Interfacial Coulomb-enhanced charge injection for efficient perovskite light-emitting diodes

Unbalanced electron-hole injection in perovskite light-emitting diodes (PeLEDs) has always been a major stumbling block limiting device performance. Here we develop a heterointerface Coulomb enhancement strategy to efficiently promote electron injection between perovskite emitter and transport layer and thereby balance the electron-hole recombination equilibrium through manipulating defect-rich positive-charge centers induced Coulomb interactions in LiF interlayer. Through multiscale polarization response characterizations combined with capacitance-voltage and electrochemical impedance spectroscopy, it is confirmed that diffusing holes trapped in LiF layer leads to the increased interfacial polarization. Moreover, the polarization response reversal and high-frequency-dependent dissipation sensitivity further corroborate the LiF-induced interfacial Coulomb enhancement mechanism. The universality of the concept is also successfully verified in devices with electron-only, hole-only, and PN structures. Consequently, the modified PeLEDs show a lower leakage current, along with a significant performance improvement by 1.9 times in external quantum efficiency (18.8%) and 5.7 times in luminance compared with control samples. This study provides a unique perspective to promote carrier transport balance by taking advantage of physical effects within interlayer.