Tailoring the refractive index and surface defects of CsPbBr3 quantum dots via alkyl cation-engineering for efficient perovskite light-emitting diodes

All inorganic CsPbBr3 perovskite quantum dots (PeQDs) have emerged as great candidates for next-generation perovskite quantum dots light-emitting diodes (PeQLEDs) applications due to their excellent optoelectronic and light-emitting properties. However, the performance of CsPbBr3 based PeQLEDs is hindered by (i) the long-chain, synthetic insulating ligands on PeQDs surfaces and (ii) the inherently high refractive index (n) of the PeQDs that often leads to internal light confinement loss. These major shortcomings are addressed by introducing a short-chain ammonium moiety, namely phenethylammonium bromide (PEABr), via spin-coating to passivate the surface of the PeQDs films. PEABr passivation can effectively annihilate the intrinsic bromide vacancies of PeQDs and simultaneously tune the refractive index of the PeQDs films. The reduced n-mismatch between the emitter and the charge transporting layers suppresses the waveguide loss after PEABr passivation and significantly elevates the external quantum efficiency (EQE) and maximum luminance of the PeQLEDs from ~ 1.0% to ~ 6.85% and ~ 1300 cd m−2 to ~ 13000 cd m−2, respectively. More importantly, the environmental stability of the PeQDs also improves remarkably following PEABr passivation. The alky cation engineering demonstrated herein is a facile yet efficient approach to simultaneously boost the performance and stability of CsPbBr3 PeQDs.