Effective Passivation of Nanostructured TiO2 Interfaces with PEG-Based Oligomeric Coadsorbents To Improve the Performance of Dye-Sensitized Solar Cells

A novel poly(ethylene glycol) (PEG) based oligomeric coadsorbent was employed to passivate TiO2 photoanodes resulting in the large increase in both open-circuit voltage (Voc) and short-circuit current density (J(sc)) primarily because of the reduced electron recombination by the effective coverage of vacant sites as well as the negative band-edge shift of TiO2. The effective suppression of electron recombination was evidenced by electrochemical impedance spectroscopy (EIS) and by stepped light-induced transient measurements of photocurrent and voltage (SLIM-PCV). The work function measurements also showed that the existence of coadsorbents on TiO2 interfaces is capable of shifting the band-edge of TiO2 photoanodes upwardly resulting in the increase in photovoltage. In addition, the coadsorbent was proven to be effective even in the presence of common additives such as UT, 4-tert-butylpyridine, and guanidinium thiocyanate. The effect of Li+ cation trapping by ethylene oxide units of the coadsorbent was particularly notable to significantly increase V-oc at a small expense of J(sc). Consequently, the introduction of novel PEG-based oligomeric coadsorbents for TiO2 photoanodes is quite effective in the improvement of photovoltaic performance because of the simultaneous increase in both V-oc and L-sc.