Role of Methyl Acetate in Highly Reproducible Efficient CsPbI3 Perovskite Quantum Dot Solar Cells

The best research-cell efficiency for quantum dot solar cells has boosted from 11.6 to 18.1% within 5 years due to the evolution of perovskite quantum dots (PQDs) that are being intensively developed along with the flourishing of perovskite thin-film photovoltaics. During the fabrication of PQD devices, as far as we know, methyl acetate (MeOAc) is an ineluctable solvent in ligand exchange for producing highly efficient solar cells. Nevertheless, the reproducibility for PQD solar cells using MeOAc treatment is poor since it has to make a trade-off between removing long-chain organic ligands for high charge transport and keeping them for the stabilization of the black crystal phase. Herein, we demonstrate the degree of MeOAc treatment on CsPbI3 PQD solid films in detail and clarify that MeOAc treatment is able to not only remove the oleyl ligands for promoting the charge transport but also passivate the surface defects in the CsPbI3 PQD solid films. It is noted that immoderate MeOAc treatment could induce the formation of the delta-phase, leading to the degradation of device performance. After locating the balance for MeOAc treatment, the CsPbI3 PQD solar cells are fabricated and optimized without using any additional modifications except MeOAc treatment, and these additive-free devices possess a conversion efficiency surpassing 12%.