JP6781985B2 - Solar cell evaluation method and evaluation device and solar cell evaluation program - Google Patents

Description

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

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

However, the above-mentioned alloy layer tends to have a faster recombination rate than the passivation film made of an insulator, and the absorption of light in the alloy layer causes a decrease in efficiency. Therefore, in recent years, solar cells of a method in which light loss and recombination are reduced instead of an alloy layer, and a new passivation film for achieving high voltage and high current and thus high efficiency are formed on the back surface side are becoming mainstream. Examples include a structure having an insulating film on the back surface 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) and so on.

Since such a solar cell having a passivation film on the back surface side is more complicated than the previous structure, it is important to optimize the back surface process, and if the back surface passivation film can be evaluated at the development stage, the optimization will be large. It will be accelerated. Further, the evaluation of the passivation film on the back surface side facilitates the identification of the cause of failure when the back surface of the solar cell deteriorates for some reason including thermal cycle, voltage, light irradiation, humidity, and aging.

The characteristics of the passivation film on the back surface side 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 a silicon-based solar cell, the carrier recombination rate in the backside passivation film can be qualitatively evaluated by changing the quantum efficiency in the region of the excitation wavelength of 900 nm to 950 nm. In this case, since the change in quantum efficiency is about 1%, high-precision measurement by a type that simultaneously measures reflection at the measurement position, for example, the internal quantum efficiency measuring device described in Patent Document 1, is required. When the solar cell has a structure capable of receiving light on both sides, the quantum efficiency can be measured by receiving light on the back side, and the carrier recombination rate in the passivation film can be qualitatively evaluated from the quantum efficiency in the short wavelength region of 300 to 500 nm.

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

FIG. 9 shows the incident light wavelength vs. internal quantum efficiency characteristic of the solar cell, which shows the effect of the recombination rate on the surface of the solar cell on the quantum efficiency. The characteristics shown in the figure are a crystalline silicon solar cell with a flat front surface and a perfect conductor electrode attached to the back surface. The thickness is 300 μm, the bonding depth is 1 μm, and the surface recombination rate of minority carriers is 4 cm on the surface side. The calculation method is / s, 27 cm / s on the back surface side, the diffusion length is 1.5 μm on the front surface side, and 200 μm on the back surface side, and the calculation method is the characteristics obtained by the continuity equation and the Drude model. In FIG. 9, the solid line I is the characteristic when the front surface recombination speed is 100 cm / s on both the front surface side and the back surface side, the broken line II is the characteristic when the back surface side recombination speed is increased to 2000 cm / s, and the dotted line III is the surface surface. The characteristics when the side recombination rate is increased to 2000 cm / s are shown. As shown in FIG. 9, it can be seen that the internal quantum efficiencies of the long wavelength and the short wavelength are reduced in both cases. In the conventional evaluation method of a solar cell, the cause of the deterioration of the performance of the solar cell is searched for from such a change in the internal quantum efficiency.

Next, another evaluation method of the 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, cavities are likely to be formed in the aluminum electrode on the back surface side, which significantly deteriorates the characteristics of the solar cell. Therefore, conventionally, the above cavities and the like have been discovered by a method using an ultrasonic flaw detector or a method of simply cutting a solar cell and observing it with an electron microscope.

JP-A-2002-353474

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

However, in a solar cell having a passive film on the back surface side, 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 deterioration of the performance of the solar cell from the change in the internal quantum efficiency. In), it is not possible to measure the internal quantum efficiency by changing the spatial resolution determined by the spot size of the excitation light and the excitation wavelength, so it is not possible to specify what is wrong with the back surface 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 deterioration of the power generation characteristics is identified by an ultrasonic flaw detector or an electron microscope, an abnormality different from the assumed cause occurs. In the case of a solar cell, no abnormality is found, and if the cause is to be investigated only by the evaluation method of the solar cell, various measurements must be performed on a round-robin basis.

Therefore, at present, an evaluation process that combines the above two conventional evaluation methods for solar cells is adopted. For example, in the case of a solar cell having a PERC structure using a p-type silicon substrate having passivation films on both the front side and the back side, a plurality of solar cells are evaluated and compared by the first conventional method, and the back side is used. Identify if there is a problem. Next, among the solar cells having a problem on the back surface side, whether there is a problem on the passivation film made of, for example, alumina on the back surface side or the part in contact with the aluminum electrode on the back surface side is determined by the second conventional method. Destroy and identify solar cells. That is, conventionally, if the solar cell is not destroyed, it is extremely difficult to identify the problematic part on the back surface side of the solar cell, and there is a problem that there is no prospect of improvement.

The present invention has been made in view of the above points, and an evaluation method and an evaluation device for a solar cell and a solar cell that can realize optimization of a manufacturing process by non-destructively evaluating the characteristics of the back surface side of the solar cell. The purpose is to provide an evaluation program.

In order to achieve the above object, the evaluation method of the solar cell of the first invention is to apply excitation light whose wavelength and spot size can be arbitrarily changed to a light receiving surface of the solar cell placed on a movable sample table. A method for evaluating a solar cell, which obtains an evaluation result of the solar cell based on each photoelectric conversion signal of the reflected light from the solar cell and the excitation light and an output signal of the solar cell. The spot size of the excitation light is controlled by an optical control step of controlling 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, and a spot by the optical control step. The 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 table with the excitation light whose size is controlled. Based on this, it is characterized by including an evaluation step of evaluating the back surface structure of the solar cell on the side opposite to the light receiving surface.

