Synergistic phase regulation and defect mitigation in quasi-2D blue perovskite LEDs: Employing novel isomeric blended cations

Quasi-2D perovskite materials hold great promise for efficient blue LEDs due to their unique multi-quantum-well structure. However, achieving high efficiency in blue quasi-2D perovskite LEDs (PeLEDs) remains challenging, largely because of uncontrolled phase distribution and defect-related non-radiative recombination. In this work, two isomeric forms of diammonium organic cations were designed and synthesized, 1,4-phenylenedimethan-aminium bibromide (m-PDMABr₂) and 1,3-phenylene-dimethanaminium bibromide (p-PDMABr₂), which introduces them as blended spacer cations together with phenethylammonium bromide (PEABr). These isomers not only suppress the formation of undesired small-n phases but also passivate defects in the perovskite film. By optimizing the blending ratio of m-PDMABr₂ to PEABr (3:7), we achieve improved phase distribution and lower defect density. As a result, the champion PeLED delivers a peak external quantum efficiency (EQE) of 13.68%. While devices using p-PDMABr₂ at the same ratio reach a maximum EQE of 12.26%. Compared to the control device based solely on PEABr (EQE = 7.11%), these represent remarkable improvements of 92.41% and 72.43%, respectively. Our study demonstrates that strategically designed isomeric spacer cations can effectively tune phase behavior and suppress defects, offering a practical materials-design strategy for high-performance blue quasi-2D PeLEDs.