Improvement in Solid-State Dye Sensitized Solar Cells by p-Type Doping with Lewis Acid SnCl4

The Lewis acid SnCl 4 is employed as a p -type dopant for 2,2′,7,7′-tetrakis( N, N -di- p -methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) for the solution process in solid-state dye sensitized solar cell. The UV–vis absorption spectra and time-resolved photoluminescence (PL) spectra are used to investigate the doping level of spiro-OMeTAD with a p -type dopant, indicating the strong molecular acceptor of SnCl 4 . X-ray photoelectron spectra (XPS) exhibiting close energy shifts of the Fermi level toward HOMO are observed when adding Li salt or SnCl 4 . A significant enhancement in fill factor of the photovoltaic devices, corresponding to the power conversion efficiency, is observed when doping with SnCl 4 . This is attributed to the low charge transport resistance of the hole transport film and high hole injection efficiency from the hole transport material to the counter electrode.