Further, in order to achieve the above object, the evaluation method of the solar cell of the second invention is performed on the light receiving surface of the solar cell placed on the sample table which can move the horizontal plane by a specified distance in the biaxial direction. A light irradiation step of irradiating an excitation light whose wavelength and spot size are controlled to desired values, a reflected light obtained by reflecting the excitation light by 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, the total reflected light intensity and the photocurrent are measured, and the internal quantum efficiency of the solar cell is obtained 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 the plurality of measurement points on the light receiving surface of the solar cell, and the wavelength of the excitation light. Including the evaluation step of obtaining the evaluation result of the solar cell based on the above, the light irradiation step has at least the spot size of the excitation light at least twice the electrode width of the surface electrode and the solar cell. The light receiving surface is irradiated with the excitation light controlled to a value as close as possible to the substrate thickness of the solar cell, and the evaluation step is characterized in that the back surface structure of the solar cell opposite to the light receiving surface is evaluated.

Further, in order to achieve the above object, in the evaluation method of the solar cell of the third invention, the light irradiation step of the second invention sets the wavelength of the excitation light to the internal quantum lower than the internal quantum efficiency of the reference sample. Controlled to a first wavelength at which efficiency is obtained or a second wavelength at which the substrate of the solar cell looks substantially transparent, the evaluation step of the fifth invention is the plurality of said when 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 respective measurement points, and the respective measurements of the plurality of measurement points when the excitation light has the second wavelength. It is characterized in that the back surface structure of the solar cell is evaluated by using the second reflectance calculated by the calculation step based on the result.

Further, in order to achieve the above object, the evaluation device for the solar cell of the fourth invention is a solar cell on which an excitation light whose wavelength and spot size can be arbitrarily changed is placed on a movable sample table. 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 the reflected light from the solar cell and the excitation light and an output signal of the solar cell. An optical 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, and the optical control means. A space of 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 table with the excitation light whose spot size is controlled by It is characterized by comprising an evaluation means for evaluating the back surface structure of the solar cell on the side opposite to the light receiving surface of the solar cell based on the distribution.

Further, in order to achieve the above object, in the solar cell evaluation device of the fifth invention, the solar cell is mounted and the horizontal plane parallel to the surface of the solar cell can be moved by a specified distance in the biaxial direction. The sample table, the moving mechanism for moving the sample table, and the excitation light whose wavelength and spot size on the light receiving surface of the solar cell are controlled to desired values are generated and irradiated to the light receiving surface of the solar cell. The light irradiating means, the reflected light reflected by the surface electrode formed on the light receiving surface, the photoelectric conversion signal of the excitation light before the light receiving surface irradiation, and the surface electrode. Based on the output signal, the excitation light intensity, the total reflected light intensity, and the light current are measured, and the calculation means for calculating the internal quantum efficiency and the reflectance of the solar cell from the measurement results and the moving mechanism are driven and controlled. The drive control means for moving the sample table so that the spots of the excitation light sequentially position the plurality of measurement points on the light receiving surface of the solar cell, and the measurement results of the plurality of measurement points were obtained. An evaluation means for obtaining an evaluation result of the solar cell based on the internal quantum efficiency and the reflectance by the calculation means and the wavelength of the excitation light is provided.
The light irradiation means controls the spot size of the excitation light to at least twice the electrode width of the surface electrode and a value as close as possible to the substrate thickness of the solar cell, and the evaluation means said. It is characterized in that the back surface structure on the side opposite to the light receiving surface of the solar cell is evaluated.

Further, in order to achieve the above object, in the solar cell evaluation apparatus of the sixth invention, the light irradiation means of the fifth invention sets the wavelength of the excitation light to an internal quantum lower than the internal quantum efficiency of the reference sample. Controlled to a first wavelength at which efficiency is obtained or a second wavelength at which the substrate of the solar cell looks substantially transparent, the evaluation means of the second invention is the plurality of said when the excitation light is at the first wavelength. The first internal quantum efficiency and the first reflectance calculated by the calculation means based on the measurement results of the respective measurement points, and the respective measurements of the plurality of measurement points when the excitation light has the second wavelength. It is characterized in that the back surface structure of the solar cell is evaluated by using the second reflectance calculated by the calculation means based on the result.

Further, in order to achieve the above object, the solar cell evaluation program of the seventh invention is a solar cell in which excitation light whose wavelength and spot size can be arbitrarily changed is placed on a movable sample table. The evaluation result of the solar cell is obtained by irradiating the light receiving surface 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. This is a solar cell evaluation program to be executed by the computer.
By the optical 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 as close as possible to the substrate thickness of the solar cell, and the optical 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 table with the excitation light having a controlled spot size. Based on the above, it is characterized by realizing an evaluation function for evaluating the back surface structure of the solar cell on the side opposite to the light receiving surface.

Further, in order to achieve the above object, the evaluation program of the solar cell of the eighth invention is a solar cell in which excitation light whose wavelength and spot size can be arbitrarily changed is placed on a movable sample table. The evaluation result of the solar cell is obtained by irradiating the light receiving surface 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. This is a solar cell evaluation program to be executed by the computer.
A light irradiation function that irradiates a light receiving surface of a solar cell placed on the sample table with excitation light in which the wavelength and spot size are controlled to desired values, and a surface formed by the excitation light on the light receiving surface. The excitation light intensity and the total reflected light intensity measured based on the photoelectric conversion signals of the reflected light obtained by being reflected by the electrodes and the excitation light before the light receiving surface irradiation, and the output signal of the surface electrode. And the inside by the calculation function to calculate the internal quantum efficiency and reflectance of the solar cell from the measurement result of the light current and the calculation function obtained from the measurement result of each of the plurality of measurement points on the light receiving surface of the solar cell. An evaluation function for obtaining an evaluation result of the solar cell is realized based on the quantum efficiency, the reflectance, and the wavelength of the excitation light.
The light irradiation function controls the spot size of the excitation light to be at least twice the electrode width of the surface electrode and a value as close as possible to the substrate thickness of the solar cell. The evaluation function is characterized in that the back surface structure of the solar cell opposite to the light receiving surface is evaluated.

