Customized Buried Interface for High Performance All-Inorganic CsSnI3-Based NIR Perovskite Light-Emitting Diodes via a Guanidinium Derivative.

CsSnI3-based perovskite light-emitting diodes (PeLEDs) show great potential in near-infrared (NIR) applications, yet device performance is limited by interfacial degradation at the acidic hole-transport layer (HTL) based on Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). Herein, a multifunctional guanidine derivative of N-(3-methoxy-phenyl)-guanidine (NMPG), is used to modify the buried interface between the CsSnI3 perovskite and the HTL. NMPG deprotonates the polystyrene sulfonic acid (PSSH) of PSS and reduces the acidity of PEDOT:PSS, while its methoxy and C═N groups coordinate with Sn2+, effectively inhibiting Sn2+ oxidation, passivating Sn (II) induced defects. This customized buried interface enables uniform and discrete growth of perovskite grain, improves charge injection balance, and enhances vertical compositional and optical homogeneity. As a result, the target PeLEDs achieve a competitive maximum external quantum efficiency (EQE) of 9.0% and a high average EQE of 8.4%, significantly outperforming the control device (EQEmax = 6.6%, EQEave = 5.5%). The target PeLEDs also demonstrate superior operational stability, with a T50 lifetime of 67.9 h, representing a 5-fold improvement compared to the control PeLEDs. This work reveals the pivotal role of buried interface chemistry and presents a viable molecular design strategy for achieving high-performance CsSnI3-based PeLEDs.