Thermodynamic Performance Study Of Three-Terminal Thermoelectric Devices Based On Two-Dimensional Heterostructure And Nanowire

In this thesis,the performance characteristics and optimal analysis of three-terminal thermoelectric heat engines and refrigerators based on two-dimensional heterostructure and nanowire are studied.In the steady-state case,we derive the expressions for the performance parameters of system,and then the parameters are optimized reasonably to improve the performance of thermoelectric devices.The main contents of this thesis are as follows:In chapter 1,we mainly introduce the research background of thermoelectric devices and the influence of different thermoelectric materials and structures on the performance of devices,and explain the advantages of low-dimensional electronic systems in improving thermoelectric performance.In chapter 2,we establish a model of the three-terminal thermionic heat engine based on semiconductor heterostructure.The model consists of two low temperature electron reservoirs and a middle heat reservoir,which are connected by the two-dimensional semiconductor heterostructure.According to Landauer formula theory and basic thermodynamic formulas,the expressions of the charge and energy currents flowing from the electron reservoirs are derived,and the output power and efficiency are defined in linear and nonlinear cases respectively.The performance characteristic graphs of the device are obtained by numerical simulation,and some conclusions are obtained by analyzing the graphs.The performance parameters of the device are optimized to get the maximum output power.In addition,the thermodynamic performance of the heat engine is analyzed by maximizing the product of output power and efficiency for working in higher efficiency.In chapter 3,a three-terminal nanowire heat engine model based on one-dimensional ballistic conductor is designed.Similar to the above model,the model also consists of two electron reservoirs and a middle heat reservoir,which are connected by the one-dimensional ballistic conductor.According to Landauer formula,the expressions of charge and energy currents are derived,and the output power and efficiency are defined.The performance characteristic graphs of the device are obtained by numerical simulation,and the performance parameters are optimized to obtain the maximum output power.The results of numerical simulation are compared with the three-terminal thermionic heat engine,and the advantages and disadvantages of the two devices are analyzed.In chapter 4,the three-terminal nanowire thermoelectric device is extended to work as a refrigerator by changing the temperature difference between the reservoirs.According to Landauer formula,the expressions of charge and energy currents are derived,the cooling rate and coefficient of performance(COP)are defined,and the working range of the refrigerator is determined.The performance characteristics of the device are analyzed by numerical simulation,and other factors affecting the performance are deeply explored.In chapter 5,we summarize the main work of this thesis,discuss the shortcomings in the work,and put forward suggestions for further research direction.