Small Molecule Approach to Passivate Undercoordinated Ions in Perovskite Light Emitting Diodes: Progress and Challenges

Perovskite light-emitting diodes (PeLEDs) hold promise for the development of next-generation display and light technologies; however, various problems related to factors such as external quantum efficiency (EQE), long-term stability, and dependence on toxic species hinder their successful debut in display and lighting markets. Research on PeLEDs involving the small-molecule approach—the incorporation of small organic molecules into or onto active perovskite layers in PeLEDs for mitigating the aforementioned issues—has burgeoned in the last eight years. This review covers recent advances and challenges in the small-molecule approach by i) surveying the chemical structures used in the small-molecule approach, ii) summarizing the methods of molecular insertion into PeLED devices, iii) comprehensively discussing the effects of small-molecule-based interfacial engineering and passivation of undercoordinated metal and halide ions on the photophysical functions of devices and their mechanisms, iv) emphasizing the small-molecule-induced enhanced performance of devices in the context of long-term stability and EQE, and v) providing perspectives and discussing challenges for future research.