Large area highly crystalline MoS 2 and WS 2 thin films were successfully grown on different substrates using radio-frequency magnetron sputtering technique. Structural, morphological and thermoelectric transport properties of MoS 2, and WS 2 thin films have been investigated systematically to fabricate high-efficient thermal energy harvesting devices. X-ray diffraction data revealed that crystallites of MoS 2 and WS 2 films are highly oriented in 002 plane with uniform grain size distribution confirmed through atomic force microscopy study. Surface roughness increases with substrate temperature and it plays a big role in electron and phonon scattering. Interestingly, MoS 2 films also display low thermal conductivity at room temperature and strongly favors achievement of higher thermoelectric figure of merit value of up to 1.98. Raman spectroscopy data shows two distinct MoS 2 vibrational modes at 380 cm −1 for E 1 2g and 410 cm −1 for A 1g. Thermoelectric transport studies further demonstrated that MoS 2 films show p-type thermoelectric characteristics, while WS 2 is an n-type material. We demonstrated high efficient pn-junction thermoelectric generator device for waste heat recovery and cooling applications.
Layered structure bismuth telluride and molybdenum disulfide thin films were successfully deposited on different substrates using radio-frequency magnetron sputtering technique. The structural, morphological, and thermoelectric transport properties of bismuth telluride and molybdenum disulfide thin films have been investigated systematically to fabricate high-efficient thermal energy harvesting thermoelectric device. The magnitude of the Seebeck coefficient of bismuth telluride thin films decreases with increase in film thickness. Bismuth telluride grown at 350 °C for 10 min, which is approximately 120 nm, displays a maximum Seebeck coefficient of −126 μV K−1 at 435 K. The performance shows strong temperature dependence when the films were deposited at 300 °C, 350 °C, and 400 °C. The power factor increases from 0.91 × 10−3 W/mK2 at 300 K to about 1.4 × 10−3 W/mK2 at 350 K. Molybdenum disulfide films show the positive Seebeck coefficient values and their Seebeck coefficient increases with film thickness. The AFM images of bismuth telluride thin films display a root-mean-square (rms) roughness of 32.3 nm and molybdenum disulfide thin films show an rms roughness of 6.99 nm when both films were deposited at 350 °C. The open-circuit voltage of the pn-junction thermoelectric generator (TEG) device increases with increase in ΔT to about 130 mV at ΔT = 120 °C. We have demonstrated a highly efficient pn-junction TEG device for waste heat recovery applications.
We report on high performance transparent Al:ZnO (AZO) thin film heaters on flexible polymer (polyethylene terephthalate) and glass substrates which demonstrate low sheet resistivity. AZO thin films were grown by radio-frequency magnetron sputtering at low Ts (below 200 °C) on flexible, transparent polyethylene terephthalate substrates that show stable and reproducible results by applying low (<10 V) voltages. This study also examined identical AZO thin films on glass substrates that showed highly reproducible heating effects due to the Joule heating effect. The potential applications are foldable and wearable electronics, pain/injury therapy smart windows, automobile window defrosters, and low-cost power electronics.
We report on the ultraviolet ͑UV͒-radiation sensing of pulsed-laser deposited In 2 O 3 : SnO 2 : ZnO films grown on glass substrates. The films demonstrate sharp increase ͑ϳ0.35 ⍀͒ in electrical resistance on UV illumination. The resistance of the films shows strong spectral ͑in the vicinity of 325 nm͒ and power dependence. This is explained due to the presence of defects located at lattice disorders that generate levels within the semiconductor band gap and originate depletion region around them when charged. This reduces the effective conduction region, increasing the effective resistance. These results show new possibilities for the low-cost high performance UV radiation sensors for biosafety.
The electrical conductivity and Seebeck coefficient of PbSe single crystals grown by the Bridgman technique display metallic behavior. The Seebeck coefficient increases linearly with increasing temperature and showed positive Seebeck values, typically valid for a p-type PbSe crystal. The electronic thermal conductivity decreases with increase in temperature. The power factor increases gradually with temperature until the maximum value of 6.51 × 10−3 W/mK2 at 260 K, other values are 5.95 × 10−3 W/mK2 at 300 K, and 5.40 × 10−3 W/mK2 at 320 K. Our results demonstrate that as-grown PbSe crystal is generically p-type due to excess in Pb and can be a potential candidate for thermoelectric power generation.
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