thermoelectric element

Abstract

A thermoelectric element according to an embodiment of the disclosure includes a first substrate, a first buffer layer disposed on the first substrate, a first electrode disposed on the first buffer layer, a P-type thermoelectric leg and an N-type thermoelectric leg disposed on the first electrode, a second electrode disposed on the P-type thermoelectric leg and the N-type thermoelectric leg, a second buffer layer disposed on the second electrode, and a second substrate disposed on the second buffer layer, wherein at least one of the first buffer layer and the second buffer layer includes silicone and an inorganic material, and a Young's modulus of at least one of the first buffer layer and the second buffer layer is 1 MPa to 65 MPa.

Description

Technical Field

[0001] This disclosure relates to thermoelectric elements, and more specifically to the structure between the substrate and the electrodes of a thermoelectric element. Background Technology

[0002] Thermoelectric phenomena are caused by the movement of electrons and holes in materials, and refer to the direct energy conversion between heat and electricity.

[0003] Thermoelectric elements are a general term for devices that utilize the thermoelectric phenomenon, and they have a structure in which P-type thermoelectric materials and N-type thermoelectric materials are joined between metal electrodes to form a PN junction pair.

[0004] Thermoelectric elements can be categorized into devices that utilize resistance-temperature changes, devices that utilize the Seebeck effect (the Seebeck effect is the phenomenon of electromotive force generated due to temperature differences), and devices that utilize the Peltier effect (the Peltier effect is the phenomenon of absorbing or generating heat through the generation of electric current). Thermoelectric elements are widely used in household appliances, electronic components, communication components, and more. For example, thermoelectric elements can be used in cooling devices, heating devices, and power generation devices. Therefore, the requirements for the thermoelectric performance of thermoelectric elements are becoming increasingly stringent.

[0005] The thermoelectric element includes a substrate, electrodes, and thermoelectric legs. Multiple thermoelectric legs are arranged in an array between an upper substrate and a lower substrate. Multiple upper electrodes are disposed between the multiple thermoelectric legs and the upper substrate, and multiple lower electrodes are disposed between the multiple thermoelectric legs and the lower substrate. In this case, one of the upper substrate and the lower substrate can be a low-temperature section, and the other can be a high-temperature section.

[0006] Meanwhile, when thermoelectric elements are applied to power generation equipment, power generation performance increases with the increase of the temperature difference between the low-temperature section and the high-temperature section. For example, the temperature of the high-temperature section can rise to 200°C or higher. When the temperature of the high-temperature section is 200°C or higher, thermal stress is applied to the substrate on the high-temperature section side due to the difference in the coefficient of thermal expansion between the substrate and the electrode on the high-temperature section side, which may damage the electrode structure. When the electrode structure is damaged, cracks will form at the bonding surface between the solder on the electrode and the thermoelectric leg, reducing the reliability of the thermoelectric element.

[0007] Meanwhile, in order to improve the heat transfer performance of thermoelectric elements, efforts are being made to increase the use of metal substrates.

[0008] Typically, thermoelectric elements can be manufactured by sequentially laminating electrodes and thermoelectric legs onto a pre-prepared metal substrate. While using a metal substrate offers advantages in thermal conductivity, it also results in reduced reliability over long-term use due to its low withstand voltage.

[0009] Therefore, there is a need for a thermoelectric element that not only improves thermal conductivity, but also its pressure resistance and thermal stress relaxation performance. Summary of the Invention

[0010] Technical issues

[0011] The present disclosure aims to provide a buffer layer for a thermoelectric element, which improves thermal conductivity, pressure resistance and thermal stress relaxation performance.

[0012] Technical solution

[0013] According to one aspect of this disclosure, a thermoelectric element is provided, comprising a first substrate, a first buffer layer disposed on the first substrate, a first electrode disposed on the first buffer layer, a P-type thermoelectric leg and an N-type thermoelectric leg disposed on the first electrode, a second electrode disposed on the P-type thermoelectric leg and the N-type thermoelectric leg, a second buffer layer disposed on the second electrode, and a second substrate disposed on the second buffer layer, wherein at least one of the first buffer layer and the second buffer layer comprises silicone resin and inorganic material, and at least one of the first buffer layer and the second buffer layer has a Young's modulus of 1 to 65 MPa.

[0014] The reference temperature for determining Young's modulus can be between 150°C and 200°C.

[0015] The silicone resin may contain polydimethylsiloxane (PDMS), and the inorganic material may be present in at least one of the first and second buffer layers at a content of 85 to 90 wt%.

[0016] Inorganic materials may include a first group of inorganic materials with a D50 of 5 to 20 μm, a second group of inorganic materials with a D50 of 20 to 30 μm, and a third group of inorganic materials with a D50 of 30 to 40 μm.

[0017] The temperature at the first substrate can be lower than the temperature at the second substrate.

[0018] The Young's modulus of the second buffer layer can be 1 to 65 MPa.

[0019] The first substrate can be an aluminum substrate, and the second substrate can be a copper substrate.

[0020] The thermoelectric element may also include a first insulating layer disposed between the first substrate and the first buffer layer.

[0021] The first insulating layer may contain aluminum oxide.

[0022] The first insulating layer may also be disposed on one of the two surfaces of the first substrate, the surface opposite to the surface facing the second substrate, and one of the side surfaces of the first substrate.

[0023] The first insulating layer may be a composite material layer formed of a composite material containing silicon and aluminum.

[0024] The thermoelectric element may further include a second insulating layer disposed between the second buffer layer and the second substrate, wherein the second insulating layer may be selected from an alumina layer, a composite layer formed of a composite material comprising silicon and aluminum, or a resin layer formed of a resin composite material comprising at least one of epoxy resin and silicone resin and an inorganic material.

[0025] The thermoelectric element may also include a heat sink disposed on a second substrate.

[0026] The thickness of the second buffer layer can be greater than the thickness of the first buffer layer.

[0027] The Young's modulus of the first buffer layer can change by less than 10% over 500 hours at 150°C to 200°C.

[0028] According to another aspect of this disclosure, a power generation system is provided, comprising a thermoelectric element according to an embodiment of this disclosure, a first fluid flowing to a first substrate of the thermoelectric element, and a second fluid flowing to a second substrate of the thermoelectric element and having a temperature of 95°C to 185°C higher than the temperature of the first fluid, wherein the resistivity change rate of the thermoelectric element is within 7% over 500 hours.

[0029] Beneficial effects

[0030] According to one embodiment of this disclosure, a thermoelectric element with excellent performance and high reliability can be obtained. Specifically, according to embodiments of this disclosure, a thermoelectric element with improved thermal conductivity, pressure resistance, and thermal stress relaxation properties can be obtained.

