Methoxy Functionalized Conjugated Passivation Ligand for Efficient Perovskite Light Emitting Diodes

Due to the advantages such as exceptional optoelectronic properties, readily tunable emission, high photoluminescence quantum efficiency (PLQE), narrow emission bandwidth, and solution processability, metal halide perovskites are attractive for applications in light-emitting diodes (LEDs). Despite the halide perovskite LEDs (PeLEDs) have achieved high external quantum efficiency (EQE) of above 20%, there are still many issues to be further investigated in the process of promoting the industrialization of PeLEDs. Unfortunately, the solution-processed polycrystalline perovskite films suffer from severe trap-mediated non-radiative recombination and ion migration. A tremendous amount of effort has been carried out to improve the performance of PeLEDs, including blocking iodide ion migration by strengthening the space restriction on carriers, preparing high-quality crystalline perovskites, and forming interface engineering between the ETL and the perovskite light-emitting layer. Since both ion migration and non-radiative recombination are highly related to the defects in perovskites, defect passivation is essential to achieve efficient and stable PeLEDs. Although ligand-assisted mediation has proven to be a useful method for passivating the imperfections of PeLEDs, the control strategy of alkyl chain length and the electron donating ability of the ligands bring great challenge to rational passivation. Herein, by considering the electron donating ability for the defect passivation efficiency and steric hindrance for the crystallization process, we find that methoxy group can be introduced to phenethylammonium molecular served as an efficient additive, namely 4-methoxy-phenethylammonium (4-MeO-PEA) to facilitate defect passivation process in perovskite light-emitting materials. We have demonstrated that the 4-MeO-PEA agent can substantially increase the crystal orientation, enlarge the crystalline grain size and mitigate the defect centers through strong bonding between the methoxy group with Pb ions. The external quantum efficiency (EQE) value of the PeLEDs with optimized passivation reaches to a maximum of 21.57%, which is one of the best records in the near infrared PeLEDs (~790 nm emission peak) to date. In addition, a threefold increase in the <i>T</i>₅₀ operational time of the devices is observed, compared to the control samples. The findings provide a simple and effective strategy to produce highly efficient perovskite films and to devise the high-performance optoelectronics devices.<br/><br/>The work is in part supported by Research Grants Council of Hong Kong, particularly, via Grant Nos. N_CUHK438/18, and CUHK Group Research Scheme.