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This work was mainly funded by ERC‐CoG‐2014, and partially funded by FCT – Fundação para a Ciência e a Tecnologia, I.P., in the scope of the Project Nos. LA/P/0037/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. Publisher Copyright: © 2023 The Authors. Advanced Materials Technologies published by Wiley-VCH GmbH. Transparent-conductive-oxide (TCO) materials and transparent devices combining photovoltage and thermoelectric effects are still scarce. Hence, a new transparent-conductive-oxide/insulating/transparent-semiconductor-oxide (TCO-I-TSO) structure combining such effects is developed. It is made of aluminum-doped zinc oxide (AZO)/SiO2/NiO thin films sequentially deposited on glass substrates. AZO exhibits thermo and photovoltage in response to gradient temperature and absorption of UV photons, while NIR photons absorption in the NiO layer. Photovoltage appears in the plane between the AZO and NiO layer when the whole sample is irradiated with near infrared light, and it also depends on the thickness of the SiO2 layer. This photovoltage is continuously monitored on samples placed in a glass window facing south. Throughout the day, the photovoltage varies from 0 to 300 µV proportionally to the light intensity. publishersversion inpress

A new concept of oxide-metal-oxide structures that combine photothermoelectric effect with high reflectance (~80%) at wavelengths in the infrared (> 1100 nm) and high transmittance in the visible range is reported here. This was observed in optimized ITO/Ag/ITO structure, 20 nm of Siver (Ag) and 40 nm of Indium Tin Oxide (ITO), deposited on Aluminum doped Zinc Oxide (AZO) thin film. These layers show high energy saving efficiency by keeping the temperature constant inside a glazed compartment under solar radiation, but additionally they also show a photothermoelectric effect. Under uniform heating of the sample a thermoelectric effect is observed (S = 40 μV/K), but when irradiated, a potential proportional to the intensity of the radiation is also observed. Therefore, in addition to thermal control in windows, these low emission coatings can be applied as transparent photothermoelectric devices.

In this work, eco-friendly magnesium-silicide (Mg2Si) semiconducting (n-type) thermoelectric pastes for building components concerning energy-harvesting devices through 3D printing, spray and electrospinning were synthetized and tested for the first time. The Mg2Si fine powders were obtained through the combination of ball milling and thermal annealing under Ar atmosphere. While the latter process was crucial for obtaining the desired Mg2Si phase, the ball milling was indispensable for homogenizing and reducing the grain size of the powders. The synthetized Mg2Si powders exhibited a large Seebeck coefficient of ~ 487 µV/K and were blended with a polymeric solution in different mass ratios to adjust the paste viscosity to the different requirements of 3D printing, electrospinning and low-pressure spray. The materials produced in every single stage of the paste synthesis were characterized by a variety of techniques that unequivocally prove their viability for producing thermoelectric parts and components. These can certainly trigger further research and development in green thermoelectric generators (TEGs) capable of adopting any form or shape with enhanced thermoelectric properties. These green TEGs are meant to compete with common toxic materials such as Bi2Te3, PbTe and CoSb that have Seebeck coefficients in the range of ~ 290–700 μV/K, similar to that of the produced Mg2Si powders and lower than that of 3D printed bulk Mg2Si pieces, measured to be ~ 4866 μV/K. Also, their measured thermal conductivities proved to be significantly lower (~ 0.2 W/mK) than that reported for Mg2Si (≥ 4 W/mK). However, it is herein demonstrated that such thermoelectric properties are not stable over time. Pressureless sintering proved to be indispensable, but difficultly achievable by long thermal annealing (even above 32 h) in inert atmosphere at 400 °C, at least for bulk Mg2Si pieces constituted by a mean grain size of 2–3 μm. Hence, for overcoming this sintering challenge and become the silicide’s extrusion viable in the production of bulk thermoelectric parts, alternative pressureless sintering methods will have to be further explored.

