Suppressing ion migration of mixed-halide perovskite quantum dots for high efficiency pure-red light-emitting diodes

Perovskite-based light-emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the "pure red" emission, i.e., in the 620-650 nm range, required for high-definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI${}_{3-x}$Br${}_x$ quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI${}_3$ QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1-dodecanethiol (1-DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure-red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m${}^{-2}$, and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half-life of 70 min at an initial luminance of 150 cd m${}^{-2}$. (© 2023 Wiley-VCH GmbH)