Superbly Bright Tin‐Based Perovskite LEDs

Abstract Tin (Sn)‐based perovskites have made notable advances with external quantum efficiency of over 20%, but still exhibit low electroluminescence brightness insufficient for outdoor displays. Here, it is demonstrated that compact phenethylammonium tin iodide (PEA 2 SnI 4 ) films with an intact crystal structure can offer high luminance by optimizing the perovskite crystallization rate simultaneously with engineering the grain surface. Ammonium thiocyanate is added to the precursor solution to generate the film with PEA 2 SnI x SCN 4‐ x and NH 4 I after spin‐coating. Sn 2+ and SCN − have a strong interaction that slows crystallization to improve PEA 2 SnI 4 crystal quality. During the subsequent annealing, I − from NH 4 I replaces SCN − in PEA 2 SnI x SCN 4‐ x by forming thiourea, which can escape from the film to leave intact PEA 2 SnI 4 crystals. It is found that the optimized PEA 2 SnI 4 emitting layers can provide outstanding film coverage, high crystallinity, low trap state density, and superior photophysical performance. Consequently, an impressive brightness of 8285 cd m −2 for pure red electroluminescence is achieved, the first report of Sn‐based perovskite light‐emitting diodes that meet outdoor display requirements.