Evidence of Spiro-OMeTAD De-doping by tert-Butylpyridine Additive in Hole-Transporting Layers for Perovskite Solar Cells

The development of solid-state hole-transporting materials (HTMs) dates back to the first reports on solid-state dye-sensitized solar cells in 1998, which provided solar cell efficiencies around 1%. The need for these components has then steadily grown with the advent in 2009 of perovskite-based photovoltaics, which cannot sustain any liquid electrolyte. Spiro-OMeTAD molecules have been for many years the material of choice for this application. When doped with LiTFSI salts and tert-butylpyridine, the resulting mixture can efficiently extract photogenerated holes in the perovskite absorber and transport them to the collecting electrode. This benchmark for hole transport in third-generation hybrid photovoltaics suffers from intrinsic limitations, which have been studied widely over the years. A detailed molecular-level understanding of the processes involved in Spiro-OMeTAD-based HTM degradation is a key requirement for the future development of new stable and efficient substitutes for this task.