According to the present invention, an evaluation for non-destructively identifying the cause on the back surface side of a solar cell when the electrode-formed solar cell fails or the designed performance cannot be obtained, which is difficult to measure the photoexcited carrier lifetime. It can be performed. Thereby, according to the present invention, the optimization of the manufacturing process can be realized.

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 in this invention. It is a flowchart for operation explanation of FIG. It is a flowchart for detailed operation explanation of each part in FIG. It is a wavelength vs. internal quantum efficiency characteristic diagram of a PERC type solar cell and a reference sample. It is a figure which the internal quantum efficiency at the excitation light wavelength of 950 nm of a solar cell is a shading plot. It is a figure which the reflectance at the excitation light wavelength of 950 nm of a solar cell is plotted by shading. It is a figure which the reflectance at the excitation light wavelength of 1200 nm of a solar cell is plotted by shading. It is an incident light wavelength vs. internal quantum efficiency characteristic diagram of a solar cell.

Next, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a configuration diagram of an embodiment of an evaluation device for a solar cell according to the present invention. The solar cell evaluation device 100 of the present embodiment combines an internal quantum efficiency measurement system with a variable excitation spot size and a variable sample table capable of highly accurate movement control of the measurement position of the solar cell as the sample to be evaluated. It is a configuration.

In FIG. 1, the white light source 101 emits white light, the white light is made into parallel light by the lens 102, chopped by an optical chopper 103 for AC measurement, and incident on the spectroscope 104. The spectroscope 104 is composed of a reflector that changes an optical path, a rotatable grating 1041 and the like, and disperses incident white light into monochromatic light having a wavelength of 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 a PC) 124, which will be described later. As a result, the spectroscope 104 emits monochromatic light dispersed from white light to an arbitrary wavelength by the PC 124 as excitation light, and enters the dark box 105.

Inside the dark box 105 is an optical and electrical system consisting of a diaphragm 106, a beam splitter 107, a parabolic mirror 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 table 117, a stepping motor 118 and 119 are housed. The sample table 117 fixed on the lab jack 116 is moved by the stepping motor 118 in the x-axis direction of the horizontal plane (the direction parallel to the longitudinal direction of the electrodes in the plane parallel to the electrode forming surface of the solar cell 201) and the stepping motor 119. It constitutes a variable sample table that moves in the y-axis direction of the horizontal plane and is positioned with high accuracy. The operation of the stepping motors 118 and 119 is controlled by the PC 124 described later. The solar cell 201, which is the sample to be evaluated, is placed and fixed on the sample table 117. The electrode 202 on the front surface side of the solar cell 201 reflects the excitation light and enters the integrating sphere 109.

The diaphragm 106 is a variable diaphragm in which the spot size of the monochromatic excitation light from the spectroscope 104 can be changed within a range of, for example, 50 μm to 3 mm, and the monochromatic excitation light having a desired spot size is incident on the beam splitter 107. .. In the present embodiment, the aperture 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 as close as possible to the substrate thickness. To control. On the surface of the solar cell 201, the light from the diaphragm 106 is imaged at the same magnification by the parabolic mirror 108, so that the spot size on the surface of the solar cell 201 is the same as that of the diaphragm 106.

The beam splitter 107 divides the optical path of the excitation light whose spot diameter is adjusted by the aperture 106 into two, one of which is reflected by the parabolic mirror 108 and incidents on the electrode 202 on the surface side of the solar cell 201, and the other is emitted. It is reflected by the parabolic 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, multi-reflects it on the inner wall, and then condenses the collected reflected light to the reflected light sensor 112 through another opening. It is incident and photoelectrically converted.

The excitation light sensor 111 outputs a current at a level corresponding to the amount of received light of the incident excitation light, supplies it to the current-voltage converter 113 to convert it into a voltage, and then supplies it to the lock-in amplifier 121. On the other hand, the reflected light sensor 112 outputs a current of a level corresponding to the amount of received light of the reflected light obtained by being reflected by the electrode 202 and the integrating sphere 109, and supplies the current to the current-voltage converter 114 to convert it into a voltage. After that, it is supplied to the lock-in amplifier 122. Further, 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 an AC voltage output from the current-voltage converters 113, 114, and 115, and have a DC voltage corresponding to the level of the same frequency component as a predetermined frequency reference signal in the AC voltage. Are generated and 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 optical current I output by 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 voltages supplied from the lock-in amplifiers 121, 122 and 123, respectively.
R = _Pr / P (1)
η _IQE = Ihc / [ePλ (1-R)] (2)
However, in Eq. (2), h is Planck's 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 calculated reflectance R and the measurement data of the 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 on paper by the printing machine 126. Visualize it. The solar cell 201, which will be described later, is evaluated based on the visualized measurement image and measurement data. In addition, the PC 124 also supplies drive signals to the stepping motors 118 and 119 and moves the sample table 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 device 100 of the present embodiment has a movable sample table mechanism including a lab jack 116, a sample table 117, a stepping motor 118 and 119, and an internal structure having a variable excitation spot size composed of other optical 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 is a feature.

