Efficient and Stable Perovskite Solar Cells Using Molybdenum Tris(dithiolene)s as p-Dopants for Spiro-OMeTAD

Metal halide perovskite solar cells have now reached efficiencies of over 22%. To date, the most efficient perovskite solar cells have the n-i-p device architecture and use 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene or poly(triarylamine) as the hole transport material (HTM), which are typically doped with lithium bis((trifluomethyl)sulfonyl)amide (Li-TFSI). Li-TFSI is hygroscopic and detrimental to the long-term performance of the solar cells, limiting its practical use. In this work, we successfully replace Li-TFSI by molybdenum tris(1-(methoxycarbonyI)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo-(tfd-CO2Me)(3), or molybdenum tris(1-(trifluoroacetyI)-2-(trifluoromethyl)ethane-1,2-dithiolene), Mo(tfd-COCF3)(3). With these two dopants, we achieve stabilized power conversion efficiencies up to 16.7% and 15.7% with average efficiencies of 14.8% +/- 1.1% and 14.4% +/- 1.2%, respectively. Moreover, we observe a significant enhancement of the long-term stability of perovskite solar cells under 85 degrees C thermal stressing in air.