Strain gauge, photoelectric conversion element, and method for measuring strain

Abstract

To provide strain gauges that do not require amplification circuits or power supplies.SOLUTION: A strain gauge 100 has a heterojunction photoelectric conversion element 10 and electrode pairs 21,22 that sandwich the heterojunction photoelectric conversion element, and at least one of the P-type semiconductor 12 and N-type semiconductor 11 at the PN junction of the heterojunction photoelectric conversion element is a piezoelectric semiconductor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a strain gauge and a method for measuring strain.

Background Art

[0002] Conventional strain gauges, as disclosed in Japanese Patent Application Laid-Open No. 2013-32918 (hereinafter referred to as Patent Document 1), generally read the strain generated by an external force applied to a metal by the resistance changed by the external force of the metal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] However, such a general strain gauge requires an amplifier circuit and a power supply to read the resistance value. Therefore, there is a demand for a strain gauge that does not require an amplifier circuit and a power supply.

[0005] According to one embodiment, the strain gauge includes a heterojunction photoelectric conversion element and an electrode pair sandwiching the heterojunction photoelectric conversion element, and at least one of the P-type semiconductor and the N-type semiconductor in the PN junction of the heterojunction photoelectric conversion element is a piezoelectric semiconductor.

[0006] According to another embodiment, the method for measuring strain is a method for measuring strain using a heterojunction photoelectric conversion element, wherein at least one of the P-type semiconductor and the N-type semiconductor in the PN junction of the heterojunction photoelectric conversion element is a piezoelectric semiconductor. An electrode pair is connected to the P-type semiconductor and the N-type semiconductor of the heterojunction photoelectric conversion element, the heterojunction photoelectric conversion element is irradiated with light, and the strain applied to the heterojunction photoelectric conversion element in the state where light is irradiated is obtained from the measured value of the voltage between the electrode pairs.

[0007] Further details will be described in the embodiments below. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of the configuration of a strain gauge according to an embodiment. [Figure 2] Figure 2 is a diagram illustrating an example of a method for manufacturing strain gauges. [Figure 3] Figure 3 shows an example of a method for applying strain to a strain gauge. [Figure 4] Figure 4 is a diagram illustrating the energy levels of the photoelectric conversion element included in the strain gauge. [Figure 5] Figure 5 shows the results of a simulation conducted by the inventors on the photoelectric conversion characteristics of a photoelectric conversion element when the energy level of the lower conduction band (CBM) of magnesium-doped zinc oxide (ZnMgO) is changed. [Figure 6] Figure 6 shows the measurement results of the open-circuit voltage of a strain gauge when the same strain is repeatedly applied to the strain gauge. [Figure 7] Figure 7 is a diagram illustrating the definition of strain applied to a strain gauge. [Figure 8] Figure 8 shows the relationship between the amount of strain applied to a strain gauge and the measured open-circuit voltage. [Figure 9] Figure 9 is a diagram illustrating the energy levels when the N-type semiconductor is zinc oxide (ZnO) and the P-type semiconductor is cadmium telluride (CdTe). [Figure 10] Figure 10 is a diagram illustrating the energy levels when the N-type semiconductor is titanium oxide (TiO2) and the P-type semiconductor is cadmium telluride (CdTe). [Figure 11] Figure 11 is a flowchart illustrating the general method for measuring strain using strain gauges. [Modes for carrying out the invention]

[0009] <1. Overview of strain gauges and strain measurement methods>

[0010] (1) The strain gauge according to this embodiment comprises a heterojunction photoelectric conversion element and an electrode pair sandwiching the heterojunction photoelectric conversion element, wherein at least one of the P-type semiconductor and the N-type semiconductor in the PN junction of the heterojunction photoelectric conversion element is a piezoelectric semiconductor.

[0011] Since at least one of the P-type semiconductor and the N-type semiconductor is a piezoelectric semiconductor, when strain is applied while light is irradiated, the energy level of the piezoelectric semiconductor changes, and the band offset between the P-type semiconductor and the N-type semiconductor changes. As a result, the voltage between the electrodes connected to the P-type semiconductor and the N-type semiconductor changes. The inventors have verified through measurements that applying strain to a heterojunction photoelectric conversion element in which at least one of the P-type semiconductor and the N-type semiconductor is a piezoelectric semiconductor changes the voltage between the electrodes, and that this change corresponds to the applied strain. Therefore, by pre-memorizing the relationship between the strain applied while light is irradiated and the change in voltage between the electrodes, the applied strain can be obtained based on the measured voltage between the electrodes. Thus, by using this strain gauge, strain can be easily measured without the need for amplification circuits or power supplies.

