The abundance of solar thermal energy and the widespread demands for waste heat recovery make thermoelectric generators (TEGs) very attractive in harvesting low-cost energy resources. Meanwhile, thermoelectric refrigeration is promising for local cooling and niche applications. In this context there is currently a growing interest in developing organic thermoelectric materials which are flexible, cost-effective, eco-friendly and potentially energy-efficient. In particular, the past several years have witnessed remarkable progress in organic thermoelectric materials and devices. In this review, thermoelectric properties of conducting polymers and small molecules are summarized, with recent progresses in materials, measurements and devices highlighted. Prospects and suggestions for future research efforts are also presented. The organic thermoelectric materials are emerging candidates for green energy conversion.

Organic Thermoelectric Materials: Emerging Green Energy Materials Converting Heat to Electricity Directly and Efficiently

In response to the thread of environmental and ecological degradation along with projected fossil fuel depletion the active search for efficient renewable energy conversion technologies has been attempted in various research areas including the field of thermoelectrics. Despite the availability of considerable amounts of waste and natural heat stored in warm fluids (<250 °C) a lack of environmentally friendly materials with high natural abundance, low manufacturing cost and high thermoelectric efficiency impedes the widespread use of thermoelectric generators for energy harvesting on a large scale. In this perspective, we examine the possibility of using organic conducting polymers in thermoelectric applications. We provide an overview of the background and the key concepts of organic thermoelectrics and illustrate some of the first prototypes of polymer-based organic thermoelectric generators.

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Towards polymer-based organic thermoelectric generators

Effect of thickness on structural, optical and electrical properties of nanostructured ZnO thin films by spray pyrolysis

The need to improve the sensitivity, selectivity and stability of ozone gas sensors capable of monitoring the environment to prevent hazard to humans has sparked research on binary metal oxides. Here we report on a novel ozone gas sensor made with ca. 0.5 μm yolk-shelled ZnCo2O4 microstructures synthesized via an eco-friendly, co-precipitation method and subsequent annealing. With these ZnCo2O4 microspheres, ozone concentrations down to 80 parts per billion (ppb) could be detected with a.c. and d.c. electrical measurements. The sensor worked within a wide range of ozone concentrations, from 80 to 890 ppb, being also selective to ozone compared to CO, NH3 and NO2. The high performance could be attributed to the large surface area to volume ratio inherent in yolk-shell structures. Indeed, ozone molecules adsorbed on the ZnCo2O4 surface create a layer of holes that affect the conductivity, as in a p-type semiconductor. Since this mechanism of detection is generic, ZnCo2O4 microspheres can be further used in other environment monitoring devices.

/pdf/yolk-shelled-znco2o4-microspheres-surface-properties-and-gas-5fs5qf0tms.pdf

Yolk-shelled ZnCo2O4 microspheres: surface properties and gas sensing application

Cadmium selenide (CdSe) thin films were deposited on a glass substrate using the chemical bath deposition method at room temperature. The films were deposited using cadmium acetate as a Cd2+ ion source and sodium selenosulfate as a Se2? ion source. The 'as-deposited' CdSe thin films are red in colour and specularly reflective. The 'as-deposited' CdSe layers grew with nanocrystalline cubic phase along with some amorphous phase present, with an optical band gap 'Eg' of 2.3 eV and electrical resistivity of the order of 105?106 ? cm. The 'as-deposited' film is annealed in air at 673 K for 4 h and the effect of annealing on structural, morphological, optical and electrical properties is studied. It is worth noting that after annealing, metastable nanocrystallite cubic phase transforms into stable well crystalline hexagonal phase and films show a 'redshift' of '0.6 eV' in their optical band gap 'Eg'. After annealing, the crystallites' size increases from 45 ? to 180 ?, which results in a decrease in electrical resistivity. These changes have been attributed to the crystallite size dependent properties of CdSe semiconductor thin films.

https://iopscience.iop.org/article/10.1088/0268-1242/20/1/001/pdf

Band gap shift, structural characterization and phase transformation of CdSe thin films from nanocrystalline cubic to nanorod hexagonal on air annealing

G.G. Rusu

Papers

On the electronic transport properties of polycrystalline ZnSe films

Optical properties of Nb-doped TiO2 thin films prepared by sol–gel method

Preparation and characterization of ZnO thin films prepared by thermal oxidation of evaporated Zn thin films

Structural and optical characterization of Al-doped ZnO films prepared by thermal oxidation of evaporated Zn/Al multilayered films

Structural and electrical properties of zinc oxides thin films prepared by thermal oxidation