Quasi-two-dimensional (quasi-2D) perovskites have emerged as promising candidates for high-performance light-emitting 

diodes (LEDs) due to their unique energy funneling mechanism. However, uncontrollable phase distribution during film 

crystallization often leads to excessive formation of lower n-phases, which hinder efficient charge transport and radiative 

recombination. In this study, we demonstrate a facile and effective strategy to modulate the phase distribution and crystallinity

of quasi-2D perovskite PEA2(FA0.7Cs0.3)n−1PbnBr3n+1 thin films using a volatile antisolvent, isopropyl alcohol (IPA). 

Structural and optical investigations revealed that the IPA treatment effectively suppressed the insulating lower n-phases 

(n<2) and promoted the growth of higher n-domains (n>3). Optimized IPA treatment of 100 µl yields a high photoluminescence

quantum yield and balanced energy funneling, whereas excessive IPA (>300 µl) leads to phase oversimplification 

and morphological defects. Consequently, the green LED fabricated with 100 µl of IPA-treated emissive layer achieved a 

remarkable peak external quantum efficiency of 19.2% and high luminance, representing a nearly fivefold improvement 

over the pristine device. This work verifies the critical role of volatile antisolvent engineering in tailoring the energy 

landscape for high-efficiency perovskite optoelectronics.