Conjugated amidine ligands enhance the performance of perovskite nanocrystal blue light-emitting diodes prepared in air with green solvents

Metal halide perovskite nanocrystals (NCs) are attracting increasing attention due to their potential in fabricating high-performance perovskite light-emitting diodes (PeLEDs). Compared to those of green and red PeLEDs, the performance of blue PeLEDs lags far behind, which seriously hinders the application of perovskite NCs in full-color lighting and display applications. Among the various strategies to improve the performance of blue PeLEDs based on perovskite NCs, surface ligand engineering shows great potential. Herein, amidine ligands, including acetamidine hydrochloride (AMCl), pentanimidamide hydrochloride (PMCl) and benzamidine hydrochloride (BMCl), are introduced into room-temperature synthesized CsPbBrxCl3−x NCs in air using green solvents, which are found to reduce both Cs+ and halide vacancies on the NC surface and suppress nonradiative recombination. The π-conjugated amidine BMCl can also improve the charge transport of perovskite NCs, leading to spectrally stable blue PeLEDs with a dramatically reduced turn-on voltage from 4.4 to 3.0 V, and an enhanced EQE of 2.30% and a luminance of 205 cd m−2 at 479 nm.