Large-area implementation and critical evaluation of the material and fabrication aspects of a thin-film thermoelectric generator based on aluminum-doped zinc oxide

Abstract

A large-area thermoelectric generator (TEG) utilizing a folded thin-film concept is implemented and the performance evaluated for near room temperature applications having modest temperature gradients (< 50 K). The TEGs with the area of ~0.33 m 2 are shown capable of powering a wireless sensor node of multiple sensors suitable e.g. for monitoring environmental variables in buildings. The TEGs are based on a transparent, non-toxic and abundant thermoelectric material, i.e. aluminium-doped zinc oxide (AZO), deposited on flexible substrates. After folding, both the electrical current and heat flux are in the plane of the thermoelectric thin-film. Heat leakage in the folded TEG is shown to be minimal (close to that of air), enabling sufficient temperature gradients without efficient heat sinks, contrary to the conventional TEGs having the thermal flux and electrical current perpendicular to the plane of the thermoelectric films. The long-term stability studies reveal that there are no significant changes in the electrical or thermoelectric properties of AZO over several months, while the contact resistance between AZO and silver ink is an issue exhibiting a continuous increase over time. The performance of the TEGs and technological implications in relation to a state-of-the-art thermoelectric material are further assessed via a computational study.

Enhanced Thermoelectric Transport and Stability in Atomic Layer Deposited-HfO2/ZnO and TiO2/ZnO-Sandwiched Multilayer Thin Films

“…One disadvantage of pure ALD ZnO, though, is its low electrical stability at high temperatures [20][21]. While this could be overcome by the incorporation of other elements, thermoelectric devices based on doped ALD ZnO thin films have been mainly limited to Al and Ga 3 [7,11,[22][23][24]. Although Al has been a well-established dopant, ALD Al-doped ZnO (AZO) has been reported to exhibit low doping efficiency of only about 13 % [19].…”

“…In addition, ALD allows high controllability over the amount and distribution of dopants. One disadvantage of pure ZnO synthesized by ALD, though, is its low electrical stability at high temperatures. , While this could be overcome by the incorporation of other elements, TE devices based on doped ZnO thin films synthesized by ALD have been mainly limited to Al and Ga. ,,− Although Al has been a well-established dopant, Al-doped ZnO (AZO) synthesized by ALD has been reported to exhibit a low doping efficiency of only about 13% . Additionally, group III elements have relatively low stability when doped in ZnO owing to the low electronegativity difference with O .…”

Stability under humidity, UV-light and bending of AZO films deposited by ALD on Kapton

“…As shown above, ALD thick films provide superior thermoelectric performance and are thereby preferred for integrating many large area thermoelectric applications. An example is a smart window that make use of AZO thermoelectric modules deposited on a curved substrate 22 . Hence, characterizing the flexibility and stability of AZO films in this type of applications is important.…”

Recent Advances in the Nanomaterials, Design, Fabrication Approaches of Thermoelectric Nanogenerators for Various Applications

“…For example, Karthikeyan et al [187] utilized thermal evaporation to deposit n-type PbTe and p-type SnTe onto a flexible polyimide substrate. The maximum zT of 0.3 [210] Copyright 2020, Elsevier.…”

“…c) A digital photograph of 11 TEG modules folded and connected in series. Reproduced with permission [210]. Copyright 2020, Elsevier.…”