In the silicon solar cell, which is an example of the solar cell to be evaluated in the present embodiment, an electrode made of silver (Ag) is often adopted as the electrode on the surface side. In the solar cell evaluation device 100 of the present embodiment, when a spot size twice the width of the Ag electrode is adopted and it is assumed that the excitation light uniformly illuminates only the circular region having the same spot size. The electrodes cover up to 61% of the spot. At this time, for example, the internal quantum efficiency at a wavelength of 950 nm is 0.75, which is spatially uniform, ignoring the reflection in the region without the electrode, and adopting the reflectance of the silver electrode of 97.5% as the reflectance of the electrode. Then, assuming that all the reflections are captured by the integrating sphere 109, the measured internal quantum efficiency is 0.721, which is 0.029 lower. This amount of decrease is almost the same as the change of about 0.02 in the internal quantum efficiency with respect to the excitation light having a wavelength of 950 nm due to the back surface structure of the solar cell shown in FIG. 6, which will be described later, and the influence of the back surface structure is hidden. Absent. With a larger spot size, the upper limit of the proportion of the electrode area shown in the excitation light spot is lowered, so that the influence of the front electrode can be made smaller, and the influence of the back surface structure of the solar cell can be affected without any special image processing. It can be visualized.

Further, the spatial resolution of the evaluation device 100 of the solar cell is such that the excitation light spot size, the minority carrier diffusion length in the main excitation region, and the size that the spots are scattered by the texture of the light receiving surface before reaching the main excitation region. It is considered to be determined by a total of three root mean squares. The minority carrier diffusion length has completely different values depending on the depth of the pn junction surface, the carrier doping concentration, and the type of substrate. In evaluating a solar cell, the minority carrier diffusion length of the substrate is unknown in most cases. It is regarded as 0 in the selection of the excitation light spot size in the form. Since the texture produces scattering that is well approximated by Lanhart's law, the size at which the spots are diffused is comparable to 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. 1 are designated by the same reference numerals. In FIG. 2, the solar cell 201 is a backside passivation (PERC) type silicon crystalline solar cell, in which the front surface side of a p-type silicon substrate 203, which is a p-type doped crystalline silicon wafer, is a light receiving surface, and the front surface side is a textured structure. A silicon nitride (SiN) film 205 is coated 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. Further, in the texture structure of the n ⁺ diffusion layer 204 and the SiN film 205, a plurality of electrodes 202 are formed in parallel with each other by firing penetration. The electrode 202 is an electrode made of silver (Ag) having a rectangular flat surface, and has an electrode width orthogonal to the longitudinal direction (direction orthogonal to the paper surface of FIG. 2) of 0.1 mm as an example, and two adjacent electrodes. The distance in the width direction (distance between electrodes) is 1.8 mm.

For example, an aluminum oxide film 206 is formed as an insulating film on the back surface side of the p-type silicon substrate 203 as a passivation film. In the aluminum oxide film 206, for example, a groove having a width of 0.1 mm is dug at 1 mm intervals, and an aluminum (Al) paste is applied from the groove and then heat-treated to form a BSF in which Al and Si are alloyed in this groove portion. A mold electrode 207 is formed. On the other hand, an electrode 208 made of Al is formed on the aluminum oxide film 206 other than the groove. Therefore, the BSF type electrode 207 and the Al electrode 208 are joined at an interval of 1 mm. Further, the electrodes 202 on the front surface side and the BSF type electrode 207 on the back surface side both have the same electrode width as 0.1 mm, but the distance between the two adjacent electrodes in the width direction (distance between the electrodes) is the electrode. 202 is different from 1.8 mm and electrode 207 is different from 1.0 mm. The size of the solar cell 201 is 156 mm in width × 156 mm in depth × 0.2 mm in 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 device 100 of FIG. 1, the flowcharts of FIGS. 3 and 4 and the wavelength vs. internal quantum efficiency characteristics of FIG. Will be described in detail with reference to. This embodiment is characterized by the processing after step S11 in FIG. 3, but in steps S1 to S10 before that, the factors of performance deterioration are isolated by the quantum efficiency spectrum measurement. Therefore, first, the evaluation device 100 measures the quantum efficiency spectrum of the solar cell 201 with the solar cell 201 placed on the sample table 117 (step S1 in FIG. 3). Further, in step S1, the quantum efficiency spectrum is measured in the same manner for the reference sample in advance.

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. 1, is made parallel light by the lens 102, passes through an optical chopper 103 having a chopping frequency of 81 Hz, and is sent to the spectroscope 104. The incident light is incident, and is produced as monochromatic excitation light having a desired wavelength λ by control from the PC 124, and subsequently shaped into a desired spot size by the aperture 106. The optical path of the monochromatic excitation light emitted from the aperture 106 is split into two by the beam splitter 107, one 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 reflected by the solar cell. It is incident on 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 through the opening of the integrating sphere 109, reflected again on the inner wall surface of the integrating sphere 109, and then condensed and integrated. It is derived from another opening of the sphere 109 and incident on 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 the 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. Further, the lock-in amplifier 123 outputs a DC voltage corresponding to the optical current I output by the solar cell 201 according to the 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-mentioned equation (2).

In step S1, the quantum efficiency spectrum of the solar cell 201 is measured by irradiating a certain point on the light receiving surface side of the solar cell 201 with excitation light having a spot size of 1 mm while varying the wavelength in the range of 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, the reference sample is the BSF type in which the All electrode is formed on the BSF layer, which is the same as the PERC type except that the back surface structure does not have a passivation film as compared with the PERC type solar cell 201. It is a solar cell. The BSF type solar cell used as a reference sample is a high quality sample showing an energy conversion efficiency of 19.3%, which is close to the value expected in the design.

