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A novel poly(ethylene glycol) (PEG) based oligomeric coadsorbent was employed to passivate TiO 2 photoanodes resulting in the large increase in both opencircuit voltage (V oc ) 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 TiO 2 . 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 TiO 2 interfaces is capable of shifting the band-edge of TiO 2 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 LiI, 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 TiO 2 photoanodes is quite effective in the improvement of photovoltaic performance because of the simultaneous increase in both V oc and J sc .

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A compact TiO2 layer (~1.1 μm) prepared by electrostatic spray deposition (ESD) and swift heavy ion beam (SHI) irradiation using oxygen ions onto a fluorinated tin oxide (FTO) conducting substrate showed enhancement of photovoltaic performance in dye-sensitized solar cells (DSSCs). The short circuit current density (Jsc = 12.2 mA cm-2) of DSSCs was found to increase significantly when an ESD technique was applied for fabrication of the TiO2 blocking layer, compared to a conventional spin-coated layer (Jsc = 8.9 mA cm-2). When SHI irradiation of oxygen ions of fluence 1 × 1013 ions/cm2 was carried out on the ESD TiO2, it was found that the energy conversion efficiency improved mainly due to the increase in open circuit voltage of DSSCs. This increased energy conversion efficiency seems to be associated with improved electronic energy transfer by increasing the densification of the blocking layer and improving the adhesion between the blocking layer and the FTO substrate. The adhesion results from instantaneous local melting of the TiO2 particles. An increase in the electron transport from the blocking layer may also retard the electron recombination process due to the oxidized species present in the electrolyte. These findings from novel treatments using ESD and SHI irradiation techniques may provide a new tool to improve the photovoltaic performance of DSSCs.