Hydroxyethyl cellulose passivation for high-efficiency pure-red perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) have exhibited tremendous potential for commercial applications in the fields of displays, lighting, and information technology. For achieving pure red electroluminescence, quasi-two-dimensional (Q-2D) perovskite based on Br/I mixed halides has been commonly used. However, during the in-situ crystallization process of perovskite films via low-temperature solution methods, the complexity of coordination among various ions leads to the presence of uncoordinated ions, resulting in numerous defects in the perovskite films. These defects significantly impact the performance and stability of PeLEDs. In this work, hydroxyethyl cellulose (HEC) was incorporated into the hole transport layer (HTL) to passivate the defects in perovskite films. Experimental results showed that the hydroxyl groups in HEC interacted with Pb²⁺/K⁺/PEA⁺ ions in the perovskite, contributing to the passivation of defects. Simultaneously, the addition of HEC inhibited the low-dimensional phases (n = 1, 2) and enhanced the high-dimensional phase (n = 3) in the Q-2D perovskite films. The optimized distribution of n phases was favorable for the radiative recombination. After the introduction of HEC, the external quantum efficiency (EQE) of pure red PeLEDs at 636 nm showed a significant improvement compared to the control device, from 5.31 % to 6.82 %. This strategy provides an excellent alterative to improve the electroluminescent efficiency of red PeLEDs.