JP2018038184A - Evaluation method and evaluation device for solar battery and evaluation program for solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve the optimization of a production process by conducting evaluation to identify, without destruction, a cause at a back side of a solar battery when designed performance is not obtained or the solar battery has failed.SOLUTION: If quantum efficiency measured by radiating excitation light with a spot size of 1 mm to one point on a light-receiving surface of a solar battery is lower than that of a reference sample at a prescribed wavelength, it is determined that its reason is due to an impact of back side structure (S1-S10). Then, the back side structure can be measured nearly without an influence of surface side structure by radiating, to the solar battery, excitation light of which the spot size is made equal to or more than twice width of a surface side electrode and close to minority carrier diffusion length as much as possible (S11, S13, S15-S21).SELECTED DRAWING: Figure 3

Description

  The present invention relates to a solar cell evaluation method, an evaluation device, and a solar cell evaluation program, and in particular, an evaluation method, an evaluation device, and an evaluation program for evaluating the performance of a solar cell based on the measurement result of the internal quantum efficiency of the solar cell. About.

  In order to suppress recombination of photoexcited carriers on the surface of the solar cell, an insulator or semiconductor thin film called a passivation film is formed on the solar light irradiation surface side (hereinafter also referred to as the surface side). In silicon-based solar cells, silicon nitride, silicon oxide, aluminum oxide or the like is used for the passivation film. Many solar cells having a passivation film made of such an insulator on the front side have a structure having an alloy layer as a BSF (Back Surface Field) layer on the back side opposite to the front side. This alloy layer behaves as a field effect passivation film.

  However, the above alloy layer is likely to have a recombination rate faster than that of a passivation film made of an insulator, and light absorption in the alloy layer causes a decrease in efficiency. Therefore, in recent years, solar cells of a type in which a new passivation film for realizing high voltage, high current, and thus high efficiency is formed on the back side instead of an alloy layer to reduce optical loss and recombination are becoming mainstream. Examples include a structure having an insulating film on the back side (PERC: Passivated Emitter and Rear Contact Cell), a structure having a diffusion layer (PERT: Passivated Emitter, Rear Totally-diffused), and a structure having a heterojunction layer (HIT: Heterojunction). with Intrinsic Thin-layer).

  Such a solar cell having a passivation film on the back side is more complicated than the previous structure, so it is important to optimize the back side process. If the back side passivation film can be evaluated at the development stage, etc., the optimization will be large. Accelerated. Further, the evaluation of the back surface side passivation film facilitates the identification of the cause of failure when the back surface of the solar cell is deteriorated for some reason including thermal cycle, voltage, light irradiation, moisture, and aging.

  The characteristics of the backside passivation film of the solar cell appear mainly as a change in spectral sensitivity in the long wavelength region. When the quantum efficiency can be measured in the silicon-based solar cell, the carrier recombination speed in the backside passivation film can be qualitatively evaluated as the quantum efficiency in the region of the excitation wavelength of 900 nm to 950 nm changes. In this case, since the change in quantum efficiency is about 1%, high-accuracy measurement using an internal quantum efficiency measurement device described in, for example, Patent Document 1 of the type that simultaneously measures reflection at a measurement position is necessary. When the solar cell has a structure capable of receiving light on both sides, the quantum efficiency measurement is performed by backside light reception, and the carrier recombination speed in the passivation film can be qualitatively evaluated from the quantum efficiency in a short wavelength region of 300 to 500 nm.

  Here, the quantum efficiency represents the probability that a photon is extracted as an external current when monochromatic light having a certain wavelength is incident on the solar cell. In evaluating the quality inside the solar cell, when the reflectance of the solar cell is R, the internal quantum efficiency obtained by dividing the quantum efficiency by the amount represented by (1-R) is often used (for example, Non-Patent Document 1). When a photon is absorbed at a position corresponding to the np junction of the solar cell, it can be extracted as an external current with a probability of almost 100%. However, when a photon is absorbed at a position away from the np junction, minority carriers resulting from the photon are np. It can be taken out as an external current only after diffusion to the junction. In this case, minority carriers do not reach the np junction with a certain probability due to radiative recombination on the surface or inside the semiconductor. Mainly due to this, when the excitation wavelength is short, most of the photons are absorbed on the surface side from the np junction, so that it is mainly affected by recombination on the surface side, and the quantum efficiency becomes smaller than 1.

  FIG. 9 shows the incident light wavelength versus internal quantum efficiency characteristics of a solar cell, showing the effect of the recombination velocity of the solar cell surface on the quantum efficiency. The characteristic shown in the figure is a crystalline silicon solar cell having a flat surface on the front side and an electrode made of a perfect conductor on the back side. The thickness is 300 μm, the junction depth is 1 μm, and the surface recombination velocity of minority carriers is 4 cm on the surface side. / s, 27 cm / s on the back surface side, diffusion length is 1.5 μm on the front surface side, and 200 μm on the back surface side, and the calculation method is a characteristic obtained by a continuous equation and Drude model. In FIG. 9, the solid line I indicates the characteristics when the surface recombination velocity is 100 cm / s on both the front and back sides, the broken line II indicates the characteristics when the back surface recombination velocity is increased to 2000 cm / s, and the dotted line III indicates the surface. The characteristic is shown when the side recombination velocity is increased to 2000 cm / s. As shown in FIG. 9, it can be seen that the internal quantum efficiencies of both the long wavelength and the short wavelength are decreasing. In the conventional solar cell evaluation method, the cause of the performance degradation of the solar cell is searched from the change of the internal quantum efficiency.

  Next, another evaluation method for a conventional solar cell will be described. Only when the reason for the low quantum efficiency on the back surface is known, the manufacturing process may be optimized while observing the structure characteristic of the cause. For example, in a solar cell having a PERC structure having insulating films on both sides, a cavity is likely to be formed in the aluminum electrode on the back surface side, which significantly deteriorates the characteristics as a solar cell. Therefore, conventionally, the above-described cavity or the like has been discovered by a method using an ultrasonic flaw detector or a method in which a solar cell is simply cut and observed with an electron microscope.

JP 2002-353474 A

P.Rappaport, Solar Energy 3 (4) 8-18 (1959)

  However, in a solar cell having a backside passivation film, when the power generation characteristics are worse than the design, a conventional solar cell evaluation method (first conventional method) for searching for the cause of the performance degradation of the solar cell from the change in internal quantum efficiency ) Cannot measure the internal quantum efficiency by changing the spatial resolution determined by the spot size and excitation wavelength of the excitation light, and therefore cannot identify what is wrong on the back side. On the other hand, in the latter conventional solar cell evaluation method (second conventional method) in which the solar cell is destroyed and the cause of the decrease in power generation characteristics is determined by an ultrasonic flaw detector or an electron microscope, an abnormality different from the assumed cause is present. If there is no abnormality found in the solar cell and an attempt is made to investigate the cause only by the evaluation method of the solar cell, various measurements must be performed brute force.

  Therefore, at present, an evaluation process in which the above two conventional solar cell evaluation methods are combined is employed. For example, in the case of a solar cell having a PERC structure using a p-type silicon substrate having a passivation film on both the front surface side and the back surface side, a plurality of solar cells are evaluated and compared by the first conventional method. Determine if there is a problem. Subsequently, in the solar cell having a problem on the back surface side, the second conventional method determines whether there is a problem with the passivation film made of alumina, for example, on the back surface side, or the portion in contact with the aluminum electrode on the back surface side. Identify by destroying solar cells. That is, conventionally, unless the solar cell is destroyed, it is extremely difficult to identify a problem portion on the back side of the solar cell, and there is a problem that improvement is not promising.

