Tailoring Energy Level and Conductivity of Perovskite Nanocrystal to Promote Hole Injection for High Performance Red‐Light Emitting Diodes

ABSTRACT Benefiting from the rapid advancement in the optoelectronic properties of PeNCs, the external quantum efficiencies (EQEs) of all primary three colors have exceeding 20% in recent years. However, imbalanced carrier injection and transport dynamics remain a critical challenge, which leads to poor carrier recombination rate within the emissive layer (EML). In this work, we report a surface‐engineering strategy using oleylammonium iodide (OLA‐I) to tailor the energy levels and electrical conductivity of PeNCs. The I − ions from OLA‐I passivate iodine vacancies on the PeNC surface, resulting in: (i) modified orbital coupling between Pb and halogen atoms, and (ii) elimination of shallow donor levels near the conduction band. These effects collectively cause an upward shift in the energy levels of the PeNCs and facilitate a transition from strong to weak n‐type character. The adjusted energy alignment and enhanced hole conductivity collectively reduce the hole injection barrier and promote more balanced injection and transport of both holes and electrons within the EML of the PeLEDs. As a result, the device performance was significantly improved, with the EQE rising from 10.19% to 20.62%. This surface ligand engineering approach establishes a new paradigm for controlling carrier dynamics in PeLEDs and offers a viable route toward high‐performance perovskite optoelectronics.