FIG. 5 shows the wavelength vs. internal quantum efficiency characteristics of the PERC type solar cell and the reference sample. In FIG. 5, the solid line characteristic a shows the wavelength vs. internal quantum efficiency characteristic of the PERC type solar cell 201, and the broken line characteristic b shows the wavelength vs. internal quantum efficiency characteristic of the reference sample. The internal quantum efficiency is calculated 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 shows the same or better characteristics as the characteristic b in the other wavelength range. .. From this, it can be estimated that the PERC type solar cell 201 having the characteristic a has a high recombination speed of a minority carrier on the back surface side. From the evaluation of the spatially averaged characteristics based on this measurement result, the wavelength selection at the time of the imaging measurement shown below is performed.

Next, the PC 124 of the evaluation device 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 the set value in the entire measurement wavelength range from 300 nm to 1250 nm. (Step S2 in FIG. 3). If the quantum efficiency is equal to or higher than the reference sample or design value in the entire measurement wavelength range, the open circuit voltage and short-circuit current of the solar cell 201 should be at the reference values, and the resistance is a factor of performance deterioration. It has become. Therefore, in this case, it can be estimated that the cause is defective electrodes or high resistance of 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 the quantum efficiency is low over the entire measurement wavelength range (step S4 in FIG. 3). In a Si-based solar cell such as the solar cell 201, the excitation wavelength is generally about 98 ± 2% at 500 nm to 750 nm, and there is almost no wavelength dependence. This is because the penetration depth of the excitation light into the silicon substrate is close to the depth of the pn junction of the solar cell, so that almost all the photoexcited carriers reach the pn junction. The internal quantum efficiency at this time is almost equal to the carrier recovery efficiency by the electrode. If 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 poor formation of the np junction and a decrease in the carrier recovery rate due to the short circuit of the np junction occur. Quantum efficiency is low over the entire measurement wavelength range. A similar low quantum efficiency spectrum is observed in the entire measurement wavelength range even when the recombination in the p-type silicon substrate 203 is extremely fast regardless of the 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 device 100 re-junctions the n ⁺ diffusion layer 204 and the p-type silicon substrate 203 at the pn junction. It is evaluated as a bond, a short circuit, or low quality in the Si crystal, and a treatment for the countermeasure is performed (step S5 in FIG. 3).

The process of step S5 will be further described together with the flowchart of FIG. 4C. The pn junction can be obtained by forming the n ⁺ diffusion layer 204 by ion diffusion or ion implantation after creating the texture structure of the solar cell surface, but especially in the ion implantation, the amount of implantation is insufficient or the heat treatment is insufficient due to the shadow of the texture shape. As a result, the junction is poorly formed, 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, and the surface of the solar cell 201 is laterally 4 mm × 7 mm in width. The PC 124 controls the stepping motors 118 and 119 to move the sample table 117 in the x-axis direction and the y-axis direction so that the excitation light spots sequentially come on the measurement points set at a pitch of 10 μm or less and 10 μm or less in the vertical direction. The internal quantum efficiency and reflectance are measured based on the signals from the lock-in amplifiers 121 to 123 while moving intermittently (step S51). Hereinafter, the measurement by the intermittent movement of the sample table 117 and the solar cell 201 will be referred to as a mapping measurement.

Subsequently, the PC 124 calculates the internal quantum efficiency of each measurement point at the irradiation light wavelength based on the measurement result in step S51 (step S52), and determines a region where the internal quantum efficiency is low from the calculation result (step). S53). Then, when the region having low internal quantum efficiency corresponds to the texture structure, measures are taken to reduce the influence of the shadow due to the texture (step S54). For example, the angle and rotation conditions at the time of ion injection are changed to improve the spatial uniformity along the xy plane of the pn junction, that is, the light receiving surface. On the other hand, when the region where the internal quantum efficiency is low is uniform, the process that affects how the doped substance is distributed in the depth direction, that is, in the direction perpendicular to the light receiving surface, due to changes in the ion implantation amount and heat treatment. The ion implantation amount and the heat treatment are optimized to improve the above conditions (step S55).

It will be described back to FIG. When the PC124 determines in step S4 that the quantum efficiency of the solar cell 201 is not lower than that of the reference sample (there is also a higher wavelength) in the entire wavelength range measured, 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 or the design value, if there is a significantly low wavelength region, the factor of performance deterioration can be estimated from that wavelength. That is, when the quantum efficiency of the excitation wavelength of 500 nm or less is low, the photoexcited carriers are concentrated closer to the surface side, which is the light receiving surface, than the pn junction surface, so that the surface due to the defect of the passivation film (that is, SiN film 205) on the surface side. It is evaluated that the recombination is fast and the carrier has not reached the pn junction surface (step S7).

Further, when 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 to the light receiving surface side. Therefore, if the quantum efficiency in this region is low, the p-type silicon The rapid 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. 4 (A). First, the 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 are set at a pitch of 1 cm or less in the horizontal direction and 1 cm or less in the vertical direction. Mapping measurement of quantum efficiency and reflectance is performed (step S81). Subsequently, the PC 124 calculates the internal quantum efficiency of each measurement point at the irradiation light wavelength based on the measurement result in step S81 (step S82), and determines a region having low quantum efficiency from the calculation result (step S83). ).

Here, in the case of single crystal silicon, when a structure rotationally symmetric with respect to the center of the crystal is observed, and in the case of polycrystalline silicon, a mottled pattern corresponding to the size of crystal grains is observed, in the p-type silicon substrate 203. Carrier recombination reduces the performance of solar cells. Therefore, in step S83, when the region having low internal quantum efficiency shows a structure peculiar to the silicon crystal such as a region concentric with respect to the center of the solar cell, it is considered to be a recombination due to low quality of the silicon crystal. Evaluate (step S84). On the other hand, when the region with low internal quantum efficiency does not show the above-mentioned structure peculiar to the silicon crystal, it is evaluated that the cause of the deterioration of 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 in which electrodes are not formed, a spatial distribution map of carrier life can be obtained by the μPCD method or the like, but in solar cells in which electrodes are already formed, the electrode region is used for the same evaluation. It is very difficult because it is necessary to devise a way to prevent photoexcitation. On the other hand, in the present embodiment, the internal quantum efficiency is selected as the amount to be measured by mapping, and the spatial resolution is reduced to about 1 cm to visualize the spatial non-uniformity of quality in a large-area solar cell.

