Optimizing the Hole-Transport Layer with Ammonium Thiocyanate for Enhanced Performance in Lead-Free Perovskite Light-Emitting Diodes

Tin-based perovskite materials are arising as promising contenders for high-efficiency pure-red perovskite light-emitting diodes. However, the primary limitation to the external quantum efficiency (EQE) of tin-based perovskite light-emitting diodes (Sn-PeLEDs) stems from rapid crystallization processes and adverse P-type self-doping effects. In this study, we have effectively controlled the speed crystallization processes of tin-based perovskites through rational interfacial engineering and improved the stability of the tin halide perovskite film. We utilized ammonium thiocyanate (NH4SCN) to alter the properties of the hole-transport layer, which consists of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Thiocyanate ions (SCN–) can form interactions with Sn–I frameworks. This not only slows the crystallization rate but also effectively suppresses the oxidation of Sn2+, enhancing its stability and passivating the defects associated with undercoordinated Sn2+. This results in smooth, uniform, and compact perovskite thin films that effectively eliminate the Sn4+ defects within the resulting tin perovskite film, leading to enhanced radiative recombination. This results in Sn-PeLEDs devices achieving a peak EQE of 5.8%, approximately 4.6-fold higher than that of the control device. Additionally, the Commission Internationale de L'Eclairage (CIE) coordinates of (0.69, 0.31) demonstrate a close conformity with the National Television System Committee (NTSC) standardized coordinates for red standard, indicating a high degree of color fidelity.