis of these films was only possible through the design of a ligand-exchange strategy that includes an intermediate step to desorb protonated OAm, which otherwise would result in the degradation of APQDs through a direct conventional ligand-exchange route. As a result of our novel ligand-exchange strategy, we were able to utilize halide-ion-pair-capped CsPbBr3 QDs in green PeLEDs with a device structure of indium tin oxide (ITO)/poly (ethylene …