Design research method of thermoelectric transistor power generation device

Abstract

The invention relates to the technical field of thermoelectric conversion and semiconductor device design, in particular to a design research method of a thermoelectric transistor power generation device. According to the specific technical scheme, on the basis of a built thermoelectric transistor theoretical model, a complete thermoelectric transistor power generation device performance design research process and method are provided through doping concentration optimization and circuit design, and therefore the output performance of a thermoelectric transistor can be optimized. According to the thermoelectric transistor power generation device obtained through optimization design, the Seebeck voltage generated by the temperature difference under the room temperature condition can directly drive the thermoelectric transistor to work normally, thermoelectric conversion is achieved, the output power and the thermoelectric conversion efficiency are greatly improved, the thermoelectric transistor power generation device can be applied to thermoelectric power generation under various temperature difference conditions, and the thermoelectric transistor power generation device has a wide application prospect. The device can supply power to different types of electric appliances, and can also be applied to various thermoelectric detection.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric conversion and semiconductor device design, and in particular to a design and research method for a thermoelectric transistor power generation device, and in particular to a temperature difference driven thermoelectric transistor power generation device. Background Art

[0002] In order to alleviate the current energy crisis, it is necessary to develop new, clean and environmentally friendly renewable energy and conversion technologies, including thermoelectric power generation. The reason is that the carriers inside the thermoelectric power generation material will move in a directional manner under the drive of the temperature field, thereby forming an electric potential difference at both ends, so that the thermoelectric generator can directly convert various cold sources or heat sources including various waste heat into electrical energy for temperature difference power generation or thermoelectric detection.

[0003] At present, in order to improve the output performance (output power and thermoelectric conversion efficiency) of thermoelectric generators, a variety of methods for optimizing the thermoelectric properties of materials have been proposed, such as band engineering, material nano-sizing, material low-dimensionality, and device structure optimization design.

[0004] For thermoelectric power generation or detection devices, there has always been a difficult problem to overcome, namely the strong coupling characteristics between the performance parameters of thermoelectric materials themselves (electrical conductivity, Seebeck coefficient and thermal conductivity). The optimization methods mentioned above have not completely solved this problem. Most optimization methods can only hope that the increase in a certain performance parameter can be greater than the decrease in another performance parameter, so it is impossible to achieve the decoupling of the thermoelectric performance parameters of the material. As a result, the thermoelectric conversion efficiency is far lower than the power generation efficiency of traditional heat engines, which greatly limits its large-scale commercialization process. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a design and research method for a thermoelectric transistor power generation device. One of the main purposes is to construct a thermoelectric transistor power generation device and realize the decoupling of thermoelectric performance parameters, that is, to construct a directly connected PNP / NPN heterojunction, and through the effect of temperature difference, due to the migration of carriers and the change of the built-in electric field, a bipolar junction transistor circuit is formed. At the same time, according to the circuit characteristics of the bipolar junction transistor (the emitter current determines the output current, and the collector voltage determines the output voltage), the conductivity (determined by the output current) and the Seebeck coefficient (determined by the output voltage) of the output end of the thermoelectric transistor power generation device can be decoupled.

[0006] The second main purpose is to provide an analytical method for design and performance research based on the working principle of thermoelectric transistor power generation devices, so that it is applicable to different substrates and thermoelectric semiconductor materials of arbitrary composition and structure and their applications. Referring to the analysis of traditional bipolar junction transistor circuits, according to the characteristics of thermoelectric transistors themselves, a complete set of analytical methods is constructed using calculation formulas such as the thermal energy balance equation, Poisson's equation, current density expression, and current continuity equation, so that the thermoelectric transistor can be in forward amplification working mode or normal operation only under the action of Seebeck voltage, that is, temperature difference power generation can be achieved without the participation of external electric or magnetic fields.

[0007] The third main purpose is to achieve a huge improvement in thermoelectric conversion efficiency under room temperature and low temperature difference conditions based on the thermoelectric transistor principle and by utilizing the decoupling between performance parameters and the amplification characteristics of transistor circuits, thus providing new research ideas and directions for the large-scale application of thermoelectric generators.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] The present invention discloses a design and research method for a thermoelectric transistor power generation device, comprising the following steps:

[0010] (1) Constructing a theoretical model of a thermoelectric transistor, wherein the theoretical model of the thermoelectric transistor is a PNP or NPN bipolar junction thermoelectric transistor (hereinafter referred to as a thermoelectric transistor or a PNP / NPN junction) constructed on a substrate of any composition and structure and made of thermoelectric materials of any composition and structure, and its structural schematic diagram is shown in FIG. Figure 2 ).

[0011] Taking the PNP junction as an example (the same below, no further description), it is composed of P-type region 1 (referred to as P1-type region), N-type region and P-type region 2 (referred to as P2-type region) directly connected, and its constituent materials are P-type thermoelectric material 1 (referred to as P1-type thermoelectric material), N-type thermoelectric material and P-type thermoelectric material 2 (referred to as P2-type thermoelectric material). The geometric structures of these regions are all rectangular structures, in which the dimensions along the X direction, Y direction and Z direction are defined as length, width and thickness respectively. The widths of the P1-type region, N-type region and P2-type region are w respectively. p1 、w n and w p2 ; In addition, the length and thickness of all regions are l x and h z .