  The present invention has been made in view of the above points, and by evaluating the characteristics of the back side of the solar cell in a non-destructive manner, a solar cell evaluation method and an evaluation device capable of realizing optimization of the manufacturing process, and a solar cell The purpose is to provide an evaluation program.

  In order to achieve the above object, the solar cell evaluation method according to the first aspect of the present invention is the light receiving surface of a solar cell mounted on a movable sample stage with excitation light whose wavelength and spot size can be arbitrarily changed. A solar cell evaluation method for obtaining an evaluation result of the solar cell based on the photoelectric conversion signals of the reflected light from the solar cell and the excitation light and the output signal of the solar cell. A light control step for controlling the spot size of the excitation light to be not less than twice the electrode width of the surface electrode of the solar cell and as close as possible to the substrate thickness of the solar cell; and the spot by the light control step The spatially distributed internal quantum efficiency of the solar cell obtained by sequentially irradiating each of the plurality of measurement points on the light receiving surface of the solar cell placed on the sample stage with the excitation light whose size is controlled Based on , Characterized in that it comprises a, an evaluation step of evaluating the opposite side of the back structure and the light receiving surface of the solar cell.

  In order to achieve the above object, the solar cell evaluation method according to the second aspect of the invention provides a light receiving surface of a solar cell mounted on a sample stage that can move a horizontal plane by a specified distance in two axial directions. A light irradiation step of irradiating excitation light having a wavelength and a spot size controlled to desired values, reflected light obtained by reflecting the excitation light with a surface electrode formed on the light receiving surface, and the light receiving surface; Based on each photoelectric conversion signal of the excitation light before irradiation and the output signal of the surface electrode, the excitation light intensity, total reflection light intensity, and photocurrent are measured, and the internal quantum efficiency of the solar cell is determined from the measurement results. And the calculation step for calculating the reflectance, the internal quantum efficiency and the reflectance by the calculation step obtained from the measurement results of each of a plurality of measurement points on the light receiving surface of the solar cell, and the wavelength of the excitation light Based on An evaluation step of obtaining an evaluation result of the solar cell, and the light irradiation step includes at least a spot size of the excitation light that is not less than twice the electrode width of the surface electrode, and the substrate of the solar cell. The excitation light controlled to a value as close as possible to the thickness is irradiated to the light receiving surface, and the evaluation step evaluates a back surface structure opposite to the light receiving surface of the solar cell.

  In order to achieve the above object, a solar cell evaluation method according to a third aspect of the invention is characterized in that, in the light irradiation step of the second aspect, the wavelength of the excitation light is lower than the internal quantum efficiency of the reference sample. The first wavelength at which efficiency is obtained or the second wavelength at which the substrate of the solar cell appears to be substantially transparent is controlled, and the evaluation step of the fifth aspect of the invention is characterized in that the plurality of the excitation light is at the first wavelength. The first internal quantum efficiency and the first reflectance calculated by the calculation step based on the measurement results of the measurement points, and the measurement of each of the plurality of measurement points when the excitation light has the second wavelength. The back surface structure of the solar cell is evaluated using the second reflectance calculated in the calculation step based on the result.

  In order to achieve the above object, a solar cell evaluation apparatus according to a fourth aspect of the present invention is a solar cell mounted on a movable sample stage with excitation light whose wavelength and spot size can be arbitrarily changed. An evaluation device for a solar cell that irradiates a light receiving surface and obtains an evaluation result of the solar cell based on each photoelectric conversion signal of reflected light from the solar cell and the excitation light and an output signal of the solar cell. A light control unit that controls at least the spot size of the excitation light to a value that is at least twice the electrode width of the surface electrode of the solar cell and is as close as possible to the substrate thickness of the solar cell; and the light control unit The space of the internal quantum efficiency of the solar cell obtained by sequentially irradiating each of the plurality of measurement points on the light receiving surface of the solar cell placed on the sample stage with the excitation light whose spot size is controlled by Based on distribution It characterized in that it comprises an evaluation unit for evaluating the opposite side of the back structure and the light receiving surface of the solar cell.

In order to achieve the above object, the solar cell evaluation apparatus according to the fifth aspect of the invention is mounted with a solar cell, and can move a horizontal plane parallel to the surface of the solar cell by a specified distance in two axial directions. A sample stage, a moving mechanism for moving the sample stage, an excitation light whose wavelength and spot size on the light receiving surface of the solar cell are controlled to desired values, and irradiated to the light receiving surface of the solar cell. Light irradiation means, reflected light reflected by the surface electrode formed on the light receiving surface, each photoelectric conversion signal of the excitation light before the light receiving surface irradiation, and the surface electrode Based on the output signal, excitation light intensity, total reflected light intensity and photocurrent are measured, and calculation means for calculating the internal quantum efficiency and reflectance of the solar cell from the measurement results, and driving control of the moving mechanism are performed. The excitation light spot Drive control means for moving the sample stage so as to sequentially position a plurality of measurement points on the light receiving surface of the solar cell, and the internal quantum efficiency by the calculation means obtained from the respective measurement results of the plurality of measurement points And an evaluation means for obtaining an evaluation result of the solar cell based on the reflectance and the wavelength of the excitation light,
The light irradiation means controls at least the spot size of the excitation light to a value that is at least twice the electrode width of the surface electrode and as close as possible to the substrate thickness of the solar cell, and the evaluation means The back surface structure opposite to the light receiving surface of the solar cell is evaluated.

  In order to achieve the above object, a solar cell evaluation apparatus according to a sixth aspect of the present invention is the light emitting means according to the fifth aspect, wherein the wavelength of the excitation light is lower than the internal quantum efficiency of the reference sample. The first wavelength at which the efficiency is obtained or the second wavelength at which the substrate of the solar cell appears to be substantially transparent is controlled, and the evaluation means of the second invention is configured such that when the excitation light is at the first wavelength, The first internal quantum efficiency and the first reflectance calculated by the calculation unit based on the measurement results of the measurement points, and the measurement of the plurality of measurement points when the excitation light has the second wavelength. The back surface structure of the solar cell is evaluated using the second reflectance calculated by the calculation unit based on the result.

In order to achieve the above object, a solar cell evaluation program according to a seventh aspect of the invention is a solar cell in which excitation light whose wavelength and spot size can be arbitrarily changed is placed on a movable sample stage The evaluation of the solar cell is obtained on the computer based on the reflected light from the solar cell and the photoelectric conversion signals of the excitation light and the output signal of the solar cell. A program for evaluating a solar cell to be executed, wherein the computer
A light control function that controls at least the spot size of the excitation light to a value that is at least twice the electrode width of the surface electrode of the solar cell and is as close as possible to the substrate thickness of the solar cell, and the light control function Spatial distribution of the internal quantum efficiency of the solar cell, obtained by sequentially irradiating each of a plurality of measurement points on the light receiving surface of the solar cell placed on the sample stage with the excitation light whose spot size is controlled And an evaluation function for evaluating the back surface structure opposite to the light receiving surface of the solar cell.

