Dopant Engineering for Spiro?OMeTAD Hole?Transporting Materials towards Efficient Perovskite Solar Cells

One of the most prominent hole-transporting material (HTM) for hybrid perovskite solar cells has been 2,2?,7,7?-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9?-spirobifluorene (spiro-OMeTAD), which is commonly doped with metal bis(trifluoromethylsulfonyl)imide (M(TFSI)n) salts that contribute to generating active radical cation HTM species. The underlying role cation, however, remains elusive. Here, effect cations (M = Li, Zn, Ca, Cu, and Sc) on doping spiro-OMeTAD analyzed by a combination techniques, including electron paramagnetic resonance spectroscopy cyclic voltammetry, complemented photovoltaic device hole mobility analysis. As result, authors reveal superiority Zn(TFSI)2 in performances as compared others, redox-active Cu(TFSI)2. This analysis thereby unravels new design principles dopant engineering HTMs photovoltaics.