Effect Of Carbon Composite On The Thermoelectric Properties Of ZnO:Al Films By Vacuum Thermal Evaporation Of Radio Frequency Atomic Source

Thermoelectric materials can convert thermal energy into electrical energy and play an important role in recovering low-grade waste heat.Among various thermoelectric materials,oxides have attracted wide attention due to their high-temperature thermal stability,controllable electro-acoustic transport properties,and mature synthetic technologies.Among them,the direct wide band gap semiconductor ZnO has potential application value in the field of thermoelectric materials due to its low cost,easy doping,and transparency.But the key to limit the application of ZnO at present is the low ZT value.The ZT value of ZnO bulk at 1273 K is only 0.65.This is because ZnO has a high resistivity,which limits the improvement of thermoelectric performance.Carbon materials have high electrical conductivity and can be a means to further improve the thermoelectric properties of ZnO.It is necessary to study the mechanism of the effect of carbon recombination on the microstructure evolution and thermoelectric properties of ZnO thin films.Aiming at the problem of the mechanism of improving the thermoelectric properties of ZnO:Al thin films by carbon composites and the charge depletion layer at the composite interface,a carbon material composite ZnO:Al thin film was prepared by RF atom source vacuum thermal evaporation method and external field treatment.The effect of carbon recombination and pulsed electric field on the microstructure and thermoelectric properties of ZnO:Al thin films reveals the mechanism of the effect of carbon recombination on the growth process and thermoelectric properties of ZnO:Al thin films.First,study the effect of film thickness on the microstructure and thermoelectric properties of ZnO:Al thin films;second,study the effect of carbon recombination on the microstructure and thermoelectric properties of ZnO:Al thin films,and determine the optimal carbon type and carbon composite amount;finally,study the pulsed electric field The effect of the treatment on the microstructure and thermoelectric properties of the thin film reveals the relationship between structural evolution and thermoelectric properties.The main conclusions are as follows:(1)The effects of film thickness on the microstructure and thermoelectric properties of ZnO:Al thin films were studied.The results show that film thickness does not affect phase composition and preferred orientation.But the increase of film thickness will increase the grain size,surface particle size and surface roughness.The increase of grain size will reduce the grain boundary and increase the carrier mobility,so that the thermoelectric parameters of the thin film change with the thickness of the film.It has an optimal power factor at 700 nm and a power factor of 627 ?W·m-1·K-2 at 560 K.The output power of the film increases with the increase of the hot-end temperature,and the 700 nm film has the highest output power.(2)The effects of carbon recombination on the microstructure and thermoelectric properties of ZnO:Al films were studied.The results show that carbon recombination will cause large particles to appear on the surface of the film,and increase surface roughness and particle size.Different types of carbon materials can improve the carrier mobility of the thin film,and CNT composite can also reduce the carrier concentration of the thin film and increase the Seebeck coefficient to obtain the best thermoelectric performance.When the amount of CNT recombination increases,the surface large particles increase,the carrier mobility increases first and then decreases,and the carrier concentration decreases first and then increases.When the CNT recombination amount is high,a charge depletion layer is generated at the recombination interface to reduce the carrier mobility,and the optimal CNT recombination amount is determined.(3)The effects of pulsed electric field treatment on the microstructure and thermoelectric properties of CNT composite ZnO:Al films were studied.The results show that the pulsed electric field treatment has little effect on the phase composition and preferred orientation of the ZnO:Al film,but it can change the surface morphology of the film,agglomerate the particles,and increase the surface particle size and roughness.Pulsed electric field treatment can increase the carrier mobility,reduce the carrier concentration,and increase the power factor by up to about 20%.Pulsed electric field treatment can optimize the charge depletion layer at the CNT composite interface in ZnO:Al thin films and improve carrier mobility.