Chelation of lithium ion with crown ether for eliminating adverse effects caused by Li-TFSI/tBP doping system in Spiro-OMeTAD

Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI)/4-tert-butylpyridine (tBP) is a classic doping system for the hole transport material Spiro-OMeTAD in typical n-i-p structure perovskite solar cells (PSCs), but this system will cause many problems such as high hygroscopicity, Li+ migration, pinholes and so on, which hinder PSC from maintaining high efficiency and stability for long-term. In this work, an effective strategy is demonstrated to improve the performance and stability of PSC by replacing tBP with 12-crown-4. The chelation of 12-crown-4 with Li+ not only improves the doping effect of Li-TFSI, but also perfectly solves the problems caused by the Li-TFSI/tBP system. The PSC based on this strategy achieved a champion power conversion efficiency (PCE) over 21%, which is significantly better than the pristine device (19.37%). More importantly, the without encapsulated device based on Li-TFSI/12-crown-4 still maintains 87% of the initial PCE even after 60 days exposure in air, while the pristine device only maintains 22% of the initial PCE under the same aging conditions. This strategy paves a novel way for constructing efficient and stable PSCs.