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 the active radical cation HTM species. The underlying role of the metal cation, however, remains elusive. Here, the effect of metal cations (M = Li, Zn, Ca, Cu, and Sr) on doping spiro-OMeTAD is analyzed by a combination of techniques, including electron paramagnetic resonance spectroscopy and cyclic voltammetry, which is complemented by photovoltaic device and hole mobility analysis. As a result, the authors reveal the superiority of Zn(TFSI)(2) salts in device performances as compared to the others, including redox-active Cu(TFSI)(2). This analysis thereby unravels new design principles for dopant engineering in HTMs for hybrid perovskite photovoltaics.

Automated summary

This study analyzed the effect of different metal cations on doping spiro-OMeTAD in hybrid perovskite solar cells, revealing the superior performance of Zn(TFSI)(2) salts compared to others. This provides new design principles for dopant engineering in HTMs for hybrid perovskite photovoltaics.