Investigation On The Performances And Optimum Theories Of Novel Thermoelectric Converters And Concentrated Solar Cells

Energy sources and environment are two major problems in our society today.Owing to the exhaustion of non-renewable resources such as fossil fuels and the increasing seriousness of environmental pollution,it is urgent to find alternative energies.The solar photovoltaic technology is one of the important ways to solve the energy crisis.However,the problems of high cost,low efficiency,and short life restrict the wide development and application of traditional solar cells.Thus,it is one of the hot issues in the research of new energy devices to develope novel thermoelectric converters and concentrated solar cells,optimize the performance parameters,improve the energy efficiency,and reduce the cost.This dissertation mainly investigates the performances of two kinds of near-field radiative thermoelectric converters,three kinds of high-efficient concentrated solar cells,and spin-Seebeck thermoelectric converter and temperature sensors.The parameters of these devices are optimized.The main contents of this dissertation include four parts.The first part,i.e.,chapter 1,includes the investigation on the application of the near field thermal radiation effect in the novel thermoelectric converters.The models of irreversible near-field thermophotovoltaic cell and thermoradiative cell are established.Based on the theory of fluctuation electrodynamics,the influences of heat transfer irreversibility on the performance of two kinds of devices are considered.According to the numerical simulation,the temperatures of the p-n junction under different performance parameters are determined.By considering the trade-off between power output and efficiency,the optimization criteria of the vacuum gap and voltage output are obtained.The second part consists of chapters 3-5,in which the models of three kinds of novel high-efficient concentrated solar cells are designed by combining the solar concentrator with the thermophotovoltaic cell,thermionic power generator,and thermoradiative cell.The effects of multiple irreversible thermal losses from the heat absorber and the cold side of the whole device to the environment are taken into account.The parametric characteristics of three kinds of concentrated solar cells at the maximum efficiency are studied.The obtained results demonstrate that we can obtain the maximum efficiency of the near-field solar thermophotovoltaic cell by optimizing the vacuum gap and voltage output;the maximum efficiency of the far-field solar thermophotovoltaic cell by optimizing the ratio of the front area of the thermal absorber to that of the emitter,the band-gap of semiconductor,and the voltage output;the maximum efficiency of the vacuum thermionic solar cell by optimizing the ratio of the front area of the thermal absorber to that of the cathode,vacuum gap,and voltage output;and the maximum efficiency of the solar thermoradiative cell by optimizing the concentrator factor,voltage output,and the semiconductor band-gap.The third part consists of chapters 6 and 7,in which the far-field and near-field thermophtovolatic cells are coupled with the solid oxide fuel cell and thermionic power generator,respectively.The obtained results show that a part of the waste heat of the solid oxide fuel cell can be converted into electricity by means of a far-field thermophtovolatic cell and a maximum power output density of hybrid systems can be obtained by optimizing the performance parameters;the radiation energy released by the cathode material of the thermionic power generator can be converted into electricity by means of a near-field thermophotovoltaic cell,and consequently,the utilization of energy can be improved.The fourth part incluedes chapter 8,in which the performance of a longitudinal spin-Seebeck based power device is investigated.The optimal design of structure parameters and voltage output and the problem of load matching at the optimum states are analyzed systematically,and the optimal criteria of important parameters are provided.In addition,the models of two temperature sensors based on the longitudinal and transverse spin-Seebeck effects are proposed.The principle of temperature measurement is introduced in detail,the relation between the open circuit voltage signal and the temperature is given,the effects of the spin angle of the hole and the thickness of the metal on the measuring sensitivity are discussed,and the performances of two kinds of temperature sensors are compared.The obtained results demonstrate that two kinds of temperature sensors can be used for measuring the temperature of the nanoscale environment.It is of great significance to investigate the optimum performances of novel high-efficient thermoelectric conversion devices and concentrated solar cells for the the development and utilization of solar energy,radioactive isotopes decay heat,industrial waste,etc.