[0031] According to embodiments of this disclosure, thermoelectric elements can be applied not only to applications implemented in small sizes, but also to applications implemented in large sizes, such as vehicles, ships, steel mills, incinerators, etc. Attached Figure Description

[0032] Figure 1 This is a cross-sectional view of a thermoelectric element;

[0033] Figure 2 It is a 3D diagram of a thermoelectric element;

[0034] Figure 3 It is a three-dimensional view of a thermoelectric element including a sealing component;

[0035] Figure 4 It is an exploded perspective view of a thermoelectric element including the sealing components;

[0036] Figure 5 This is a cross-sectional view of a thermoelectric element according to an embodiment of the present disclosure;

[0037] Figure 6 This is a cross-sectional view of a thermoelectric element according to another embodiment of the present disclosure;

[0038] Figure 7 This is a cross-sectional view of a thermoelectric element according to yet another embodiment of the present disclosure;

[0039] Figure 8 This is a cross-sectional view of a thermoelectric element according to another embodiment of the present disclosure;

[0040] Figure 9 An example of the bonding structure between the second substrate (380) and the heat sink (390);

[0041] Figure 10 It is a graph showing the relationship between the temperature of the substrate and thermal stress in the thermoelectric element according to Comparative Example 1;

[0042] Figure 11 It is a graph showing the rate of change of resistance between the high-temperature and low-temperature sections of the thermoelectric element, based on the temperature difference, according to the example and comparative examples; and

[0043] Figure 12 It is a graph showing the change in Young's modulus of thermoelectric elements based on the example and comparative examples, measured over time when exposed to 200°C. Detailed Implementation

[0044] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0045] However, the technical spirit of this disclosure is not limited to the embodiments to be described and can be implemented in various forms, and one or more elements in the embodiments can be selectively combined and replaced for use within the scope of the technical spirit of this disclosure.

[0046] Furthermore, unless specifically defined and described, the terms used in the embodiments of this disclosure (including technical and scientific terms) can be interpreted in terms of meaning commonly understood by those skilled in the art, and commonly used terms, such as those defined in a dictionary, can be understood in terms of their meaning in the context of the relevant art.

[0047] Furthermore, the terminology used in the description is not intended to limit this disclosure but is used to describe the embodiments.

[0048] In the specification, unless the context clearly indicates otherwise, the singular form may also include the plural form, and when disclosed as at least one (or one or more) of "A, B and C", it may include one or more of all possible combinations of A, B and C.

[0049] Furthermore, terms such as first, second, A, B, (a), (b) may be used to describe elements in the embodiments of this disclosure.

[0050] The terminology is only used to distinguish components from other components, and the nature, order, sequence, etc. of the components are not limited by the terminology.

[0051] Furthermore, when a particular element is disclosed as being “connected,” “linked,” or “coupled” to other elements, these elements may include not only cases where they are directly connected, linked, or coupled to other elements, but also cases where they are connected, linked, or coupled to other elements through elements that are between these elements and other elements.

[0052] Furthermore, when an element is disclosed as being formed "above or below" another element, the term "above or below" includes cases where the two elements are in direct contact with each other, as well as cases where at least one other element is disposed between the two elements (indirect contact). Moreover, when the term "above or below" is expressed, it can include not only the meaning of an element in an upward direction, but also the meaning of a downward direction.

[0053] Figure 1 This is a cross-sectional view of a thermoelectric element. Figure 2 It is a 3D diagram of a thermoelectric element. Figure 3 It is a three-dimensional diagram of a thermoelectric element including sealing components, and Figure 4 It is an exploded perspective view of a thermoelectric element including a sealing component.

[0054] refer to Figure 1 and Figure 2 The thermoelectric element 100 includes a lower substrate 110, a lower electrode 120, a P-type thermoelectric leg 130, an N-type thermoelectric leg 140, an upper electrode 150, and an upper substrate 160.

[0055] A lower electrode 120 is disposed between the lower substrate 110 and the lower surfaces of the P-type thermoelectric legs 130 and N-type thermoelectric legs 140, and an upper electrode 150 is disposed between the upper substrate 160 and the upper surfaces of the P-type thermoelectric legs 130 and N-type thermoelectric legs 140. Therefore, multiple P-type thermoelectric legs 130 and multiple N-type thermoelectric legs 140 are electrically connected through the lower electrode 120 and the upper electrode 150. A pair of P-type thermoelectric legs 130 and N-type thermoelectric legs 140 disposed between the lower electrode 120 and the upper electrode 150 and electrically connected to each other can form a single-cell battery.

[0056] For example, when a voltage is applied to the lower electrode 120 and the upper electrode 150 through leads 181 and 182, the substrate (through which current flows from the P-type thermocouple 130 to the N-type thermocouple 140 due to the Peltier effect) can absorb heat to act as a cooling element, and the substrate (through which current flows from the N-type thermocouple 140 to the P-type thermocouple 130) can be heated to act as a heating element. Optionally, when there is a temperature difference between the lower electrode 120 and the upper electrode 150, the charges in the P-type thermocouple 130 and the N-type thermocouple 140 move due to the Seebeck effect, and thus generate electricity.

[0057] Here, the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 can be bismuth telluride (Bi-Te) based thermoelectric legs, which include bismuth (Bi) and tellurium (Te) as main raw materials. The P-type thermoelectric leg 130 can be a bismuth telluride (Bi-Te) based thermoelectric leg, which includes at least one of antimony (Sb), nickel (Ni), aluminum (Al), copper (Cu), silver (Ag), lead (Pb), boron (B), gallium (Ga), tellurium (Te), bismuth (Bi), and indium (In). For example, the P-type thermoelectric leg 130 may include Bi-Sb-Te, which is the main raw material, with a content of 99 to 99.999 wt%; and may include at least one of nickel (Ni), aluminum (Al), copper (Cu), silver (Ag), lead (Pb), boron (B), gallium (Ga), and indium (In), with a content of 0.001 to 1 wt% based on 100 wt% of the total weight. The N-type thermoelectric leg 140 may be a bismuth telluride (Bi-Te) based thermoelectric leg, comprising at least one of selenium (Se), nickel (Ni), aluminum (Al), copper (Cu), silver (Ag), lead (Pb), boron (B), gallium (Ga), tellurium (Te), bismuth (Bi), and indium (In). For example, the N-type thermoelectric leg 140 may comprise Bi-Se-Te, which is the main raw material, in a content of 99 to 99.999 wt%; and may comprise at least one of nickel (Ni), aluminum (Al), copper (Cu), silver (Ag), lead (Pb), boron (B), gallium (Ga), and indium (In), in a content of 0.001 to 1 wt% based on 100 wt% of the total weight.

