JPH0410572B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a method and apparatus for evaluating the characteristics of a solar cell, in particular quantum efficiency (number of electrons flowing/number of photons absorbed) and/or energy conversion efficiency (output from a solar cell). The present invention relates to a method and apparatus for measuring the electric energy generated/energy of incident light. BACKGROUND ART In recent years, emphasis has been placed on the use of solar energy as an energy alternative to oil, and as part of this, the field of use of solar cells is rapidly expanding. Recently, development is progressing from small-power solar cells to medium-power solar cells to replace dry batteries. In the process of developing such solar cells, it is extremely important to evaluate the solar cells, especially to measure energy conversion efficiency and quantum efficiency. In other words, the top priority in the development of solar cells is to put highly efficient ones into practical use. Conventionally, the typical method for evaluating the characteristics of solar cells is to use an artificial light source (solar simulator) as a light source and examine the efficiency using the output (V-I) characteristics when light is irradiated onto the solar cell. It is. In this evaluation method, it is necessary to finish the measurement before the characteristics change due to the temperature rise of the element due to irradiation from the solar simulator. Therefore, high-speed measurement is required, and high-power solar Batteries require equipment that can measure large currents in addition to high-speed measurements, which poses the problem of making evaluation equipment complex and expensive. In addition, in conventional evaluation methods, the characteristics of the solar simulator are not necessarily constant, nor is its intensity constant, and in some cases xenon lamps or monochromatic light are used, and the characteristics of such irradiated light are not always constant. The reality is that it has not always been easy to objectively and accurately evaluate solar cells due to variations in solar cell intensity, intensity, and differences in irradiation light. Purpose of the Invention This invention has been made in view of the above circumstances, and its basic purpose is to provide a new evaluation method and device that are completely different from conventional solar cell evaluation methods and devices. be. This invention is based on photothermal spectroscopy (PTS), which was newly invented by the present inventors.
The purpose of this research is to provide a new method and device for evaluating solar cells using spectroscopy. Conventionally, the absorbance measurement method, which calculates the reciprocal of absorbance by measuring the transmittance of light, has been widely known as a spectroscopic method using light to measure the absorption spectrum of various substances. Photoacoustic spectroscopy has been developed to measure absorbance using the photoacoustic effect. In response, the present inventors have developed a photothermal spectroscopy method that should also be referred to as a new third spectroscopy method. This photothermal spectroscopy involves irradiating a sample with light of different wavelengths and directly detecting the temperature rise of the sample relative to the wavelength of the irradiated light using a highly sensitive thermosensitive element such as a thermistor placed in contact with the sample. This method measures the spectrum of the temperature rise of the sample in response to irradiation light. As a result of various studies on the application of the above-mentioned photothermal spectroscopy, the present inventors have found that by using photothermal spectroscopy, the quantum efficiency and energy conversion efficiency of solar cells can be derived regardless of the type and intensity of irradiated light. They discovered this and came up with this invention. Therefore, an object of the present invention is to provide a method and apparatus for evaluating solar cells, which allow more accurate comparison between solar cells, and which are not complicated and easy to handle. Configuration of the Invention In order to achieve the above objects, the solar cell evaluation method and device of the present invention have the following configuration. That is, in the solar cell evaluation method of the first invention, a solar cell to be evaluated is placed in a sample chamber that is thermally isolated from the surroundings, and a load is connected to the solar cell and a load is not connected, respectively.
The solar cell is irradiated with light of a selected wavelength and the temperature rise of the solar cell due to the irradiation light is directly detected, and the temperature rise value of the solar cell due to the irradiation light in the load connected state and the temperature rise value due to the irradiation light in the load disconnected state are calculated. This method is characterized in that the energy conversion efficiency of the solar cell is determined using the temperature rise value of the solar cell. Here, the specific method for determining energy conversion efficiency is as follows. In other words, the value of the temperature rise of the solar cell due to the irradiation light in the load connected state is subtracted from the temperature rise value of the solar cell due to the irradiation light in the load disconnected state, and the subtracted value is
The value divided by the temperature rise value of the solar cell due to the irradiation light when the load is not connected is used as the energy conversion efficiency. Further, in the solar cell evaluation method of the second invention, a solar cell to be evaluated is placed in a sample chamber that is thermally isolated from the surroundings, and a variable load is connected to the solar cell and a variable load is not connected to the solar cell.
