Thermophotovoltaic Cells Based On N-type Bismuth Telluride Thin Film

Thermophotovoltaic technology is an emerging green and clean energy technology.Thermophotovoltaic cells that convert low-temperature radiation into electrical energy can be applied in many fields such as aerospace and military.Some III-V compound semiconductors with narrow band gaps can absorb long-wavelength infrared photons and suitable for makeing thermophotovoltaic(TPV)cells.In this thesis,a narrow band gap semiconductor bismuth telluride(Bi₂Te₃)was selected as the thermophotovoltaic materials for investigating whether it is possible to make thermophotovoltaic cells which can absorb low temperature radiation.The works of this research include making n-Bi₂Te₃/p-Si and n-Bi₂Te₃/p-Ge thermophotovoltaic cells and discussing the factors that influencing the cell's performance.The details of the research are as followings:1.Firstly,a thermophotovoltaic cells of n-Bi₂Te₃/p-Si that can absorb infrared radiation was prepared by using radio frequency magnetron sputtering technology.In order to improve the quality of Bi₂Te₃thin films and reduce the recombination of carriers in the transport process,the prepared samples were annealed for 10 hours in an annealing furnace.The columnar structure in the films is clear,and the two elements of Bi and Te in the films formed at different substrate temperatures maintain a stable atomic ratio(about 36:64).The diffraction peaks of the Bi₂Te₃films grow along the C axis after annealing.The crystallinity of the Bi₂Te₃films becomes better.It is found that the resistivity of Bi₂Te₃films increased after annealing.2.The property of the thermophotovoltaic cells is investigated.The results show that the n-Bi₂Te₃/p-Si heterojunction has good p-n junction characteristics.The open circuit voltage and short circuit current of the cell increase with radiation temperatures.The energy band structure of p-Si/n-Bi₂Te₃heterojunction was simulated by Silvaco TCAD,and was used to explain the small open-circuit voltage and short-circuit current of n-Bi₂Te₃/p-Si thermophotovoltaic cells.3.The n-Bi₂Te₃/p-Ge thermophotovoltaic cells was fabricated by using radio frequency magnetron sputtering technology.Compared with n-Bi₂Te₃/p-Si heterojunction,the p-Ge/n-Bi₂Te₃heterojunction has a smaller valence band offset,which attributes to the movement of the photo-generated holes from n-Bi₂Te₃side to the p-Ge side,which improve the output capacity of the cell.Silvaco TCAD was used to simulate the band structure of p-Si/n-Bi₂Te₃heterojunction,p-Ge/n-Bi₂Te₃heterojunction,and the n-Bi₂Te₃/p-Ge heterojunction with different doping concentrations.The band structures were compared and analyzed through explaining the barrier height,depletion width and valence band offset.The electrical properties(IV curve of heterojunction,open circuit voltage,short circuit current)of n-Bi₂Te₃/p-Ge thermophotovoltaic cells were tested under different radiation temperature.Compared with the n-Bi₂Te₃/p-Si thermophotovoltaic cells,the output current of the n-Bi₂Te₃/p-Ge thermophotovoltaic cells increases significantly.And the reverse current also becomes bigger.On the basis of the band structure and the carrier transportation,a reasonable explanation is given.