This will be described by returning to FIG. When the PC124 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, it is evaluated that the solar cell 201 of the sample has a light confinement defect ( 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 reflected and absorbed many times in the solar cell, so that the non-uniformity in the depth direction of the photoexcited carriers disappears. , There is no wavelength dependence. In this wavelength region, the more times multiple reflections of excitation light are performed by light confinement, the longer the tail of the quantum efficiency spectrum to the longer wavelength. If the quantum efficiency in this wavelength region is low, the optical confinement structure may be defective.

The evaluation of step S9 will be further described with reference to the flowchart shown in FIG. 4 (B). 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 is 10 μm wide × 10 μm long or more in the horizontal direction. The reflectance mapping measurement of the measurement points set at a pitch of 10 μm or less in the vertical direction 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 of each measurement point in step S91 corresponds to or is uniform with the grain boundary (step S92), and the change in reflectance is crystallized. When it is determined that it corresponds to the grain boundary, it is evaluated that the deterioration in the performance of the solar cell is due to the influence of anisotropy due to the crystal orientation (step S93). Since such changes are likely to occur in the chemical process using potassium hydroxide solution, we will consider adopting a process that is less affected by the plane orientation, such as a mixture of phosphoric acid and nitric acid and plasma etching. On the other hand, when it is determined that the reflectance is uniform, the texture design / conditions are reviewed (step S94).

This will be described by returning to FIG. 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 around 900 nm, that is, 750 nm or more and 1100 nm or less, the solar cell 201 is on the back surface side as shown in FIG. It is determined that recombination of the minority carriers has occurred in (step S10), and the following processing specific to the present invention is performed. Since photoexcited carriers begin to be generated near the back surface of the solar cell at an excitation wavelength of 900 nm to 1000 nm, if the quantum efficiency in this wavelength region is low, rapid minority carrier recombination due to a passivation film defect 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 surface structure (step S11), and in the case of a solar cell having a uniform back surface such as the All-BSF type, the back surface process is improved (step S11). Step S12). On the other hand, if there is a back surface side structure such as a PERC type solar cell, it is determined whether or not there is a front surface electrode (step S13), and if there is no front surface electrode, the spot size of the excitation light is set to about the substrate thickness by the throttle 106. (Step S14) If there is a surface electrode, the spot size of the excitation light is set to twice or more the electrode width and as close as possible to the substrate thickness by the throttle 106 (step S15). Here, the smaller the spot size of the excitation light in the mapping measurement, the better the spatial resolution, but the spatial resolution in the evaluation of the back surface structure is the minority carrier diffusion in the direction parallel to the surface of the substrate and the texture structure on the front surface side. Due to the influence of the bleeding of the excitation light spots, which is about the thickness of the substrate, it does not improve more than a certain level.

Since it is difficult to increase the excitation power with a small spot size, and because the S / N ratio decreases when the spot size is made smaller than necessary, in the present embodiment, when the solar cell has a back surface structure but no front 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 located on the front surface side of the solar cell having a back surface structure like the solar cell 201 shown in FIG. 2, the larger the spot size, the more the influence of the electrode 202 on the front surface side can be averaged and suppressed. Therefore, in the present embodiment, in step S15 above, the spot size of the excitation light is set to be at least twice the electrode width in order to suppress the influence of the electrode 202, and after satisfying this condition, the spot size is set as close as possible to the substrate thickness. To do. As described above, the spot size determined in step S15 is sufficiently affected by the excitation light incident from the front surface side of the solar cell to be evaluated, and the back surface side structure is practically sufficient without being affected by the front surface side structure of the solar cell. It is an observable size.

Here, since the solar cell 201 is of the PERC type shown in FIG. 2 and has an electrode 202 on the front surface side and an electrode 207 on the back surface side, the spot size of the excitation light is set to 2 of the electrode width by step S15. The value is more than doubled 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, 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, which is more than twice as large and is the closest to the substrate thickness.

Subsequently, the PC 124 sets the wavelength λ of the excitation light of the spot size determined in step S14 or step S15 to 750 nm or more and 1100 nm or less by controlling the spectroscope 104, and in the example, 950 nm, and is lateral to the surface of the solar cell 201. 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 for a range of 1 mm x 1 mm or more in the vertical direction. In the embodiment, the range of 4 mm in the horizontal direction x 7 mm in the vertical direction is 0. 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 S16). Then, the PC 124 calculates the internal quantum efficiency by the above equation (2) based on the quantum efficiency mapping measurement value, and calculates the reflectance by the above equation (1) based on the reflectance mapping measurement value (step S17). .. 6 and 7 show an example of the internal quantum efficiency and reflectance calculated in step S17.

FIG. 6 shows a scale 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 a region between electrodes having low internal quantum efficiency, and the internal quantum efficiency at the excitation light wavelength of 950 nm is almost uniform in the x-axis direction, and the electrodes of the electrode 207 on the back surface side in the y-axis direction. Regions with high internal quantum efficiency and regions with low internal quantum efficiency appear alternately at intervals of 1 mm, which is an interval. That is, although FIG. 6 is a diagram of the internal quantum efficiency from the front surface side (light receiving surface), the change in the internal quantum efficiency due to the structure on the back surface side excluding the feature of the electrode 202 on the front surface side is the display 125 and the printing press 126. Is visualized by. As described above, FIG. 6 shows that the internal quantum efficiency of the solar cell 201 at the excitation light wavelength of 950 nm is influenced by the electrode 207 on the back surface side.