The solar cell is irradiated with light of a selected wavelength and the temperature rise of the solar cell due to the irradiation light is directly detected, and the value of the temperature rise of the solar cell due to the irradiation light in the variable load connected state and the voltage generated in the variable load are calculated. This method is characterized in that the quantum efficiency of the solar cell is determined using the temperature rise value of the solar cell due to irradiation light in a state where no load is connected. Here, the specific method for determining the quantum efficiency is as follows. In other words, when the variable load is connected, the temperature rise value due to the irradiation light is detected by changing the load, the voltage generated in the load is detected at the same time, each temperature rise value is multiplied by the energy determined by the wavelength of the irradiation light, and the temperature rise value when the load is not connected is detected. Create a graph with the value normalized by the temperature rise value on the vertical axis and the voltage generated at the load on the horizontal axis, and on the graph, calculate the temperature rise value when the load value is set to practically zero. Each point within the range from the corresponding point to the point where the temperature rise value is the lowest is approximated by a straight line, and the quantum efficiency is determined from the slope of the straight line. Note that the above-mentioned linear approximation is performed by, for example, the method of least squares. Furthermore, the solar cell evaluation device of the third invention includes a sample chamber thermally isolated from the surroundings for accommodating the solar cell to be evaluated, and a wavelength selected for the solar cell installed in the sample chamber. irradiating means for irradiating light; temperature detecting means for directly detecting a temperature rise in the solar cell due to the irradiated light; variable load voltage detecting means having a variable load connected to the solar cell so as to be openable and closable; and the temperature detecting means. and storage and calculation means for storing and calculating the detection signal from the variable load voltage detection means, and the storage and calculation means stores and calculates the temperature of the solar cell detected by the temperature detection means in a state where no load is connected. The temperature rise value due to the irradiation light, the temperature rise value due to the irradiation light of the solar cell detected by the temperature detecting means in a state where a load is connected, and the generated voltage are stored and calculated to determine the quantum efficiency of the solar cell and/or the generated voltage. Alternatively, the method is characterized in that the energy conversion efficiency is determined. Here, the storage calculation means stores a temperature rise value due to the irradiation light of the solar cell detected by the temperature detection means in the load disconnected state, and a temperature rise value of the solar cell detected by the temperature detection means in the load connected state. The temperature rise value caused by the irradiation light is stored, and the stored temperature rise value in the load disconnected state is subtracted from the stored temperature rise value in the load disconnected state, and the subtracted value is calculated as the temperature rise value in the load disconnected state. It is designed to divide by the value and output the value as data of energy conversion efficiency. Further, the memory calculation means stores a temperature rise value due to the irradiation light of the solar cell detected by the temperature detection means in the load disconnected state, and each load value obtained by changing the load value by the variable load voltage detection means in the load connected state. The temperature rise value due to the irradiation light of the solar cell corresponding to the irradiation light and the generated voltage are memorized, and the temperature rise value due to the irradiation light obtained by changing the load value in the load connected state is multiplied by the energy of the wavelength of the irradiation light. A value obtained by normalizing this value by the temperature rise value due to irradiation light in a state where no load is connected is stored as a function, and the temperature rise from the normalized value when the load in that function is substantially zero. Values within the range up to the normalized value corresponding to the lowest value are approximated by a straight line, and the slope of the straight line is calculated and output as data as quantum efficiency. Furthermore, the irradiation light means includes a light source, a wavelength selector for selecting the light of a wavelength to be irradiated to the solar cells from the light from the light source, and an irradiation light intermittent means for intermittent the irradiation light to the solar cells. It is said to be configured with the following. Here, the wavelength selector is comprised of a spectroscope having a dispersion element that separates light from a light source, or a plurality of bandpass filters each having a different wavelength band. The irradiation light intermittent means includes a light interrupter (so-called shutter), a drive means for inserting and removing the light interrupter into and out of the optical path of the irradiation light to the solar cell, and a control section for controlling the drive means. The optical circuit breaker is configured such that the opening timing thereof is controlled by the result of processing and determining the output signal of the temperature detecting means, and the opening timing is set at a preset opening time. The irradiation light intermittent means includes a light interrupter, a drive means for inserting and removing the light interrupter into and out of the optical path of the irradiation light to the solar cell, and a control section for controlling the drive means. The control unit is configured to include a timer for setting the opening time and cut-off time of the optical interrupter. Alternatively, the irradiation light intermittent means may include an optical interrupter (so-called chopper) in which a light transmitting part and a light shielding part are alternately formed, a driving means for driving the optical interrupter, and a control section for controlling the driving means. The irradiation/interruption time is controlled by controlling the drive speed of the optical interrupter at a preset speed. On the other hand, the temperature detection means is constituted by two heat-sensitive elements having substantially the same characteristics within the measurement range, and a circuit for detecting the difference in output between the two heat-sensitive elements,
One heat-sensitive element is placed in contact with the solar cell to directly detect the temperature of the solar cell, and the other heat-sensitive element is placed near the solar cell to detect the temperature around the solar cell. By detecting the difference in output, the configuration is configured to detect the temperature rise of only the solar cells, which eliminates the influence of ambient temperature changes. Here, the output difference detection circuit is constituted by a DC bridge or an AC bridge incorporating both the heat-sensitive elements. Furthermore, the variable load voltage detection means is configured to sequentially change the value of the load based on the output signal of the determination means for processing and determining the output signal of the temperature detection means;
The voltage and current values generated at each load value are sequentially sent to the storage calculation means. Examples Examples of the solar cell evaluation method and evaluation apparatus of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an example of the apparatus used in the solar cell evaluation method of the present invention, that is, an embodiment of the third invention, and shows a solar cell 1 to be evaluated.
is arranged in a sample chamber 2 that is thermally isolated from the surroundings. In the illustrated example, the sample chamber 2 is composed of a double wall including an inner wall 2A made of a heat insulating material and an outer wall 2B made of a heat insulating material.
Filling the space between B with a liquid (not shown),
Although the structure is designed to have better heat insulation, a single wall may be used in some cases. On one side of the outer wall 2B of the sample chamber 2 is a condenser lens 3 for concentrating the irradiated light toward the solar cell.
