Vanadium oxide as new charge recombination blocking layer for high efficiency dye-sensitized solar cells

Vanadium pentoxide (V₂O₅) was used as a novel blocking layer in dye-sensitized solar cells (DSCs), leading to a significant efficiency increase from 8.78% to 9.65%. The addition of V₂O₅ layer to nanocrystalline (nc)-TiO₂ increased peak external quantum efficiency (EQE) from~80% to ~88-89%. Cyclic Voltammetry analysis indicated a positive shift of Fermi-level in case of TiO₂/V₂O₅ based cells supported by an increase of its capacitance comparing to bare TiO₂ based cells. Electrochemical impedance spectroscopy (EIS) results exhibited a ~5 times higher charge recombination resistance (R_CT) in V₂O₅ layer modified DSCs than conventional cells, which indicated that back charge transfer from TiO₂ to tri-iodide in the electrolyte was substantially suppressed. Transient photovoltage measurements on conventional and V₂O₅ layer modified cells were conducted and their decays were fitted to calculate the electron recombination lifetime (τ_n), which increased by a factor of ~3 in V₂O₅-based DSCs. This indicated that V₂O₅ significantly reduced the recombination rate at TiO₂/electrolyte interface, further supporting that V₂O₅ functioned as a new effective surface passivation layer.