[0058] P-type thermoelectric legs 130 and N-type thermoelectric legs 140 can be formed in bulk or stacked form. Typically, bulk P-type thermoelectric legs 130 or bulk N-type thermoelectric legs 140 can be obtained through the following processes: producing ingots by heat-treating thermoelectric materials, crushing and sieving the ingots to obtain powder for the thermoelectric legs, sintering the powder, and cutting the sintered material. In this case, P-type thermoelectric legs 130 and N-type thermoelectric legs 140 can be polycrystalline thermoelectric legs. For polycrystalline thermoelectric legs, the powder for the thermoelectric legs can be compressed at 100 to 200 MPa during sintering. For example, when P-type thermoelectric legs 130 are sintered, the powder for the thermoelectric legs can be sintered at 100 to 150 MPa, preferably 110 to 140 MPa, and more preferably 120 to 130 MPa. Furthermore, when the N-type thermoelectric leg 140 is sintered, the powder used for the thermoelectric leg can be compressed under conditions of 150 to 200 MPa, preferably 160 to 195 MPa, and more preferably 170 to 190 MPa. Similarly, when the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 are polycrystalline thermoelectric legs, the strength of the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140 can be increased. The stacked P-type thermoelectric leg 130 or the stacked N-type thermoelectric leg 140 can be obtained by forming unit components by coating an adhesive containing thermoelectric material onto a sheet substrate, and subsequently stacking and cutting the unit components.

[0059] In this case, a pair of P-type thermoelectric legs 130 and N-type thermoelectric legs 140 may have the same shape and volume, or have different shapes and volumes. For example, due to the different conductivity characteristics of the P-type thermoelectric legs 130 and N-type thermoelectric legs 140, the height or cross-sectional area of ​​the N-type thermoelectric leg 140 may be formed to be different from the height or cross-sectional area of ​​the P-type thermoelectric leg 130.

[0060] In this case, the P-type thermoelectric leg 130 or the N-type thermoelectric leg 140 can be cylindrical, polygonal, elliptical, or similar in shape.

[0061] Optionally, the P-type thermocouple 130 or the N-type thermocouple 140 may have a stacked structure. For example, the P-type thermocouple 130 or the N-type thermocouple 140 may be formed by stacking multiple structures coated with semiconductor material on a sheet substrate and then dicing these structures. This prevents material loss and improves electrical conductivity. Each structure may include a conductive layer with an open pattern, thereby increasing adhesion between structures, reducing thermal conductivity, and increasing electrical conductivity.

[0062] Optionally, the P-type thermoelectric leg 130 or the N-type thermoelectric leg 140 can be formed with different cross-sections in one thermoelectric leg. For example, in one thermoelectric leg, the cross-section of the two ends facing the electrode can be formed to be larger than the cross-section between the two ends. Therefore, since the temperature difference between the two ends can be larger, the thermoelectric efficiency can be increased.

[0063] The performance of a thermoelectric element according to an embodiment of this disclosure can be expressed as a thermoelectric performance index (quality factor, ZT). The thermoelectric performance index (ZT) can be expressed as Equation 1.

[0064] [Formula 1]

[0065] ZT=α 2 ·σ·T / k

[0066] Here, α is the Seebeck coefficient [V / K], σ is the conductivity [S / m], and α 2 σ is the power factor (W / mK) 2 Furthermore, T is temperature, and k is thermal conductivity [W / mK]. k can be expressed as a·cp·ρ, where a is thermal diffusivity [cm]. 2 / S], cp is specific heat [J / gK], and ρ is density [g / cm³]. 3 ].

[0067] To obtain the thermoelectric performance index of a thermoelectric element, a Z meter is used to measure the Z value (V / K), and the measured Z value can be used to calculate the thermoelectric performance index (ZT).

[0068] Here, the lower electrode 120, disposed between the lower substrate 110 and the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140, and the upper electrode 150, disposed between the upper substrate 160 and the P-type thermoelectric leg 130 and the N-type thermoelectric leg 140, may each include at least one of copper (Cu), silver (Ag), aluminum (Al), and nickel (Ni), and may each have a thickness of 0.01 mm to 0.3 mm. When the thickness of the lower electrode 120 or the upper electrode 150 is less than 0.01 mm, its function as an electrode may deteriorate and its conductivity may decrease. When the thickness of the lower electrode 120 or the upper electrode 150 is greater than 0.3 mm, the conductivity may decrease due to the increase in resistance.

[0069] Furthermore, the lower substrate 110 and upper substrate 160, which face each other, can be metal substrates with a thickness ranging from 0.1 mm to 1.5 mm. When the thickness of the metal substrate is less than 0.1 mm or greater than 1.5 mm, the reliability of the thermoelectric element may deteriorate due to excessively high heat dissipation characteristics or thermal conductivity. Moreover, when the lower substrate 110 and upper substrate 160 are metal substrates, multiple insulating layers 170 can be formed between the lower substrate 110 and the lower electrode 120, and between the upper substrate 160 and the upper electrode 150, respectively. Each insulating layer 170 may contain a material with a thermal conductivity of 1 to 20 W / mK.

[0070] In this case, the lower substrate 110 and the upper substrate 160 may have different dimensions. For example, the volume, thickness, or area of ​​one of the lower substrate 110 and the upper substrate 160 may be formed to be larger than the volume, thickness, or area of ​​the other. Therefore, the heat absorption or heat dissipation performance of the thermoelectric element can be increased. Preferably, the volume, thickness, or area of ​​the lower substrate 110 may be formed to be larger than at least one of the volume, thickness, or area of ​​the upper substrate 160. In this case, when disposed in a high-temperature region for the Seebeck effect or a heating region for the Peltier effect, or when a sealing member (described later) for protecting the thermoelectric module from external environmental influences is disposed on the lower substrate 110, the lower substrate 110 may be formed to be larger than at least one of the volume, thickness, and area of ​​the upper substrate 160. In this case, the area of ​​the lower substrate 110 may be formed to be in the range of 1.2 to 5 times the area of ​​the upper substrate 160. When the area of ​​the current substrate 110 is less than 1.2 times the area of ​​the upper substrate 160, the effect of improving heat transfer efficiency is not significant. However, when the area of ​​the current substrate 110 is more than 5 times the area of ​​the upper substrate 160, the heat transfer efficiency is significantly reduced, and the basic shape of the thermoelectric module may be difficult to maintain.