A transmission window 4 is provided on the inner wall 2A at a position corresponding to the condenser lens 3.
Therefore, the irradiated light from outside the sample chamber is irradiated onto the solar cell 1 through the condenser lens 3 and the transmission window 4. A highly sensitive heat-sensitive element 5, such as a thermistor, for detecting the temperature of the solar cell 1 is directly attached to the solar cell 1, and a heat-sensitive element 5 for the solar cell is installed near the solar cell 1. A reference heat-sensitive element 6 made of a highly sensitive heat-sensitive element such as a thermistor having substantially the same characteristics is arranged. The latter heat-sensitive element 6 is provided to eliminate the influence of the temperature around the solar cell 1 on measurement errors and to detect a temperature rise in the solar cell 1 itself. Note that it is desirable that both of the heat-sensitive elements 5 and 6 be arranged at a position where the irradiation light is not directly incident. Further, in the sample chamber 2, a half mirror 7 is disposed as necessary near the irradiation optical path from the condenser lens 3 to the solar cell 1. This half mirror 7
After calibrating the wavelength distribution of the light source 8, which will be described later,
In order to eliminate measurement errors caused by variations in intensity due to the wavelength of the light source 8 (i.e., to standardize output data), a part of the irradiated light is guided to a carbon black 9 installed in the sample chamber 2 as necessary. The position in the irradiation optical path (i.e., the position where part of the irradiation light is reflected to the carbon black 9) is determined by a rotational drive means such as a motor (not shown).
and a position away from the irradiation optical path (that is, a position where a part of the irradiation light is not reflected to the carbon black 9). The carbon black 9 also includes a standard heat sensitive element 10 such as a thermistor having substantially the same characteristics as each of the heat sensitive elements 5 and 6 described above.
However, it is installed in a position where it is not directly exposed to the irradiation light. Note that during normal measurement without performing the calibration of the wavelength distribution of the light source 8 as described above, the half mirror 7 is kept out of the irradiation optical path. The light source 8 is a high-intensity light source, such as a xenon light source, and a filter 1 is provided on the front side of the light source 8 to cut out unnecessary infrared light from the light source 8.
1 and a condenser lens 12 are arranged in that order. Further, in the optical path between the condenser lens 12 and the condenser lens 3 on the sample chamber 2 side, there is a shutter 14 as a light interrupter that constitutes a part of the first irradiation light interrupting means 13, and a second A chopper 16 as a rotary optical interrupter constituting a part of the irradiation light interrupter 15 and a spectrometer 17 as a wavelength selector are provided in that order. The shutter 14 is connected to a driving means 18 such as a motor for opening and closing the optical path by inserting and removing the shutter into and out of the optical path, and the shutter driving means 18 includes a driving circuit for driving and controlling the shutter. It is electrically connected to 19.
On the other hand, the chopper 16 is cut out at a predetermined angle with respect to the center of rotation to serve as a light transmitting section, and the remaining angle range is used as a light shielding section. The optical path is configured to be repeatedly opened and closed. A chopper driving means 20 such as a motor is connected to the chopper 16, and a drive circuit 21 for controlling the chopper driving means 20 is connected to the chopper 16.
are electrically connected. In addition, Chiyotsupa 16
A synchronizing signal generator 22 is provided for outputting a signal synchronized with the opening and closing of the optical path by the chopper 16. In the above example, the first irradiation light intermittent means 13 consisting of the shutter 14 etc. and the second irradiation light intermittent means 15 consisting of the chopper 16 etc. are both installed, but in reality both are installed. It is not necessary to install them, and only one of them may be installed. The spectroscope 17 is for selecting the wavelength of the irradiation light to be irradiated onto the solar cell 1 from the light source 18, and is for changing the selected wavelength by rotating the dispersion element 17A such as a plane diffraction grating. A selection driver 23 is attached. Note that the wavelength selector is composed of a plurality of bandpass filters each having a different wavelength band instead of the spectrometer 17, and by replacing the filter through which the light from the light source 8 should pass, the light irradiated to the solar cell 1 can be changed. The configuration may be such that the wavelength of the wavelength is selected. In this case, a plurality of filters may be attached to a rotating disk, for example, and the wavelength of the light irradiated to the solar cell 1 may be changed by rotating the rotating disk using a wavelength selection driver such as a motor. I can do it. Note that in some cases, a single wavelength laser light source or a variable wavelength laser light source may be used as the light source 8 instead of the high-intensity light source, and in that case, a wavelength selector such as the spectrometer 17 can be omitted. The solar cell heat-sensitive element 5 and the reference heat-sensitive element 6 are connected to an output difference detection circuit 23 that detects the output difference between them. This output difference detection circuit 2
Reference numeral 3 is for detecting the temperature rise value of only the solar cell 1 with the influence of ambient temperature removed. The oscillator 25 generates an AC signal of, for example, 10 KHz to drive the bridge 24. The output of this AC bridge 24 is sent to a synchronization detection circuit 26. This synchronous detection circuit 26 is for synchronous rectification (synchronous detection) of the output of the AC bridge 24 in synchronization with the AC signal of the oscillator 25, and therefore the output level of the synchronous detection circuit 26 corrects the ambient temperature. This corresponds to the temperature rise value of the solar cell 1. The output of this synchronization detection circuit 26 is sent to a data processing/control section 27. Here, when the chopper 16 is used as the irradiation light intermittent means, the synchronization detection circuit 26 outputs an AC signal for driving the AC bridge 24 and the chopper 16.