[0012] The substrate materials of any composition and structure described in the present invention include but are not limited to any structure, such as single crystals, polycrystals, microcrystals, nanocrystals and amorphous crystals of various crystalline phases and their composite structures, in blocks, films or fibers of any composition, such as metals, ceramics, plastics, polymers, latex, various fibers, and other organic, inorganic and various composite materials, such as metal aluminum, Al2O3 sheets / films, Si sheets / films, SiO2 films, AlN sheets / films, polyvinyl chloride sheets / films, elastic silicone sheets / films, nylon fibers, glass fibers, etc.

[0013] The thermoelectric materials of any composition and structure include but are not limited to any structure, such as single crystal, polycrystalline, microcrystalline, nanocrystalline, amorphous, and bulk, film or fiber-shaped organic, inorganic and various composite thermoelectric materials of various crystal phases, such as bismuth telluride (Bi x Sb 1-x )2(Te y Se 1-y )3, x / y=0-1) based, lead telluride (PbTe) based, GeTe based, tin telluride (SnTe) based, cobalt antimonide (CoSb3) based, zinc antimonide based, magnesium silicon (Mg2Si) based, Si 1-x Ge x (x=0-1) thermoelectric materials such as alloys, Si semiconductors, Ge semiconductors, etc.

[0014] (2) Determine the formation principle of the thermoelectric transistor; that is, under the action of a gradient temperature field, the thermoelectric transistor undergoes carrier redistribution due to the Seebeck effect, resulting in a forward bias at the low temperature end and a reverse bias at the high temperature end, forming a bipolar junction transistor circuit, namely a thermoelectric transistor;

[0015] Taking the PNP junction as an example, when the PNP junction is in an isothermal field, that is, when there is no temperature gradient, the hole carriers that can move freely inside the P1-type region and the P2-type region are evenly distributed, and their hole carrier concentrations are equal to the acceptor doping concentrations inside their respective regions, such as Figure 3 (a) In addition, there is a built-in voltage at the junction of the P1-N junction and the N-P2 junction, as shown in Figure 4 At this time, the drift potential formed by the built-in voltage and the diffusion potential formed by the carrier concentration gradient are in a dynamic equilibrium state.

[0016] Then, a gradient temperature field is applied along the X direction. On the one hand, due to the Seebeck effect, the hole carriers in the P1-type region and the P2-type region will move from the high temperature (the highest temperature is T h ) end to the low temperature end (the lowest temperature is T c ) migrate and eventually gather at the low temperature end, such as Figure 3As shown in (b), the number of carriers at the high temperature end and the low temperature end is different, which in turn produces a potential difference, namely the Seebeck voltage, but the internal acceptor doping ion concentration remains fixed.

[0017] On the other hand, the built-in voltage of the P1-N junction and the N-P2 junction will change with the increase of the temperature at the high temperature end. Therefore, under the influence of temperature distribution, the balance between the diffusion potential and the drift potential inside the PNP junction is broken, especially at the low temperature end of the P1-N junction. At this time, the large amount of hole carriers in the low temperature P1 type region and the reduction of the built-in voltage make the excess hole carriers enter the N type region. At the same time, because the number of negative ions in the high temperature end P2 region is greater than the number of holes, it is negatively charged, so that the holes entering the low temperature end N type region pass through the N type region and enter the high temperature end P2 type region. Subsequently, under the guidance of the wire, the holes entering the high temperature end P2 type region will flow back to the high temperature end N type region along the wire. This migration process of hole carriers is consistent with the common base circuit of the bipolar junction transistor.

[0018] Therefore, under the action of temperature difference, the PNP junction will form a bipolar junction transistor circuit, that is, a thermoelectric transistor. At this time, the low temperature end of the P1-N junction is the emitter, the N-type region is the base, and the high temperature end of the N-P2 junction is the collector (or vice versa, that is, the low temperature end of the N-P2 junction is the emitter, the N-type region is the base, and the high temperature end of the P1-N junction is the collector).

[0019] (3) Analysis of the temperature distribution inside the thermoelectric transistor. Taking into account the influence of factors such as Thomson heat, Fourier conduction heat, Peltier heat and Joule heat, the temperature distribution curve inside the thermoelectric transistor can be obtained through the thermal energy balance equation, the thermal conductivity, electrical conductivity and Seebeck coefficient expressions of thermoelectric materials and the current density equation.

[0020] For example, according to formula (1), the one-dimensional thermal energy balance equation is used to analyze the influence of factors such as Thomson heat, Fourier conduction heat, Peltier heat and Joule heat on the internal temperature distribution of the thermoelectric transistor:

[0021]

[0022] Among them, κ p (T p ) is the thermal conductivity of the P-type thermoelectric material, T p (x) is the temperature distribution inside the P-type thermoelectric material, S p (T p ) is the Seebeck coefficient of P-type thermoelectric material, j p (x) is the current density inside the P-type thermoelectric material, σ p (T p) is the electrical conductivity of the P-type thermoelectric material;

[0023] 2) Select a suitable thermoelectric material model according to the actual situation. For example, take the degenerate semiconductor material thermoelectric model as an example (the same below, no further description), and use formulas (2), (3) and (4) to describe the changes in thermal conductivity, Seebeck coefficient and electrical conductivity of the thermoelectric material respectively;

[0024] κ p (T p )=D p ρ p C p (2)

[0025]

[0026] σ p (T p )=P a eμ h (T p ) (4)

[0027] Among them, D p is the thermal diffusion coefficient of the P-type thermoelectric material, ρ p is the density, C p is the heat capacity, is the effective mass of carriers of P-type thermoelectric materials, k B is the Boltzmann constant, r is the scattering factor, h is the Planck constant, e is the electron charge, μ h (T p ) is the hole mobility of P-type material that changes with temperature, P a is the acceptor doping concentration of the P-type thermoelectric material;

[0028] 3) Use the current density expression to construct boundary conditions, such as constructing boundary conditions along the temperature gradient direction (x direction) according to formulas (5), (6) and (7):

[0029]

[0030] x=0 T p (x) = T h (6)

[0031] x=l x T p (x) = T c (7)

[0032] Where E(x) is the electric field strength inside the material, T h is the maximum temperature, T cis the lowest temperature; at this time, the temperature is unidirectionally distributed along the X direction, so the temperature inside the P-type thermoelectric material changes with the position in the X direction.

