Flexible thermoelectric and photosensitive thin-film material based on nanostructured ZnO:In layer covered by nanocellulose

Abstract

In this study, to create new flexible thermoelectric and photosensitive thin-film material for in-plane thermoelectric generator (TEG) and broadband photodetector (PD) we deposited nanostructured indium-doped zinc oxide (ZnO:In) thin films on polyimide (PI) substrates by using the inexpensive and scalable method Successive Ionic Layer Adsorption and Reaction (SILAR). To reduce the resistivity of the ZnO:In film in the ZnO:In/PI composition to about 0.02 Ω∙m, it was annealed in a vacuum at 300 °C. To protect ZnO:In from the influence of gases and environmental moisture, the composition ZnO:In/PI was coated with nanocellulose (NC) manufactured by TEMPO-mediated oxidation of cheap and abundant herbaceous plant. An analysis of the surface morphology using scanning electron microscopy (SEM) using secondary electron (SE) and backscattered electron (BSE) images combined with energy dispersive X-ray spectrometry (EDS) made it possible to select the optimal mode for the formation of a continuous nanocellulose coating in the prepared in this way NC/ZnO:In/PI sample. By using ZnO:In/PI and NC/ZnO:In/PI test samples with ohmic aluminum contacts we determined output thermoelectric characteristics and time-dependent photoresponses depending on the illumination wavelength λ, bias voltage U and irradiance intensity Pλ. It has been experimentally established that both samples are suitable for use as broadband photodetectors. Their spectral responsivity Rλ data are from 2 to 0.1 A/W in the UV–visible-NIR detection range. The external quantum efficiencies (EQEs) for UV and blue light are especially high, at the level of hundreds of percent. But even under red and NIR illuminations, the obtained ZnO:In/PI and NC/ZnO:In/PI test samples demonstrate Rλ and EQE values, which exceed those of modern photodetectors based on zinc oxide and its composites. The specific detectivity D* is in the level of 1010-1012 Jones (cm∙s−1/2∙W−1) for all U, λ and Pλ, which is similar to D* values obtained for the known broadband photodetectors based on ZnO-contained compositions.