Surface Passivation with Selected Phosphine Oxide Molecules for Efficient Pure‐Blue Mixed‐Halide Perovskite Quantum Dot Light‐Emitting Diodes

Abstract Passivation of defects in halide perovskite using phosphine oxide or alkyl‐phosphonate has recently obtained a few remarkable achievements. However, effective application of phosphine oxide or alky‐phosphonate in passivating perovskite quantum dots (QDs) are seldom reported due to solubility issue or difficulty of amount control. In this work, two bifunctional organic molecules containing phosphine oxide groups, 2,4,6‐Tris[3‐(diphenylphosphinyl)phenyl]‐1,3,5‐triazine (PO‐T2T) and 2,7‐bis(diphenylphosphoryl)‐9,9′‐spirobifluorene (SPPO13), are deposited on QDs films by thermal evaporation. The molecules, both as passivation agents as well as electron transporting materials, exhibit stark contrast in passivating QDs and in light‐emitting diodes (LEDs) performance. A competition between charge transfer and defect passivation between the QDs and the molecules is proposed. In film, electron transfer from the QDs to PO‐T2T dominates and quench the QDs, while the passivation effect of PO‐T2T on the QDs dominates in driving device and enhances luminance of the LEDs. In contrast, passivation effect of SPPO13 on the QDs dominates both in films and in LEDs. A maximum EQE of 2.67% is obtained for the pure‐blue LED based on SPPO13‐passivated QDs films. This work provides a guide on the selection of passivation agents based on phosphine oxide and a promising passivation method for high‐efficient perovskite QD LEDs.