[0033] 4) Use a linear or nonlinear temperature distribution analytical model to describe the temperature distribution of the P region (i.e., the emitter and collector). If an approximate analytical model or formulas (8) and (9) is used, replace T on the right side of the equal sign in formula (1) with p Using a linear temperature profile T L replace.

[0034]

[0035]

[0036] Among them, T L (x) is the linear distribution expression of temperature.

[0037] (4) Determine the carrier concentration distribution of the emitter, base and collector as well as the built-in voltage of the P1-N junction and the N-P2 junction. According to the Seebeck effect described in step (2), the hole carriers inside the thermoelectric transistor will decrease at the high temperature end and increase at the low temperature end. The hole carrier concentration distribution inside the thermoelectric transistor is obtained under steady-state conditions using the current density expression, Poisson's equation and current continuity equation; in addition, the built-in voltage of the P1-N junction and the N-P2 junction is obtained using the built-in voltage expression of the abrupt junction or non-abrupt junction; the variation of the intrinsic carrier concentration in different regions with temperature is described by the expression of the carrier concentration variation law.

[0038] Specifically: ① Use Poisson's equation to describe the electric potential. For example, according to formula (10), the electric field strength E(x) in formula (5) is described. According to formula (11), the one-dimensional Poisson's equation is used to express the electric potential.

[0039]

[0040] in, is the electric potential distribution;

[0041]

[0042] Among them, ε r is the relative dielectric constant of the P-type thermoelectric material, ε0 is the vacuum dielectric constant, and p(x) is the hole carrier concentration distribution under the action of temperature distribution. Because the majority of carriers inside the P-type thermoelectric material are holes, the influence of electron carriers and donor doping ions is ignored in the Poisson equation.

[0043] ② Use the current continuity equation to describe the relationship between the hole carrier concentration and the current density. For example, according to formula (12), a one-dimensional current continuity equation is used to describe the relationship between the hole carrier concentration and the current density:

[0044]

[0045] Where q is the electron charge;

[0046] ③ Use the built-in voltage expression of the abrupt junction or non-abrupt junction to describe the built-in voltage of the model PN or NP junction. For example, according to formulas (13) and (14), the built-in voltage of the P1-N junction and the N-P2 junction are represented by the built-in voltage expression of the abrupt junction respectively:

[0047]

[0048]

[0049] Where x1 and x2 represent the connection positions of the conductors in the P1 and P2 regions, respectively. V bi1 (x1) and V bi2 (x2) are the built-in voltages of the P1-N junction and the N-P2 junction, respectively. B is the Boltzmann constant, T p1 (x1) and T p2 (x2) are the temperature distribution inside the P1 and P2 regions respectively; P a1 、N d and P a2 are the acceptor or donor doping concentrations inside the P1-type, N-type, and P2-type regions, respectively. i1 (x1) and n i (x1) are the intrinsic carrier concentrations of the P1-type and N-type regions in the P1-N junction, and n i (x2) and p i2 (x2) are the intrinsic carrier concentrations inside the N-type and P2-type regions in the N-P2 junction;

[0050] ④ Select an appropriate expression of carrier concentration variation to describe the distribution of intrinsic carrier concentration in different regions. For example, the distribution of intrinsic carrier concentration in different regions can be described according to formulas (15), (16), (17) and (18):

[0051]

[0052]

[0053]

[0054]

[0055] in, and are the effective carrier masses of thermoelectric materials in the P1, N and P2 regions, respectively, T n (x1) and T n (x2) are the temperature distribution inside the N-type region of the P1-N junction and the N-P2 junction, respectively. gp1 、E gn and E gp2 are the energy gaps of the constituent materials in the P1-type, N-type and P2-type regions, m e The mass of the electron.

[0056] (5) With the goal of normal operation of the thermoelectric transistor, ensure that the emitter-base circuit is forward biased and forward-conducting, and the base-collector circuit is reverse biased. On this basis, the basic conditions for the thermoelectric transistor to be in the forward amplification working mode are established;

[0057] Specifically: According to the formation principle of the thermoelectric transistor described in step (2), the low temperature end of the P1 type region in the PNP junction is the emitter, the N type region is the base, and the high temperature end of the P2 type region is the collector. At the same time, in the thermoelectric transistor circuit, there is no external power supply. The Seebeck voltage generated by the Seebeck effect serves as the external voltage, and the Seebeck voltage is directly related to the Seebeck coefficient and the temperature difference. On the one hand, the Seebeck coefficient is inversely proportional to the doping concentration of the constituent material; on the other hand, since the temperature is distributed along the X direction, there will be temperature differences of different sizes at different positions in the X direction. Therefore, it is necessary to adjust the doping concentration of the emitter, base and collector and the position in the X direction to ensure that the thermoelectric transistor is in the forward amplification working mode. With this goal in mind, the thermoelectric transistor needs to meet the following three conditions:

[0058] 1) Ensure that the doping ion concentration of the emitter, base and collector is at a temperature of T c must be greater than their respective intrinsic carrier concentrations; expressed by equations (19), (20) and (21);

[0059] P al >p il (T c ) (19)

[0060] N d >n i (T c ) (20)

[0061] P a2 >p i2 (T c ) (twenty one)

[0062] Among them, p i1 (T c ), n i (T c ) and p i2 (T c ) are the emitter, base and collector at a temperature of T c The intrinsic carrier concentration at can be calculated according to formulas (15), (16) and (18).