Furthermore, in order to achieve the above object, a solar cell evaluation program according to an eighth aspect of the invention is a solar cell in which excitation light whose wavelength and spot size can be arbitrarily changed is placed on a movable sample stage. The evaluation of the solar cell is obtained on the computer based on the reflected light from the solar cell and the photoelectric conversion signals of the excitation light and the output signal of the solar cell. A program for evaluating a solar cell to be executed, wherein the computer
A light irradiation function for irradiating the light receiving surface of the solar cell placed on the sample stage with excitation light whose wavelength and spot size are controlled to desired values, and a surface on which the excitation light is formed on the light receiving surface Excitation light intensity and total reflection light intensity measured on the basis of reflected light obtained by reflection on the electrode, each photoelectric conversion signal of the excitation light before irradiation of the light receiving surface, and an output signal of the surface electrode And the calculation function for calculating the internal quantum efficiency and reflectance of the solar cell from the measurement result of the photocurrent, and the internal by the calculation function obtained from the measurement results of each of a plurality of measurement points on the light receiving surface of the solar cell Based on the quantum efficiency and the reflectance, and the wavelength of the excitation light, realize an evaluation function to obtain the evaluation result of the solar cell,
In the light irradiation function, the light receiving surface is configured to control at least the excitation light spot size to a value that is at least twice the electrode width of the surface electrode and as close as possible to the substrate thickness of the solar cell. The evaluation function evaluates the back surface structure on the side opposite to the light receiving surface of the solar cell.

  According to the present invention, the non-destructive evaluation of the cause of the back side of the solar cell when the electrode-formed solar cell fails or when the designed performance is not obtained is difficult to measure the photoexcited carrier lifetime. It can be performed. Thereby, according to this invention, optimization of a manufacturing process is realizable.

It is a block diagram of one Embodiment of the evaluation apparatus of the solar cell of this invention. It is sectional drawing of an example of the solar cell evaluated by this invention. It is a flowchart for operation | movement description of FIG. It is a flowchart for detailed operation | movement description of each part in FIG. It is a wavelength vs. internal quantum efficiency characteristic figure of a PERC type solar cell and a reference sample. It is the figure which plotted the internal quantum efficiency in the excitation light wavelength of 950 nm of a solar cell with light and shade. It is the figure which plotted the reflectance in the excitation light wavelength of 950 nm of a solar cell with a light / dark plot. It is the figure which plotted the light reflectivity in the excitation light wavelength of 1200 nm of a solar cell. It is an incident light wavelength vs. internal quantum efficiency characteristic view of a solar cell.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of a solar cell evaluation apparatus according to the present invention. The solar cell evaluation apparatus 100 of the present embodiment combines an internal quantum efficiency measurement system with a variable excitation spot size and a variable sample stage that can move and control the measurement position of a solar cell, which is a sample to be evaluated, with high accuracy. It is a configuration.

  In FIG. 1, a white light source 101 emits white light, the white light is converted into parallel light by a lens 102, is chopped by an optical chopper 103 for AC measurement, and is incident on a spectroscope 104. The spectroscope 104 includes a reflecting mirror that changes an optical path, a rotatable grating 1041, and the like, and splits incident white light into monochromatic light having one wavelength λ determined by the rotation of the grating 1041. The rotation angle of the grating 1041 is controlled by a control signal from a personal computer (hereinafter referred to as PC) 124 described later. Thereby, the spectroscope 104 emits monochromatic light separated from white light into an arbitrary wavelength by the PC 124 as excitation light and enters the dark box 105.

  In the dark box 105, an optical and electrical system including a diaphragm 106, a beam splitter 107, parabolic mirrors 108 and 110, an integrating sphere 109, an excitation light sensor 111, a reflected light sensor 112, and current-voltage converters 113, 114, and 115. And a mechanical system including a lab jack 116, a sample stage 117, and stepping motors 118 and 119 are housed. The sample table 117 fixed on the lab jack 116 is stepped by a stepping motor 118 in the horizontal x-axis direction (direction parallel to the longitudinal direction of the electrode in a plane parallel to the electrode forming surface of the solar cell 201), and the stepping motor 119. Thus, a variable sample stage that is moved with respect to the horizontal direction in the y-axis direction and positioned with high accuracy is configured. The operations of the stepping motors 118 and 119 are controlled by a PC 124 described later. On the sample stage 117, a solar cell 201 as a sample to be evaluated is placed and fixed. The electrode 202 on the surface side of the solar cell 201 reflects the excitation light and enters the integrating sphere 109.

  The aperture 106 is a variable aperture capable of changing the spot size of the monochromatic excitation light from the spectroscope 104 within a range of, for example, 50 μm to 3 mm, and makes the monochromatic excitation light having a desired spot size enter the beam splitter 107. . In the present embodiment, the diaphragm 106 has a spot diameter of excitation light applied to the solar cell 201 that is at least twice the electrode width of the electrode 202 of the solar cell 201 and is as close as possible to the substrate thickness. To control. Since the light from the aperture 106 is imaged at the same magnification by the parabolic mirror 108 on the surface of the solar cell 201, the spot size on the surface of the solar cell 201 is the same as that of the aperture 106.

  The beam splitter 107 bisects the optical path of the excitation light whose spot diameter is adjusted by the diaphragm 106, one of which is reflected by the parabolic mirror 108 and incident on the electrode 202 on the surface side of the solar cell 201, and the other is released. The light is reflected by the object mirror 110 and incident on the excitation light sensor 111 for photoelectric conversion. The integrating sphere 109 introduces the excitation light reflected by the electrode 202 into the inside through the opening, causes multiple reflection on the inner wall, condenses the light, and collects the reflected light through another opening to the reflected light sensor 112. Incident and photoelectrically converted.

  The excitation light sensor 111 outputs a current having a level corresponding to the amount of received excitation light, supplies the current to the current-voltage converter 113 to convert it into a voltage, and then supplies the voltage to the lock-in amplifier 121. On the other hand, the reflected light sensor 112 outputs a current at a level corresponding to the amount of received light of the reflected light reflected by the electrode 202 and the integrating sphere 109 and supplies it to the current-voltage converter 114 to convert it into a voltage. After that, it is supplied to the lock-in amplifier 122. The current-voltage converter 115 converts the output current of the solar cell 201 taken out from the electrode 202 into a voltage and supplies it to the lock-in amplifier 123.

The lock-in amplifiers 121, 122, and 123 are supplied with the AC voltage output from the current-voltage converters 113, 114, and 115, and the DC voltage corresponding to the level of the same frequency component as the predetermined frequency reference signal in the AC voltage. Are supplied to the PC 124, respectively. By keeping conjunction with pre-calibration, the lock-in amplifier 121 outputs a DC voltage representing the excitation light intensity P, the lock-in amplifier 122 outputs a DC voltage representing the total reflected light intensity P _r of the electrode 202, the lock The in-amplifier 123 outputs a DC voltage corresponding to the photocurrent I output from the solar cell 201. The PC 124 calculates the reflectance R and the internal quantum efficiency η _IQE based on the following equations based on the DC voltage supplied from the lock-in amplifiers 121, 122, and 123, respectively.
R = P _r / P (1)
η _IQE = Ihc / [ePλ (1-R)] (2)
In equation (2), h is the Planck constant, c is the speed of light, e is the elementary charge, and λ is the wavelength of the excitation light.

