Fully Non-conjugated Phosphorylated Chitosan Enhances Hole Injection for Efficient Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) show great promise for next-generation displays, offering high efficiency and excellent color purity. However, imbalanced charge injection limits performance due to the energy barrier between the indium tin oxide (ITO) anode and the perovskite layer. To address this, a fully non-conjugated phosphorylated chitosan (NCPC), derived from biomass polymers, is introduced as an efficient hole injection layer (HIL) in PeLEDs for the first time. This material enhances interface interactions with both ITO and hole-transport layer (HTL), significantly improving device performance. The incorporation of NCPC as a HIL aligns energy levels favorably between ITO and the HOMO of poly(9-vinylcarbazole) (PVK), reducing both hole injection barriers and non-radiative charge recombination at the interface. Red, green, and blue PeLEDs utilizing NCPC as a HIL achieved maximum external quantum efficiency (EQEmax) values of 25.35% (670 nm), 25.45% (512 nm), and 14.22% (489 nm), representing relative enhancements of 55.05%, 61.59%, and 58.53% compared to PEDOT-based devices. Notably, the EQEmax of 25.35% for red PeLEDs at 670 nm is among the highest two reported values to date. Furthermore, NCPC-based PeLEDs exhibited reduced turn-on voltages due to facilitated hole injection. These findings pave new paths for designing high-efficiency HIL materials for PeLEDs while promoting environmentally friendly natural products.