FIG. 7 shows a shade 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 having low reflectance, the reflectance at the excitation light wavelength of 950 nm is almost uniform in the x-axis direction, and between the electrodes of the electrodes 202 on the surface side in the y-axis direction. Areas with high reflectance and areas with low reflectance appear alternately at intervals of 1.8 mm, which is a distance. As described above, 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 (1200 nm in the example) to perform the reflectance mapping measurement of each of the 20 × 70 measurement points described above. (Step S18). Then, in a region where the internal quantum efficiency calculated in step S17 is lower than a 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 shade 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 the reflectance is not increased by the electrode 202 on the surface side. This is because the incident light is not absorbed by the p-type silicon substrate 203 at this wavelength of 1200 nm, so that the structure on the back surface side can be seen through. This is because the region where the electrode 207, which is the alloy layer on the back surface side, absorbs, looks darker than the insulating film region which shows high reflectance due to total reflection. That is, FIG. 8 shows that the structure on the back surface side of the electrode 207 and the like can be observed by the reflectance measured using the excitation light having a wavelength of 1200 nm.

When the PC124 determines in step S19 that the reflectance is higher than the set value, it determines that the conductivity of the aluminum oxide film 206 that functions as the passivation film on the back surface side is higher than the design value, and reviews the film forming conditions. (Step S20). On the other hand, when the PC124 determines in step S19 that the reflectance is equal to or less than the set value, it 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 the electrode 207 is poorly formed. The firing conditions of the layer are reviewed (step S21). At the time of determination in steps S20 and S21, it is necessary to eliminate the influence of the electrode 202 on the surface as seen by the reflectance measured by the excitation light having a wavelength of 1100 nm or less (950 nm in the example).

As described above, according to the solar cell evaluation device 100 of the present embodiment, the solar cell 201 to be evaluated can be moved in the biaxial direction of the horizontal plane with high accuracy in the measurement system capable of measuring the internal quantum efficiency with high accuracy. If the quantum efficiency measured by combining the stand 117 and irradiating a point on the light receiving surface side of the solar cell 201 with excitation light having a spot size of 1 mm is lower than that of the reference sample at a certain wavelength, the reason is that. It is judged that this is due to the influence of the back surface side structure, and the solar cell is irradiated with excitation light whose spot size is at least twice the width of the front 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. Therefore, it is possible to perform non-destructive evaluation of the back surface side structure of the solar cell on which the electrodes are already formed, which is difficult to measure the photoexcited carrier lifetime, and to promote the optimization of the manufacturing process.

Further, according to the solar cell evaluation device 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 of 950 nm and performing mapping measurement, and absorption into the silicon substrate. Based on the reflectance obtained by irradiating a silicon-based solar cell with excitation light having a wavelength of 1200 nm and measuring the mapping, the aluminum oxide film 206 having a back surface structure and the electrode 207 which is an alloy layer can obtain the efficiency as designed. Can be evaluated.

The present invention is not limited to the above embodiments. For example, the quantum efficiency spectrum of the reference sample may be substituted with the quantum efficiency spectrum of the solar cell to be evaluated that has not failed, or in design. A theoretically obtained quantum efficiency spectrum may be used instead. Further, although the internal quantum efficiency and the reflectance are visualized as a shading plot in FIGS. 6 to 8, they can also be visualized by using contour lines.

The present invention also includes a program for evaluating a solar cell in which the operation of the flowchart shown in FIGS. 3 and 4 is executed by the PC 124. The solar cell evaluation program may be distributed via a communication network and downloaded to the execution program storage memory of PC124 (assumed to be in the block of PC124 in FIG. 1), or may be reproduced from a recording medium. It may be downloaded to the above memory, and the download method does not matter.

The present invention relates to single crystal silicon, polycrystalline silicon, amorphous silicon, gallium arsenic single crystal, indium gallium arsenic single crystal, gallium phosphorus single crystal, indium gallium phosphorus single crystal, germanium single crystal, chalcopyrite-based I-III-VI group. A solar cell composed of at least one of a compound, a perovskite compound, cadmium tellurium, zinc oxide, titanium oxide, tin oxide, and a silicon germanium single crystal can be evaluated as a solar cell to be evaluated. Very widespread and useful.

100 Solar cell evaluation device 101 White light source 102 Lens 103 Optical chopper 104 Spectrometer 105 Dark box 106 Aperture 107 Beam splitter 108, 110 Parabolic mirror 109 Integrating sphere 111 Excitation light sensor 112 Reflected light sensor 113, 114, 115 Current-voltage conversion Instrument 116 Lab Jack 117 Sample Base 118, 119 Stepping Motors 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)

