Realization of high efficiency pure red CsPbI3 quantum dot light emitting diodes by polarity screening

Perovskite quantum dots (QDs) are considered ideal materials for the next generation of light-emitting diodes (LEDs) due to their high color purity and tunable emission. The surface characteristics of QDs, especially the small-sized pure red QDs, significantly impact their optoelectronic performance, with surface defects remaining a major obstacle to achieving high-performance LEDs. Among the QDs synthesized by thermal injection, there are some QDs with poor ligand coverage and low crystallinity, and it is difficult for traditional post-treatment methods to effectively passivate these QDs. Here, we propose a new post-processing strategy using a mixed solution of isopropanol and methyl acetate to dissolve NH 4 I to selectively screen small-sized QDs. This post-processing strategy can remove the low crystallinity QDs with poor ligand coverage and effectively passivate the remaining QDs in a halogen-rich environment. As a result of screening out lower-quality QDs, the overall performance of the QDs has been optimized, with the PLQY increasing from 79 % to 95 % and the lifetime improving from 12.7 ns to 13.7 ns. The EQE of devices based on the optimized QDs is 27.15 %, higher than the 19.46 % of the control devices.