High-Voltage and Green-Emitting Perovskite Quantum Dot Solar Cells via Solvent Miscibility-Induced Solid-State Ligand Exchange

Advances in surface chemistry and manipulation of CsPbI3 perovskite quantum dots (PQDs) have enabled the replacement of native long-chain ligands with short-chain ligands, leading to their photovoltaic applications; however, there are no reports on those of wide-bandgap and green-emitting CsPbBr3 PQDs that are promising in high-voltage and colorful building-integrated photovoltaics. Binding energies required for ligand adsorption/desorption alter according to halide compositions of PQDs because of different soft/hard acid/base interactions, and therefore, the surface ligand-exchange process for CsPbBr3 PQDs should be developed. Herein, we demonstrate the utilization of CsPbBr3 PQDs in green light-emitting solar cells with a high open-circuit voltage (VOC) of 1.6 V, realized via solvent miscibility-induced ligand exchange. Carboxylate esters with different alkyl chain lengths are used; longer carboxylate esters show high miscibility with hydrophobic substances, leading to more efficient ligand exchange with preserving CsPbBr3 PQD size but at the same time undesired less film thickness because of the stripping-out of as-cast CsPbBr3 PQDs. Based on these results, we devise a suitably optimized solvent mixture of carboxylate esters to enable efficient ligand exchange with suppressed stripping-out phenomena. Therefore, the resultant CsPbBr3 PQD solids show a power conversion efficiency of 4.23% and a VOC of ∼1.6 V with green electroluminescence under applied voltage.