The PC 124 outputs the measurement data of the calculated reflectance R and internal quantum efficiency η _{IQE to} the display 125 and the printing machine 126, which are external output devices, respectively, displays an image on the display 125, and prints it on paper by the printing machine 126. Visualize. Based on the visualized measurement image and measurement data, evaluation of the solar cell 201 described later is performed. The PC 124 also supplies control signals to the stepping motors 118 and 119 and moves the sample stage 117 in the x-axis direction and the y-axis direction on the horizontal plane to specify the excitation light irradiation position of the solar cell 201. Do.

The solar cell evaluation apparatus 100 according to the present embodiment includes a movable sample stage mechanism including a lab jack 116, a sample stage 117, stepping motors 118 and 119, and an internal excitation variable size including other optical systems and electrical systems. by linking the quantum efficiency measurement system, the measurement of the total reflected light intensity P _r of the conditions of measurement of the photocurrent I, measured in conjunction with the movement of the sample stage 117, and to perform the selection of the excitation spot size There are features.

  In a silicon solar cell which is an example of the solar cell to be evaluated according to the present embodiment, an electrode made of silver (Ag) is often used as the electrode on the surface side. In the solar cell evaluation apparatus 100 of the present embodiment, when a spot size that is twice the width of the Ag electrode is adopted, and it is assumed that the excitation light uniformly illuminates only within the same circular area as the spot size, The electrode covers up to 61% of the spot. At this time, for example, the internal quantum efficiency at a wavelength of 950 nm is 0.75 spatially uniform, the reflection in the region where no electrode is present is ignored, and the reflectivity of the silver electrode is 97.5% as the reflectivity of the electrode. If all the reflections are captured by the integrating sphere 109, the measured internal quantum efficiency is 0.721, which is 0.029 lower. This decrease width is substantially the same as the change of about 0.02 in internal quantum efficiency with respect to excitation light having a wavelength of 950 nm, which is caused by the back surface structure of the solar cell shown in FIG. Absent. At a larger spot size, the upper limit of the ratio of the electrode area shown in the excitation light spot is lowered, so that the influence of the front electrode can be reduced, and the influence of the back surface structure of the solar cell can be performed without performing special image processing. Can be visualized.

  The spatial resolution of the solar cell evaluation apparatus 100 is such that the excitation light spot size, the minority carrier diffusion length in the main excitation region, and the size at which the spot is scattered by the texture of the light receiving surface until reaching the main excitation region, It is considered to be determined by a total of three root mean squares. The minority carrier diffusion length is completely different depending on the depth of the np junction surface, the carrier doping concentration, and the type of the substrate. When evaluating solar cells, the minority carrier diffusion length of the substrate is unknown in most cases. In selection of the excitation light spot size in the form, it is regarded as 0. Since the texture causes scattering that is well approximated by the Runhart's law, the size of the diffused spot is about the same as the thickness of the solar cell.

FIG. 2 shows a cross-sectional view of an example of a solar cell evaluated in the present invention. In the figure, the same components as those in FIG. In FIG. 2, a solar cell 201 is a back surface passivation (PERC) type silicon crystal solar cell, and a surface side of a p-type silicon substrate 203 which is a p-type doped crystalline silicon wafer is used as a light-receiving surface, and the surface side has a textured structure. In this case, a silicon nitride (SiN) film 205 is formed on the surface of the n ⁺ diffusion layer 204. The SiN film 205, which is an insulating film, functions as a passivation film and an antireflection film. In addition, in the texture structure of the n ⁺ diffusion layer 204 and the SiN film 205, a plurality of electrodes 202 are formed in parallel to each other by firing penetration. The electrode 202 is a silver (Ag) electrode having a rectangular plane, and the electrode width orthogonal to the longitudinal direction (direction perpendicular to the paper surface of FIG. 2) is 0.1 mm as an example. The interval in the width direction (distance between electrodes) is 1.8 mm.

  On the back side of the p-type silicon substrate 203, for example, an aluminum oxide film 206 is formed as a passivation film as an insulating film. For example, a 0.1 mm wide groove is formed at an interval of 1 mm in the aluminum oxide film 206, and an aluminum (Al) paste is applied on the groove and then heat-treated, whereby Al and Si are alloyed in this groove portion. A mold electrode 207 is formed. On the other hand, an Al electrode 208 is formed on the aluminum oxide film 206 other than the trench. Therefore, the BSF type electrode 207 and the Al electrode 208 are joined at an interval of 1 mm. The front electrode 202 and the BSF electrode 207 on the rear surface have the same electrode width of 0.1 mm, but the distance between the two adjacent electrodes in the width direction (distance between the electrodes) 202 is different from 1.8 mm, and the electrode 207 is different from 1.0 mm. The size of this solar cell 201 is 156 mm width × 156 mm depth × 0.2 mm thickness.

  Next, regarding the evaluation method for evaluating the PERC type solar cell 201 having the cross-sectional structure of FIG. 2 by the solar cell evaluation apparatus 100 of FIG. 1, the flow charts of FIGS. 3 and 4 and the wavelength vs. internal quantum efficiency characteristics of FIG. Will be described in detail. The present embodiment is characterized in the processing after step S11 in FIG. 3, but the performance degradation factor is determined by quantum efficiency spectrum measurement in steps S1 to S10 before that. Therefore, first, the evaluation apparatus 100 performs the quantum efficiency spectrum measurement of the solar cell 201 in a state where the solar cell 201 is placed on the sample stage 117 (step S1 in FIG. 3). In step S1, the quantum efficiency spectrum is similarly measured in advance for the reference sample.

  Here, the white light emitted from the white light source 101 which is a two-lamp type light source of, for example, a halogen lamp and a xenon lamp in FIG. Incident light is made monochromatic excitation light having a desired wavelength λ under the control of the PC 124, and then shaped into a desired spot size by the stop 106. The monochromatic excitation light emitted from the diaphragm 106 is divided into two optical paths by the beam splitter 107, one of which is reflected by the radiation mirror 110 and incident on the excitation light sensor 111, and the other is reflected by the radiation mirror 108 and is solar cell. The light enters the electrode 202 on the surface side of 201. The monochromatic wavelength light incident on the electrode 202 is reflected by the electrode 202, introduced into the integrating sphere 109 from the opening of the integrating sphere 109, reflected again by the inner wall surface of the integrating sphere 109, and then condensed and integrated. The light is derived from another opening of the sphere 109 and enters the reflected light sensor 112.

The lock-in amplifier 121 outputs a DC voltage indicating the excitation light intensity P based on the photoelectric conversion signal of monochromatic excitation light obtained by the excitation light sensor 111 and the current-voltage converter 113. The lock-in amplifier 122 outputs a DC voltage representing the total reflected light intensity P _r of the electrode 202 obtained by the reflected light sensor 112 and the current-voltage converter 114. The lock-in amplifier 123 outputs a DC voltage corresponding to the photocurrent I output from the solar cell 201 in response to an output signal from the electrode 202 obtained via the current-voltage converter 115. The PC 124 measures the quantum efficiency spectrum based on the DC voltage supplied from the lock-in amplifiers 121, 122, and 123, and calculates the internal quantum efficiency by the above-described equation (2).