[0012] (2) Preferably, the strain gauge obtains the strain applied to the heterojunction photoelectric conversion element when light is irradiated from the measured voltage between the electrode pair. This allows for easy measurement of strain without the need for an amplification circuit or power supply.

[0013] (3) Preferably, the strain gauge obtains the strain applied to the heterojunction photoelectric conversion element when light is irradiated by the change in electromotive force between the electrode pair. This allows for easy measurement of strain without the need for an amplification circuit or power supply.

[0014] (4) Preferably, the N-type semiconductor is a piezoelectric semiconductor. By applying strain, the energy level order on the N-type semiconductor side changes, and the band offset between the P-type semiconductor and the N-type semiconductor changes.

[0015] (5) Preferably, the P-type semiconductor is crystallized selenium. Selenium has a high light absorption coefficient for visible light. Therefore, the photoelectric conversion of the photoelectric conversion element can be improved.

[0016] (6) Preferably, the P-type semiconductor and the N-type semiconductor are a combination in which the band offset decreases as the strain applied to the heterojunction photoelectric conversion element increases. Thereby, the strain applied by the voltage change can be measured.

[0017] (7) Preferably, the P-type semiconductor and the N-type semiconductor are a combination in which the open-circuit voltage between the electrode pairs is maximized when the strain at the upper limit of the set strain measurement range is applied. Thereby, using this strain gauge, it becomes possible to measure the application of strain within the set measurement range.

[0018] (8) Preferably, the electrode connected to the N-type semiconductor among the electrode pairs is a transparent electrode. By using a transparent electrode, the light irradiated to the strain gauge is transmitted and reaches the photoelectric conversion element.

[0019] (9) The method for measuring strain according to the present embodiment is a method for measuring strain using a heterojunction photoelectric conversion element, in which electrode pairs are connected to the P-type semiconductor and the N-type semiconductor of the heterojunction photoelectric conversion element, and at least one of the P-type semiconductor and the N-type semiconductor at the PN junction of the heterojunction photoelectric conversion element is a piezoelectric semiconductor, the heterojunction photoelectric conversion element is irradiated with light, and the strain applied to the heterojunction photoelectric conversion element in the state where light is irradiated is obtained from the measured value of the voltage between the electrode pairs.

[0020] By pre-memorizing the relationship between the applied strain and the change in voltage between electrodes under light irradiation, the applied strain can be obtained based on the measured voltage between the electrodes. Therefore, by using this strain gauge, strain can be easily measured without the need for amplification circuits or power supplies.

[0021] <2. Examples of strain gauges and strain measurement methods>

[0022] Figure 1 is a schematic diagram of the configuration of the strain gauge 100 according to this embodiment. Referring to Figure 1, the strain gauge 100 comprises a photoelectric conversion element 10 and electrode pairs 21 and 22 that sandwich the photoelectric conversion element 10.

[0023] The photoelectric conversion element 10 is a heterojunction type photoelectric conversion element in which at least one of the N-type semiconductor 11 and the P-type semiconductor 12 in the PN junction is a piezoelectric semiconductor. For example, in the photoelectric conversion element 10, the N-type semiconductor 11 is a piezoelectric semiconductor, and for example, it is a wurtzite-type piezoelectric semiconductor oriented along the c axis. For example, the wurtzite-type piezoelectric semiconductor is a piezoelectric semiconductor made of a zinc oxide-based material, such as magnesium-doped zinc oxide (ZnMgO(ZMO)).

[0024] The P-type semiconductor 12 is a thin film of crystalline selenium (Se). Selenium has a high visible light absorption coefficient. Therefore, it can improve the photoelectric conversion of the photoelectric conversion element 10.

[0025] Electrode 21 of the electrode pair 21,22 is connected to the N-type semiconductor 11. Electrode 22 of the electrode pair 21,22 is connected to the P-type semiconductor 12. Electrode 21 is a transparent electrode, for example, an ITO (Indium-Tin Oxide) transparent electrode. By using a transparent electrode, light irradiated onto the strain gauge 100 is transmitted through and reaches the photoelectric conversion element 10. Electrode 22 may be an opaque electrode, for example, a gold (Au) electrode.