[0071] Furthermore, heat dissipation patterns, such as uneven patterns, can be formed on the surface of at least one of the lower substrate 110 and the upper substrate 160. Therefore, the heat dissipation performance of the thermoelectric element can be improved. When an uneven pattern is formed on the surface in contact with the P-type thermoelectric leg 130 or the N-type thermoelectric leg 140, the bonding characteristics between the thermoelectric leg and the substrate can also be enhanced. The thermoelectric element 100 includes a lower substrate 110, a lower electrode 120, a P-type thermoelectric leg 130, an N-type thermoelectric leg 140, an upper electrode 150, and an upper substrate 160.

[0072] like Figure 3 and Figure 4As shown, multiple sealing members 190 may also be disposed between the lower substrate 110 and the upper substrate 160. These sealing members may be disposed on the side surfaces of the lower electrode 120, the P-type thermoelectric leg 130, the N-type thermoelectric leg 140, and the upper electrode 150 between the lower substrate 110 and the upper substrate 160. Therefore, the lower electrode 120, the P-type thermoelectric leg 130, the N-type thermoelectric leg 140, and the upper electrode 150 can be sealed to prevent them from being affected by external moisture, heat, contamination, etc. Here, the sealing member 190 may include: a sealing shell 192, which is disposed at a predetermined distance from the side surfaces of the outermost portions of the multiple lower electrodes 120, the multiple P-type thermoelectric legs 130 and the multiple N-type thermoelectric legs 140, and the multiple upper electrodes 150; a sealing material 194, which is disposed between the sealing shell 192 and the lower substrate 110; and a sealing material 196, which is disposed between the sealing shell 192 and the upper substrate 160. Similar to the above, the sealing shell 192 can contact the lower substrate 110 and the upper substrate 160 through sealing materials 194 and 196. Therefore, when the sealing shell 192 is in direct contact with the lower substrate 110 and the upper substrate 160, heat conduction occurs through the sealing shell 192, thus preventing the problem of temperature difference reduction between the lower substrate 110 and the upper substrate 160. Here, sealing materials 194 and 196 may include at least one of epoxy resin and silicone resin, or a strip with at least one of epoxy resin and silicone resin coated on both surfaces. Sealing materials 194 and 195 can be used for hermetic sealing between the sealing shell 192 and the lower substrate 110, and between the sealing shell 192 and the upper substrate 160, which can increase the sealing effect between the lower electrode 120 and the P-type thermoelectric leg 130, and between the N-type thermoelectric leg 140 and the upper electrode 150, and can be interchanged with decorative materials, decorative layers, waterproof materials, waterproof layers, etc. Here, sealing material 194, which performs a seal between the sealing shell 192 and the lower substrate 110, may be disposed on the upper surface of the lower substrate 110, while sealing material 196, which performs a seal between the sealing shell 192 and the upper substrate 160, may be disposed on the side surface of the upper substrate 160. Therefore, the area of ​​the lower substrate 110 may be larger than the area of ​​the upper substrate 160. Simultaneously, a guide groove G may be formed in the sealing shell 192, leading out leads 180 and 182 connected to the electrodes. Therefore, the sealing shell 192 may be an injection-molded product made of plastic or similar materials and may be interchangeable with a sealing cap. However, the above description of the sealing member is merely an example, and the sealing member may be modified in various forms. Although not shown, thermal insulation material may also be included to surround the sealing member. Optionally, the sealing member may include thermal insulation components.

[0073] The terms "lower substrate 110, lower electrode 120, upper electrode 150 and upper substrate 160" are used above, but they are arbitrarily referred to as upper and lower parts only for ease of understanding and description, and their positions can be reversed, so that the lower substrate 110 and lower electrode 120 can be disposed on the upper side, while the upper electrode 150 and upper substrate 160 can be disposed on the lower side.

[0074] Figure 5 This is a cross-sectional view of a thermoelectric element according to an embodiment of the present disclosure. Figure 6 This is a cross-sectional view of a thermoelectric element according to another embodiment of the present disclosure. Figure 7 This is a cross-sectional view of a thermoelectric element according to yet another embodiment of the present disclosure, and Figure 8 This is a cross-sectional view of a thermoelectric element according to another embodiment of the present disclosure. (The details regarding...) Figures 1 to 4 The overlapping description of content that is identical.

[0075] refer to Figures 5 to 8 According to an embodiment of the present disclosure, the thermoelectric element 300 includes a first substrate 310, a first insulating layer 320 disposed on the first substrate 310, a first buffer layer 330 disposed on the first insulating layer 320, a plurality of first electrodes 340 disposed on the first buffer layer 330, a plurality of P-type thermoelectric legs 350 and a plurality of N-type thermoelectric legs 355 disposed on the plurality of first electrodes 340, a plurality of second electrodes 360 disposed on the plurality of P-type thermoelectric legs 350 and the plurality of N-type thermoelectric legs 355, a second buffer layer 370 disposed on the plurality of second electrodes 360, and a second substrate 380 disposed on the second buffer layer 370.

[0076] As shown in the figure, the heat sink 390 may also be disposed on the second substrate 380. Although not shown, a sealing member may also be disposed between the first substrate 310 and the second substrate 380.

[0077] Typically, when the thermoelectric element 300 is activated, the high-temperature portion of the thermoelectric element 300 may be exposed to high temperatures, and due to the difference in thermal expansion coefficients between the electrodes and the substrate, shear stress may be transmitted to the interface between the electrodes and the substrate. In this specification, the shear stress transmitted to the interface between the electrodes and the substrate due to the difference in thermal expansion coefficients is referred to as thermal stress. When the thermal stress exceeds a predetermined level, cracks will be applied to the bonding surface between the solder provided on the electrodes and the thermoelectric legs, and the cracks will degrade the performance of the thermoelectric element and reduce its reliability. Specifically, when a heat sink is further provided on the substrate located at the high-temperature portion of the thermoelectric element 300, the difference in thermal expansion coefficients between the substrate and the heat sink may significantly affect the durability and reliability of the thermoelectric element 300.

[0078] According to embodiments of the present disclosure, the first buffer layer 330 and the second buffer layer 370 may be disposed between the first substrate 310 and the first electrode 340, and between the second electrode 360 ​​and the second substrate 380, respectively. The first buffer layer 330 and the second buffer layer 370 can alleviate the thermal stress caused by the difference in thermal expansion coefficients between the electrode and the substrate.

