Interfacial\nDecoupling Layer Enabled Low‑<i>n</i> Phase Enrichment\nfor Blue Quasi-2D Perovskites

The random <i>n</i>-monolayer phase distributions\nand\nimpurity phases impose challenges to achieving blue-emission quasi-2D\nperovskite light emitting diodes (PeLEDs), and their formation mechanism\nis unclear. Here, we uncover the reasons behind the phase formation\nand distribution in blue-emission quasi-2D perovskites by probing\ninto the molecular interactions at the buried interface between substrates\nand perovskites and propose a mechanistic model to depict the film\nformation process. Furthermore, an interfacial decoupling layer, perfluorinated\nionomer, was employed to successfully mitigate the negative impact\nof substrates on the phase formation and distribution of blue-emission\nquasi-2D perovskites, resulting in an ordered phase distribution and\na reduction of undesired phases. Besides, this interfacial layer effectively\nsuppressed the nonradiative recombination losses, leading to enhanced\nphotoluminescence quantum yield from 12.71% to 60.13% and notable\nblue shift (∼10 nm) even without incorporating Cl ions. As\na result, blue PeLEDs based on this strategy achieved an external\nquantum efficiency reaching 12.09%.