Precursor-solvent coordination control for defect suppression in perovskite light-emitting diodes

Defect formation in perovskite nanograins in the polycrystalline films is governed by the solution-state coordination chemistry of halide perovskite precursor species, which have been employed to form less-defective films with large grains in solar cells. However, the coordination dynamics of bromoplumbate complexes in solution to form small grains for light-emission have been rarely studied in the context of defect suppression. In this work, we investigated the interplay between crown ether complexation and solvent coordination strength in perovskite precursor solutions, which governs the dispersion of precursor species and the formation of bromoplumbate complexes. Both crown ethers and polar aprotic solvents such as N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) act as Lewis bases, competing for coordination with lead cations in the precursor solution. In weakly coordinating DMF, crown ethers can more effectively complex with precursors, shifting the coordination equilibrium toward high-valent bromoplumbate species unlike in strongly coordinating DMSO. This control yielded defect-suppressed perovskite films with nanograins with higher photoluminescence compared to those formed in strongly coordinating solvents of DMSO. These insights into bromoplumbate chemistry provide a basis for rational solvent and additive selection toward defect suppression and enhanced light-emitting performance.