Thermoelectric properties of mesoporous TiO₂ thin films through annealing temperature and ratio of surfactant

To obtain good properties of thermoelectric devices, low thermal conductivity and high electrical conductivity are required. But, it is difficult to control these factors individually, optimized structure is also difficult to obtain. Ordered mesoporous structure reduces the thermal conductivity. So, it can be used as thermoelectric device. In this work, a study has been focused on the mesoporous titania thin film by control on annealing temperature to apply in thermoelectric devices. Crystallization of titania occurred at high temperature from anatase to rutile. The mesoporous titania thin film was synthesized by sol-gel and evaporation-induced self-assembly process using titanium tetraisopropoxide. At low temperature, mesoporous titania has ordered structure. However the ordered structure collapsed after high temperature annealing. Although an ordering of pores disappeared by high temperature annealing, porous nature could be maintained due to limited grain growth and crystallization from interior pores. So, thermoelectric properties could be expressed. Moreover, according to molar ratio of surfactant/precursor also could effectively improve a Seebeck coefficient. The mesoporous titania film with 28% porosity after annealing at 900°C showed a maximum absolute value of Seebeck coefficient as -343.9μV/K at 537K. Finally figure of merit, ZT value was 1.213×10^-3 at 303K.