Bifunctional sulfanilic acid doping enhances the efficiency of sky-blue perovskite light-emitting diodes

Quasi-two-dimensional (Q-2D) perovskites are promising for light-emitting diodes (PeLEDs) but face performance limitations from defect states in solution-processed films and inherent phase impurities. Particularly, the low-n (n = 1) phase acts as a dominant non-radiative recombination pathway. To address this, we introduced sulfanilic acid (SA) as an additive into the Q-2D perovskite precursor, which is a bifunctional ligand featuring both sulfonic acid (-SO₃H) and amino (-NH₂) groups. The -SO₃H and -NH₂ moieties of SA selectively passivate uncoordinated Pb²⁺ and Br⁻ ions, respectively, effectively reducing defect state density and suppressing non-radiative recombination. Concurrently, the -SO₃H group interacts with the -NH₂ group of the PEA⁺, which suppresses the formation of the n = 1 phase and increases the proportion of the n = 2 phase, thereby promoting radiative recombination. Ultimately, a sky-blue (484 nm) PeLED with a maximum external quantum efficiency (EQE) of 8.09 % was achieved.