A non-ionic fluorinated p-dopant enables the construction of efficient and stable perovskite solar cells

Abstract

The Li-TFSI/t-BP system is essential for doping the hole-transporting layer (HTL) to construct efficient perovskite solar cells (PSCs). However, the hygroscopicity and Li⁺ migration of Li-TFSI, as well as the corrosiveness and volatility of t-BP, can have negative impacts on the efficiency and stability of PSCs. Herein, a novel non-ionic fluorinated p-dopant 1-[bis(trifluoromethanesulfonyl)methyl]-2,3,4,5,6-pentafluorobenzene (PFB-TFSI) is developed to replace the Li-TFSI/t-BP system. The non-ionic structure of PFB-TFSI allows it to dissolve in chlorobenzene without t-BP. Moreover, due to the lower HOMO level of PFB-TFSI, it can directly oxidize PTAA to generate [PTAA]⁺ radical cations without post-treatment, achieving effective doping of PTAA. The moisture resistance of the HTL is also improved due to the presence of multiple fluorine atoms in PFB-TFSI. Ultimately, compared to 21.98% efficiency of the PSC based on PTAA:Li-TFSI/t-BP, the PSC based on PTAA:PFB-TFSI achieved higher efficiency (24.22%). Furthermore, the long-term stability of the PSC based on PTAA:PFB-TFSI is greatly improved, retaining 88% of its initial efficiency after aging for 300 hours at 85 °C and 50–70% relative humidity, whereas the PSC based on PTAA:Li-TFSI/t-BP only retains 63%.