Rational ligand pair with short and long ligands for stable and efficient LEDs

Abstract

In this study, the ratio control over Pb to DDA was conducted to tune the band structure of PNCs. The post-synthetic surface treatment with Pb-DDA was enhanced PLQY from 46% to near unity. Based on the ratio control, highest occupied molecular orbital (HOMO) became shallow with increasing DDA ratio. Further, the charge injection of PNCs with different ratio was measured in hole only devices. The charge injection was best at Pb-DDA2, implying trade-off between energy level and ligand density in charge injection ability. Consequently, the ratio control over Pb to DDA was resulted in highly efficient LEDs, optimizing charge injection. To further enhance the stability of PNCs, additional NiBr2 was treated in PNCs, called Ni-DDA. There was no significant different in PLQY. Finally, LED devices were fabricated to compared Pb-DDA and Ni-DDA. Even if the device efficiencies were similar with each other, the device stability of Ni-DDA was enhanced compared to Pb-DDA.