Bifunctional additive engineering in quasi-2D perovskites for efficient and stable blue light-emitting diodes via phase modulation and defect passivation

Blue perovskite light-emitting diodes (PeLEDs) based on mixed halide quasi-two-dimensional (Q-2D) perovskites encounter obstacles including phase instability, defect-induced non-radiative recombination, and ion migration. This work proposes a bifunctional molecular, L-alanine benzyl ester p-toluenesulfonate (LABEP), to synergistically modulate phase distribution and passivate defects in Br/Cl-mixed Q-2D perovskite films. The sulfonic (-SO₃H) and amino (-NH₂) groups in LABEP coordinate with undercoordinated Pb²⁺, suppressing the formation of n = 1 phases while promoting higher-n phases (n ≥ 2), thereby enhancing quantum confinement and yielding a hypsochromic emission at 478 nm. LABEP also reduces surface roughness of the perovskite thin film and improves interfacial contact, significantly alleviating shunt current. Furthermore, hydrogen bonding between LABEP and halide ions inhibits ion migration, stabilizing the perovskite structure under operational bias. As a result, the external quantum efficiency (EQE) of the PeLED shows a 2.6-fold enhancement at 478 nm with a narrow FWHM of 20.7 nm. Spectral and operational stability is also markedly enhanced, stemming from suppressed defect-assisted recombination and ion migration. Our findings establish a molecular engineering strategy for achieving efficient and stable blue PeLEDs, offering pivotal perspectives into phase engineering and defect management in perovskite optoelectronics.