Replacing Li+ in Li-TFSI with a benzene ring: constructing non-ionic p-dopants for stable and efficient perovskite solar cells

Abstract

Li-TFSI/tBP is a classic doping system for the hole transport materials in efficient perovskite solar cells (PSCs), but the ultra-hygroscopicity and Li⁺ migration of Li-TFSI, the volatility of tBP, and the polarity of acetonitrile promoting the solubility of Li-TFSI in chlorobenzene have negative impacts on the performances of PSCs. Herein, by replacing the hygroscopic Li⁺ in Li-TFSI with a benzene ring, we developed a novel non-ionic p-dopant (N-phenyl-bis(trifluoromethanesulfonimide)), (Ph-TFSI), which solves the above problems existing in the Li TFSI/tBP doping system due to the absence of hygroscopic Li⁺ and good solubility in chlorobenzene. In addition, owing to the lower HOMO energy level of Ph-TFSI, it can accept electrons from PTAA to generate [PTAA]⁺ radicals for effective doping without post-treatment of oxygen and light. PSCs based on Ph-TFSI doped PTAA achieved an efficiency of 21.82%, which is better than those of PSCs based on Li-TFSI/tBP doped PTAA (20.11%). Furthermore, due to the absence of hygroscopic Li⁺, tBP and acetonitrile, the long-term stability of PSCs based on Ph-TFSI doped PTAA is significantly improved, retaining 88% of the initial efficiency after 30 days of exposure in air, while PSCs based on Li-TFSI/tBP doped PTAA only maintains 63% of the initial efficiency under the same aging conditions. Finally, the universality of Ph-TFSI was studied by doping another classic hole transport material Spiro-OMeTAD. The results showed that Ph-TFSI can also effectively dope Spiro-OMeTAD, and the corresponding PSC achieved good device performance.