Improving the performance of pure-red 2D tin-based perovskite light-emitting diodes through N-methylthiourea ligand engineering

Two-dimensional tin (Sn)-based perovskite light-emitting diodes (PeLEDs) are emerging as competitive candidates for toxic lead (Pb)-based perovskites due to their excellent optoelectronic properties and environmental friendliness. However, the device performance of PEA₂SnI₄ PeLEDs is still far behind that of Pb-based devices because of several fatal problems, such as fast crystallization, high defect density and easy oxidation of Sn²⁺. Herein, a ligand engineering strategy based on N-methylthiourea (N-MTU) was proposed to modify PEA₂SnI₄ perovskite films to obtain highly efficient pure-red PEA₂SnI₄ PeLEDs. The characterization results demonstrate that the N-MTU additive can not only significantly improve the crystallinity, morphology, and antioxidant properties but also effectively passivate defects and slow the crystallization rate by forming hydrogen bonds and coordinating interactions between the N-MTU and PEA₂SnI₄ perovskite. Finally, pure-red PEA₂SnI₄ PeLEDs modified with N-MTU exhibit a high external quantum efficiency (EQE) of 2.35%, better stability (T₅₀ = 12.03 min) and a world-record maximum luminance of 509 cd m⁻². This work reveals new prospects for the selection of effective ligand additives for Sn-based perovskites.