Property of the nano-thick TiO₂ films using an ALD at low temperature

We fabricated 10 nm-TiO₂ thin films for DSSC (dye sensitized solar cell) electrode application using ALD (atomic layer deposition) method at the low temperatures of 150°C and 250°C. We characterized the cross-sectional microstructure, phase, chemical binding energy, and absorption of the TiO₂ using TEM, HRXRD, XPS, and UV-VIS-NIR, respectively. TEM analysis showed a 10 nm-thick flat and uniform TiO₂ thin film regardless of the deposition temperatures. Through XPS analysis, it was found that the stoichiometric TiO₂ phase was formed and confirmed by measuring main characteristic peaks of Ti 2p¹, Ti 2p³, and O 1s indicating the binding energy status. Through UV-VIS-NIR analysis, ALD-TiO₂ thin films were found to have a band gap of 3.4 eV resulting in the absorption edges at 360 nm, while the conventional TiO₂ films had a band gap of 3.0 eV (rutile)∼3.2 eV (anatase) with the absorption edges at 380 nm and 410 nm. Our results implied that the newly proposed nano-thick TiO₂ film using an ALD process at 150°C had almost the same properties as thsose of film at 250°C. Therefore, we confirmed that the ALD-processed TiO₂ thin film with nano-thickness formed at low temperatures might be suitable for the electrode process of flexible devices.