Multifunctional ligand-manipulated luminescence and electric transport of CsPbI3 perovskite nanocrystals for red light-emitting diodes

Perovskite nanocrystal (NC) light-emitting diodes (LEDs) are promising for high-quality displays due to their excellent optoelectronic properties, but the highly labile surface and insulating long-chain capping ligands of NCs are the main constraint for improving device performance. Herein we developed a facile post-treatment for CsPbI3 NCs with 2-thiophenethylamine chloride (TEAC) to eliminate trap states and replace the native ligands on NCs, enabling manipulation of their luminescence and electrical properties. Hence, the modified CsPbI3 NCs exhibit a high photoluminescence quantum yield of 92.5 % even after the purification processes due to the comprehensive defect suppression of TEAC ligands originating from the synergistic effect of halogen compensation and coordination of S atom in the thiophene ring with Pb2+. Moreover, with the assistance of the highly conductive TEAC ligands, CsPbI3 NC films show significant improvement in carrier transport properties. Based on the elaborate surface reconstruction of CsPbI3 NCs, we achieve an external quantum efficiency of 17.3 % with a high operational lifetime of 9.8 h at an initial luminance of 100 cd m−2 for red perovskite LEDs (PeLEDs), which is a more than 2-fold improvement compared to the control NC-based device. We demonstrate that this high performance of the fabricated PeLEDs is attributed to the resurfacing chemistry of CsPbI3 NCs by the thiophene-based ligand passivation, simultaneously enabling the trap-defect elimination and efficient charge transport in the CsPbI3 NC film.