[0026] The photoelectric conversion element 10 may be stacked on the substrate 23. For example, an electrode 21 is placed on the substrate 23, and an N-type semiconductor 11, a P-type semiconductor 12, and an electrode 22 are stacked on top of it in that order. In this case, the substrate 23 is a flexible transparent substrate, for example, a PET (polyethylene terephthalate) substrate. As a result, light irradiated onto the strain gauge 100 is transmitted through and reaches the photoelectric conversion element 10.

[0027] A voltmeter 24 can be connected to electrodes 21 and 22. By connecting the voltmeter 24 between electrodes 21 and 22, the open-circuit voltage between electrodes 21 and 22, i.e., the electromotive force, can be measured.

[0028] Figure 2 is a diagram illustrating an example of a manufacturing method for the strain gauge 100. The strain gauge 100 is manufactured by the steps S1 to S5 shown in Figure 2.

[0029] For details, refer to Figure 2. First, a substrate 23, such as a PET substrate, is prepared, and an ITO thin film is formed on its upper surface (Step S1). The ITO thin film may be formed by an etching process, such as vapor deposition etching. This forms an electrode 21 on the substrate 23.

[0030] Next, magnesium-doped zinc oxide (ZnMgO) is deposited on the ITO thin film by sputtering to form an N-type semiconductor 11 of ZnMgO (step S2). This forms the N-type semiconductor 11 on the electrode 21.

[0031] Next, tellurium (Te) and selenium (Se) are deposited on a thin film of ZnMgO, for example by resistance heating deposition (step S3), and then annealed at a high temperature (step S4). As a result, selenium crystallizes on the N-type semiconductor 11, and a P-type semiconductor 12 is formed.

[0032] Next, gold (Au) is deposited onto the entire thin film of crystalline selenium, for example, by resistance heating (step S5). This forms a thin gold film on the P-type semiconductor 12, and the electrode 22 is formed.

[0033] The strain gauge 100 measures strain by utilizing the change in the photoelectric conversion element 10 from the state when no strain is applied, when compressive strain (hereinafter referred to as strain) is applied during light irradiation. Figure 3 shows an example of how strain is applied to the strain gauge 100. As shown in Figure 3, as an example, the strain gauge 100 is set on the flexible substrate 200 with the P-type semiconductor 12 side of the photoelectric conversion element 10 facing the flexible substrate 200. Light is irradiated onto the strain gauge 100 from the side opposite to the flexible substrate 200, and light energy E is supplied to the photoelectric conversion element 10 from the N-type semiconductor 11 side. In this state, a curvature is applied to the flexible substrate 200, thereby supplying strain to the strain gauge 100.

[0034] Figure 4 is a diagram illustrating the energy levels of the photoelectric conversion element 10. In Figure 4, Type A represents the energy levels when no strain is applied to the photoelectric conversion element 10, and Type B represents the energy levels when strain is applied.

[0035] Referring to Figure 4, at the PN junction (boundary) of the photoelectric conversion element 10, a band offset ΔEc occurs, which is the energy level difference between the piezoelectric semiconductor magnesium-doped zinc oxide (ZnMgO) (N-type semiconductor 11) and crystalline selenium (Se) (P-type semiconductor 12).

[0036] When strain is applied to a piezoelectric semiconductor oriented along the c-axis, polarization occurs within the N-layer, which is the piezoelectric semiconductor. In the embodiment, the photoelectric conversion element 10 is composed of magnesium-doped zinc oxide (ZnMgO), which is a wurtzite-type piezoelectric semiconductor in which the N-type semiconductor 11 is oriented along the c-axis. Therefore, when strain is applied, polarization occurs within the N-layer.

[0037] When polarization occurs within the N layer, the negative polarization charge increases at the PN junction. This increase in negative polarization charge at the PN junction causes electrons (negative) in the conduction band to repel, attracting holes in the valence band and generating piezoelectric polarization charge. As a result, as shown in "After Change" in Figure 4, the energy level of the Conduction Band Minimum (CBM) in the zinc oxide window layer becomes higher than in "Before Change" when no strain is applied. Consequently, the band offset ΔEc at the PN junction is improved (reduced).