openaire: EC/H2020/645241/EU//TransFlexTeg Simultaneously transparent and flexible conductive materials are in demand to follow the current trend in flexible technology. The search for materials with compliant optoelectronic properties, while simultaneously retaining their electric conductivity at high strain deformation, comprises promising opportunities in modern nanotechnology. Copper iodide (CuI) is not only the most transparent and highly conductive p-type material, but its optimization has contributed to improved ZT values in planar thin-film thermoelectrics. In this work, the readiness of CuI thin films to transparent, flexible technology is evidenced. A maximum ZT value of 0.29 for single CuI thin films of ca. 300 nm in thickness is reported. Values of open-circuit voltage Voc, short circuit current Isc and power output of p-n thermoelectric modules of Gallium-doped zinc oxide (GZO) and CuI thin films deposited on a transparent flexible Kapton® (type CS) substrate are reported, and a prototype of a flexible transparent thermoelectric generatorbased on 17 p-n modules was constructed. Bending analysis of CuI thin films reveals interesting, distinct results when submitted to compression and tension analysis-a behaviour not seen in conventional semiconducting thin films under equivalent strain conditions. A plausible account for such diversity is also included.

This work was mainly funded by H2020-ICT-2014-1, RIA, TransFlexTeg-645241, and ERC-CoG-2014, CapTherPV, 647596, and partially funded by FEDER funds through the COMPETE 2020 Program and National Funds through FCT - Portuguese Foundation for Science and Technology under the project UID/CTM/50025/2013. Developments in thermoelectric (TE) transparent p-type materials are scarce and do not follow the trend of the corresponding n-type materials - a limitation of the current transparent thermoelectric devices. P-type thermoelectric thin films of CuI have been developed by three different methods in order to maximise optical transparency (>70% in the visible range), electrical (σ = 1.1 × 104 Sm-1) and thermoelectric properties (ZT = 0.22 at 300 K). These have been applied in the first planar fully transparent p-n type TE modules where gallium-doped zinc oxide (GZO) thin films were used as the n-type element and indium thin oxide (ITO) thin films as electrodes. A thorough study of power output in single elements and p-n modules electrically connected in series and thermally connected in parallel is inclosed. This configuration allows for a whole range of highly transparent thermoelectric applications. publishersversion published

The electronic and optical properties of p-type copper oxides (CO) strongly depend on the production technique as it influences the obtained phases: cuprous oxide (Cu2O) or cupric oxide (CuO), the most common ones. Cu films deposited by thermal evaporation have been annealed in air atmosphere, with temperature between 225 and 375 °C and time between 1 and 4 h. The resultant CO films have been studied to understand the influence of processing parameters in the thermoelectric, electrical, optical, morphological, and structural properties. Films with a Cu2O single phase are formed when annealing at 225 °C, while CuO single phase films can be obtained at 375 °C. In between, both phases are obtained in proportions that depend on the film thickness and annealing time. The positive sign of the Seebeck coefficient (S), measured at room temperature (RT), confirms the p-type behavior of both oxides, showing values up to 1.2 mV·°C–1 and conductivity up to 2.9 (Ω·m)−1. A simple detector using Cu2O have been fabricate...

This work reports the optimization of V2O5 Seebeck coefficient to obtain high sensitivity and transparent temperature sensors. It is observed that the film thickness plays a major role on the thermoelectric properties, together with the annealing step, obtaining a Seebeck coefficient of −690 μV K−1, for 75 nm thick V2O5 films deposited on glass, after an annealing step of 1 h at 773 K, in air. The V2O5 films are also deposited and optimized on polyimide substrates, but lower annealing temperature is required, 573 K for 3 h, to maintain the flexibility of the substrate and simultaneously high Seebeck coefficient, −591 μV K−1. These films are used in a simple design sensor and tested on the surface of a microfluidic channel (500 μm) made of polydimethylsiloxane, while having hot water flowing through it. The response time is below 1 s and the recovery time around 5 s.