This work reports the optimization of V2O5 Seebeck coefficient to obtain high sensitivity and transparent temperature sensors. It is observed that the film thickness plays a major role on the thermoelectric properties, together with the annealing step, obtaining a Seebeck coefficient of −690 μV K−1, for 75 nm thick V2O5 films deposited on glass, after an annealing step of 1 h at 773 K, in air. The V2O5 films are also deposited and optimized on polyimide substrates, but lower annealing temperature is required, 573 K for 3 h, to maintain the flexibility of the substrate and simultaneously high Seebeck coefficient, −591 μV K−1. These films are used in a simple design sensor and tested on the surface of a microfluidic channel (500 μm) made of polydimethylsiloxane, while having hot water flowing through it. The response time is below 1 s and the recovery time around 5 s.

The thermoelectric (TE) properties of vanadium pentoxide (V2O5) alloyed with graphite (G) were studied as a function of its incorporation percentage. Variable weight percentages of graphite powder (0–50%) were added to V2O5 powder and their mixtures were evaporated by a thermal evaporation technique to form thin films with a thickness in the range of 30–80 nm. In the infrared wavelength region, the transmittance of the obtained films increased as the G percentage was increased, while in the visible range, it decreased with G up to 10%. The TE properties were improved when G was in the range of 10–30%, while it decreased for the other percentages: Seebeck coefficient (S) changed from 0.6 mV/K to 0.9 mV/K and was zero with a G of 50%; the electrical conductivity varied slightly from 5 (Ωm)−1 to 0.7 (Ωm)−1 while the mobility improved from 0.07 cm2/V s to 1.5 cm2/V s and the respective carrier concentration was reduced, from 1 × 1018 cm−3 to 4 × 1016 cm−3. These films were applied as temperature sensors evaluating the thermovoltage as a function of thermal gradient between two electrodes, in which one was maintained at room temperature.