Effects of rubrene co-sensitized TiO₂ photoanode on the performance of ruthenium dye N719 sensitized solar cells

A notable organic semiconductor of rubrene with better charge-transport property and wide adsorption spectra is firstly employed as a co-adsorbent into N719 sensitized dye sensitized solar cells (DSSCs). After co-sensitized the TiO₂ photoanode with rubrene, a short circuit current density (J_sc) of 18.69 mA cm^{- 2}, an open circuit voltage (V_oc) of 0.73 V and a fill factor (FF) of 0.56 corresponding to an overall conversion efficiency (η) of 7.64% under AM 1.5 G solar irradiation are achieved, which is 40% higher than that for DSSCs without rubrene (η = 5.46%, J_sc = 14.29 mA cm^{- 2}, V_oc = 0.67 V, and FF = 0.57) under the same condition. The higher η value of co-sensitized solar cells is attributed to the enhanced photovoltaic parameters J_sc and V_oc. The combined light harvesting of N719 and rubrene in the region of 300-750 nm and the better charge-transport property of rubrene which promote the electron transfer together lead to the high J_sc, while V_oc is enhanced owing to the retarded charge recombination and the prolonged electron lifetime due to the formation of a compact molecular layer composed of rubrene and N719 molecular. Mechanistic investigations are carried out by various electrochemical and spectral characterizations.