Double synchronous detection is performed in synchronization with two types of signals: 6 and 6 synchronous signals (signals generated by the synchronous signal generator 22). In the above-described example, the output difference detection circuit 23 is constituted by the AC bridge 24, but it goes without saying that it may be constituted by a DC bridge depending on the case. Furthermore, as mentioned above, the standard carbon black 9 installed as necessary is also configured to detect the temperature rise value of the carbon black itself, which is free from the influence of ambient temperature. That is, the standard heat-sensitive element 1 attached to the carbon black 9
0 is also connected to the output difference detection circuit 23, and the output difference detection circuit 23 is connected to a bridge that detects the output difference between the solar cell thermal element 5 and the reference thermal element 6, and the standard thermal element 10 and the reference thermal element 6. It can be configured with a double bridge that is a combination of bridges that detect the output difference with the element 6. In some cases, one end of a single bridge may be configured to be switched between the solar cell heat-sensitive element 5 and the reference heat-sensitive element 10. In the above example, a heat-sensitive element for detecting the ambient temperature of the solar cell 1 is commonly used as a means for detecting the ambient temperature of the standard carbon black 9, but in some cases another heat-sensitive element may be used for carbon black. It may be installed near the black 9. A variable load voltage detection circuit 30 is connected to the solar cell 1 to be evaluated. This variable load voltage detection circuit 30 basically includes a variable load 30A whose load value for the solar cell 1 is changed by being controlled by an external signal, and a variable load 3
It is composed of a switch means 30B for opening and closing between 0A and the solar cell 1, and a voltage detection circuit 30C for detecting the electromotive force of the solar cell 1 generated in the load. Current detector 3 for detecting the current flowing through the solar cell
0D is provided. The voltage detection circuit 30C
The detection output of the solar cell 1, that is, the electromotive force V of the solar cell 1, and the detection output of the current detector 30D, that is, the current i flowing through the solar cell 1, are sent to the storage calculation section 27A of the data processing/control section 27. The data processing/control unit 27 is a memory that stores and calculates the electromotive force V and current i of the solar cell 1 from the variable load voltage detection circuit 30 and the output of the synchronization detection circuit 26 (temperature rise value of the solar cell 1). A calculation unit 27A, a display unit 27B that displays data obtained by the storage calculation unit 27A, and a display unit 27B that displays the value of the load 30A of the variable load voltage detection circuit 30 and shutter drive according to signals from the storage calculation unit 27A. The configuration includes a control section 27C that controls the circuit 19, the chopper drive circuit 21, and the like. Regarding the control of the shutter drive circuit 19, for example, the control section 27C is controlled by the synchronization detection circuit 2.
The structure includes a determination circuit that processes and determines a signal corresponding to the temperature rise value of the solar cell itself outputted from 6, and a timer that sets the opening time of the shutter 14, and the result of processing and determination of the temperature rise value signal. It is only necessary to output a shutter open command signal based on this, and output a shutter cutoff command signal when the opening time set in the timer has elapsed. Specifically, the determination circuit that processes and determines the solar cell temperature increase value signal as described above is configured by a circuit that differentiates the temperature increase value and a circuit that compares and determines the differential value with a reference level, When the differential value of the temperature rise value is a negative value (that is, when the temperature rise value is decreasing), the shutter open command signal is output when the absolute value of the differential value falls below a certain level. Just configure it. Alternatively, regarding the control of the shutter drive circuit, the control section 27C may be configured to include a timer for setting the shutoff time of the shutter 14 and a timer for setting the open time of the shutter 14, and when the set shutoff time has elapsed. The shutter opening command signal may be output, and the shutter shutoff command signal may be output when a set opening time has elapsed. On the other hand, regarding the control of the chopper drive circuit 21, the control section 27C is configured to include chopper rotation speed control means for controlling the rotation speed of the chopper 16 to a preset speed, and by controlling the rotation speed, the chopper 16 is A configuration may be adopted in which the irradiation time and cutoff time of the irradiation light are determined. Furthermore, the load of the variable load voltage detection circuit 30 is 30A.
Regarding the control of the value of, for example, the control unit 27C,
The load value change command signal may be configured to be output in synchronization with the opening command signal or the shutoff command signal of the shutter 14. That is, shutter 14
The load value change command signal may be output when the cut-off time or open time of the timer has elapsed for a time set in advance on a timer, or when the differential value of the temperature rise value becomes less than or equal to a certain value. Or Chiyotsupa 1
The chopper 16 receives a signal synchronized with the operation of the chopper 16 from the synchronization signal generator 22 of the chopper 16.
