Healing Grain Boundaries With Carbon Nanotubes Enables Large‐Area Red Tin‐Based Perovskite LEDs

ABSTRACT Two‐dimensional (2D) tin (Sn)‐based perovskites are promising lead‐free emitters for red light‐emitting diodes (LEDs), but their intrinsically low carrier mobility and poor film morphology severely limit large‐area performance. Here, we introduce a one‐step antisolvent‐assisted approach that disperses amino‐functionalized multi‐walled carbon nanotubes (CNTs) along the grain boundaries of phenethylammonium tin iodide (PEA 2 SnI 4 ) films. The CNTs provide conductive pathways that accelerate carrier diffusion, while their ammonium groups regulate crystallization and improve film uniformity. Transient absorption microscopy and transport measurements confirm that carrier conduction is more than doubled in CNT‐modified films. As a result, large‐area (150 mm 2 ) PEA 2 SnI 4 LEDs achieve a maximum external quantum efficiency of 2.35% and a peak luminance of 5028 cd m −2 , exceeding the threshold for outdoor‐readable displays. This grain‐boundary engineering strategy directly addresses the transport and morphology limitations of 2D Sn‐based perovskites and establishes a scalable route to high‐performance, lead‐free optoelectronics.