  In step S1, the quantum efficiency spectrum of the solar cell 201 is measured by irradiating one point on the light receiving surface side of the solar cell 201 with excitation light having a spot size of 1 mm while changing the wavelength in the range from 300 nm to 1250 nm. In step S1, the quantum efficiency spectrum of the reference sample is measured in the same manner as described above. Here, as compared with the PERC type solar cell 201, the reference sample is the same as the PERC type except that the back surface structure has no passivation film. The BSF type in which an Al electrode is formed on the BSF layer. It is a solar cell. A BSF type solar cell used as a reference sample is a high quality sample showing 19.3% of energy conversion efficiency close to a value expected by design.

  FIG. 5 shows the wavelength versus internal quantum efficiency characteristics of a PERC type solar cell and a reference sample. In FIG. 5, the solid line characteristic a indicates the wavelength versus internal quantum efficiency characteristic of the PERC type solar cell 201, and the broken line characteristic b indicates the wavelength versus internal quantum efficiency characteristic of the reference sample. The internal quantum efficiency is obtained by calculation from the measured quantum efficiency spectrum. Comparing both characteristics a and b, the characteristic a is inferior to the characteristic b in the wavelength range from 800 nm to 1050 nm, but the characteristic a is equal to or better than the characteristic b in other wavelength ranges. . From this, it can be estimated that the PERC type solar cell 201 having the characteristic a has a high recombination rate of minority carriers on the back surface side. From the evaluation of the spatially averaged characteristics based on this measurement result, wavelength selection in the following imaging measurement is performed.

  Next, the PC 124 of the evaluation apparatus 100 determines whether or not the quantum efficiency of the solar cell 201 measured in step S1 is equal to or higher than the quantum efficiency of the reference sample or a set value in the entire measurement wavelength range from 300 nm to 1250 nm. (Step S2 in FIG. 3). When the quantum efficiency is equal to or higher than the reference sample or the design value in the entire measurement wavelength range, the open-circuit voltage and the short-circuit current of the solar cell 201 should be the values according to the reference, and the resistance causes the performance degradation. It has become. Therefore, in this case, it can be presumed that the cause is electrode failure or high resistance in the p-type silicon substrate 203 (step S3 in FIG. 3).

On the other hand, when the quantum efficiency of the solar cell 201 is lower than the quantum efficiency of the reference sample or the set value, it is determined whether or not it is low over the entire measurement wavelength range (step S4 in FIG. 3). In a Si solar cell such as the solar cell 201, the excitation wavelength is generally about 98 ± 2% when the excitation wavelength is 500 nm to 750 nm, and there is almost no wavelength dependency. This is because almost all of the photoexcited carriers reach the np junction because the penetration length of the excitation light into the silicon substrate is close to the depth of the np junction of the solar cell. The internal quantum efficiency at this time is almost equal to the carrier recovery efficiency by the electrode. When the quantum efficiency is lower than the reference sample or the design value in the wavelength range of the excitation light of 500 nm to 750 nm, recombination due to formation failure of the np junction or reduction in carrier recovery due to short circuit of the np junction occurs. The quantum efficiency is low over the entire measurement wavelength range. A low quantum efficiency spectrum is observed in a similar entire measurement wavelength range even when recombination in the p-type silicon substrate 203 is extremely fast regardless of position due to poor crystal quality. Therefore, when the quantum efficiency of the solar cell 201 is lower than the reference sample or the design value in the entire measurement wavelength range, the PC 124 of the evaluation apparatus 100 performs re-measurement at the np junction between the n ⁺ diffusion layer 204 and the p-type silicon substrate 203. A combination, short circuit, or low quality in the Si crystal is evaluated, and a countermeasure is taken (step S5 in FIG. 3).

The process of step S5 will be further described with reference to the flowchart of FIG. The np junction can be obtained by forming the texture structure on the surface of the solar cell and then forming the n ⁺ diffusion layer 204 by ion diffusion or ion implantation. In particular, in ion implantation, the amount of implantation or heat treatment is insufficient due to the shadow of the texture shape. As a result, junction formation is poor, and the quantum efficiency is likely to decrease.

  Therefore, the solar cell 201 is irradiated with excitation light having a wavelength of 500 nm or more and 750 nm or less and a spot size of 10 μm or less, preferably 1 μm or less. The PC 124 controls the stepping motors 118 and 119 so that the sample stage 117 is moved in the x-axis direction and the y-axis direction so that the excitation light spots sequentially come to the measurement points set at a pitch of 10 μm or less and 10 μm or less in the vertical direction. While moving intermittently, the internal quantum efficiency and reflectance are measured based on the signals from the lock-in amplifiers 121 to 123 (step S51). Hereinafter, the measurement by intermittent movement of the sample stage 117 and the solar cell 201 is referred to as mapping measurement.

  Subsequently, the PC 124 calculates the internal quantum efficiency at the irradiation light wavelength at each measurement point based on the measurement result of Step S51 (Step S52), and determines a region where the internal quantum efficiency is low from the calculation result (Step S52). S53). If the region with low internal quantum efficiency corresponds to the texture structure, a measure is taken to reduce the influence of the shadow caused by the texture (step S54). For example, the angle and rotation conditions at the time of ion implantation are changed, and a device for improving the spatial uniformity along the xy plane of the np junction, that is, the light receiving surface is performed. On the other hand, when the region where the internal quantum efficiency is low is uniform, the process that affects the distribution of the doped material in the depth direction, that is, the direction perpendicular to the light receiving surface, by changing the amount of ion implantation or heat treatment The ion implantation amount and heat treatment are optimized to improve the conditions (step S55).

  Returning to FIG. If the PC 124 determines in step S4 that the quantum efficiency of the solar cell 201 is not lower than that of the reference sample in the entire wavelength range (there is also a higher wavelength), it detects which region the lower wavelength region is ( Step S6). This is because, when the quantum efficiency spectrum of the solar cell to be evaluated is compared with that of the reference sample and the design value, if there is a markedly low wavelength region, the performance degradation factor can be estimated from the wavelength. That is, when the quantum efficiency at an excitation wavelength of 500 nm or less is low, photoexcited carriers are concentrated closer to the surface side that is the light receiving surface than the np junction surface, and thus the surface due to the defect of the surface side passivation film (ie, SiN film 205). It is evaluated that recombination is fast and carriers have not reached the np junction surface (step S7).

  If it is detected in step S6 that the wavelength region where the quantum efficiency of the solar cell 201 is lower than that of the reference sample is around 800 nm (700 nm to 900 nm), it is evaluated as recombination on the substrate (step S8). That is, in this case, most of the photoexcited carriers are absorbed by the p-type silicon substrate 203 and reach the junction surface after diffusion toward the light-receiving surface side. Therefore, if the quantum efficiency in this region is low, the p-type silicon The fast carrier recombination on the substrate 203 is a determinant of performance.

  The process of step S8 will be further described with reference to the flowchart of FIG. First, excitation light having a wavelength of 500 nm or more and 750 nm or less is irradiated onto the solar cell 201 with a large spot size of 1 mm or more, preferably about 1 cm, and the measurement points set at a pitch of 1 cm or less in the horizontal direction and 1 cm or less in the vertical direction are set. Mapping measurement of quantum efficiency and reflectance is performed (step S81). Subsequently, the PC 124 calculates the internal quantum efficiency at the irradiation light wavelength at each measurement point based on the measurement result in step S81 (step S82), and determines a region having a low quantum efficiency from the calculation result (step S83). ).