The load value change command signal may be output in synchronization with the blocking or opening of the optical path. FIG. 2 shows a specific example of the AC bridge 24 used in the output difference detection circuit 23 for detecting the output difference between the solar cell heat-sensitive element 5 and the reference heat-sensitive element 6. In FIG. In FIG. 2, an operational amplifier 28 operates as an AC bridge operational amplifier, and an operational amplifier 29 operates as a bandpass filter at the oscillation frequency of the oscillator 25, for example, 10 KHz. Next, the overall operation and measurement method of the apparatus described above when evaluating a solar cell will be explained. The heat-sensitive element 5 is attached to the solar cell 1 to be measured in advance, and the variable load voltage detection circuit 30 is connected to the sample chamber 2 at a predetermined position. Set the wavelength of the light to be irradiated. At the time of the first measurement, the switch means 30B is opened so that the variable load 30A is not connected to the solar cell 1, that is, an open circuit is established. And Shutter 14 or Chotsupar 16
When the optical path is opened, the solar cell 1 is irradiated with light of the above wavelength, and all of the energy absorbed by the solar cell 1 out of the energy of the irradiated light becomes heat, causing the temperature of the solar cell 1 to rise. The temperature of this solar cell 1 is detected by a heat sensitive element 5. On the other hand, the temperature around the solar cell 1 also rises, and the surrounding temperature is detected by the heat sensitive element 6. The temperature difference between the two is detected by the output difference detection circuit 23, and the temperature of the solar cell 1 is calculated by subtracting the ambient temperature from the temperature of the solar cell 1, that is, the temperature of the solar cell 1 is corrected for the ambient temperature.
A signal corresponding to the temperature rise value is output from the synchronization detection circuit 26, and the signal is sent to the data processing/control section 27. When the irradiation time for the solar cell 1 reaches the opening time of the shutter 14 preset by the timer,
Alternatively, when the light transmission time determined by the rotation speed of the chopper 16 is reached, the optical path of the light irradiated to the solar cell 1 is blocked by the shutter 14 or the shielding part of the chopper 16. Although the temperature of the solar cell 1 rapidly decreases due to this optical path interruption, the rate of decrease of the ambient temperature is extremely slow. However, since the ambient temperature is corrected as described above, the data processing/control unit 27 is given as the temperature rise value due to the irradiation light of the solar cell 1 itself, with the influence of the ambient temperature removed. FIG. 3 shows the waveform of the temperature change of the solar cell 1 measured in this way with respect to time. In FIG. 3, the broken line A shows the temperature change of the solar cell 1 without correction for the ambient temperature, the broken line B shows the change of the ambient temperature, and the solid line C shows the temperature change of the solar cell 1 with the correction made for the ambient temperature. 3 shows a temperature change, that is, an output waveform of the synchronization detection circuit 26. The output waveform C of the synchronization detection circuit 26 and the maximum temperature rise value (ΔT in FIG. 3) during each irradiation period are stored in the storage/calculation unit 27B as the temperature rise value when the solar cell 1 is in a load-unconnected state. On the other hand, when the switch means 30B in the variable load voltage detection circuit 30 is closed, that is, when the variable load 30A is connected to the solar cell 1,
Measure the temperature rise value of the solar cell by irradiating light with the same wavelength as in the measurement in the load disconnected state described above, and at the same time measure the electromotive force V and current i of the solar cell 1,
These measured values are stored in the storage/calculation section 27B. In this case, the value of the variable load 30A is sequentially changed, and at each load value, the temperature rise value of the solar cell 1,
Measure and store the electromotive force V and current i. Note that the measurement of the temperature rise value at each load value is corrected for the ambient temperature as in the case described above. When a load is connected in this way, some of the absorbed energy becomes electrical energy,
The remaining energy turns into heat, increasing the temperature of the solar cell. After the measurement at a certain load value is completed and the optical path is cut off, the timing at which irradiation for measurement at the next different load value is started is as described above in the case of the shutter 14. It is controlled by the setting of a timer, or by the differential value of the temperature rise being less than a certain value, and if the chopper 16 is used, it is controlled by its rotation speed. It is determined that In any case, the timing at which irradiation is restarted after the optical path is interrupted is set or controlled so that the temperature of the solar cell 1 has sufficiently decreased to become approximately the same as the ambient temperature. Of course, depending on the case, the measurement at a certain load value may be repeated two or more times. In actual measurements, either the shutter 14 or the chopper 16 may be used, but usually the shutter 14 is used when the response speed of the heat sensitive element is slow.
