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

Abstract

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 δ-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%.

Colloidal Quantum Dot Solar Cells: Progressive Deposition Techniques and Future Prospects on Large‐Area Fabrication

“…[ 29b ] However, the processing window of the MeOAc and FAI treatments is very narrow and the ability to remove the original ligand is limited. [ 29b,91,93 ]…”

Perovskite Quantum Dots in Solar Cells

“…They demonstrated that the device undergoing three-cycle MeOAc treatment can achieve the highest PCE of 12.85% staying phase stability. [41] However, the pure solvent treatment brings about some shortcomings. First, the ligand exchanging rate and degree depend on the amount of adventitious water as well as the extent of ester hydrolyzation.…”

“…To date, MAPbX 3 , FAPbX 3 , and CsPbX 3 QDs with high have been successfully synthesized as well as their hybridization. However, MA-based PQDs exhibit poor chemical stability due to their low Ligand engineering CsPbI 3 PQDs 10.8% - [28] FAPbI 3 PQDs 8.4% 226 h (continuous illumination) 99% of initial PCE [37] CsPbI 3 PQDs 11.9% - [38] CsPbI 3 PQDs 14.6% - [39] CsPbI 3 PQDs 11.2% 1 month (20% RH in air) 80% of initial PCE [24] CsPbBr 3 PQDs 4.2% - [40] CsPbI 3 PQDs 12.9% - [41] CsPbI 3 PQDs 14.1% -…”

“…They demonstrated that the device undergoing three‐cycle MeOAc treatment can achieve the highest PCE of 12.85% staying phase stability. [ 41 ]…”

Application of Perovskite Quantum Dots as an Absorber in Perovskite Solar Cells

“…Exchange chemistry is favorable for the mitigation of defect density, amelioration of film quality, improvement of light absorption, and acceleration of charge transport. Both ion exchange and ligand change can contribute to the advancement of perovskite QDs and QD‐based solar cells [27, 28] . The passivation engineering strategy can be achieved by ion passivation and ligand passivation [29, 30] .…”