Multifunctional Naphthol Sulfonic Salt Incorporated in Lead-Free 2D Tin Halide Perovskite for Red Light-Emitting Diodes

Tin halide perovskites are promising lead-free candidates for light-emitting diodes (LEDs), but their performance is hindered by the poor crystallinity quality and the oxidation of tin. It is necessary but challenging to simultaneously realize modulating crystallization, suppressing oxidation, and passivating defects to boost the device's performance. Here, naphthol sulfonic salt is demonstrated as an effective multifunctional additive. The sulfonic group can retard crystallization by forming intermediate complexes with perovskite to form a pinhole-free film. The reducing hydroxyl group can prevent Sn2+ from oxidation and hinder the migration of I– ions. The high electron density of the naphthol ring can enhance the electrostatic attraction toward undercoordinated Sn2+ to passivate the defects. The synergistic effect of the multifunctional additive contributes to a boosted efficiency of 0.72% and a brightness of 132 cd m–2 for quantum-well structure phenethylammonium tin iodide ((PEA)2SnI4) LEDs, which represents the most effective lead-free perovskite LEDs in pure-red regions as far as we know.