Enhancement of Photothermoelectric Performance of TiO₂ Promoted by the Seebeck Effect

Photothermoelectric (PTE) materials interconvert light, heat, and electrical energy, showing significant potential for applications in the fields of energy, healthcare, and intelligent sensing. However, the research on PTE properties is still in its infancy. In particular, there are relatively few PTE materials operating in the visible light band. In this study, we investigated the photothermoelectric effect of rutile-phase Ti_1-xNb_xO₂ bulk materials with varying Nb doping concentrations (x = 0.01, 0.05, 0.14, 0.20) in the visible light band. By tuning the band structure and Seebeck coefficient (S), the PTE effect was achieved within the 635 nm visible light band. Nb doping effectively modulated light absorption, carrier transport, and thermoelectric properties. As the Nb content increases, the absorptance at 635 nm rises from 43% for Ti_0.99Nb_0.01O₂ to 53% for Ti_0.8Nb_0.2O₂. However, the variation of the photothermoelectric voltage (U_PTE) is consistent with that of the Seebeck coefficient. Under 0.9 mW laser irradiation, the U_PTE first decreases from 20.23 μV for Ti_0.99Nb_0.01O₂, reaches a minimum of 17.05 μV for Ti_0.86Nb_0.14O₂, and then increases to 17.24 μV for Ti_0.8Nb_0.2O₂. Due to its small band gap (E_g), Ti_0.86Nb_0.14O₂ demonstrated the lowest resistance (R), with its Photothermoelectric power (P_PTE) being 3.2 times that of Ti_0.8Nb_0.2O₂ under 0.9 mW illumination. Additionally, Nb doping significantly reduces the thermal conductivity (κ), with Ti_0.8Nb_0.2O₂’s κ dropping to 1.7 W·m^-1K^-1. This study not only provides a novel approach for the design of PTE materials in the visible light range but also promotes the development of self-powered sensors.