Hard-Soft-Acid-Base Management Enabled Bright and Stable Pure-Blue Perovskite Quantum Dot LEDs

Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs) have achieved external quantum efficiencies (EQEs) exceeding 20% at a practical luminance (>1000 cd m^-2) for real-world applications in the green and red regions. However, the pure-blue perovskite QD LEDs still suffer from low efficiency at high luminance: the EQE of the reported best device at 600 cd m^-2 is below 7.0%. One of the limiting factors is weak ligand-surface binding because of the dynamic ligand-binding nature. In this work, we employ first-principles calculations to evaluate the hard-soft-acid-base interaction strength and search for the appropriate alkali metal ions to resolve this limiting factor. We found that rubidium ions have the most compatible softness with bromine dangling bonds in the strongly confined QDs, leading to stronger bonding. This strategy enabled the photoluminescence quantum yield of the QD film to be 81%. The low-defect QD films ensured efficient carrier recombination, enabling pure-blue perovskite QD LEDs to generate an EQE peak of 15.7% with a luminance of 3916 cd m^-2, and the EQE remains at 14.9% under a higher luminance of 5371 cd m^-2. This represents an achieved record EQE × luminance: a 35-fold improvement compared to the best previous pure-blue perovskite LED.