Multi-cation synergy improves crystallization and antioxidation of CsSnBr3for lead-free perovskite light-emitting diodes.

Tin (Sn) perovskites have emerged as promising alternatives to address the toxicity concerns associated with lead-based (Pb) perovskite light-emitting diodes (PeLEDs). However, the inherent oxidation of Sn perovskite films leads to a serious efficiency roll-off in PeLEDs at increased current densities. Although three-dimensional CsSnBr₃perovskites exhibit decent carrier mobilities and thermal stability, their rapid crystallization during solution processing results in inadequate surface coverage. This inadequate coverage increases non-radiative recombination and leakage current, thereby hindering Sn PeLED performance. Herein, we present a multi-cation synergistic strategy by introducing the organic cations formamidinium (FA⁺) and thiophene ethylamine (TEA⁺) into CsSnBr₃perovskites. The addition of organic cations delays crystallization by forming hydrogen bonds interacting with the CsSnBr₃. The smaller FA⁺enters the perovskite lattice and improves crystallinity, while the larger TEA⁺cation enhances surface coverage and passivates defect states. By further optimizing the interface between PEDOT:PSS and perovskite layers through the use of ethanolamine and a thin layer of LiF, we achieved a red Sn-based PeLED with an emission wavelength of 670 nm, a maximum luminance of 151 cd m^-2, and an external quantum efficiency of 0.21%.