[0038] In other words, when strain is applied to the photoelectric conversion element 10, the band offset ΔEc (matching) of the conduction band energy levels between magnesium-doped zinc oxide (ZnMgO) and crystallized selenium (Se) changes (improves) from the state without strain (Type A). As a result, the open-circuit voltage and short-circuit current between electrodes 21 and 22 during light irradiation change according to the strain.

[0039] Thus, in the photoelectric conversion element 10, which is a heterojunction type photoelectric conversion element, by using a piezoelectric semiconductor in at least one of the N-type semiconductor 11 and the P-type semiconductor 12, the band alignment of the PN junction (boundary) can be easily controlled by applying strain to the photoelectric conversion element 10. In this case, the N-type semiconductor 11 and the P-type semiconductor 12 are chosen so that the band offset ΔEc decreases as the strain applied to the photoelectric conversion element 10 increases. Furthermore, the N-type semiconductor 11 and the P-type semiconductor 12 are chosen so that the energy level of the lower end of the conduction band (CBM) of the N-type semiconductor 11 is lower than the energy level of the lower end of the conduction band (CBM) of the P-type semiconductor 12. This makes it easier for an energy level shift due to polarization to occur compared to the opposite state.

[0040] In this regard, magnesium-doped zinc oxide (ZnMgO) can be used as an N-type semiconductor with a piezoelectric effect, and band alignment control at the boundary with crystalline selenium (Se) is easy. Therefore, magnesium-doped zinc oxide (ZnMgO) is suitable as a material for constituting the N-type semiconductor 11 of the photoelectric conversion element 10.

[0041] Figure 5 shows the results of a simulation conducted by the inventors on the photoelectric conversion characteristics of photoelectric conversion element 10 when the energy level of the lower band boundary (CBM) of magnesium-doped zinc oxide (ZnMgO) is changed. The simulation was performed using the one-dimensional device simulator SCAPS (Solar Cell Capacitance Simulator) (M. Burgelman et al., Thin Sol. Films 361-362(2000)527.), and the current density, voltage, conversion efficiency, and open-circuit voltage were calculated for each changed band offset value ΔEc.

[0042] Figure 5 shows the simulation results L1 for a band offset ΔEc of -0.4[eV] (ΔEc=-0.4[eV]), L2 for a band offset ΔEc of -0.3[eV] (ΔEc=-0.3[eV]), L3 for a band offset ΔEc of -0.2[eV] (ΔEc=-0.2[eV]), and L4 for a band offset ΔEc of ±0.0[eV] (ΔEc=±0.0[eV]), representing the relationship between current density and voltage calculated using SCAPS. Furthermore, Figures 5 show the simulation results L5 and L6 for band offsets ΔEc of -0.5, -0.4, -0.3, -0.2, -0.1, and ±0.0[eV], respectively, obtained from simulation results L1 to L4.

[0043] From the simulation results L5 and L6 in Figure 5, it can be seen that the open-circuit voltage changes significantly in response to the change in the band offset ΔEc. Furthermore, it can be seen that the conversion efficiency improves as the band offset ΔEc decreases (improves).

[0044] Figure 6 shows the measurement results of the open-circuit voltage of the strain gauge 100 when the same strain is repeatedly applied to the strain gauge 100. The open-circuit voltage is measured using a voltmeter 24 connected between electrodes 21 and 22. In the measurement in Figure 6, the strain gauge 100 under light irradiation was subjected to three conditions: no strain (no strain), -0.31% strain applied, and +0.31% strain applied. Each condition was repeated three times, and the open-circuit voltage was measured for each condition. The measured values ​​of the open-circuit voltage are shown as bar graphs, and the average value is shown as a line graph.

[0045] The strain ε applied to the strain gauge 100 is defined as shown in equation (1) in Figure 7. That is, referring to Figure 7, the strain ε is expressed as h / 2r, where h is the thickness of the flexible substrate 200 on which the strain gauge 100 is set on the upper surface, and r is the radius of curvature when the upper surface is curved with a convex shape.

[0046] In the measurement shown in Figure 6, the negative strain ε represents the strain applied to the strain gauge 100 when the radius of curvature r is negative, that is, when the upper surface of the flexible substrate 200 on which the strain gauge 100 is set is concave.

