Surface ligand engineering of pure-red perovskite nanocrystals with enhanced stability by diphenylammonium halide molecules†

Abstract

Perovskite nanocrystals (NCs) exhibit remarkable potential for light-emitting applications due to their solution processability, high photoluminescence quantum yield (PLQY), and tunable bandgaps. However, surface defects on NCs and the insulating nature of the surrounding long-chain ligands often impede the performance of the resulting perovskite light-emitting diodes (PeLEDs). Innovative strategies to address these challenges are crucial for advancing the environmental stability of perovskite NCs and high-efficiency PeLEDs. In this study, red light-emitting CsPbBr_xI_3−x NCs were synthesized via the hot-injection method, employing diphenylammonium iodide (DPAI) and diphenylammonium bromide (DPABr) as surface passivating ligands. These ligands not only compensated for surface defects of NCs through released I⁻ and Br⁻ anions but also improved charge carrier injection by π-conjugated benzene rings. Consequently, the PLQY was improved from 55% of the pristine NCs to 80% and 78% for those passivated with DPAI and DPABr ligands, respectively. The environmental stability and thermal stability of perovskite NCs were also enhanced under ambient conditions. The optimized red PeLED with the DPAI-modified perovskite NCs showed 2.8-fold higher luminance and 3.5-fold higher current efficiency than the control device. Similarly, the device based on the DPABr-modified NCs also exhibited significant improvements, showcasing the potential of surface ligand engineering with diphenylammonium halides in advancing PeLED performance.