High‐Performance NIR‐II Sn‐Based Perovskite LEDs Enabled by the Functionalization of Sulfaguanidine

ABSTRACT Eco‐friendly CsSnI 3 ‐based perovskite light‐emitting diodes (PeLEDs) with the emission peak extending to the near‐infrared‐II (NIR‐II) region hold tremendous potential for applications in biological monitoring, night vision, and optical communications. However, the various defects caused by the instability of Sn 2+ within the CsSnI 3 film, and the non‐equilibrium carrier injection rate in the devices are the two major factors that limit the device performance. Here, we report high‐performance NIR‐II CsSnI 3 ‐based PeLEDs achieved by employing functional sulfaguanidine (SG) molecules. Due to the strong S═O─Sn coordination bonds, NH 2 ···I − hydrogen bonds could be formed between CsSnI 3 and SG, which effectively eliminated various Sn(II)‐related defects in the CsSnI 3 film. Moreover, the SG molecules significantly improved the morphological uniformity and regulated the carrier injection balance, resulting in more balanced carrier injection that enhanced the effective radiation recombination rate. Consequently, the optimized CsSnI 3 ‐SG PeLEDs achieved a breakthrough external quantum efficiency (EQE) of 8.1%, which is the highest efficiency reported for CsSnI 3 ‐based PeLEDs to date.