Efficient biodegradable flexible hydrophobic thermoelectric material based on biomass-derived nanocellulose film and copper iodide thin nanostructured layer

Abstract

Here we applied solar energy converted into biomass to produce efficient biodegradable flexible hydrophobic thermoelectric (TE) material with nanocellulose (NC) film as environmentally friendly functional substrate. We used fast-growing perennial herb Miscanthus × giganteus to manufacture flexible 12 µm thick NC film with stable monoclinic cellulose structure (Iβ), high crystallinity index (CI = 78%) and average crystallite size 3 – 4 nm. Through the low-temperature cheap and scalable method Successive Ionic Layer Adsorption and Reaction (SILAR) we deposited copper iodide (CuI) films on NC substrates and thus obtained non-toxic TE materials CuI/NC, which can be water-repellent, as their contact angles reach 140°. In the most efficient TE sample CuI/NC, the obtained via SILAR 0.39 µm thick nanostructured CuI film consists of cubic (111)-oriented γ-CuI crystals with faceted surfaces of ~200–300 nm. The high electrical conductivity (σ) and shape of the σ vs. temperature (T) curve of this CuI/NC sample is realized through suppression of grain boundary scattering due to tunneling currents in CuI. The CuI/NC material has large thermoelectric power factor (PF) that grows with increasing temperature and reaches value 140 μW·m−1·K−2 at T = 333 K. This PF is the record for biodegradable flexible thermoelectric materials. At ΔT = 40 K the CuI/NC-based single p-CuI thermoelectric leg generates open circuit voltage 3.5 mV, short circuit current 4 µA, and power 3.8 nW, and these output parameters can be further improved through a thickening the CuI film in CuI/NC by increasing the number of SILAR cycles.