[0063] 2) For the emitter-base circuit to achieve forward bias and forward conduction, it is necessary to satisfy the conditions that the emitter potential is greater than the base potential, the built-in voltage of the emitter-base is greater than zero, and the Seebeck voltage in the emitter-base circuit is greater than the built-in voltage;

[0064] Specifically: ① Use formula (22) to describe the potential relationship between the emitter and the base:

[0065]

[0066] in, and are the emitter potential and the base potential respectively;

[0067] It is worth noting that since the thermoelectric transistor is not affected by an external power supply, its formation and operating voltage are derived from the Seebeck effect caused by the movement of hole carriers. Therefore, the potential relationship in the emitter-base circuit can be expressed by the concentration relationship between the two. The carriers in the emitter region can move freely, so its potential can be expressed by the hole carrier concentration distribution. However, the base region is completely depleted, with only immobile donor doping ions, so its potential can be determined by the donor doping concentration. Then, equation (22) can be transformed into equation (23):

[0068] p1(x1)>N d (twenty three)

[0069] Where p1(x1) is the hole carrier concentration distribution of the emitter (P1 type region) under the action of temperature distribution.

[0070] ② Use formula (13) to calculate the built-in voltage between emitter and base, and its value must be greater than zero.

[0071] ③ Taking degenerate thermoelectric semiconductor materials as an example, formulas (24) and (25) (taking degenerate thermoelectric semiconductor materials as an example) are used to express the Seebeck voltage in the emitter-base circuit, and formula (26) is used to express the relationship between the Seebeck voltage and the built-in voltage in the emitter-base circuit:

[0072] Vs1 (x1)=ΔT(x1)S p1 (twenty four)

[0073]

[0074] Where V s1 (x1) is the Seebeck voltage in the emitter region, S p1 is the Seebeck coefficient in the emitter region;

[0075] V e (x1)=V s1 (x1)-V bil (x1)>0 (26)

[0076] Where V e (x1) is the emitter voltage, that is, formula (22) or (23), the emitter-base built-in voltage calculated using formula (13) is greater than zero, and formula (26) is established, which means that condition 2) is established.

[0077] 3) For the base-collector circuit to achieve reverse bias, the base potential must be greater than the collector potential and the base-collector built-in voltage must be greater than zero. That is, the collector and base potential relationship described by formula (27) or (28) must be satisfied:

[0078]

[0079] In the formula, and are the base potential and collector potential respectively.

[0080] Similarly, formula (27) can be replaced by formula (28):

[0081] N d >p2(x2) (28)

[0082] In the formula, p2(x2) is the concentration distribution of hole carriers along the X direction of the collector (P2 type region) under the action of temperature distribution. Therefore, on the basis of satisfying the above three conditions, the thermoelectric transistor can be in the forward amplification working mode under the action of temperature difference through Seebeck voltage driving, thereby realizing its normal operation or temperature difference power generation.

[0083] (6) Taking the maximum output power of the thermoelectric transistor as the optimization goal, the equivalent circuit method and Kirchhoff's law are used to construct a calculation formula to find the doping concentration and geometric size corresponding to the maximum output power of the thermoelectric transistor, that is, to optimize the output performance of the thermoelectric transistor. The search method includes but is not limited to the enumeration method, the analytical method, etc., and the performance optimization software can be selected from various analysis and optimization software such as MATLAB but is not limited to it.

[0084] (7) Select appropriate software (any software type and usage method, such as ANSYS, MATLAB, etc.) to calculate, analyze, and optimize the operating parameters (such as carrier concentration, device size, etc.) and output performance (such as output voltage, current, power, and thermoelectric conversion efficiency, etc.) of thermoelectric transistors.

[0085] (8) According to the input voltage and power requirements of the electrical device, a thermoelectric transistor power generation device can be formed by combining several different or identical PNP or NPN bipolar junction thermoelectric transistors in series, parallel or a combination of series and parallel. Then, according to the optimization design process and method described in steps (1) to (6), the structure, geometric shape, geometric size, spacing between transistors, temperature field and electric field distribution, output voltage, output current, output power and thermoelectric conversion efficiency of each thermoelectric transistor in the power generation device are optimized to maximize the output power and thermoelectric conversion efficiency of the power generation device and complete its optimization design.

[0086] The present invention is applicable to the research, design, analysis and optimization of any thermoelectric transistor power generation device, thermometer, detector and other devices and instruments related to thermoelectricity or thermoelectric difference based on the thermoelectric transistor principle, and the development of thermoelectric transistor devices. The thermoelectric transistor thermoelectric power generation device developed by the invention can be applied to the temperature difference between various cold sources or heat sources and the environment with no limit on the absolute value of the high and low temperature ends for thermoelectric power generation or thermoelectric detection.

