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

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.