Oxygen pressure tunes thermoelectric properties of WO3−x thin films grown by pulsed laser deposition

This study investigates the thermoelectric performance of sub-stoichiometric tungsten oxide ( WO 3 − x ) thin films within a temperature range of 320 to 670 K. The films were synthesized via pulsed laser deposition (PLD) by ablating a WO 3 target onto silica substrates maintained at 500 °C. By varying the oxygen partial pressure (P O 2 ) from vacuum to 27 Pa, WO 3 − x thin films with tunable composition and structure were synthesized. Physico-chemical characterization revealed a progressive evolution from oxygen-deficient, weakly crystalline or structurally disordered WO 3 − x films towards more oxidized and crystalline tungsten oxide upon increasing P O 2 . Carbon-related signals were also detected in the deposited films. The films exhibited negative Seebeck coefficients between −10 and −55 μ V K − 1 , with post-stabilization electrical resistivities ranging from 4 × 1 0 − 4 to 4.7 × 1 0 − 3 Ω cm. Notably, the film deposited at 15 Pa exhibited the highest power factor of approximately 225 μ W m − 1 K − 2 at 660 K, whereas the 27 Pa sample was too resistive for reliable transport measurements. These results demonstrate a promising approach for tuning the thermoelectric performance of tungsten oxide thin films by controlling the oxygen pressure during deposition and, consequently, the balance between oxygen deficiency, structural order and charge transport.