[0087] The present invention has the following beneficial effects:

[0088] 1. The analytical method for designing and studying the performance of thermoelectric transistor power generation devices disclosed in the present invention forms a bipolar junction transistor circuit by using the Seebeck effect under the action of temperature difference by constructing directly connected PNP / NPN junctions, thus proposing the concept of thermoelectric transistor for the first time.

[0089] 2. The analytical method for designing and studying the performance of thermoelectric transistor power generation devices disclosed in the present invention combines the Seebeck effect with the principle of bipolar junction transistors and utilizes the circuit characteristics of bipolar junction transistors to decouple the strong correlation between conductivity and Seebeck coefficient.

[0090] 3. The analytical method based on the design and performance research of thermoelectric transistor power generation devices disclosed in the present invention has established a complete set of thermoelectric transistor power generation device performance research and analysis processes and optional calculation models, and has given specific analysis processes and calculation models using degenerate thermoelectric semiconductors as an example. Through doping concentration optimization and circuit design, it is ensured that the thermoelectric transistor power generation devices can work normally or achieve thermoelectric conversion when directly driven by the Seebeck voltage generated by the temperature difference without the need for an external power supply or magnetic field.

[0091] 4. The analytical method for designing and studying the performance of thermoelectric transistor power generation devices based on the principle of thermoelectric transistors disclosed in the present invention has achieved a significant improvement in the output power and thermoelectric conversion efficiency of thermoelectric transistor power generation devices by optimizing the doping concentration and device geometry. The present invention can be applied to the research and development and optimization design of thermoelectric power generation devices, thermoelectric detection devices and other thermoelectric devices related to thermoelectric or thermoelectric applications in various fields such as thermoelectric power generation and thermoelectric detection, and other possible thermoelectric devices related to thermoelectric or thermoelectric applications, providing a new direction for the large-scale commercial application of thermoelectric power generation devices, which will greatly promote the development of the thermoelectric field.

[0092] 5. The present invention discloses an analysis method based on the design and performance research of thermoelectric transistor power generation devices, which shows that the thermoelectric transistor can form a bipolar junction transistor circuit through the Seebeck effect under the action of temperature difference to achieve thermoelectric conversion, thereby improving the thermoelectric conversion efficiency and output power. Therefore, it can be used for temperature difference power generation and thermoelectric detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 Flowchart of analytical methods for design and performance study of thermoelectric transistor power generation devices;

[0094] Figure 2 It is a schematic diagram of the structure of a PNP device;

[0095] Figure 3 Schematic diagram of carrier distribution inside the PNP junction; (a) is the carrier distribution diagram when the PNP junction is in a uniform temperature field; (b) is the carrier distribution diagram when the PNP junction is in a gradient temperature field;

[0096] Figure 4 Schematic diagram of the built-in voltage of the PNP junction when the temperature is uniformly distributed; (a) is a schematic diagram of the formation principle of the built-in voltage of the PNP junction; (b) is a schematic diagram of the change of doping ion concentration inside the P1-N junction and the N-P2 junction;

[0097] Figure 5 Schematic diagram of the formation principle of a thermoelectric transistor;

[0098] Figure 6 The temperature distribution diagram inside the Bi2Te3-based thermoelectric transistor;

[0099] Figure 7 P-type Bi 0.5 Sb 1.5 Distribution curve of hole concentration inside Te3;

[0100] Figure 8A diagram of suitable ranges of base doping concentration, emitter doping concentration and emitter position of Bi2Te3-based thermoelectric semiconductor materials for satisfying forward bias and forward conduction in an emitter-base circuit;

[0101] Fig. 9 A diagram of suitable ranges of base doping concentration, collector doping concentration and collector position for Bi2Te3-based thermoelectric semiconductor materials to meet reverse bias in a base-collector circuit;

[0102] Fig.10 is the equivalent circuit diagram of the thermoelectric transistor;

[0103] Fig.11 The maximum output power of Bi2Te3-based thermoelectric transistor varies with the base doping concentration;

[0104] Fig.12 The output power of Bi2Te3-based thermoelectric transistor varies with the collector doping concentration and collector position; (a) is the output power of Bi2Te3-based thermoelectric transistor varies with the collector doping concentration and collector position; (b) is the output power of Bi2Te3-based thermoelectric transistor varies with the emitter doping concentration and emitter position;

[0105] Fig.13 Schematic diagram of the structure of a thermoelectric transistor power generation device consisting of 10 thermoelectric transistors connected in series. DETAILED DESCRIPTION

[0106] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0107] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0108] The present invention discloses an analysis method based on the design and performance research of a thermoelectric transistor power generation device, and the research and analysis method flow is as follows: Figure 1 As shown, the specific implementation steps are as follows:

[0109] Step 1: Construct a theoretical model of a thermoelectric transistor. On a substrate of arbitrary composition and structure, design a PNP or NPN bipolar junction thermoelectric transistor (hereinafter referred to as a thermoelectric transistor) composed of thermoelectric materials of arbitrary composition and structure.

[0110] Taking a PNP type thermoelectric transistor as an example, the transistor is formed by directly connecting a P1 type region, an N type region and a P type region 2, and its constituent materials are respectively a P type thermoelectric material 1, an N type thermoelectric material and a P type thermoelectric material 2. Figure 2 The geometric structures of these regions are all cuboid structures, where the dimensions along the X, Y, and Z directions are defined as length, width, and thickness, respectively. The widths of the P1-type region, the N-type region, and the P2-type region are w p1 、w n and w p2 ; In addition, the length l of all regions x Equal to 10mm, thickness h z Equal to 0.5mm.

