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

The Lewis acid SnCl4 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 SnCl4. X-ray photoelectron spectra (XPS) exhibiting close energy shifts of the Fermi level toward HOMO are observed when adding Li salt or SnCl4. A significant enhancement in fill factor of the photovoltaic devices, corresponding to the power conversion efficiency, is observed when doping with SnCl4. 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.