Enhanced surface hydroxylation of nanocrystalline anatase films improves photocurrent output and electron lifetime in dye sensitized solar cell photoanodes

Anatase TiO2 nanocrystalline films were prepared from commercial (Alfa Aesar 5 nm and 10 nm) and aqueous-solution synthesized precursors (aqueous TiO2) by screen printing with the purpose of elucidating the influence of surface hydroxylation on dye sensitized solar cell (DSSC) performance. These two commercial TiO2 sources were selected as they possessed similar nanocrystallite size and mesoporous film interfacial surface area with our in-house variety. In this way it was possible to distinguish the effect of surface hydroxylation on DSSC photocurrent output and electron lifetime from other film surface properties. Their morphological features were characterized in terms of particle size, shape, Brunauer–Emmett–Teller (BET) surface area, topography and their surface hydroxyl groups quantified using thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of the DSSCs composed of the aqueous TiO2, Alfa Aesar 5 nm and 10 nm photoelectrodes were probed via electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD). The combined EIS and OCVD results showed that photoelectrodes composed of surface hydroxyl-rich TiO2 nanocrystalline material exhibit longer electron lifetime attributed to enhanced surface-dye binding that suppresses interfacial recombination. As a result of the stabilized surface hydroxyl-dye (N719) binding, the photocurrent output from the OH-rich anatase photoanodes (aqueous and Alfa Aesar 5 nm TiO2,) was a remarkable 85–108% higher than that of the OH-poor film (Alfa Aesar 10 nm) despite their equivalent surface area and porosity.