[0111] like Figure 2 As shown, this embodiment uses Al2O3 as the substrate and P-type Bi 0.5 Sb 1.5 Te3 and N-type Bi2Te 2.97 Se 0.03 As P-type and N-type thermoelectric materials, the design and performance study of thermoelectric transistors are described.

[0112] Step 2: Determine the formation principle of the thermoelectric transistor; when the PNP junction is in an isothermal field, that is, when there is no temperature gradient, the hole carriers that can move freely inside the P1-type region and the P2-type region are evenly distributed, and their hole carrier concentrations are equal to the acceptor doping concentration inside their respective regions, such as Figure 3 (a) In addition, there is a built-in voltage at the junction of the P1-N junction and the N-P2 junction, such as Figure 4 As shown. At this time, the drift potential formed by the built-in voltage and the diffusion potential formed by the carrier concentration gradient are in a dynamic equilibrium state. Then, a gradient temperature field is applied along the X direction. On the one hand, due to the Seebeck effect, the hole carriers inside the P1-type region and the P2-type region will migrate from the high-temperature end to the low-temperature end, and finally gather at the low-temperature end, resulting in a difference in the number of carriers at the high-temperature end and the low-temperature end, and then a potential difference is generated, which is the Seebeck voltage, but the internal acceptor doping ions (concentration) remain fixed, as shown. Figure 3(b) As shown. On the other hand, the built-in voltage of the P1-N junction and the N-P2 junction will change as the temperature of the high-temperature end increases. Therefore, under the influence of temperature distribution, the balance between the diffusion potential and the drift potential inside the PNP junction is broken, especially at the low-temperature end of the P1-N junction. At this time, the large accumulation of hole carriers and the reduction of the built-in voltage cause the excess hole carriers to enter the N-type region at the low-temperature end. Since the number of negative ions at the high-temperature end of the P2 region is greater than the number of holes, it is negatively charged. These holes that enter the N-type region at the low-temperature end will pass through the N-type region and enter the high-temperature end of the P2-type region. Subsequently, under the guidance of the wire, the holes that enter the P2-type region at the high-temperature end will flow back to the N-type region at the high-temperature end, as shown in FIG. Figure 5 As shown. This hole carrier migration process is consistent with the common base circuit of the bipolar junction transistor. Therefore, under the action of temperature difference, the PNP junction will form a bipolar junction transistor circuit, that is, a thermoelectric transistor. At this time, the low temperature end of the P1-N junction is the emitter, the N-type region is the base, and the high temperature end of the N-P2 junction is the collector.

[0113] Step 3: Using insulating Al2O3 as substrate and P-type Bi 0.5 Sb 1.5 Taking Te3 thermoelectric material as an example, substituting formulas (2), (3), (4), (5) and (8) into formula (9), the P-type Bi can be obtained by integral solution: 0.5 Sb 1.5 The temperature distribution curve inside the Te3 thermoelectric material, such as Figure 6 Because its internal temperature distribution is one-dimensional, along the X direction, when x is equal to 0, the temperature is the highest, equal to 353K, and when x is equal to 10mm, the temperature is the lowest, equal to 303K.

[0114] Step 4: Using the current continuity equation, when in steady state, equation (12) simplifies to:

[0115]

[0116] And because P-type Bi 0.5 Sb 1.5 Te3 thermoelectric material is in the temperature range of 303K to 353K, which is lower than P-type Bi 0.5 Sb 1.5 The intrinsic excitation temperature of Te3 material is assumed to be equal to the generation rate and recombination rate of hole carriers. 0.5 Sb 1.5 The total number of hole carriers (total concentration) in Te3 material will not change before and after the temperature distribution is applied. Since the hole carrier concentration distribution is affected by temperature, the P-type Bi 0.5 Sb 1.5The total number of hole carriers inside Te3 material can be expressed as:

[0117]

[0118] The left side of the equal sign in the formula represents the P-type Bi when no temperature distribution is applied 0.5 Sb 1.5 The total number of hole carriers inside the Te3 material, the right side shows the P-type Bi 0.5 Sb 1.5 The total number of hole carriers inside Te3 material.

[0119] Substituting formula (11) and (30) into formula (10), we find that:

[0120]

[0121] Therefore, formula (5) can be simplified as:

[0122]

[0123] Finally, by combining equations (29) and (32), we can obtain the P-type Bi under the action of temperature gradient: 0.5 Sb 1.5 The hole carrier concentration distribution inside the Te3 thermoelectric material, such as Figure 7 As shown. It can be found that as the position of x changes from 0 to 10mm, the hole carrier concentration increases at the low temperature end and decreases at the high temperature end. These changing trends are consistent with the theoretical mechanism of the Seebeck effect. Therefore, the balance between the diffusion potential and the drift potential at the junction of the P1-N junction is broken, and the hole carriers will enter the low temperature end of the N-type region from the low temperature end of the P1-N junction. The holes entering the N-type region at the low temperature end pass through the N-type region and enter the high temperature end of the P2 region under the action of the negative electric field at the high temperature end of the P2 region (formed because the number of negative ions is greater than the number of holes), and flow back to the high temperature end of the N-type region under the guidance of the wire, and finally form a common base bipolar junction transistor circuit. From the perspective of quantitative analysis, it is proved that the formation of the thermoelectric transistor circuit is feasible.