The light receiving surface of the solar cell placed on the movable sample table is irradiated with excitation light whose wavelength and spot size can be arbitrarily changed, and the photoelectric conversion signals of the reflected light from the solar cell and the excitation light are obtained. A method for evaluating a solar cell, which obtains an evaluation result of the solar cell based on the light and the output signal of the solar cell.
An optical control step 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 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 table with the excitation light whose spot size is controlled by the light control step. An evaluation step for evaluating the back surface structure of the solar cell opposite to the light receiving surface based on the spatial distribution of quantum efficiency, and
A method for evaluating a solar cell, which comprises. A light irradiation step of irradiating a light receiving surface of a solar cell placed on a sample table that can move a horizontal plane by a specified distance in a biaxial direction with excitation light having a wavelength and a spot size controlled to desired values.
The excitation light is based on the reflected light obtained by being 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 output signal of the surface electrode. Then, the excitation light intensity, the total reflected light intensity, and the light current are measured, and the internal quantum efficiency and the reflectance of the solar cell are calculated from the measurement results.
Evaluation result of the solar cell based on the internal quantum efficiency and reflectance by the calculation step obtained from the measurement results of each of the plurality of measurement points on the light receiving surface of the solar cell and the wavelength of the excitation light. Including evaluation steps to get
In the light irradiation step, the excitation light is subjected to the light receiving surface in which the spot size of the excitation light is controlled to be at least twice the electrode width of the surface electrode and a value as close as possible to the substrate thickness of the solar cell. Irradiate to
The evaluation step is a method for evaluating a solar cell, characterized in that the back surface structure of the solar cell opposite to the light receiving surface is evaluated. The light irradiation step controls the wavelength of the excitation light to a first wavelength at which an internal quantum efficiency lower than the internal quantum efficiency of the reference sample can be obtained or a second wavelength at which the substrate of the solar cell looks 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 is at the first wavelength, and the said. When the excitation light is at the second wavelength, the back surface structure of the solar cell is evaluated by using the second reflectance calculated by the calculation step based on the measurement results of the plurality of measurement points. 2. The method for evaluating a solar cell according to claim 2. The light receiving surface of the solar cell placed on the movable sample table is irradiated with excitation light whose wavelength and spot size can be arbitrarily changed, and the photoelectric conversion signals of the reflected light from the solar cell and the excitation light are obtained. An evaluation device for a solar cell that obtains an evaluation result of the solar cell based on the light and the output signal of the solar cell.
An optical 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 a plurality of measurement points on the light receiving surface of the solar cell placed on the sample table with the excitation light whose spot size is controlled by the light control means. An evaluation means for evaluating the back surface structure of the solar cell opposite to the light receiving surface based on the spatial distribution of quantum efficiency, and
An evaluation device for a solar cell, which comprises. A sample table on which a solar cell is placed and which can move a horizontal plane parallel to the surface of the solar cell by a specified distance in the biaxial direction,
A moving mechanism for moving the sample table and
A light irradiation means for generating excitation light in which the wavelength and the spot size on the light receiving surface of the solar cell are controlled to desired values and irradiating the light receiving surface of the solar cell.
The irradiated excitation light is based on the 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 output signal of the surface electrode. , A calculation means for measuring the excitation light intensity, the total reflected light intensity, and the light current, and calculating the internal quantum efficiency and the reflectance of the solar cell from the measurement results.
A drive control means for driving and controlling the movement mechanism to move the sample table so that the spot of the excitation light sequentially positions a plurality of measurement points on the light receiving surface of the solar cell.
An 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 the spot size of the excitation light to be at least twice the electrode width of the surface electrode and a value as close as possible to the substrate thickness of the solar cell.
The evaluation means is a solar cell evaluation device for evaluating the back surface structure of the solar cell on the side opposite to the light receiving surface. The light irradiation means controls the wavelength of the excitation light to a first wavelength at which an internal quantum efficiency lower than the internal quantum efficiency of the reference sample can be obtained or a second wavelength at which the substrate of the solar cell looks substantially transparent. ,
The evaluation means includes the first internal quantum efficiency and the first reflectance calculated by the calculation means based on the measurement results of the plurality of measurement points when the excitation light is at the first wavelength, and the said. When the excitation light is at the second 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. 5. The solar cell evaluation device according to claim 5. The light receiving surface of the solar cell placed on the movable sample table is irradiated with excitation light whose wavelength and spot size can be arbitrarily changed, and the photoelectric conversion signals of the reflected light from the solar cell and the excitation light are obtained. This is a solar cell evaluation program that causes a computer to evaluate a solar cell that obtains the evaluation result of the solar cell based on the output signal of the solar cell and the output signal of the solar cell.
On the computer
An optical control function that controls the spot size of the excitation light to be 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 table with the excitation light whose spot size is controlled by the light control function. An evaluation function that evaluates the back surface structure of the solar cell on the side opposite to the light receiving surface based on the spatial distribution of quantum efficiency.
A program for evaluating solar cells, which is characterized by the realization of. The light receiving surface of the solar cell placed on the movable sample table is irradiated with excitation light whose wavelength and spot size can be arbitrarily changed, and the photoelectric conversion signals of the reflected light from the solar cell and the excitation light are obtained. This is a solar cell evaluation program that causes a computer to evaluate a solar cell that obtains the evaluation result of the solar cell based on the output signal of the solar cell and the output signal of the solar cell.
On the computer
A light irradiation function that irradiates the light receiving surface of the solar cell placed on the sample table with excitation light whose wavelength and spot size are controlled to desired values, respectively.
The excitation light is based on the reflected light obtained by being 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 output signal of the surface electrode. A calculation function for calculating the internal quantum efficiency and reflectance of the solar cell from the measurement results of the excitation light intensity, the total reflected light intensity, and the light current measured in
Evaluation result of the solar cell based on the internal quantum efficiency and reflectance by the calculation function obtained from the measurement results of each of the plurality of measurement points on the light receiving surface of the solar cell and the wavelength of the excitation light. Realize the evaluation function and obtain
The light irradiation function controls the spot size of the excitation light to be at least twice the electrode width of the surface electrode and a value as close as possible to the substrate thickness of the solar cell. Irradiate to
The evaluation function is a solar cell evaluation program characterized in that the back surface structure of the solar cell opposite to the light receiving surface is evaluated.

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