[0047] Referring to Figure 6, it was found that when the same strain ε was applied to the strain gauge 100 multiple times, the change in the open-circuit voltage from the unstrained open-circuit voltage in each measurement was approximately the same. Furthermore, it was found that the trend of change in the open-circuit voltage from the unstrained state was the same when -0.31% strain was applied and when +0.31% strain was applied. From this, it was confirmed that the strain gauge 100 has reproducibility in the change of open-circuit voltage when strain is applied.

[0048] Figure 8 shows the relationship between the amount of strain applied to the strain gauge 100 and the measured open-circuit voltage. The measurements in Figure 8 were taken by applying strains of -0.31 to +0.42% to the strain gauge 100 under light irradiation, and measuring the open-circuit voltage at each application.

[0049] Referring to Figure 8, it was found that the open-circuit voltage of the strain gauge 100 changes depending on the magnitude of the applied strain ε. By changing the applied strain ε from -0.31% to +0.42%, the measured change in open-circuit voltage was 0.15 [V]. From the measurements in Figure 8, it was confirmed that the strain gauge 100 has a correlation between the amount of applied strain and the open-circuit voltage.

[0050] From the above measurements, it was confirmed that the strain gauge 100 has reproducibility in the change in open-circuit voltage with respect to the amount of strain applied, and that there is a correlation between the amount of strain applied and the open-circuit voltage. Therefore, by pre-measuring the correlation between the amount of strain applied and the change in open-circuit voltage, it becomes possible to measure the amount of strain applied based on the measured value of the open-circuit voltage. In other words, by using the strain gauge 100, the strain applied to the photoelectric conversion element 10 when light is irradiated can be obtained from the measured value of the voltage between electrodes 21 and 22, without using an amplification circuit or power supply. Specifically, the strain applied to the photoelectric conversion element 10 when light is irradiated can be obtained by the change in electromotive force between electrodes 21 and 22. As a result, the applied strain can be easily measured by using the strain gauge 100.

[0051] Preferably, the N-type semiconductor 11 and the P-type semiconductor 12 are paired such that the open-circuit voltage between electrodes 21 and 22 is maximized when a strain at the upper limit of the strain measurement range set for measurement using the strain gauge 100 is applied. This makes it possible to measure the applied strain within the set measurement range using the strain gauge 100.

[0052] The N-type semiconductor 11 and P-type semiconductor 12 of the photoelectric conversion element 10 only need to be piezoelectric semiconductors at least one of them. The N-type semiconductor 11 is not limited to being the only piezoelectric semiconductor. As another example, both the N-type semiconductor 11 and the P-type semiconductor 12 of the photoelectric conversion element 10 may be piezoelectric semiconductors. For example, the N-type semiconductor 11 may be zinc oxide (ZnO) and the P-type semiconductor 12 may be cadmium telluride (CdTe). As yet another example, only the P-type semiconductor 12 of the N-type semiconductor 11 and P-type semiconductor 12 may be piezoelectric semiconductors. For example, the N-type semiconductor 11 may be titanium oxide (TiO2) and the P-type semiconductor 12 may be cadmium telluride (CdTe).

[0053] Figure 9 is a diagram illustrating the energy levels when the N-type semiconductor 11 is zinc oxide (ZnO) and the P-type semiconductor 12 is cadmium telluride (CdTe), and Figure 10 is a diagram illustrating the energy levels when the N-type semiconductor 11 is titanium oxide (TiO2) and the P-type semiconductor 12 is cadmium telluride (CdTe). These diagrams show the energy levels when no strain is applied (no strain) (ST10, ST20), when a small strain is applied (low strain) (ST11, ST21), and when a large strain is applied (high strain) (ST12, ST22), respectively.

[0054] For details, refer to Figure 9. When there is no strain (ST10), the energy level E10 at the lower end of the conduction band (CBM) and the energy level E30 from the CBM to the upper end of the valence band (VBM (Valence Band Maximum)) of zinc oxide (ZnO) change to energy levels E11 and E31, respectively, when the strain is small (ST11), and change to energy levels E12 and E32, respectively, when the strain is large (ST12).

[0055] Furthermore, when there is no strain (ST10), the energy level E20 at the lower end of the conduction band (CBM) and the energy level E40 from the CBM to the upper end of the valence band (VBM) of cadmium telluride (CdTe) change to energy levels E21 and E41, respectively, when the strain is small (ST11), and change to energy levels E22 and E42, respectively, when the strain is large (ST12).