[0124] Step 5: Figure 8 It is the suitable range of base doping concentration, emitter doping concentration and emitter position that satisfies forward bias and forward conduction in the emitter-base circuit. It can be found from the figure that the suitable range of base doping concentration is 0.162×10 19 cm -3 to 0.33×10 19 cm -3 The appropriate range of the emitter doping concentration and the corresponding emitter position changes with the change of the base doping concentration. Fig. 9It is the appropriate range of base doping concentration, collector doping concentration and collector position that meets the reverse bias in the base-collector circuit. It can be found that the minimum value of the base doping concentration is 0.22×10 19 cm -3 , as shown by the blue line in the figure. The appropriate range of the collector doping concentration and the corresponding collector position changes with the change of the base doping concentration. Finally, combined with Figure 8 and Fig. 9 The calculation results in can determine that when the base doping concentration is 0.22×10 19 cm -3 to 0.33×10 19 cm -3 When the base doping concentration changes within a certain range, the thermoelectric transistor can meet normal working conditions and thus realize current conduction. The emitter doping concentration, emitter position, collector doping concentration and collector position will be affected by the base doping concentration, and the appropriate range of these parameters will change with the change of the base doping concentration.

[0125] Step 6: Use the equivalent circuit method to calculate the output performance of the Bi2Te3-based thermoelectric transistor. Fig.10 Give its equivalent circuit diagram. Fig.10 The equivalent circuit shown above can be used to construct a formula for calculating the output performance of a thermoelectric transistor using Kirchhoff's laws:

[0126] V e (x1)=V s1 (x1)-V bi1( x1)=I e (x1)[R e (x1)+R j ] (33)

[0127] V c (x2) = V bi2 (x2)-V s2 (x2)-V L (x2) = I c (x2)[R c (x2)+R j ] (34)

[0128] V L (x2) = I c (x2)R L (35)

[0129] I e (x1)=I c (x2) (36)

[0130]

[0131]

[0132] Where, V c (x2) is the collector voltage.

[0133] The Seebeck voltage V in the emitter-base circuit s1 (x1) Similarly, the Seebeck voltage V in the base-collector circuit s2 (x2) can also be expressed as formula (39):

[0134] V s2 (x2) = ΔT(x2)S p2 (39)

[0135]

[0136] According to the above relationship, when the output resistance R L After being connected to the output end of the thermoelectric transistor, the output power can be expressed as formula (41):

[0137] P out =I c (x2)V L (x2) = I e (x1)V L (x2) (41)

[0138] Then substitute equations (33), (34), (35), (36), (37) and (38) into equation (41), and the output power P out Convert to formula (42):

[0139] P out =I e (x1)[V bi2 (x2)-V s2 (x2)-I e (x1)R c (x2)-I e (x1)R j ] (42)

[0140] In addition to output power, another indicator that determines the output performance of a thermoelectric transistor is the thermoelectric conversion efficiency. The present invention provides the conversion efficiency of the thermoelectric transistor under the condition of obtaining the maximum output power, and formula (43) provides its expression:

[0141] η=P max / Q h (43)

[0142]

[0143] Where η is the conversion efficiency of the thermoelectric transistor, P max is the maximum output power of the thermoelectric transistor, Q h is the heat absorbed by the high temperature end of the thermoelectric transistor base-collector circuit, S pnp is the total Seebeck coefficient of the thermoelectric transistor, K and R in are the total thermal resistance and total internal resistance of the thermoelectric transistor, respectively, and their respective expressions are:

[0144]

[0145] R in =R e (x1)+R c (x2)+2R j (46)

[0146] Where κ p1 , κ n and κ p2 are the total thermal conductivities of the emitter, base, and collector, respectively. In addition, it can be found from formula (46) that the total internal resistance of the thermoelectric transistor is equal to the sum of the emitter resistance, collector resistance, and contact resistance.

[0147] Fig.11 is the calculated relationship between the maximum output power of Bi2Te3-based thermoelectric transistor and the base doping concentration; Fig.12 (a) is the relationship between the output power of Bi2Te3-based thermoelectric transistor and the collector doping concentration and collector position; Fig.12 (b) is the relationship between the output power of Bi2Te3-based thermoelectric transistor emitter doping concentration and emitter position. It can be found from the figure that when the lowest temperature is 353K and the temperature difference is 50K, when the base doping concentration is 0.28×10 19 cm -3 , the emitter doping concentration is 0.233×10 19 cm -3 , the emitter position is 10 mm, and the collector doping concentration is 0.338×10 19 cm -3 When the collector position is 0mm, the maximum output power of the thermoelectric transistor can reach 16.95mW, and the corresponding thermoelectric conversion efficiency can reach 9.1%, which is 3.4 times the theoretical conversion efficiency of traditional thermoelectric devices when zT is equal to 1 under the same conditions.

[0148] The thermoelectric transistor is obtained for the first time according to the analytical method based on the design and performance research of the thermoelectric transistor power generation device. The thermoelectric transistor can form a bipolar junction transistor circuit through the Seebeck effect under the action of temperature difference, thereby improving the thermoelectric conversion efficiency and output power, and can therefore be used for thermoelectric power generation and thermoelectric detection.

