JP2002280583A - Method for evaluating performance of hybrid thin film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for accurately evaluating the performance of a hybrid thin film solar cell which can be displayed under natural sunshine, using a solar simulator. SOLUTION: According to the method for evaluating the performance of the hybrid thin film solar cell having an amorphous silicon type photoelectric conversion unit and a crystalline silicon type photoelectric conversion unit laminated one above the other at a light incident side, the ratio of maximum peak intensity in a wavelength range of 800-900 nm to maximum peak intensity in the wavelength range of 450-500 nm in a spectrum distribution of pseudo sunshine composed of a single xenon lamp type solar simulator in Class A in the JIS standard and an additional filter having a transmittance of 70% or more in the long wavelength range of 400-700 nm and a minimum transmittance of 10% or less in the wavelength range of 800-900 nm ranges from 0.5 to 2.0 and the performance of the solar cell is evaluated from the value of output power, based on irradiation with the pseudo sunshine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thin-film solar cell, and more particularly, to a method for evaluating the performance of a hybrid thin-film solar cell.

[0002]

2. Description of the Related Art In recent years, thin-film solar cells have been diversified, crystalline thin-film solar cells have been developed in addition to conventional amorphous thin-film solar cells, and hybrid thin-film solar cells obtained by laminating these have been put into practical use. .

In general, a semiconductor thin-film solar cell comprises a first electrode, a first electrode and a second electrode which are sequentially laminated on at least a surface of an insulating substrate.
The semiconductor thin-film photoelectric conversion unit described above and the second electrode are included. Then, one photoelectric conversion unit includes an i-type layer sandwiched between a p-type layer and an n-type layer.

[0004] The i-type layer that occupies most of the thickness of the photoelectric conversion unit is a substantially intrinsic semiconductor layer, and the photoelectric conversion action mainly occurs in the i-type layer. Therefore, it is preferable that the i-type photoelectric conversion layer is thicker for light absorption.

On the other hand, the p-type or n-type conductive layer plays a role of generating a diffusion potential in the photoelectric conversion unit, and one of the important characteristics of the thin-film solar cell depends on the magnitude of the diffusion potential.
The value of the open-circuit voltage, which is one of the two, is affected. However, these conductive type layers are inactive layers that do not directly contribute to photoelectric conversion, and light absorbed by impurities doped in the conductive type layers is a loss that does not contribute to power generation. Therefore, it is preferable that the p-type and n-type conductive layers be as thin as possible within a range where a sufficient diffusion potential is generated, and have a much smaller thickness than the i-type layer.

For this reason, a photoelectric conversion unit or a thin-film solar cell has an i-type which occupies a major part thereof regardless of whether the p-type and n-type conductive layers contained therein are amorphous or crystalline. An amorphous photoelectric conversion layer is called an amorphous unit or an amorphous thin film solar cell, and an i-type layer having a crystalline photoelectric conversion layer is called a crystalline unit or a crystalline thin film solar cell.

As a method of improving the conversion efficiency of a thin-film solar cell, there is a method of stacking two or more photoelectric conversion units to form a tandem type. In this method,
A front unit including a photoelectric conversion layer having a large band gap is arranged on the light incident side of a thin-film solar cell, and a small band gap (for example, Si-G
By arranging a rear unit including a photoelectric conversion layer (such as an e-alloy), photoelectric conversion can be performed over a wide wavelength range of incident light, thereby improving the photoelectric conversion efficiency of the entire solar cell. Among such tandem-type thin-film solar cells, those that include both an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit are particularly referred to as hybrid thin-film solar cells.

For example, the wavelength of light that can be photoelectrically converted by amorphous i-type silicon is up to about 800 nm on the longer wavelength side, whereas crystalline i-type silicon is about 110 nm longer than that.
It is possible to photoelectrically convert light having a wavelength of about 0 nm. Here, the amorphous silicon photoelectric conversion layer having a large light absorption coefficient requires a thickness of 0.3 μm or less for a single photoelectric conversion unit to absorb light. In order to sufficiently absorb long-wavelength light, the silicon photoelectric conversion layer needs to be 2 in the case of a single photoelectric conversion unit.
It preferably has a thickness of about 3 μm or more. That is, it is generally desired that the crystalline photoelectric conversion layer has a thickness that is about 10 times as large as that of the amorphous photoelectric conversion layer. However, in hybrid type thin film solar cells,
Each photoelectric conversion layer can be made relatively thin as compared with the case of a single unit.