[0056] It is known that the energy levels E10, E20, E30, and E40 in the unstrained state (ST10) are 4.5 [eV], 3.37 [eV], 4.3 [eV], and 1.5 [eV], respectively. Therefore, the band offset ΔEc10 between zinc oxide (ZnO) and cadmium telluride (CdTe) in the unstrained state (ST10) is approximately -0.2 to -0.3 [eV].

[0057] When the N-type semiconductor 11 is zinc oxide (ZnO) and the P-type semiconductor 12 is cadmium telluride (CdTe), the energy band of zinc oxide (ZnO) rises towards the junction interface when strain is applied, while the energy band of cadmium telluride (CdTe) falls. That is, when the strain is small (ST11), the band offset △Ec11 is a negative value and is greater than the band offset △Ec10. When the strain is large (ST12), the band offset △Ec12 is greater than the band offset △Ec11 and is a positive value.

[0058] Therefore, when the N-type semiconductor 11 is zinc oxide (ZnO) and the P-type semiconductor 12 is cadmium telluride (CdTe), the energy levels of both zinc oxide (ZnO) and cadmium telluride (CdTe) change in accordance with the application of strain, resulting in a large change in band offset. As a result, when the photoelectric conversion element 10 of the strain gauge 100 uses zinc oxide (ZnO) as the N-type semiconductor 11 and cadmium telluride (CdTe) as the P-type semiconductor 12, the open-circuit voltage changes rapidly with small strains. Therefore, even with this strain gauge 100, it becomes possible to detect minute strains with high sensitivity.

[0059] Furthermore, referring to Figure 10, the energy levels E50 at the lower end of the conduction band (CBM) and E70 from the CBM to the upper end of the valence band (VBM) of titanium oxide (TiO2) when there is no strain (ST20) change to energy levels E51 and E71, respectively, when the strain is small (ST21), and change to energy levels E52 and E72, respectively, when the strain is large (ST22).

[0060] Furthermore, when there is no strain (ST20), the energy level E60 at the lower end of the conduction band (CBM) and the energy level E80 from the CBM to the upper end of the valence band (VBM) of cadmium telluride (CdTe) change to energy levels E61 and E81, respectively, when the strain is small (ST21), and change to energy levels E62 and E82, respectively, when the strain is large (ST22).

[0061] It is known that the energy levels E50, E60, E70, and E80 in the unstrained state (ST20) are 4.4~4.6 [eV], 4.3 [eV], 3.0~3.2 [eV], and 1.5 [eV], respectively. Therefore, the band offset ΔEc20 between titanium oxide (TiO2) and cadmium telluride (CdTe) in the unstrained state (ST20) is approximately -0.2~-0.3 [eV].

[0062] When the N-type semiconductor 11 is titanium oxide (TiO2) and the P-type semiconductor 12 is cadmium telluride (CdTe), the energy band of cadmium telluride (CdTe) drops from the junction interface when strain is applied, while the energy band of titanium oxide (TiO2) remains constant regardless of the presence or absence of applied strain. That is, when the strain is small (ST21), the band offset △Ec21 is a negative value and is larger than the band offset △Ec20. When the strain is large (ST22), the band offset △Ec22 is larger than the band offset △Ec21 and is a positive value.

[0063] Therefore, when the N-type semiconductor 11 is titanium oxide (TiO2) and the P-type semiconductor 12 is cadmium telluride (CdTe), the energy level of only one of the two (cadmium telluride (CdTe)) changes, while the energy level of the other (titanium oxide (TiO2)) remains unchanged. As a result, the change in open-circuit voltage due to strain application changes more gradually over a wide range of strains compared to the case where both are piezoelectric elements (Figure 9). Therefore, by using this strain gauge 100, it is possible to measure strain over a wide measurement range.

[0064] Figure 11 is a flowchart illustrating the outline of a strain measurement method using the strain gauge 100 according to this embodiment. Referring to Figure 11, first, the strain gauge 100 is set up (step S101). Setting up the strain gauge 100 involves connecting electrodes 21 and 22 to the N-type semiconductor 11 and P-type semiconductor 12 of the photoelectric conversion element 10, setting it on the flexible substrate 200, and connecting a voltmeter 24 between the electrode pairs 21 and 22.

[0065] Light is shone onto the photoelectric conversion element 10 of the set strain gauge 100 (step S103), and the open-circuit voltage between the electrode pair 21 and 22 is measured with the voltmeter 24 (step S105).

