21.15%-Efficiency and Stable γ -CsPbI 3 Perovskite Solar Cells Enabled by an Acyloin Ligand.

Cesium lead triiodide (CsPbI 3 ) is a promising light-absorbing material for constructing perovskite solar cells (PSCs) owing to its favorable bandgap and thermal tolerance. However, the high density of defects in the CsPbI 3 film not only act as recombination centers, but also facilitate ion migration, leading to lower PCE and inferior stability compared with the state-of-the-art organic-inorganic hybrid PSC counterpart. Theoretical analyses suggest that the effective suppression of defects in CsPbI 3 film is helpful for improving the device performance. Herein, the stable and efficient γ -CsPbI 3 PSCs are demonstrated by developing an acyloin ligand (1,2-di(thiophen-2-yl)ethane-1,2-dione (DED)) as a phase stabilizer and defect passivator. The experiment and calculation results confirm that carbonyl and thienyl in DED can synergistically interact with CsPbI 3 by forming a chelate to effectively passivate Pb-related defects and further suppress ion migration. Consequently, DED-treated CsPbI 3 PSCs yield a champion PCE of 21.15%, which is one of the highest PCE among all the reported CsPbI 3 PSCs to date. In addition, the unencapsulated DED-CsPbI 3 PSC can retain 94.9% of itsinitial PCE when stored under ambient conditions for 1000 h and 92.8% of its initial PCE under constant illumination for 250 h.