Energy-level modification of perovskite nanocrystals by dipole ligand treatment for green light-emitting diodes

Abstract

Perovskite nanocrystals (NCs) have high photoluminescence quantum yields (PLQYs) and defect tolerance. They are promising candidates for next-generation display materials. However, to realize high-efficiency light-emitting diode (LED) devices, the carrier transport layers should be carefully optimized for NCs with different energy levels. In this work, we functionalized the surface of perovskite NCs with dipole ligands to tailor their energy level positions, thus manipulating the carrier injection process in LED devices. We first identified that holes were minority carriers in our device structure, and then revealed the recombination region close to the PTAA/NCs interface by incorporating a luminescent indicator. To promote hole injection, we utilized the dipole moment of surface ligands to tailor the energy level of perovskite NCs. When treated with a series of dipole ligands, namely benzoic acid (BA), 4-(trifluoromethyl)benzoic acid (CF₃BA) and 4-dimethylaminobenzoic acid (DMABA), the energy levels of NCs could be shifted by up to 0.4 eV. In particular, the VBM of NCs treated with DMABA was reduced from 5.91 to 5.68 eV, which significantly lowered the hole injection barrier in the LED devices. Consequently, the LED exhibited significantly improved performance, with maximum luminance increasing from 31 145 to 64 383 cd m⁻², external quantum efficiency (EQE) increasing from 5.72 to 8.77%, and a 6.2-fold prolongation of T₅₀ lifetime from 2.24 to 13.9 h. This work demonstrates ligand-mediated energy level shifts as a means to predictably control the electronic properties of perovskite NCs for high-efficiency LED devices.