The active absorber layer plays a crucial role in a perovskite solar cell. Herein, we used high boiling point γ-butyrolactone (GBL) as the main solvent, Pb(SCN)2 and dimethyl sulfoxide (DMSO) as an effective additive in the FA0.83MA0.17Cs0.05PbI(3−x)Brx solution to improve the quality of perovskite films. The GBL will delay the crystallization speed of the perovskite, and lead to the grain growth assisted by thiocyanate. The synergistic effect of the solvent engineering and additive engineering is beneficial to the slow growth of the grain size. It is found that the addition of Pb(SCN)2 increases Gibbs free energy barrier for the nucleation, leading to the formation of fewer nuclei, which results in a high quality of perovskite absorbers with larger grains and smoother surfaces. The synergistic effect of solvents and Pb(SCN)2 on the morphology and photovoltaic performances is investigated. Compared to devices without the additive, the efficiency of devices with 5% Pb(SCN)2-doped FA0.83MA0.17Cs0.05PbI(3−x)Brx is raised to 19.01% from 15.21%. We believe this breakthrough regarding high efficiency perovskite solar cells will help for their transitions.
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