  Here, when a single crystal silicon has a rotationally symmetric structure with respect to the center of the crystal, and in the case of polycrystalline silicon, a spot pattern corresponding to the size of a crystal grain is observed, the p-type silicon substrate 203 contains The carrier recombination of the solar cell decreases the performance of the solar cell. Therefore, in step S83, when the region having a low internal quantum efficiency shows a structure specific to a silicon crystal such as a concentric region with respect to the center of the solar cell, the recombination is due to the low quality of the silicon crystal. Evaluate (step S84). On the other hand, when the region where the internal quantum efficiency is low does not show the structure peculiar to the silicon crystal, it is evaluated that the cause of lowering the performance of the solar cell to be evaluated is recombination or short circuit at the np junction ( Step S85).

  By the way, for solar cells and semiconductor wafers where electrodes are not formed, a spatial distribution map of carrier lifetime can be obtained by the μPCD method, etc. It is necessary to devise a method that does not cause photoexcitation, which is very difficult. On the other hand, in the present embodiment, the internal quantum efficiency is selected as the amount of mapping measurement, and the spatial resolution is reduced to about 1 cm, thereby making it possible to visualize the spatial nonuniformity of quality in a large area solar cell.

  Returning to FIG. 3, the description will be continued. When the PC 124 detects in step S6 that the wavelength region where the quantum efficiency of the solar cell 201 is lower than that of the reference sample is 1000 nm or more and 1250 nm or less, the PC 124 evaluates that a light confinement defect occurs in the sample solar cell 201 ( Step S9). For example, in the wavelength region of 1050 nm or more, the penetration length of the excitation light is 1 mm or more, and the excitation light is absorbed after being reflected many times in the solar cell, so the non-uniformity of the photoexcited carrier in the depth direction is eliminated. There is no wavelength dependency. In this wavelength region, the higher the number of multiple reflections of excitation light due to light confinement, the longer the tail of the quantum efficiency spectrum to longer wavelengths. If the quantum efficiency in this wavelength region is low, the optical confinement structure may be defective.

  The evaluation in step S9 will be further described with reference to the flowchart shown in FIG. First, the solar cell 201 is irradiated with excitation light having a wavelength of 500 nm or more and 750 nm or less and a spot size of 10 μm or less, preferably 1 μm or less, and the surface of the solar cell 201 has a lateral direction of 10 μm × longitudinal 10 μm or more. The reflectance mapping of the measurement points set at a pitch of 10 μm or less and 10 μm or less in the vertical direction is performed (step S91). Subsequently, the PC 124 determines whether the reflectance structure indicated by the measurement result at each measurement point in step S91 corresponds to the crystal grain boundary or is uniform (step S92), and the change in reflectance is a crystal. When it is determined that it corresponds to the grain boundary, it is evaluated that the performance degradation of the solar cell is due to the anisotropy due to the crystal orientation (step S93). Since such changes are likely to occur in a chemical process using a potassium hydroxide solution, the use of a process that is less susceptible to surface orientation, such as a hydrofluoric acid / nitric acid mixture or plasma etching, will be considered. On the other hand, when it is determined that the reflectance is uniform, the texture design / conditions are reviewed (step S94).

  Returning to FIG. 3, the description will be continued. When the PC 124 detects in step S6 that the wavelength region where the quantum efficiency of the solar cell 201 is lower than that of the reference sample is near 900 nm, that is, not less than 750 nm and not more than 1100 nm, as shown in FIG. It is determined that minority carrier recombination has occurred (step S10), and processing specific to the present invention is performed. At the excitation wavelength of 900 nm to 1000 nm, photoexcited carriers begin to be generated even near the back surface of the solar cell. Therefore, when the quantum efficiency in this wavelength region is low, fast minority carrier recombination due to a defective passivation film on the back surface side is suspected.

  Following step S10, it is determined whether or not the solar cell to be evaluated has a back side structure (step S11). In the case of a solar cell with a uniform back side such as an Al-BSF type, the back side process is improved ( Step S12). On the other hand, if there is a back side structure such as a PERC type solar cell, it is determined whether or not there is a surface electrode (step S13). If there is no surface electrode, the aperture size is set to about the substrate thickness by the aperture 106. (Step S14) If there is a surface electrode, the aperture size of the excitation light is set to at least twice the electrode width and as close as possible to the substrate thickness by the aperture 106 (Step S15). Here, the smaller the spot size of the excitation light for mapping measurement, the better the spatial resolution, but the spatial resolution for evaluating the back surface structure is minority carrier diffusion in the direction parallel to the surface of the substrate and the texture structure on the surface side. Due to the influence of bleeding of the excitation light spot of about the thickness of the substrate due to the above, it is not improved to some extent.

  If the spot size is small, it is difficult to increase the excitation power, and if the spot size is reduced more than necessary, the S / N ratio is lowered. Therefore, in this embodiment, the solar cell has a back surface structure but there is no surface electrode. In step S14, the spot size is selected to be about the thickness of the substrate. On the other hand, when the electrode 202 is on the surface side of the solar cell having the back surface structure like the solar cell 201 shown in FIG. 2, the influence of the electrode 202 on the front surface side can be averaged and suppressed as the spot size is larger. Therefore, in this embodiment, in step S15 described above, the spot size of the excitation light is set to at least twice the electrode width in order to suppress the influence of the electrode 202, and the spot size as close as possible to the substrate thickness is satisfied after satisfying this condition. To do. As described above, the spot size determined in step S15 is practically sufficient for the back side structure without being substantially affected by the surface side structure of the solar cell by the excitation light incident from the surface side of the solar cell to be evaluated. The size is observable.

  Here, the solar cell 201 is of the PERC type shown in FIG. 2, and the electrode 202 exists on the front surface side and the electrode 207 exists on the back surface side. Therefore, the spot size of the excitation light is set to 2 of the electrode width in step S15. The value is more than double and is as close as possible to the substrate thickness. As an example, the solar cell 201 has a substrate thickness of 0.12 mm, and selectable spot sizes are 0.8 mm, 0.4 mm, 0.2 mm, and 0.1 mm, and the electrode width of the electrode 202 is 0.1 mm. The spot size was determined to be 0.2 mm or more and the closest 0.2 mm to the substrate thickness.

  Subsequently, the PC 124 controls the spectroscope 104 to set the wavelength λ of the excitation light having the spot size determined in step S14 or step S15 to 750 nm or more and 1100 nm or less, and in the embodiment, 950 nm. With respect to the range of 1 mm × 1 mm or more, measurement points set at a pitch of 0.2 mm or less in the horizontal direction and 0.2 mm or less in the vertical direction, and in the example, the range of 4 mm × 7 mm in the horizontal direction is set to 0.5 mm in the horizontal direction. Quantum efficiency mapping measurement and reflectance mapping measurement are performed on 20 × 70 measurement points set at a pitch of 2 mm and 0.1 mm in the vertical direction (step S <b> 16). Then, the PC 124 calculates the internal quantum efficiency according to the equation (2) based on the mapping measurement value of the quantum efficiency, and calculates the reflectance according to the equation (1) based on the mapping measurement value of the reflectance (step S17). . An example of the internal quantum efficiency and the reflectance calculated in step S17 is shown in FIGS.

