Flexible in-plane thermoelectric modules based on nanostructured layers ZnO and ZnO:In

Abstract

In this study, with the aim of developing flexible in-plane thermoelectric module we deposited via SILAR method 0.3–1.4 thick nanostructured layers of undoped and indium doped zinc oxide on Kapton polyimide (PI) substrates and thus prepared ZnO:In/PI and ZnO/PI samples. We analyzed surface morphology, crystal structure, chemical composition, optical, electrical and thermoelectric properties of ZnO and ZnO:In thin films grown via SILAR on PI substrates. It was shown that ZnO:In/PI samples are consisted of flower-like ZnO:In microstructures with rod petals having pencil-like ends. ZnO/PI samples have lily flower-like ZnO microstructures with rounded petals. Despite the fact that crystal structure and optical properties of the nanostructured ZnO:In and ZnO films were almost the same, their morphology determined the electrical and thermoelectric properties. More compact 1.4 µm thick ZnO layer in sample ZnO/PI provided the best thermoelectric power factor ≈ 8 µW/(m·K2) due to its lower resistivity at near-room ≈ 0.15 Ω cm. Among four samples of the prepared flexible in-plane thermoelectric modules with single legs in the form of PI strips 3 cm long and 0.5 cm wide, covered with the semiconductor film ZnO or ZnO:In and having thin-film Al ohmic contacts at the edges, the TE module based on ZnO/PI showed the best output characteristics. At the temperature difference 50 К, its output power density reaches 10 µW/cm2, which is commensurate with the up-to-date values for solid miniature and flexible TEGs.