Interfacial Decoupling Layer Enabled Low-n Phase Enrichment for Blue Quasi-2D Perovskites

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