  FIG. 6 shows a density plot of the internal quantum efficiency of the solar cell 201 at an excitation light wavelength of 950 nm. In the figure, the x-axis direction is the longitudinal direction of the electrodes 202 and 207, and the y-axis direction is the width direction of the electrodes 202 and 207 (the same applies to FIGS. 7 and 8 described later). In the figure, the black region shows the region between the electrodes having a low internal quantum efficiency, and the internal quantum efficiency at the excitation light wavelength of 950 nm is substantially uniform in the x-axis direction, and the electrode of the back-side electrode 207 in the y-axis direction. Regions having a high internal quantum efficiency and regions having a low internal quantum efficiency appear alternately at intervals of 1 mm, which is the distance between them. That is, FIG. 6 is a diagram of the internal quantum efficiency from the front surface side (light receiving surface), but the characteristics of the electrode 202 on the front surface side are excluded, and the change in the internal quantum efficiency due to the structure on the back surface side is the display 125 and the printer 126. It is visualized by. Thus, FIG. 6 shows that the internal quantum efficiency of the solar cell 201 at the excitation light wavelength of 950 nm is affected by the electrode 207 on the back surface side.

  FIG. 7 shows a density plot of the reflectance of the solar cell 201 at an excitation light wavelength of 950 nm. In the figure, the black region shows the region between the electrodes with low reflectance, and the reflectance at the excitation light wavelength of 950 nm is substantially uniform in the x-axis direction, and between the electrodes of the surface side electrode 202 in the y-axis direction. Regions with high reflectivity and regions with low reflectivity appear alternately at intervals of 1.8 mm. Thus, FIG. 7 shows only the reflectance of the electrode 202 on the surface side as the reflectance of the solar cell 201 at the excitation light wavelength of 950 nm.

  Following step S17, the PC 124 controls the spectroscope 104 to switch the wavelength λ of the excitation light to 1200 nm or more (in the embodiment, 1200 nm), and performs the mapping measurement of the reflectance at each of the 20 × 70 measurement points described above. This is performed (step S18). Then, in the region where the internal quantum efficiency calculated in step S17 is lower than the predetermined value, it is determined whether or not the reflectance measured in step S18 is higher than the set value (step S19).

  FIG. 8 shows a density plot of the reflectance of the solar cell 201 at an excitation light wavelength of 1200 nm. In FIG. 8, non-uniform reflectance is observed in a region where there is no increase in reflectance due to the electrode 202 on the surface side. This is because the incident light is not absorbed by the p-type silicon substrate 203 at the wavelength of 1200 nm, and the structure on the back surface side is seen through. This is because the region absorbed by the electrode 207, which is the alloy layer on the back side, appears darker than the insulating film region that exhibits high reflectivity due to total reflection. That is, FIG. 8 shows that the structure on the back side of the electrode 207 and the like can be observed by the reflectance measured using excitation light having a wavelength of 1200 nm.

  When the PC 124 determines that the reflectance is higher than the set value in step S19, the PC 124 determines that the conductivity of the aluminum oxide film 206 functioning as a passivation film on the back surface side is higher than the design value, and reviews the film formation conditions. (Step S20). On the other hand, when it is determined in step S19 that the reflectance is equal to or lower than the set value, the PC 124 determines that the conductivity of the electrode 207, which is the alloy layer on the back surface side, is lower than the design value, and that the electrode 207 is poorly formed. Review the firing conditions of the layer (step S21). When determining in steps S20 and S21, it is necessary to eliminate the influence of the surface electrode 202 that is seen by the reflectance measured with excitation light having a wavelength of 1100 nm or less (950 nm in the embodiment).

  Thus, according to the solar cell evaluation apparatus 100 of the present embodiment, the sample that can move the solar cell 201 to be evaluated with high accuracy in the biaxial direction of the horizontal plane in a measurement system that can measure the internal quantum efficiency with high accuracy. If the quantum efficiency measured by combining the stage 117 and irradiating excitation light with a spot size of 1 mm to a certain point on the light receiving surface side of the solar cell 201 is lower than that of the reference sample at a certain wavelength, the reason is The surface-side structure is determined by irradiating the solar cell with excitation light that is determined to be due to the influence of the back-side structure and has a spot size at least twice the width of the surface-side electrode 202 and as close as possible to the substrate thickness at that wavelength. The back side structure can be measured and evaluated almost without being affected by the above. For this reason, non-destructive evaluation of the back side structure of the solar cell on which electrodes are already formed, which makes it difficult to measure photoexcited carrier lifetime, etc., can be promoted, and optimization of the manufacturing process can be promoted.

  Moreover, according to the solar cell evaluation apparatus 100 of the present embodiment, the internal quantum efficiency obtained by irradiating the silicon-based solar cell with the wavelength of the excitation light having the spot size set to 950 nm and mapping measurement, and the absorption to the silicon substrate Based on the reflectance obtained by irradiating the silicon-based solar cell with excitation light having a wavelength of 1200 nm and mapping measurement, the back surface structure aluminum oxide film 206 and the alloy layer electrode 207 have the efficiency as designed. Can be evaluated.

  The present invention is not limited to the above embodiment. For example, the quantum efficiency spectrum of the reference sample may be replaced with the quantum efficiency spectrum of the solar cell to be evaluated that has not failed. A quantum efficiency spectrum obtained theoretically may be substituted. Moreover, although the internal quantum efficiency and the reflectance are visualized as a density plot in FIGS. 6 to 8, they can be visualized using contour lines.

  The present invention also includes a solar cell evaluation program that causes the PC 124 to execute the operations of the flowcharts shown in FIGS. 3 and 4. The solar battery evaluation program may be distributed via the communication network and downloaded to the execution program storage memory of the PC 124 (assumed to be in the block of the PC 124 in FIG. 1) or reproduced from the recording medium. It may be downloaded to the above memory, and the downloading method is not limited.

  The present invention includes single crystal silicon, polycrystalline silicon, amorphous silicon, gallium arsenide single crystal, indium gallium arsenide single crystal, gallium phosphide single crystal, indium gallium phosphide single crystal, germanium single crystal, chalcopyrite group I-III-VI A solar cell composed of at least one of a compound, a perovskite compound, cadmium tellurium, zinc oxide, titanium oxide, tin oxide, and silicon germanium single crystal can be used as an evaluation target solar cell. Very useful in a wide range.

