Unlocking the effect of film thickness on the thermoelectric properties of thermally evaporated Cu2−xSe thin films

Abstract

Miniaturization is crucial to realize thermoelectric (TE) devices as an energy source for smart utilities. The present work reports the bulk-like ZT value realized in Cu_2−xSe thin films in the mid-temperature range. The effect of varying the film thickness on the structural and TE properties were systematically studied, and the obtained results were compared with that of their bulk counterpart. The detailed structural characterizations revealed the nonstoichiometric polycrystalline nature of Cu_2−xSe with the unusual presence of monoclinic and cubic phases. Upon increasing the film thickness, the TE measurements showed a simultaneous increase in the electrical conductivity (σ) and Seebeck coefficient (S) due to increased grain size and uniformity. Due to the simultaneous increase in σ and S, an ultrahigh power factor (PF) value of 5185 μW m⁻¹ K⁻² and a bulk-like figure of merit ZT ≈ 1.2 were achieved.