Weakly Coordinated Co‐Solvent Strategy Enables Anti‐Solvent‐Free Fabrication of High‐Efficiency Perovskite Light‐Emitting Diodes

Abstract The processing solvents strongly impact the crystallization and optoelectronic properties of the resultant perovskites. However, limited by the solubility of perovskites, available processing solvents for perovskite light‐emitting diodes (PeLEDs) are restricted to only a few strongly coordinated and polar solvents, such as dimethyl sulfoxide (DMSO). The strong coordination capability of DMSO with Pb 2+ excessively affects the crystallization of perovskites, often necessitating anti‐solvent engineering to regulate the crystallization process. Here, a strategy of weakly coordinated co‐solvent comprising 2‐methoxyethanol (2‐ME) and propylene carbonate (PC) is proposed to fabricate quasi‐2Dperovskites and PeLEDs. This co‐solvent exhibits synergistic properties—complementary coordination capability and dielectric constant—yielding superior solvation capability compared to either solvent alone. Crucially, the tunable, moderate solvation strength of the 2‐ME:PC mixture facilitates perovskites crystallization while suppressing detrimental low‐dimensional phase growth, enabling anti‐solvent‐free fabrication of high‐quality formamidinium‐based quasi‐2D perovskites. Employing this optimized co‐solvent, pure green PeLEDs are achieved that comply with Rec. 2020 standards, boasting a remarkable external quantum efficiency of 26.2%. This work presents an effective strategy for the facile fabrication of high‐performance PeLEDs, while also guiding the selection of additional perovskite processing solvents.