Engineering long-term stability into perovskite solar cells via application of a multi-functional TFSI-based ionic liquid
Xiaoxin Gao, Bin Ding, Hiroyuki Kanda, Zhaofu Fei, Wen Luo, Yi Zhang, Naoyuki Shibayama, Andreas Züttel, Farzaneh Fadaei‐Tirani, Rosario Scopelliti, Sachin Kinge, Bao Zhang, Yaqing Feng, Paul J. Dyson, Mohammad Khaja Nazeeruddin
Abstract
Organic-inorganic metal-halide perovskite solar cells (PSCs) have achieved a certified power-conversion efficiency (PCE) of 25.5%. However, long-term stability and air stability of the PSCs are still major concerns and hamper commercialization. Herein, we employ a multi-functional ionic liquid (IL), 1,3-bis(cyanomethyl)imidazolium bis(trifluoromethylsulfonyl)imide ([Bcim][TFSI]), which contains an imidazolium cation functionalized with nitrile (CN) groups and the TFSI anion and is, additionally, able to form an extensive network of low-barrier H bonds, as an additive in perovskite-precursor solutions. Because of a combination of the Lewis-basic CN groups and the hydrophobic TFSI anion in the IL, highly crystalline perovskite films with large grain sizes are obtained. The IL-modified perovskite films afford PSCs with long-term stability and PCEs > 21%. The stability of unencapsulated devices retain >95% of their original efficiency after 1,000 h of aging. This study demonstrates the considerable potential of TFSI-based ILs to improve the performance of PSCs.