[0009]

When a thin film solar cell is shipped from a factory, the light quantity of a single-lamp solar simulator having a spectrum distribution of class A according to JIS is generally measured using a standard cell having a reference output performance. After adjusting,
The output performance of the solar cell is evaluated under the light irradiation.
Products that do not satisfy the specified output performance are excluded from shipment as defective products. Such a single lamp solar simulator includes a single xenon lamp and an air mass filter.

According to the JIS standard, regarding the energy distribution for each light wavelength division of the solar simulator, a solar simulator for measuring bulk crystal solar cells (JIS C 891).
3) and a solar simulator for measuring an amorphous thin-film solar cell (JIS C 8933) are separately specified. However, most of the commercially available solar simulators satisfying the grade A of the JIS standard generally satisfy the grade A for both the standards of the bulk crystal solar cell and the amorphous thin film solar cell. As such a solar simulator, for example, there is a solar simulator SUN-130i manufactured by Spire, USA.

However, such a solar simulator 1
When the performance of a hybrid thin-film solar cell is evaluated using 30i, even among solar cells that are evaluated to meet the performance standards that can be shipped, the expected performance is exhibited under actual sunlight outdoors. The present inventor has found that some of these are not included.

Accordingly, an object of the present invention is to provide a performance evaluation method that can more accurately predict the performance that a hybrid thin-film solar cell can exhibit under actual sunlight outdoors using a solar simulator. I have.

[0013]

According to the present invention, there is provided an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit which are sequentially stacked from the light incident side, and the amorphous photoelectric conversion unit is mainly composed of 400 to 400 nm. The crystalline photoelectric conversion unit is mainly responsible for the photoelectric conversion action in the wavelength range of 800 nm.
In a method for evaluating the performance of a hybrid thin-film solar cell having a photoelectric conversion effect in a wavelength range of
The solar cell is illuminated with simulated sunlight obtained by using a xenon single-lamp solar simulator having a spectrum distribution of Class A in IS standard and an additional filter, and the additional filter has a wavelength range of 400 to 700 nm. At 70%
In addition to having the above transmittance, the minimum value has a transmittance of 10% or less in the wavelength range of 800 to 900 nm, and the spectral distribution of the simulated sunlight radiated to the solar cell has the wavelength range of 450 to 500 nm. The ratio of the highest peak intensity in the wavelength range of 800 to 900 nm to the highest peak intensity is in the range of 0.5 to 2.0. It is characterized in that the performance of the battery is evaluated.

Incidentally, such an additional filter can be formed by using a film having a multilayer structure including a plurality of high refractive index layers and a low refractive index layer.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION First, the present inventor has found that a solar cell which is evaluated to satisfy a performance standard that can be shipped based on measurement using a solar simulator 130i can be used outdoors under actual sunlight. In order to clarify the causes that may include those that cannot perform the intended performance, the solar simulator 130
The spectral distribution of the simulated sunlight irradiated from i was examined in detail. The result is shown in the graph of FIG.

In the graph of FIG. 2, the horizontal axis represents the wavelength (n
m), and the vertical axis indicates the light intensity of each spectrum (arbitrary unit)
Is represented. As observed in this graph,
An abnormally high intensity peak based on the xenon emission line exists within the wavelength range of 800 to 900 nm.

On the other hand, in a hybrid thin-film solar cell, it is difficult to manufacture the hybrid photoelectric conversion unit with good reproducibility so that the relation between the amorphous photoelectric conversion unit and the crystalline photoelectric conversion unit included in the hybrid thin-film solar cell is exactly the same. That is, depending on the manufacturing lot, the ratio of the thickness of the amorphous unit to the thickness of the crystalline unit may be slightly changed, or the crystal quality of the photoelectric conversion layer in the crystalline unit may be changed.

