Phase Homogenization via Decoupled Nucleation and Growth for High-Efficiency Quasi-Two-Dimensional Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites with multiquantum-well structures hold great potential for light-emitting diodes (LEDs) due to their cascaded energy funnels, yet their performance is hampered by defect-rich low-n phases and disordered crystallization. Here, we present a phase-homogenization strategy that combines a self-adaptive solvent by doping ethyl acetate (EA) with dimethyl phosphonate (DPP), which simultaneously modulates the polarity and evaporation kinetics of EA, guiding the crystal growth and phase distribution of quasi-2D perovskites. The strong coordination of DPP with Pb2+ also passivates deep-level traps, thereby drastically reducing nonradiative low-n-phase recombination. We further use the bridging molecules to enhance perovskite/transport layer interfaces by incorporating sodium 4-amino-1-naphthalenesulfonate tetrahydrate (SANT) into the PEDOT/PSS hole transport layer, which weakens PEDOT–PSS electrostatic attraction, enhancing conductivity while reducing acid-induced corrosion of the ITO electrode and perovskite film. SANT also templates perovskite nucleation via its functional groups, promoting ordered crystallite growth. Overall, the resulting green-emitting quasi-2D perovskite LEDs achieve a peak external quantum efficiency (EQE) of 32.81% (average 30.74%) and a luminance of 44338 cd m–2, with a lower surface temperature during operation. Moreover, the devices exhibit a 10-fold enhancement in operational stability compared to the control counterparts. Our findings provide a strategy for combining crystallization control and interface passivation in quasi-2D PeLEDs.