If the response speed is sufficiently fast, a chopper 16 can be used. In this way, measurements are sequentially performed under different loads, and finally the measurements over the entire load value range are completed. Note that the above-mentioned measurements can be performed at various different wavelengths, but in that case, the measured value of the solar cell temperature rise value should be normalized by the measured value of the heat-sensitive element 10 of the standard carbon black 9. is desirable. That is, the light source 8 has wavelength characteristics,
Since the intensity differs depending on the wavelength, it is desirable to eliminate the influence of the wavelength characteristics of the light source 8 in order to perform an absolute evaluation of the characteristics of the solar cell 1. In the above-mentioned device, the half mirror 7 is inserted into the optical path to guide the irradiated light to the carbon black 9, and the heat-sensitive element 10
The temperature rise value is measured for each wavelength in the entire measurement wavelength range. The specific measurement method in this case is the same as the measurement for solar cell 1. The temperature rise value of the solar cell 1 is normalized by dividing the temperature rise value of the solar cell 1 by the temperature rise value of the carbon black 9 obtained in this way at each wavelength. Note that the measurement of the carbon black 9 can be performed simultaneously with the measurement of the solar cell 1 when the half mirror 7 is provided as described above, and in such a simultaneous measurement, the measured value of the solar cell 1 can be Although it is possible to standardize on the spot, it is of course necessary to measure carbon black 9 separately from the measurement of solar cell 1, store the measured value, and read out the measured value of carbon black when measuring solar cell 1. The measured values of the solar cell 1 may be standardized by In the latter case, a normal mirror can be used instead of the half mirror 7. Next, the principle of how to determine the quantum efficiency and energy conversion efficiency of a solar cell using each measurement value as described above will be explained. When a solar cell is irradiated with light of a certain wavelength, the irradiation energy is a fixed value depending on the wavelength, that is, E (eV/photon). If the solar cell is irradiated with light of that wavelength for t seconds and the intensity of the light absorbed by the solar cell is I (photon/sec), then
The total energy obtained by the solar cells is expressed as EIt...(1). When a load is connected to the solar cell, this total energy EIt becomes thermal energy and electrical energy taken out to the external load of the solar cell. Here, if the electromotive force of the solar cell due to the irradiation light is V and the current flowing through the solar cell is i, the time during which the current flows is the same as the irradiation time t, so
The electrical energy due to the irradiation light is Vit...(2). If the heat generated by the irradiation light is Qsc, then from (1) and (2) EIt = (thermal energy) + (electrical energy) = Qsc + Vit...(3). Therefore, Qsc=EIt−Vit…(4). When no load is connected, all the energy absorbed by the solar cell becomes heat, so if Qoc is the heat of an open circuit with no load connected, it is given by Qoc = EIt...(5). Therefore, the following equation (6) is derived from equations (4) and (5). Qsc／Qoc＝EIt−Vit／EIt …(6) If we rewrite this equation (6) as an expression for temperature change, ΔTsc／ΔToc＝EIt−Vit−KΔT／EIt−KΔT ⁰ …(7) However, (7 ), ΔTsc is the temperature change due to the solar cell irradiation light when the load is connected,
ΔToc represents the temperature change due to the irradiation light of the solar cell when no load is connected. Also KΔT
is the heat lost by heat conduction from the solar cell to its surroundings when the temperature changes when a load is connected,
KΔT ⁰ represents the heat lost to the surroundings when the temperature changes in an open circuit. however
Since both KΔT and KΔT ⁰ are extremely small, they can be ignored, and therefore equation (7) can be expressed as follows. ΔTsc/ΔToc=1−Vi/EI…(8) Here, quantum efficiency nq is expressed as nq=i/I…(9) From (8), ΔTsc/ΔToc=1−nq・V/E …(10) becomes. In equation (10), nq・V/E is nq・V/E=iV/IE=np (11), which is the energy conversion efficiency np, that is, the electric energy extracted to the outside out of the incident energy. It represents a percentage. If transformed into equation (10), E(ΔTsc/ΔToc)=−nqV+E (12). Therefore, if we graph equation (12) by plotting the electromotive force V on the horizontal axis and E (ΔTsc/ΔToc) on the vertical axis, the slope corresponds to nq, and by finding the slope, we can calculate the quantum Efficiency is required. On the other hand, the energy conversion efficiency np is expressed as np (%) = (1 - ΔTsc / ΔToc) × 100 (13) from equations (10) and (11), so it can be easily calculated from the values of ΔTsc and ΔToc. You can ask for it. Note that the energy conversion efficiency np is the above-mentioned V~E (ΔTsc/
ΔToc) plot (that is, each measurement point corresponding to each load value), but usually when evaluating a solar cell, it is calculated from np at each point.
Expressed as the largest. FIG. 4 shows a specific flow for actually determining the quantum efficiency and energy conversion efficiency of a solar cell according to the above principles. In FIG. 4, if the wavelength of the light irradiated to the solar cell is selected by the irradiation means, the irradiation energy E (ev/photon) is determined. The value of the energy E corresponding to this wavelength is stored in advance in the memory calculation section 27A or other appropriate memory, and the value of E corresponding to the wavelength is automatically read out by selecting the wavelength. Then, the temperature rise value ΔToc of the solar cell when the solar cell is irradiated with light of the wavelength with no load connected is measured and the value is stored. Also, the temperature rise value ΔTsc of the solar cell when the solar cell is irradiated with light of the same wavelength with a load connected.
is measured by sequentially changing the load value, and the electromotive force V generated in the solar cell and the current i flowing through the solar cell at each load value are also measured, and ΔTsc, V, and i at each load value are memorized. let Note that it is of course desirable to store the temperature rise values ΔToc and ΔTsc of the solar cell itself after correction for the ambient temperature as described above, and more preferably to store the temperature rise values of the solar cell itself after making corrections for the ambient temperature as described above. Therefore, it is preferable to store the standardized temperature rise value. Next, divide the temperature rise value ΔTsc when the load is connected by the temperature rise value ΔToc when the load is not connected to obtain ΔTsc/ΔToc, and multiply this by the energy E of the irradiated light to obtain E(ΔTsc /ΔToc)
seek. Note that this calculation is of course performed for each load value. Then, with the vertical axis y as E (ΔTsc/ΔToc) and the horizontal axis x as electromotive force V, V~E (ΔTsc/ΔToc) is converted into a function to obtain a graph A, and each point on the graph A (i.e., each load value (corresponding to each measurement point) is stored, and linear approximation is performed to each stored point by the least squares method. Note that the linear approximation of graph A indicates that the temperature rise value is the lowest from the point where the load value is effectively zero by shooting the load (i.e., the point where the electromotive force V measured by the load is zero). Perform this on measurement points within the range up to the point where . Then, the slope a of the obtained straight line y=-ax+b is determined.