By the way, as described above, the amorphous unit can photoelectrically convert light having a long wavelength of about 800 nm, while the crystalline unit photoelectrically converts light having a long wavelength of about 1100 nm. be able to. Therefore, in a hybrid thin film solar cell, about 80
Light having a wavelength up to about 0 nm is mainly photoelectrically converted by the front amorphous unit, and light having a wavelength longer than about 700 nm is mainly photoelectrically converted by the rear crystalline unit.

In such a situation, a conventional amorphous thin-film solar cell including only a single amorphous unit has a structure shown in FIG.
The performance is evaluated using a solar simulator having a spectrum distribution as shown in FIG.
High intensity peaks in the nm wavelength range had little effect on the performance evaluation. However, in a hybrid thin-film solar cell, the 800-900
High intensity peaks in the nm wavelength range will directly affect the output of the crystalline unit. Therefore, in the hybrid thin-film solar cell, based on the fact that the thickness and crystalline quality of the crystalline unit contained in it vary slightly from production lot to production lot, the performance evaluated by the solar simulator and the actual outdoor sunlight It is considered that the performance that can be exhibited is sometimes deviated to a degree that cannot be ignored.

The present inventor has conceived of evaluating the performance of a hybrid thin-film solar cell by using a filter having a light-transmitting characteristic as shown in the graph of FIG. 1 in combination with a solar simulator 130i. Was. In this graph, the horizontal axis represents wavelength (nm), and the vertical axis represents light transmittance (%). That is, FIG.
Has a transmittance of 70% or more in a wavelength range of 400 to 700 nm, and has a transmittance of 8% with a minimum value of 10% or less in a wavelength range of 800 to 900 nm. This is because the purpose is to relatively lower the extraordinarily high maximum peak intensity in the wavelength range of 800 to 900 nm compared to the maximum peak intensity in the wavelength range of 400 to 700 nm.

The filter having the light-transmitting characteristics as shown in FIG. 1 can be formed using a film having a multilayer structure including a plurality of high refractive index layers and low refractive index layers. For example, high refractive index layers are TiO ₂ , Al ₂ O ₃ , S
It can be formed using iO ₂ or the like, and the low refractive index layer can be formed using MgF or CaF.

FIG. 3 is similar to FIG. 2 except that the filter having the light transmitting characteristics of FIG.
5 shows a spectrum intensity distribution in pseudo sunlight obtained by combining the above. From the comparison between FIG. 3 and FIG. 2,
It can be seen that by passing the simulated sunlight of the solar simulator 130i through the filter of FIG. 1, the abnormally high peak intensity within the wavelength range of 800 to 900 nm is appropriately reduced. The solar simulator 130
After passing the simulated sunlight of i through the additional filter, the ratio I2 / I1 of the highest peak intensity I2 in the wavelength range of 800 to 900 nm to the highest peak intensity I1 in the wavelength range of 450 to 500 nm is obtained. It is preferably in the range of 0.5 to 2.0. The reason is that if the peak intensity ratio I2 / I1 is smaller than 0.5, the output of the crystalline unit in the hybrid thin-film solar cell is estimated to be smaller than that under actual sunlight. This is because if the ratio I2 / I1 is larger than 2.0, the output of the crystalline unit in the hybrid thin-film solar cell will be largely estimated as compared with the actual sunlight.

Example As an example, the performance of a hybrid thin-film solar cell actually manufactured was evaluated by the method according to the present invention. These hybrid solar cells are manufactured in lots from 0 to 16, and in each of the lots, the amorphous unit is 270 nm thick and the crystalline unit is 1.9 μm thick. Was.

The lot numbers 0 to 1 thus produced
The performance of the hybrid thin-film solar cell No. 6 was evaluated by the conventional method and the method of the present invention. That is, in the conventional method, the performance was evaluated using only the solar simulator 130i, and in the method of the present invention, the performance was evaluated using the filter of FIG. 1 together with the solar simulator 130i. In other words, the simulated sunlight used in the conventional method has the spectral distribution of FIG. 2, and the simulated sunlight used in the method of the present invention has the spectral distribution of FIG. The result of the performance evaluation is shown in FIG. In this graph, the horizontal axis indicates the lot number of the hybrid thin-film solar cell whose performance was evaluated, and the vertical axis indicates the evaluation output (W) of those solar cells.