[0079] In this case, the first buffer layer 330 and the second buffer layer 370 may each comprise silicone resin and inorganic material, and the Young's modulus may be 1 to 65 MPa, preferably 5 to 60 MPa, and more preferably 10 to 50 MPa. In this specification, Young's modulus may refer to the Young's modulus at a temperature of 200°C or lower, and preferably to the Young's modulus at a temperature between 150°C and 200°C. When a thermoelectric element is used to generate electricity, the power generation performance increases with the increase of the temperature difference between the high-temperature and low-temperature portions of the thermoelectric element. Therefore, the temperature of the high-temperature portion of the thermoelectric element may be 150°C or higher, preferably 180°C or higher, and more preferably 200°C or higher. Therefore, in this specification, the reference temperature for defining the Young's modulus of the first buffer layer 330 and the second buffer layer 370 may be a temperature between 150°C and 200°C. When the Young's moduli of the first buffer layer 330 and the second buffer layer 370 each meet this value range, the thermal stress between the substrate and the electrode can be minimized because the buffer layers elongate along with the substrate when it thermally expands, thus preventing cracking in the thermoelectric legs. Here, the Young's modulus at each temperature can be measured using a dynamic mechanical analysis (DMA) device. In this embodiment, a Rheometric Scientific DMA device of model RDA-700 is used to measure the Young's modulus at each temperature in a 10×23×0.05mm sample at a heating rate of 5°C / min and a frequency of 1Hz.

[0080] In this case, when the Young's modulus of the first buffer layer 330 and the second buffer layer 370 is less than 1 MPa, the first buffer layer 330 and the second buffer layer 370 become difficult to support between the substrate and the electrode, and the reliability of the thermoelectric element is easily weakened under minor external impacts or vibration environments. On the other hand, when the Young's modulus of the first buffer layer 330 and the second buffer layer 370 exceeds 65 MPa, the possibility of cracks forming at the interface in the thermoelectric element increases due to the increased thermal stress between the substrate and the electrode.

[0081] According to embodiments of this disclosure, the Young's modulus of the first buffer layer 330 may differ from that of the second buffer layer 370. For example, when the first substrate 310 is a low-temperature region and the second substrate 380 is a high-temperature region, that is, when the temperature at the first substrate 310 is lower than the temperature at the second substrate 380, the Young's modulus of the second buffer layer 370 (which is a buffer layer in the high-temperature region) will be lower than that of the first buffer layer 330. Therefore, even when the substrate at the high-temperature region thermally expands, since the buffer layer can elongate together, the thermal stress between the substrate and the electrode can be minimized, and the problem of cracks in the thermoelectric leg can be prevented.

[0082] In this case, the silicone resin contained in the first buffer layer 330 and the second buffer layer 370 may include polydimethylsiloxane (PDMS), and the inorganic material may include at least one oxide, carbide, and nitride of aluminum, titanium, zirconium, boron, and zinc. Here, the molecular weight of PDMS may be from 5,000 to 30,000 g / mol, and preferably from 15,000 to 30,000 g / mol. When the molecular weight of PDMS meets this range, the interchain bonding strength of PDMS can be increased, and therefore the Young's modulus of the first buffer layer 330 and the second buffer layer 370 may be from 1 to 65 MPa, and preferably from 10 to 50 MPa. In this case, the first buffer layer 330 and the second buffer layer 370 may also include a crosslinking agent, and the molecular weight of the crosslinking agent may be from 500 to 2,000 g / mol, and preferably from 1,000 to 2,000 g / mol. As the molecular weight of the crosslinking agent increases, the chain length of the crosslinking agent increases, and therefore the first buffer layer 330 and the second buffer layer 370 can be increased.

[0083] Meanwhile, in each of the first buffer layer 330 and the second buffer layer 370, the content of inorganic material can be 85 to 90 wt%. In this case, the inorganic material may include a first inorganic material group (where D50 is 5 to 20 μm), a second inorganic material group (where D50 is 20 to 30 μm), and a third inorganic material group (where D50 is 30 to 40 μm). For example, the content of the first inorganic material group may be 1 to 20 wt% of all inorganic materials, and preferably 5 to 15 wt%; the content of the second inorganic material group may be 10 to 30 wt% of all inorganic materials, and preferably 15 to 25 wt%; and the content of the third inorganic material group may be 60 to 80 wt% of all inorganic materials, and preferably 65 to 75 wt%. In this case, the D50 of the inorganic material in the first buffer layer 330 and the second buffer layer 370 may be 30 to 40 μm. Similar to the above, when the content of inorganic material in the first buffer layer 330 and the second buffer layer 370 is 85 to 90 wt% and includes multiple groups of inorganic materials classified by particle size, the thermal conductivity of the first buffer layer 330 and the second buffer layer 370 can be increased to 2 W / mK or higher, and preferably 3 W / mK or higher, because the heat dissipation path can be optimized.

[0084] Similar to the above, the first buffer layer 330 and the second buffer layer 370 according to the embodiments of this disclosure can not only reduce the thermal stress caused by the difference in thermal expansion coefficients between the substrate and the electrode, but also enhance the insulation bonding strength and thermal conductivity between the substrate and the electrode.

[0085] In this case, each of the first buffer layer 330 and the second buffer layer 370 may have a thickness of 10 to 80 μm, preferably 20 to 60 μm, and more preferably 30 to 45 μm. Here, in terms of thermal conductivity, it is advantageous that each of the first buffer layer 330 and the second buffer layer 370 is set as thin as possible while maintaining thermal stress relaxation performance, insulation performance, and adhesion performance. When the first substrate 310 is a low-temperature section and the second substrate 380 is a high-temperature section, since the second buffer layer 370 requires higher thermal stress relaxation performance, the thickness of the second buffer layer 370 may be greater than the thickness of the buffer layer 330.

[0086] Meanwhile, as described above, assuming that the first substrate 310 is disposed on the low-temperature side of the thermoelectric element 300 and the second substrate 380 is disposed on the high-temperature side of the thermoelectric element 300, since the wire is connected to the first electrode 340, a higher withstand voltage may be required on the low-temperature side than on the high-temperature side, while a higher thermal conductivity may be required on the high-temperature side.

[0087] Therefore, according to embodiments of this disclosure, the first substrate 310 may be an aluminum substrate, and the second substrate 380 may be a copper substrate. Compared to an aluminum substrate, a copper substrate has higher thermal conductivity and electrical conductivity. Therefore, when the first substrate 310 is made of an aluminum substrate and the second substrate 380 is made of a copper substrate, both high withstand voltage performance at the low-temperature side and high heat dissipation performance at the high-temperature side can be satisfied.

[0088] To enhance the withstand voltage performance at the cryogenic section, a first insulating layer 320 may be disposed between the first substrate 310 and the first buffer layer 330. According to embodiments of this disclosure, withstand voltage performance refers to the characteristic of maintaining a 2.5 kV alternating current (AC) voltage and a 1 mA current for 10 seconds without insulation breakdown. In this specification, withstand voltage performance can be measured by disposing of the insulating layer on the substrate, subsequently connecting one terminal to the substrate, and connecting the other terminals to nine points on the insulating layer, respectively, to test whether it maintains a 2.5 kV AC voltage and a 1 mA current for 10 seconds without insulation breakdown.