DESCRIPTION OF SYMBOLS 100 Solar cell evaluation apparatus 101 White light source 102 Lens 103 Optical chopper 104 Spectrometer 105 Dark box 106 Diaphragm 107 Beam splitter 108, 110 Parabolic mirror 109 Integrating sphere 111 Excitation light sensor 112 Reflection light sensor 113, 114, 115 Current voltage conversion Instrument 116 Lab jack 117 Sample stage 118, 119 Stepping motor 121, 122, 123 Lock-in amplifier 124 Personal computer (PC)
125 display 126 printing machine 201 solar cell 202 Ag electrode 203 p-type silicon substrate 204 n ⁺ diffusion layer 205 SiN film 206 aluminum oxide film 207 BSF type electrode 208 Al electrode

Claims (8)

Irradiate the light receiving surface of a solar cell mounted on a movable sample stage with excitation light whose wavelength and spot size can be arbitrarily changed, and each photoelectric conversion signal of reflected light from the solar cell and the excitation light And a solar cell evaluation method for obtaining an evaluation result of the solar cell based on the output signal of the solar cell,
A light control step of controlling at least the spot size of the excitation light to a value that is at least twice the electrode width of the surface electrode of the solar cell and as close as possible to the substrate thickness of the solar cell;
The inside of the solar cell obtained by sequentially irradiating each of a plurality of measurement points on the light receiving surface of the solar cell placed on the sample stage with the excitation light whose spot size is controlled by the light control step Based on the spatial distribution of quantum efficiency, an evaluation step for evaluating the back surface structure opposite to the light receiving surface of the solar cell;
The evaluation method of the solar cell characterized by including. A light irradiation step of irradiating a light receiving surface of a solar cell mounted on a sample stage that can move a horizontal plane by a specified distance in two axial directions with excitation light having a wavelength and a spot size controlled to desired values,
Based on the reflected light obtained by reflecting the excitation light on the surface electrode formed on the light receiving surface, each photoelectric conversion signal of the excitation light before irradiation of the light receiving surface, and the output signal of the surface electrode Measuring the excitation light intensity, total reflected light intensity and photocurrent, and calculating the internal quantum efficiency and reflectance of the solar cell from the measurement results;
Evaluation result of the solar cell based on the internal quantum efficiency and the reflectance by the calculation step obtained from the respective measurement results of the plurality of measurement points on the light receiving surface of the solar cell, and the wavelength of the excitation light An evaluation step to obtain
In the light irradiation step, at least the spot size of the excitation light is controlled to a value that is at least twice the electrode width of the surface electrode and close to the substrate thickness of the solar cell as much as possible. Irradiate
The evaluation step includes evaluating a back surface structure opposite to the light receiving surface of the solar cell. In the light irradiation step, the wavelength of the excitation light is controlled to a first wavelength at which an internal quantum efficiency lower than an internal quantum efficiency of a reference sample is obtained or a second wavelength at which the substrate of the solar cell appears to be substantially transparent. ,
The evaluation step includes the first internal quantum efficiency and the first reflectance calculated by the calculation step based on the measurement results of the plurality of measurement points when the excitation light has the first wavelength, The back surface structure of the solar cell is evaluated using the second reflectance calculated by the calculation step based on the measurement results of the plurality of measurement points when the excitation light has the second wavelength. The method for evaluating a solar cell according to claim 2. Irradiate the light receiving surface of a solar cell mounted on a movable sample stage with excitation light whose wavelength and spot size can be arbitrarily changed, and each photoelectric conversion signal of reflected light from the solar cell and the excitation light And a solar cell evaluation device for obtaining an evaluation result of the solar cell based on the output signal of the solar cell,
Light control means for controlling at least the spot size of the excitation light to a value that is at least twice the electrode width of the surface electrode of the solar cell and as close as possible to the substrate thickness of the solar cell;
The inside of the solar cell obtained by sequentially irradiating each of the plurality of measurement points on the light receiving surface of the solar cell placed on the sample stage with the excitation light whose spot size is controlled by the light control means Based on the spatial distribution of quantum efficiency, an evaluation means for evaluating the back surface structure opposite to the light receiving surface of the solar cell;
A solar cell evaluation apparatus comprising: A sample stage on which a solar cell is mounted and movable in a biaxial direction on a horizontal plane parallel to the surface of the solar cell;
A moving mechanism for moving the sample stage;
A light irradiating means for generating excitation light in which the wavelength and the spot size on the light receiving surface of the solar cell are each controlled to a desired value and irradiating the light receiving surface of the solar cell;
Based on the reflected light reflected by the surface electrode formed on the light receiving surface, the photoelectric conversion signals of the excitation light before the light receiving surface irradiation, and the output signal of the surface electrode Measuring means for measuring the excitation light intensity, the total reflection light intensity and the photocurrent, and calculating the internal quantum efficiency and reflectance of the solar cell from the measurement results;
Drive control means for driving and controlling the moving mechanism to move the sample stage so that the spot of the excitation light sequentially positions a plurality of measurement points on the light receiving surface of the solar cell;
Evaluation means for obtaining an evaluation result of the solar cell based on the internal quantum efficiency and the reflectance by the calculation means obtained from the measurement results of the plurality of measurement points, and the wavelength of the excitation light,
With
The light irradiation means controls at least the spot size of the excitation light to a value that is at least twice the electrode width of the surface electrode and as close as possible to the substrate thickness of the solar cell,
The evaluation means evaluates a back surface structure opposite to the light receiving surface of the solar cell, and evaluates the solar cell. The light irradiation means controls the wavelength of the excitation light to a first wavelength at which an internal quantum efficiency lower than an internal quantum efficiency of a reference sample is obtained or a second wavelength at which the substrate of the solar cell appears to be substantially transparent. ,
The evaluation means includes a first internal quantum efficiency and a first reflectance calculated by the calculation means based on the measurement results of the plurality of measurement points when the excitation light has the first wavelength, The back surface structure of the solar cell is evaluated using the second reflectance calculated by the calculation means based on the measurement results of the plurality of measurement points when the excitation light has the second wavelength. The solar cell evaluation apparatus according to claim 5. Irradiate the light receiving surface of a solar cell mounted on a movable sample stage with excitation light whose wavelength and spot size can be arbitrarily changed, and each photoelectric conversion signal of reflected light from the solar cell and the excitation light And a solar cell evaluation program for causing a computer to execute evaluation of the solar cell to obtain an evaluation result of the solar cell based on the output signal of the solar cell,
In the computer,
A light control function for controlling at least the spot size of the excitation light to be not less than twice the electrode width of the surface electrode of the solar cell and as close as possible to the substrate thickness of the solar cell;
The inside of the solar cell obtained by sequentially irradiating each of the plurality of measurement points on the light receiving surface of the solar cell placed on the sample stage with the excitation light whose spot size is controlled by the light control function Based on the spatial distribution of quantum efficiency, an evaluation function for evaluating the back surface structure opposite to the light receiving surface of the solar cell;
A program for evaluating a solar cell characterized by realizing the above. Irradiate the light receiving surface of a solar cell mounted on a movable sample stage with excitation light whose wavelength and spot size can be arbitrarily changed, and each photoelectric conversion signal of reflected light from the solar cell and the excitation light And a solar cell evaluation program for causing a computer to execute evaluation of the solar cell to obtain an evaluation result of the solar cell based on the output signal of the solar cell,
In the computer,
A light irradiation function for irradiating the light receiving surface of the solar cell placed on the sample stage with excitation light in which the wavelength and the spot size are controlled to desired values, and
Based on the reflected light obtained by reflecting the excitation light on the surface electrode formed on the light receiving surface, each photoelectric conversion signal of the excitation light before irradiation of the light receiving surface, and the output signal of the surface electrode A calculation function for calculating the internal quantum efficiency and the reflectance of the solar cell from the measurement results of the excitation light intensity, total reflection light intensity and photocurrent,
Evaluation result of the solar cell based on the internal quantum efficiency and the reflectance by the calculation function obtained from the measurement results of the plurality of measurement points on the light receiving surface of the solar cell, and the wavelength of the excitation light To achieve the evaluation function
In the light irradiation function, the light receiving surface is configured to control at least the excitation light spot size to a value that is at least twice the electrode width of the surface electrode and as close as possible to the substrate thickness of the solar cell. Irradiate
The evaluation function evaluates a back surface structure opposite to the light receiving surface of the solar cell.

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