First, the performance of hybrid type thin film solar cells of all lot numbers was evaluated by the conventional method. The result is shown by the polygonal line A in the graph of FIG. According to the broken line A, the lot numbers 0 to 1
All six hybrid thin-film solar cells are evaluated as having an output exceeding 8.5 W specified as a shippable standard.

However, when the output of those solar cells was measured outdoors under the climate and weather where natural sunlight closest to the AM1.5 reference sunlight was obtained, lot numbers 0 to 9 and 11 to 16 were measured. Although the product with the output of 8.5W or more of the standard that can be shipped was obtained, the lot number 10
With respect to the product (1), only an output of 8.2 W was obtained.
This means that if the product of Lot No. 10 whose performance has been evaluated to satisfy the shippable standard by the conventional method is actually shipped, it is a defective product that cannot exhibit the expected performance under actual use conditions outdoors. Will be.

Next, the performance of the hybrid thin-film solar cells of all the lot numbers described above was evaluated by the method of the present invention. The result is shown by the polygonal line B in the graph of FIG. According to the broken line B, the hybrid type thin-film solar cells of lot numbers 0 to 9 and 11 to 16 are evaluated as having an output exceeding the dispatchable standard of 8.5 W. .
It is rated as an unsuitable product with an output of less than 5W. That is, it is clear that the performance evaluation method according to the present invention has higher reliability in quality control of the hybrid thin-film solar cell than the conventional method.

Further, for example, when attention is paid to the performance of the products of lot numbers 2 and 3, the lot number 2
It is evaluated that the output of the product No. 3 is slightly higher than that of the product No. 3, but in the method of the present invention, on the contrary, the product No. 2 has higher output performance than the lot No. 3. In other words, the performance evaluation method according to the present invention is expected to have higher accuracy than the conventional method, not only in the quality control of the hybrid thin-film solar cell according to the shipping standard, but also in the relative performance comparison between products of different lots. Can be done.

[0029]

As described above, according to the present invention, a performance evaluation that can more accurately predict the performance that a hybrid thin-film solar cell can exhibit under actual sunlight outdoors using a solar simulator. A method can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing light transmission characteristics of a filter that can be preferably used in a performance evaluation method of a hybrid thin-film solar cell according to one embodiment of the present invention.

FIG. 2 Solar simulator SUN- manufactured by Spire.
It is a graph which shows the spectrum distribution in 130i of simulated sunlight.

FIG. 3 is a graph showing a spectrum distribution in simulated sunlight when the filter of FIG. 1 is used in addition to the solar simulator 130i.

FIG. 4 is a graph showing the results of evaluating the output performance of hybrid thin-film solar cells manufactured in various lots by a conventional method and the method of the present invention.

Claims (2)

[Claims] 1. An amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit which are sequentially stacked from a light incident side, wherein the amorphous photoelectric conversion unit mainly performs a photoelectric conversion action in a wavelength range of 400 to 800 nm. A method for evaluating the performance of a hybrid thin-film solar cell in which the crystalline photoelectric conversion unit mainly performs photoelectric conversion in a wavelength range of 700 to 1100 nm, comprising: a xenon single-lamp solar simulator having a class A spectrum distribution according to JIS. And irradiating the solar cell with simulated sunlight obtained using an additional filter. The additional filter has a transmittance of 70% or more in a wavelength range of 400 to 700 nm, and 800 to 90.
In the wavelength range of 0 nm, the minimum value has a transmittance of 10% or less, and in the spectral distribution of the simulated sunlight irradiated on the solar cell, the maximum peak intensity in the wavelength range of 450 to 500 nm is 800 to A method in which the ratio of the highest peak intensity in the wavelength range of 900 nm is in the range of 0.5 to 2.0, and the performance of the solar cell is evaluated based on the magnitude of the output power based on the irradiation of the simulated sunlight. . 2. The method of claim 1, wherein the additional filter comprises a film having a multilayer structure including a plurality of high and low refractive index layers.