[0066] When measuring strain using a computer, the computer pre-stores the relationship between the applied strain and the change in open-circuit voltage, as shown in Figure 8. This relationship may be obtained experimentally by actually changing the strain and measuring the open-circuit voltage, as shown above, and then input into the computer. The relationship between the applied strain and the open-circuit voltage may also be stored as a calculation formula that uses the open-circuit voltage as a parameter to calculate the strain. In this case, the computer obtains the strain by substituting the measured open-circuit voltage into the pre-stored calculation formula (step S107).

[0067] Thus, by using the strain gauge 100 according to this embodiment, strain can be easily measured without the need for an amplification circuit or power supply.

[0068] <3. Addendum> The present invention is not limited to the above embodiments, and various modifications are possible. [Explanation of Symbols]

[0069] 10: Photoelectric conversion element 11: N-type semiconductor 12: P-type semiconductor 21: Electrode 22: Electrode 23: Circuit board 24: Voltmeter 100: Gauge 200: Flexible circuit board E: Light energy E10: Energy level E11: Energy level E12: Energy level E20: Energy level E21: Energy level E22: Energy level E30: Energy level E31: Energy level E32: Energy level E40: Energy level E41: Energy level E42: Energy level E50: Energy level E51: Energy level E52: Energy level E60: Energy level E61: Energy level E62: Energy level E70: Energy level E71: Energy level E72: Energy level E80: Energy level E81: Energy level E82: Energy level L1: Simulation results L2: Simulation results L3: Simulation results L4: Simulation results L5: Simulation results h: thickness r: radius of curvature

Claims

1. A heterojunction photoelectric conversion element, The heterojunction type photoelectric conversion element is sandwiched between two electrode pairs, In the PN junction of the heterojunction type photoelectric conversion element, at least one of the P-type semiconductor and the N-type semiconductor is a piezoelectric semiconductor. The P-type semiconductor and the N-type semiconductor are a combination that results in a smaller band offset as the strain applied to the heterojunction photoelectric conversion element increases. Strain gauge.

2. From the measured voltage between the electrode pair, the strain applied to the heterojunction photoelectric conversion element when light is irradiated can be obtained. The strain gauge according to claim 1.

3. The strain applied to the heterojunction photoelectric conversion element when the aforementioned light is irradiated is obtained by the change in the electromotive force between the electrode pair. The strain gauge according to claim 2.

4. A heterojunction type photoelectric conversion element, The heterojunction type photoelectric conversion element is sandwiched between two electrode pairs, In the PN junction of the heterojunction type photoelectric conversion element, at least one of the P-type semiconductor and the N-type semiconductor is a piezoelectric semiconductor. The P-type semiconductor is crystalline selenium. Strain gauge.

5. The P-type semiconductor and the N-type semiconductor are a combination that maximizes the open-circuit voltage between the electrode pair when a strain at the upper limit of the set strain measurement range is applied. A strain gauge according to any one of claims 1 to 4.

6. The electrode connected to the N-type semiconductor among the electrode pair is a transparent electrode. A strain gauge according to any one of claims 1 to 4.

7. A heterojunction type photoelectric conversion element having a PN junction, At least one of the P-type semiconductor and the N-type semiconductor in the PN junction is a piezoelectric semiconductor. The P-type semiconductor and the N-type semiconductor are a combination that results in a smaller band offset as the strain applied to the heterojunction photoelectric conversion element increases. Photoelectric conversion element.

8. The N-type semiconductor is the piezoelectric semiconductor. The photoelectric conversion element according to claim 7.

9. A heterojunction type photoelectric conversion element having a PN junction, At least one of the P-type semiconductor and the N-type semiconductor in the PN junction is a piezoelectric semiconductor. The P-type semiconductor is crystalline selenium. Photoelectric conversion element.

10. A method for measuring strain using a heterojunction type photoelectric conversion element, A heterojunction photoelectric conversion element in which at least one of the P-type semiconductor and N-type semiconductor in the PN junction is a piezoelectric semiconductor is irradiated with light. The method is to obtain the strain applied to the heterojunction photoelectric conversion element when the light is irradiated, from the measured voltage between the electrode pair connected to the P-type semiconductor and the N-type semiconductor. Method for measuring strain.

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