Effect of plasma treatment with various gases on nanocrystalline TiO2 for dye-sensitized solar cell (DSSC)

Titanium dioxide (TiO₂) photocatalyst with anatase phase has been extensively investigated for Dye-sensitized solar cell (DSSC). The chemical activation of OH group on TiO₂ surface can provide valuable electron transfer from sensitizer dye to TiO₂. The plasma treatment is suggested as improving hydrophilic property of nano-structured TiO₂ surface, and has different effects on TiO₂ surface depending on the gas to increase dye adsorption. Therefore, TiO₂ is treated with the plasma using gases to improve the high-sensitivity of DSSCs. In this work, a low temperature radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system was utilized for plasma treatment with various gases such as O₂, H₂, CH₄, and N₂. In a low-temperature plasma, it was possible to modify the skin layer of the substrate without a phase transition. We confirmed that the efficiency of DSSC was significantly dependent on gases used for the plasma treatment. The surface chemistry and characteristics by plasma treatment were investigated by various analysis methods. Each of gas differently affected conversion efficiency of DSSC with plasma-treated TiO₂ compared to untreated DSSC under AM 1.5 G spectral illumination of 100 mWcm^-2. XPS (X-ray photoelectron spectroscope), and TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) were used for the surface analysis of TiO₂.