Preparation Of Antimony Based Thermoelectric Thin Film And Thermoelectric Generation

Thermoelectric materials are environment friendly materials, which can convert heat into electricity. Thermoelectric generators based on semiconductor matirials are widely used as sustainable energy sources. Researches in the past a few years indicate that thin film thermoelectric materials possess higher figure of merit （ZT） and better thermoelectric performance than traditional bulk thermoelectric materials. Conversion efficiency of thermoelectric generators depends on the property of thermoelectric materials. Thin film and doping are the main future methods to improve the thermoelectric performance of thermoelectric materials. In this paper, ZnSb and CoSb₃ are P type and N type thermoelectric materials, respectively, thermoelectric generators were prepared on polymide substrate. The details are as follows:P type ZnSb thin film was deposited on polymide substrate by radio frequency magnetron sputtering, the influence of different annealing temperature, Ti co-sputtering, Ti prefabricated layer, In co-sputtering, In prefabricated layer were investigated. Results indicate that 325 ℃ was the best annealing temperature; Sample with 4 minutes Ti co-sputtering has better thermoelectric properties than other Ti co-sputtering samples, with the increasing of the temperature the highest powerfactor was 3.12mWm^-1K^-2; Sample with 3 minutes Ti prefabricated layer has better thermoelectric properties than other Ti prefabricated layer samples, the highest powerfactor reached to 2.81 mWm^-1K^-2. Sample with 1 minute In co-sputtering has better thermoelectric properties than other In co-sputtering samples, with the increasing of the temperature, the powerfactor increased from 1.08mWm^-1K^-2 to 3.76mWm^-1K^-2 and then fell suddenly; Sample with 8 minutes In prefabricated layer has the best thermoelectric properties of all the In fabricitaed layer samples, powerfactor gradually increased from 1.32mWm^-1K^-2 to 7.52mWm^-1K^-2. When compared with other samples doped by different methods, samples with In prefabricated layer have the best thermoelectric properties. Therefore, in this paper samples with 8 minutes In prefabricated layer were used as the P type materials to prepare thermoelectric generator.N type CoSb₃ thin film was deposited on polymide substrate by magnetron sputtering, the influence of different In content was studied. Results indicated that crystallinity of In doped samples was improved. Samples with 60 seconds In co-sputtering when the direct-current power is 27W have better properties, the highest powerfactor is 1.26 ×10^-3Wm^-1K^-2 and then powerfactor fell suddenly when temperature was above 170℃.The influence of different electrode materials was investigated. Cu, Al, Mo, Ni were used as different electrode materials, respectively. Results indicated that when the electrode materials were Cu and Mo, the output power was higher than the samples with Al and Ni electrode materials. The output power of samples with Cu or Mo electrode fell suddenly when the temperature was above 220 ℃, the possible reason was the different thermo expansivity with electrode materials and thermoelectric materials and also the electrode materials were oxidated. To improve the electrode,2 methods of different thickness Ni prefabrication layer,300nm Cu electrical layer, 100nm Ni covering layer and different thickness of Mo prefabrication layer,300nm Cu electrical layer,80nm Mo covering layer were used. Results revealed that output power of generators with 300nm Cu electrical layer and 80nm Mo covering layer were higher than other samples. The output power was still stable after 3 times thermal cycle test. The method of 300nm Cu electrical layer and 80nm Mo covering layer was used to produce electrodes of thermoelectric generators. Thermoelectric generators had been prepared with 7 identical p-n couples, which is connected in series to form a one dimensional array. The test results showed that the output voltage and current correspond well with the output character of series batteries. The maximum output voltage, current and output power of our divice with 7 couples were 323mV,0.8mA and 260.08μW when the temperature difference reached 210℃. The maximum output power of the flexible thin film thermoelectric generator produced per couple and per unit temperature difference was 0.177μW per K-Couple.