Since this slope a corresponds to the quantum efficiency nq as is clear from equation (12), this value is recorded and displayed as the quantum efficiency. On the other hand, energy efficiency is calculated according to the above equation (13) using the temperature rise value ΔTsc with the load connected and the temperature rise value ΔToc with the load not connected, which are stored as described above. is determined for each load value, and the value is recorded and displayed. In this case, the highest energy conversion efficiency may be extracted from among the energy conversion efficiencies corresponding to each load and recorded and displayed. FIG. 5 shows that the present inventors have produced an amorphous silicon solar cell according to the method of the present invention.
Correlation characteristics between solar cell electromotive force V and EΔTsc/ΔToc when actually irradiated with 632.8 nm He-Ne laser light (i.e., corresponding to graph A in Figure 4), and electromotive force V and output power shows the correlation between In this case, the maximum energy conversion efficiency np under the optimal load was calculated to be 19%, and the quantum efficiency nq was calculated to be 68%. In addition, apart from the example shown in FIG. 5, the present inventors investigated the maximum energy conversion efficiency np and quantum efficiency nq under optimal load for silicon (Si) solar cells and GaAs solar cells according to the method of this invention. are shown in Table 1.

[Table] Effects of the Invention According to the solar cell evaluation method and device of the present invention, the quantum efficiency and/or energy conversion efficiency of a solar cell can be accurately determined regardless of the quantitative value of irradiated light, that is, differences in intensity or characteristics. Therefore, the solar cell can be objectively evaluated, and the apparatus can be relatively simple and cost-effective.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the solar cell evaluation device of the present invention, FIG. 2 is a wiring diagram showing an example of an AC bridge as an output difference detection circuit used in the device of FIG. 1, and FIG. A waveform diagram showing changes in the detected temperature of a solar cell, FIG. 4 is a flowchart showing a specific flow for determining the energy efficiency np and quantum efficiency nq of a solar cell by the method of this invention, and FIG. Therefore, it is a diagram showing a graph for actually determining the quantum efficiency of a solar cell. DESCRIPTION OF SYMBOLS 1...Solar cell, 2...Sample chamber, 5...Thermosensitive element for solar cell, 6...Thermosensitive element for reference, 8...Light source, 9
...Carbon black, 10...Standard heat-sensitive element, 1
3...First irradiation light intermittent means, 14...Shutter (light interrupter), 15...Second irradiation light intermittent means, 16
...Chopper (optical interrupter), 17...Spectroscope as a wavelength selector, 17A...Dispersive element, 23...Output difference detection circuit, 24...AC bridge, 26...Synchronization detection circuit, 27...Data processing/control unit, 27A ...Memory operation section, 30...Variable load voltage detection circuit, 30A...
Variable load, 30B...switch means, 30C...voltage detection circuit.

Claims (1)

[Claims] 1. A solar cell to be evaluated is placed in a sample chamber that is thermally isolated from the surroundings, and a selected wavelength is measured with and without a load connected to the solar cell. By irradiating the solar cell with light and directly detecting the temperature rise of the solar cell due to the irradiation light, the value of the temperature rise of the solar cell due to the irradiation light in a load connected state and the temperature rise of the solar cell due to the irradiation light in a load disconnected state are determined. A solar cell evaluation method characterized by determining the energy conversion efficiency of a solar cell using a value. 2. Subtract the temperature rise of the solar cell due to the irradiation light in the load connected state from the temperature rise of the solar cell due to the irradiation light in the load disconnected state, and use the subtracted value as the temperature rise of the solar cell due to the irradiation light in the load disconnected state. 2. The solar cell evaluation method according to claim 1, wherein a value divided by a temperature increase value is used as the energy conversion efficiency. 3 Place the solar cell to be evaluated in a sample chamber that is thermally isolated from the surroundings, and apply light of a selected wavelength to the solar cell with and without a variable load connected to the solar cell. directly detects the temperature rise of the solar cell due to the irradiation light when the variable load is connected, the voltage generated in the variable load, and the temperature rise of the solar cell due to the irradiation light when the load is not connected. 1. A solar cell evaluation method characterized by determining quantum efficiency of a solar cell using a temperature rise value of . 4 In the variable load connected state, the temperature rise value due to the irradiation light is detected by changing the load, and at the same time the voltage generated in the load is detected, and each temperature rise value is multiplied by the energy determined by the wavelength of the irradiation light, and the temperature in the load disconnected state is detected. Create a graph with the value normalized by the rise value on the vertical axis and the voltage generated at the load on the horizontal axis, and on the graph, correspond to the temperature rise value when the load value is set to practically zero. Claim 3, characterized in that each point within the range from the point where the temperature rise value is the lowest to the point where the temperature rise value is the lowest is approximated by a straight line, and the quantum efficiency is determined from the slope of the straight line.