[0149] Step 7: Connect 10 thermoelectric transistors in series to form a thermoelectric transistor power generation device, such as Fig.13 As shown, the above steps (1) to (6) are used to optimize the design of the thermoelectric transistor generator. The structure, geometric shape, geometric size, spacing between transistors, temperature field and electric field distribution, output voltage, output current, output power and thermoelectric conversion efficiency of each thermoelectric transistor in the thermoelectric transistor power generation device are optimized to maximize the output power and thermoelectric conversion efficiency of the power generation device and complete its optimized design.

[0150] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A design and research method for a thermoelectric transistor power generation device, characterized in that: The following steps are involved: (1) Constructing a theoretical model of a thermoelectric transistor; that is, constructing a PNP or NPN bipolar junction thermoelectric transistor on a substrate using thermoelectric materials, referred to as a PNP / NPN junction; (2) Determine the formation principle of the thermoelectric transistor; that is, under the action of a gradient temperature field, the thermoelectric transistor undergoes carrier redistribution due to the Seebeck effect, resulting in a forward bias at the low temperature end and a reverse bias at the high temperature end, forming a bipolar junction transistor circuit, namely a thermoelectric transistor; (3) Analyze the temperature distribution inside the thermoelectric transistor through the thermal energy balance equation, the thermal conductivity, electrical conductivity and Seebeck coefficient expressions of the thermoelectric material, and the current density equation; (4) determining the carrier concentration distribution of the emitter, base and collector and the built-in voltage of the P1-N junction and the N-P2 junction under the action of the gradient temperature field; wherein P1 and P2 refer to the P-type region 1 and the P-type region 2 in the bipolar junction thermoelectric transistor; (5) With the goal of normal operation of the thermoelectric transistor, ensure that the emitter-base circuit is forward biased and forward-conducting, and the base-collector circuit is reverse biased. On this basis, the basic conditions for the thermoelectric transistor to be in the forward amplification working mode are established; (6) Taking the maximum output power of the thermoelectric transistor as the optimization goal, the equivalent circuit method and Kirchhoff's law are used to construct a theoretical calculation formula to find the doping concentration and geometric dimensions corresponding to the maximum output power of the thermoelectric transistor. On this basis, the output power and conversion efficiency are calculated, thereby optimizing the output performance of the thermoelectric transistor power generation device.

2. The design and research method of a thermoelectric transistor power generation device according to claim 1, characterized in that: In step (2), under the action of temperature difference, the low temperature end of the P1-N junction is the emitter, the N-type region is the base, and the high temperature end of the N-P2 junction is the collector, or the low temperature end of the N-P2 junction is the emitter, the N-type region is the base, and the high temperature end of the P1-N junction is the collector.

3. The design and research method of a thermoelectric transistor power generation device according to claim 1, characterized in that: Also includes: (7) The output voltage, current, power and thermoelectric conversion efficiency of the thermoelectric transistor power generation device under the maximum output power mode are calculated by simulation optimization, and then the similarities and differences between the two optimization modes are compared.

4. The design and research method of a thermoelectric transistor power generation device according to claim 3, characterized in that: Also includes: (8) Connecting the same or different thermoelectric transistors in series, in parallel, or in series and parallel to form a thermoelectric transistor power generation device, and optimizing the design of the thermoelectric transistor power generation device using the above steps (1) to (7).

5. The design and research method of a thermoelectric transistor power generation device according to claim 1, characterized in that: The specific implementation process of step (3) is as follows: 1) analyzing the influence of Thomson heat, Fourier conduction heat, Peltier heat and Joule heat on the internal temperature distribution of the thermoelectric transistor through the thermal energy balance equation; 2) describing the thermoelectric properties of the material based on the theoretical model of the thermoelectric material; 3) constructing the boundary conditions using the current density equation; 4) describing the temperature distribution of the thermoelectric transistor using a linear or nonlinear temperature distribution analytical model.

6. The design and research method of a thermoelectric transistor power generation device according to claim 1, characterized in that: The specific implementation process of step (4) is as follows: 1) using Poisson's equation to describe the electric potential; 2) using the current continuity equation to describe the relationship between hole carrier concentration and current density; 3) using the built-in voltage expression of the abrupt junction or non-abrupt junction to describe the built-in voltage of the model P1-N or N-P2 junction; 4) using the expression of the law of carrier concentration variation with temperature to describe the distribution of intrinsic carrier concentration in different regions.

7. The design and research method of a thermoelectric transistor power generation device according to claim 1, characterized in that: In step (5), the conditions that the thermoelectric transistor meets are: 1) ensuring that the doping ion concentrations of the emitter, base, and collector are at a temperature of T c must be greater than their respective intrinsic carrier concentrations; 2) For the emitter-base circuit to achieve forward bias and forward conduction, it is necessary to satisfy that the emitter potential is greater than the base potential, the built-in voltage of the emitter-base is greater than zero, and the Seebeck voltage in the emitter-base circuit is greater than the built-in voltage; 3) For the base-collector circuit to achieve reverse bias, it is necessary to satisfy that the base potential is greater than the collector potential and the built-in voltage of the base-collector is greater than zero.

8. The design and research method of a thermoelectric transistor power generation device according to claim 4, characterized in that: In step (8), the structure, geometric shape, geometric dimensions, spacing between transistors, temperature field and electric field distribution, output voltage, output current, output power and thermoelectric conversion efficiency of each thermoelectric transistor in the thermoelectric transistor power generation device are optimized to maximize the output power and thermoelectric conversion efficiency of the power generation device and complete the optimized design.

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