[0089] According to embodiments of this disclosure, the first insulating layer 320 may comprise aluminum oxide. Here, the first insulating layer 320 may be an aluminum oxide layer separately stacked on the first substrate 310, or it may be an aluminum oxide layer oxidized by a surface treatment of the first substrate 310 (which is an aluminum substrate). For example, the aluminum oxide layer may be formed by anodizing the first substrate 310, which is an aluminum substrate, or by an immersion process or a spraying process.

[0090] According to another embodiment of this disclosure, the first insulating layer 320 may include a composite material comprising silicon and aluminum. Here, the composite material may be at least one of oxides, carbides, and nitrides comprising silicon and aluminum. For example, the composite material may include at least one of Al-Si bonds, Al-O-Si bonds, Si-O bonds, Al-Si-O bonds, and Al-O bonds. Similar to the above, composite materials comprising at least one of Al-Si bonds, Al-O-Si bonds, Si-O bonds, Al-Si-O bonds, and Al-O bonds may have excellent insulating properties and thus achieve high withstand voltage performance. Optionally, the composite material may be an oxide, carbide, or nitride, and may also include titanium, zirconium, boron, zinc, etc., as well as silicon and aluminum. For this purpose, the composite material may be obtained by a process of heat-treating aluminum after mixing at least one of an inorganic binder and an organic-inorganic mixed binder. The inorganic binder may, for example, include at least one of silicon dioxide (SiO2), metal alkoxides, boron oxide (B2O3), and zinc oxide (ZnO2). Inorganic binders are inorganic particles, but can also be sols or gels to act as adhesives when in contact with water. In this case, at least one of silicon dioxide (SiO2), metal alkoxides, and boron oxide (B2O3) is used to increase the adhesion between aluminum particles or to the first substrate 310, while zinc oxide (ZnO2) can be used to increase the strength of the first insulating layer 320 and increase its thermal conductivity.

[0091] Here, the content of the composite material may be 80 wt% or higher of the entire first insulation layer 320, preferably 85 wt% or higher, and more preferably 90 wt% or higher.

[0092] In this case, a surface roughness Ra of 0.1 μm or greater can be formed on the first insulating layer 320. The surface roughness is formed when the particles constituting the composite material protrude from the surface of the first insulating layer 320, and can be measured using a surface roughness meter. The surface roughness meter uses a probe to measure the cross-sectional profile and calculates the surface roughness using the peak line, valley line, average line, and a reference length of the cross-sectional profile. In this specification, surface roughness may refer to the arithmetic mean roughness (Ra) obtained by the centerline averaging method. The arithmetic mean roughness (Ra) can be obtained using the following formula 2.

[0093] [Formula 2]

[0094]

[0095] That is, when the average line direction is set to the x-axis and the height direction is set to the y-axis, and the cross-sectional curve obtained by the probe of the surface roughness measuring instrument is extracted to be as many as the reference length L and expressed as a function (f(x)), the value obtained by Equation 2 can be expressed in micrometers.

[0096] Similar to the above, when the surface roughness Ra of the first insulating layer 320 is 0.1 μm or higher, the contact area with the first buffer layer 330 increases, and therefore the bonding strength with the first buffer layer 330 can be increased. Specifically, as described above, when the first buffer layer 330 contains PDMS, the bonding strength between the first insulating layer 320 and the first buffer layer 330 can be further increased because the PDMS in the first buffer layer 330 easily penetrates between the multiple grooves formed by the surface roughness of the first insulating layer 320.

[0097] In this case, the first insulating layer 320 can be formed on the first substrate 310 by a wet process. Here, the wet process can be a spray coating process, a dip coating process, a screen printing process, or a similar process. Therefore, the thickness of the first insulating layer 320 is easy to control, and composite materials of various compositions can be applied.

[0098] In this case, the thickness of the first substrate 310 can be 0.1 to 2 mm, preferably 0.3 to 1.5 mm, and more preferably 0.5 to 1.2 mm, and the thickness of the first insulating layer 320 can be 10 to 100 μm, preferably 20 to 80 μm, and more preferably 30 to 60 μm. When the thickness of the first insulating layer 320 meets this range, both high thermal conductivity and high voltage withstand performance can be achieved simultaneously.

[0099] Similar to the above, when the first insulating layer 320 and the first buffer layer 330 are disposed on the first substrate 310 and the first electrode 340 is disposed on the first buffer layer 330, the withstand voltage performance at the low-temperature section side can be further improved compared to the case where the first buffer layer 330 is not disposed. Specifically, when the first insulating layer 320 is an alumina layer formed by surface treatment of the first substrate 310, and the first buffer layer 330 is disposed on the first insulating layer 320, the withstand voltage performance can be improved while minimizing thermal resistance.

[0100] refer to Figure 6 When the first insulating layer 320 comprises aluminum oxide, the first insulating layer 320 can be disposed on both surfaces of the first substrate 310. That is, an additional first insulating layer 322 can be disposed on the surface of the first substrate 310 opposite to the surface on which the first insulating layer 320 is disposed. Therefore, the withstand voltage performance can be improved without increasing the thermal resistance of the first substrate 310, and surface corrosion of the first substrate 310 can be prevented.

[0101] Optional, such as Figure 7 As shown, when the first insulating layer 320 comprises aluminum oxide, the first insulating layer 320 can also be disposed on the side surface of the first substrate 310. That is, at least one of the first insulating layer 320 disposed on one side of the first substrate 310 and the first insulating layer 322 disposed on the other surface can form an extension 324 extending along the first substrate 310, such that the first insulating layer 320 and the first insulating layer 322 can be connected to each other at the side surface of the first substrate 310. Therefore, the first insulating layer, such as an aluminum oxide layer, can be formed on the entire surface of the first substrate 310, and can further improve the withstand voltage performance at the low temperature side. When the first substrate 310 is surface treated to form an aluminum oxide layer, it is easy to form an aluminum oxide layer on both surfaces of the first substrate 310 (such as on the side surface of the first substrate 310). Figure 6 In the illustrated embodiment), or an aluminum oxide layer is formed on the entire surface of the first substrate 310 (such as on...). Figure 7 (As shown in the embodiment).