Method for evaluating solar cells described in Section 1. 5 Each point within the range from the point corresponding to the temperature rise value when the load value is substantially zero on the graph to the point where the temperature rise value is the lowest,
5. The solar cell evaluation method according to claim 4, wherein the slope of the linear approximation is determined by a least squares method. 6. A sample chamber thermally isolated from the surroundings for accommodating the solar cells to be evaluated; irradiation means for irradiating the solar cells installed in the sample chamber with light of a selected wavelength; and irradiation light. temperature detection means for directly detecting the temperature rise of the solar cell caused by the solar cell; variable load voltage detection means having a variable load connected to the solar cell so as to be openable and closable; and detection signals from the temperature detection means and the variable load voltage detection means. and storage/calculation means for storing and calculating the temperature increase value due to the solar cell irradiation light detected by the temperature detection means when the load is not connected, and the temperature increase value due to the irradiation light of the solar cell detected by the temperature detection means when the load is not connected. The quantum efficiency and/or energy conversion efficiency of the solar cell is determined by storing and calculating the temperature rise value caused by the irradiation light of the solar cell and the generated voltage detected by the temperature detection means in the state where A solar cell evaluation device characterized by: 7. The storage calculation means stores a temperature rise value caused by the solar cell irradiation light detected by the temperature detection means in a load disconnected state, and a temperature rise value caused by the solar cell irradiation light detected by the temperature detection means in the load connected state. , and subtract the stored temperature rise value in the load connected state from the stored temperature rise value in the load disconnected state, and divide the subtracted value by the temperature rise value in the load disconnected state. 7. The solar cell evaluation device according to claim 6, which outputs data as energy conversion efficiency. 8. The storage calculation means stores the temperature rise value due to the solar cell irradiation light detected by the temperature detection means in the load disconnected state, and each load value obtained by changing the load value by the variable load voltage detection means in the load connected state. The temperature rise value due to the irradiation light of the solar cell corresponding to the irradiation light and the generated voltage are memorized, and the temperature rise value due to the irradiation light obtained by changing the load value in the load connected state is multiplied by the energy of the wavelength of the irradiation light. A value obtained by normalizing this value by the temperature rise value due to irradiation light in a state where no load is connected is stored as a function, and the temperature rise from the normalized value when the load in that function is substantially zero. A claim in which values within a range up to the normalized value corresponding to the lowest value are approximated by a straight line, and the slope of the straight line is calculated and output as data as quantum efficiency. The solar cell evaluation device according to item 6. 9. The irradiation light means includes a light source, a wavelength selector for selecting a wavelength of light to be irradiated onto the solar cells from the light from the light source, and an irradiation light intermittent means for intermittent the irradiation light to the solar cells. A solar cell evaluation device according to claim 6, which is configured to include the following. 10. The solar cell according to claim 9, wherein the wavelength selector includes a spectroscope having a dispersion element that separates light from a light source, or a plurality of bandpass filters each having a different wavelength band. Evaluation device. 11 The irradiation light intermittent means is composed of a light interrupter, a drive means for inserting and removing the light interrupter into and out of the optical path of the irradiation light to the solar cell, and a control section for controlling the drive means, and Claim 9: The optical circuit breaker is configured such that the opening timing thereof is controlled by the result of processing and determining the output signal of the temperature detecting means, and the opening timing is set at a preset opening time.
Solar cell evaluation device described in section. 12. The irradiation light intermittent means comprises a light interrupter, a drive means for inserting and removing the light interrupter into and out of the optical path of the irradiation light to the solar cell, and a control means for controlling the drive means. 10. The solar cell evaluation device according to claim 9, wherein the opening time and cut-off time of the optical circuit breaker are controlled by a timer provided in the control means. 13. The irradiation light intermittent means is constituted by a light interrupter in which a light transmitting part and a light shielding part are formed alternately, a driving means for driving the optical interrupter, and a control part for controlling the driving means. 10. The solar cell evaluation device according to claim 9, wherein the irradiation/interruption time is controlled by controlling the driving speed of the optical interrupter at a preset speed. 14. The temperature detection means is constituted by two heat-sensitive elements having substantially the same characteristics within the measurement range, and a circuit for detecting the difference in output between the two heat-sensitive elements,
One heat-sensitive element is placed in contact with the solar cell to directly detect the temperature of the solar cell, and the other heat-sensitive element is placed near the solar cell to detect the temperature around the solar cell. 7. The solar cell evaluation device according to claim 6, wherein the solar cell evaluation device is configured to detect a temperature rise of only the solar cell with the influence of ambient temperature change removed by detecting a difference in output. 15. The solar cell evaluation device according to claim 6, wherein the output difference detection circuit is constituted by a DC bridge or an AC bridge incorporating both the heat-sensitive elements. 16 The variable load voltage means is configured such that the load value is sequentially changed by the output signal of the determination means for processing and determining the output signal of the temperature detection means, and the voltage and current value generated at each load value are sequentially changed. 7. The solar cell evaluation device according to claim 6, wherein the solar cell evaluation device is configured to be sent to the storage calculation means.