Degradation of perovskite structure by halide migration under thermal stress in quasi-2D blue perovskite light-emitting diodes

Quasi-2D metal-halide perovskites are promising materials for blue perovskite light-emitting diodes (PeLEDs) owing to their high luminescence efficiency and tunable bandgap; however, severe thermal degradation remains a critical barrier to their commercialization. Herein, we elucidate the detailed degradation mechanism of phenylethylammonium (PEA)₂(CsPbBr_3-xCl_x)-based quasi-2D blue PeLEDs under thermal stress. As degradation proceeded, the devices suffered drastic performance losses: the current density and luminance dropped by 77% and 87%, respectively, accompanied by a spectral shift of electroluminescence from 490.6 nm to 495.8 nm. The degraded films exhibited blurred grain boundaries, irregular multilayer platelet aggregation, complete loss of the n = 2 phase, and markedly reduced crystallinity. Photoluminescence (PL) studies revealed significantly enhanced nonradiative recombination, manifested by vanishing shoulder peaks in the spectrum and a significantly shortened average PL lifetime. Further analysis confirmed the halide loss, metallic Pb formation, surface oxidation, and accumulation of degradation-related species. We demonstrate that the thermal decomposition of phenylethylammonium chloride coupled with halide ion migration causes an irreversible collapse of the quasi-2D structure, thereby accelerating phase separation and defect formation and providing critical insights for achieving thermally robust blue PeLEDs.