[0102] Meanwhile, as described above, the heat sink can also be disposed on the high-temperature side. The second substrate 380 and the heat sink 390 on the high-temperature side can be integrally formed, but the second substrate 380 and the heat sink 390 can be bonded to each other separately. In this case, when a metal oxide layer is formed on the second substrate 380, it is difficult to bond the second substrate 380 and the heat sink 390 together. Therefore, in order to increase the bonding strength between the second substrate 380 and the heat sink 390, a metal oxide layer may not be formed between the second substrate 380 and the heat sink 390. That is, when the second substrate 380 is a copper substrate, a copper oxide layer may not be formed on the surface of the copper substrate. For this purpose, the copper substrate can be pre-treated to prevent oxidation. For example, when the copper substrate is plated with a metal layer (e.g., nickel) that is less prone to oxidation than copper, it is possible to prevent the formation of a metal oxide layer on the copper substrate.

[0103] Meanwhile, according to yet another embodiment of this disclosure, such as Figure 8 As shown, a second insulating layer 375 that contacts the second substrate 380 may also be provided between the second buffer layer 370 and the second substrate 380.

[0104] In this case, the description of the second insulating layer 375 can be the same as the description of the first insulating layer 320 above. That is, the second insulating layer 375 can be an alumina layer or a composite material layer made of a composite material containing silicon and aluminum.

[0105] Optionally, the second insulating layer 375 and the second buffer layer 370 may have the same composition.

[0106] Optionally, the second insulating layer 375 may comprise silicone resin and inorganic materials, having a composition different from that of the second buffer layer 370, and having a Young's modulus greater than that of the second buffer layer 370. For example, when the Young's modulus of the second buffer layer 370 is 1 to 65 MPa, the Young's modulus of the second insulating layer 375 may be 70 to 150 MPa. When the Young's modulus of the second insulating layer 375 meets this range, the mechanical rigidity between the second substrate 380 and the second electrode 360 ​​can be maintained.

[0107] Therefore, the molecular weight of the silicone resin contained in the second insulating layer 375 can be smaller than that of the silicone resin contained in the second buffer layer 370, the content of the silicone resin contained in the second insulating layer 375 can be greater than that of the silicone resin contained in the second buffer layer 370, and the content of the inorganic material contained in the second insulating layer 375 can be less than that of the inorganic material contained in the second buffer layer 370. For example, the content of the inorganic material can be 60 to 85 wt% of the second insulating layer 375, and preferably 80 to 85 wt%.

[0108] Simultaneously, the second buffer layer 370 can be formed by coating a composite material in an uncured or semi-cured state onto the second insulating layer 375, and subsequently setting and pressing a plurality of pre-aligned second electrodes 360. Therefore, some side surfaces of the plurality of second electrodes 360 can be embedded in the second buffer layer 370. In this case, the height of each side surface of the plurality of second electrodes 360 embedded in the second buffer layer 370 can be 0.1 to 1.0 times the thickness of the plurality of second electrodes 360, preferably 0.2 to 0.9 times, and more preferably 0.3 to 0.8 times. Similar to the above, when some side surfaces of the plurality of second electrodes 360 are embedded in the second buffer layer 370, the contact area between the plurality of second electrodes 360 and the second buffer layer 370 increases, and thus the heat transfer performance, bonding strength, and thermal stress relaxation performance between the plurality of second electrodes 360 and the second buffer layer 370 can be further improved.

[0109] More specifically, since the thickness of the second buffer layer 370 between the multiple second electrodes 360 decreases from the side surface of each electrode toward the central region, the apex can be in a smooth “V” shape.

[0110] Although not shown, according to another embodiment of this disclosure, the positions of the second buffer layer 370 and the second insulating layer 375 may be changed. For example, the second buffer layer 370 may be disposed in contact with the second substrate 380, and the second insulating layer 375 may be disposed between the second buffer layer 370 and the second electrode 360. The Young's modulus of the second buffer layer 370 may be from 1 to 65 MPa, and the Young's modulus of the second insulating layer 375 may be from 70 to 150 MPa. Therefore, the second buffer layer 370 may be in direct contact with the second substrate 380 and extend according to the thermal expansion of the second substrate 380, and may be used to minimize the thermal stress applied to the second electrode 360, while the second insulating layer 375 may be in direct contact with multiple second electrodes 360 and may be used to maintain insulation and mechanical strength.

[0111] Meanwhile, according to embodiments of this disclosure, the second substrate 380 and the heat sink 390 can be joined by separate fastening members.

[0112] Figure 9 An example of the bonding structure between the second substrate 380 and the heat sink 390 is shown.

[0113] refer to Figure 9 The heat sink 390 and the second substrate 380 can be fastened together by a plurality of fastening members 400. For this purpose, a through-hole S for the fastening members 400 to pass through can be formed in each of the heat sink 390 and the second substrate 380. Here, a separate insulator 410 can also be provided between the through-hole S and the fastening member 400. The separate insulator 410 can be an insulator surrounding the outer peripheral surface of the fastening member 400 or an insulator surrounding the wall surface of the through-hole S. Therefore, the insulation distance of the thermoelectric element can be increased.

[0114] In this case, according to another embodiment of the present disclosure, a buffer layer made of the same material as the second buffer layer 370 may also be disposed between the second substrate 380 and the heat sink 390. Therefore, it is possible to prevent the problem that the second substrate 380 and the heat sink 390 are partially spaced apart from each other due to the difference in the coefficient of thermal expansion between them.

[0115] Similar to the above, according to the embodiments of this disclosure, thermoelectric elements with excellent thermoelectric and bonding properties can be obtained.

[0116] The effects of embodiments according to the present disclosure will now be described in more detail using comparative examples and examples.

[0117] Including PDMS and inorganic materials, and in Figure 5 A buffer layer with a Young's modulus of 25 MPa at 200°C, as shown in the structure, is applied to a thermoelectric element according to the example; comprising PDMS and inorganic materials, and in Figure 5The buffer layer with a Young's modulus of 75 MPa at 200°C, as shown in the structure, was applied to the thermoelectric element according to Comparative Example 1; while in the thermoelectric element according to Comparative Example 2, Figure 5 The buffer layer in the structure shown is replaced with a polyimide layer. More specifically, the PDMS contained in the buffer layer applied to the thermoelectric element according to the example has a molecular weight of 15,000 to 30,000 g / mol, and the content of inorganic material in the buffer layer is 85 to 90 wt%; the PDMS contained in the buffer layer applied to the thermoelectric element according to Comparative Example 1 has a molecular weight of 5,000 to 15,000 g / mol, and the content of inorganic material in the buffer layer is 80 to 85 wt%.

[0118] Figure 10 This is a graph showing the relationship between the substrate temperature and thermal stress in the thermoelectric element according to Comparative Example 1. First, in the thermoelectric element according to Comparative Example 1, interfacial breakdown was observed between the substrate and the electrode when the substrate temperature was 145°C. Therefore, in the thermoelectric element according to Comparative Example 1, as a result of evaluating the thermal stress relative to the substrate temperature, the thermal stress was observed to be 670 MPa when the substrate temperature was approximately 145°C. Therefore, the critical fracture stress of the thermoelectric element was determined to be 670 MPa.

[0119] Meanwhile, the results in Table 1 were obtained as a result of the correlation between the elastic modulus of the test buffer layer and the thermal stress between the substrate and the electrode.

[0120] [Table 1]

[0121] Elastic modulus (MPa) Thermal stress (MPa) 3 250 65 660 100 900 200 1,150 300 1,450 1000 2,850

[0122] That is, it is known that thermal stress decreases as the elastic modulus of the buffer layer decreases. Specifically, when the elastic modulus is 65 MPa or less, the known thermal stress is 660 MPa, which is below the critical fracture stress.

[0123] Meanwhile, in order to improve the power generation performance of the thermoelectric element applied to the power generation device, it is preferable that, under the condition that the temperature of the high-temperature part of the thermoelectric element is 150°C to 200°C and the temperature of the low-temperature part is 15°C to 55°C (that is, the temperature difference between the high-temperature part and the low-temperature part is 95°C to 185°C), the interface between the electrode and the substrate does not crack for 500 hours, and the rate of change of resistance is maintained within 7%, preferably within 6%, and more preferably within 5%. Even when the thermoelectric element is exposed to high temperature for a long time, it is preferable that the rate of change of Young's modulus is maintained within 10%, preferably within 7%, and more preferably within 5%.

[0124] Figure 11 It is a graph showing the rate of change of resistance between the high-temperature and low-temperature sections of the thermoelectric element, based on the temperature difference, according to the example and comparative examples. Figure 12 It is a graph showing the change in Young's modulus of thermoelectric elements based on the example and comparative examples, measured over time when exposed to 200°C.

[0125] refer to Figure 11 In the example, even when the temperature difference between the high-temperature part and the low-temperature part of the thermoelectric element is 145°C or higher, the resistance change rate remains within 7%. However, in Comparative Examples 1 and 2, even when the temperature difference between the high-temperature part and the low-temperature part of the thermoelectric element is less than 145°C, the resistance change rate exceeds 7%. Furthermore, when the temperature difference between the high-temperature part and the low-temperature part is 145°C or higher, the resistance change rate increases rapidly due to thermal stress, thereby causing the connection to break.

[0126] refer to Figure 12 Even when the buffer layer according to the example is exposed to 150°C to 200°C for a long time, the Young's modulus change rate remains within the range of 10%. However, it can be seen that the Young's modulus of the buffer layer according to Comparative Example 1 increases rapidly by more than 10% with the increase of exposure time at approximately 200°C.

[0127] Therefore, in the thermoelectric element according to the embodiments of this disclosure, since the interface between the electrode and the substrate does not break, the rate of change of resistance is maintained within 7% even when the temperature of the high-temperature part is about 200°C, and even when the thermoelectric element is exposed to about 200°C for a long time, the rate of change of Young's modulus is maintained within 10%, indicating that the thermoelectric element has high reliability.

[0128] The thermoelectric element according to embodiments of this disclosure can be applied to a power generation system that generates electricity by utilizing the temperature difference between a high-temperature section and a low-temperature section. For example, a first fluid flows to a first substrate of the thermoelectric element, i.e., the low-temperature section, while a second fluid (whose temperature is higher than that of the first fluid) flows to a second substrate, i.e., the high-temperature section, thus creating a temperature difference between the first and second substrates and generating electricity. In this case, the temperature of the second fluid may be, for example, 95°C to 185°C, higher than the temperature of the first fluid.

[0129] Although preferred embodiments of the present disclosure have been described above, those skilled in the art can make various modifications and changes to the present disclosure within the spirit and scope of the claims described later.

Claims

1. A thermoelectric element comprising: a first substrate; a first buffer layer disposed on the first substrate; a first electrode disposed on the first buffer layer; a P-type thermoelectric leg and an N-type thermoelectric leg disposed on the first electrode; a second electrode disposed on the P-type thermoelectric leg and the N-type thermoelectric leg; a second buffer layer disposed on the second electrode; and a second substrate disposed on the second buffer layer, wherein the first substrate is an aluminum substrate, wherein the second substrate is a copper substrate, wherein a temperature at the first substrate is lower than a temperature at the second substrate, wherein an aluminum oxide layer is further disposed between the first substrate and the first buffer layer, wherein the first buffer layer and the second buffer layer contain a silicone resin and an inorganic material, wherein a Young's modulus of the second buffer layer is lower than a Young's modulus of the first buffer layer, wherein a thickness of the second buffer layer is greater than a thickness of the first buffer layer, wherein the Young's modulus of the second buffer layer is 1 to 65 MPa, and wherein a reference temperature for defining the Young's modulus is a temperature between 150°C and 200°C.

2. The thermoelectric element according to claim 1, wherein: the silicone resin contains polydimethylsiloxane (PDMS); and a content of the inorganic material in at least one of the first buffer layer and the second buffer layer is 85 to 90 wt%. a molecular weight of the PDMS is 5000 to 30000 g / mol.

3. The thermoelectric element of claim 2, wherein, the inorganic material contains a first inorganic material group having a D50 of 5 to 20 pm, a second inorganic material group having a D50 of 20 to 30 pm, and a third inorganic material group having a D50 of 30 to 40 pm.

4. The thermoelectric element of claim 2, wherein, a content of the first inorganic material group is 1 to 20 wt% of the inorganic material, a content of the second inorganic material group is 10 to 30 wt% of the inorganic material, and a content of the third inorganic material group is 60 to 80 wt% of the inorganic material.

5. The thermoelectric element of claim 4, wherein, a change rate of the Young's modulus of the first buffer layer at 150°C to 200°C for 500 hours is within 10%.

6. The thermoelectric element of claim 1, wherein, 7. The thermoelectric element according to claim 1, further comprising an insulating layer disposed between the second substrate and the second buffer layer, the insulating layer is selected from the group consisting of an aluminum oxide layer, a composite layer formed of a composite material containing silicon and aluminum, and a resin layer formed of a resin composite containing at least one of an epoxy resin and a silicone resin and an inorganic material. wherein, a certain side surface of the second electrode is embedded in the second buffer layer.

8. The thermoelectric element of claim 7, wherein, 9. The thermoelectric element according to claim 1, further comprising a heat sink disposed on the second substrate.

10. A power generation system comprising: the thermoelectric element according to claim 1, a first fluid flowing to the first substrate of the thermoelectric element, and a second fluid flowing to the second substrate of the thermoelectric element and having a temperature higher than that of the first fluid by 95°C to 185°C, wherein a resistance change rate of the thermoelectric element for 500 hours is within 7%. ​

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