JP2008251799A - Solar battery and solar battery module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar battery that facilitates the entry of sunlight into a photoelectric conversion layer, and achieves high photoelectric conversion efficiency by confining light incident on the photoelectric conversion layer in the battery, and to provide a solar battery module. <P>SOLUTION: The index of the refraction of the photoelectric conversion layer 130 is set to be larger than that of a transparent conductive film 120. Thus, an entry into the side of the photoelectric conversion layer 130 is facilitated when light that entered the transparent conductive film 120 reaches the boundary of the photoelectric conversion layer 130. This enables the light incident on the photoelectric conversion layer 130 to be confined within the photoelectric conversion layer 130 as much as possible. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solar cell and a solar cell module using an optical waveguide as a substrate.

  In recent years, the spread of solar cells has been promoted as a renewable energy source with a low environmental load. In order to further increase the spread of solar cells, it is necessary to reduce the cost of solar cells, and to that end, it is indispensable to reduce manufacturing costs. In particular, with respect to silicon-based solar cells, it is an indispensable condition to reduce the material cost of a silicon substrate that occupies about 40% of the cost. As a means of reducing the material cost of silicon substrates, development of solar cells that reduce the amount of silicon used by using inexpensive materials other than silicon for the substrate and forming a silicon thin film on the substrate as a device Has been intensively studied.

  Further, as solar cells other than silicon-based solar cells, those using an organic film for the solar cell layer and those using a sensitizing dye have been studied. In such solar cells as well as silicon-based solar cells, it has been studied to reduce the amount of expensive organic films and sensitizing dyes used, and there is a method for producing a solar cell layer on an inexpensive substrate. It has been studied earnestly.

  An example of a conventional solar cell is shown in FIG. In the solar cell 900, a solar cell layer including an upper electrode (transparent conductive film) 902 that also serves as an antireflection film, a semiconductor film 901, and a lower electrode 903 that also serves as a reflection film is formed on a glass substrate 904. Has been. The solar cell 900 has a mechanism in which carriers are generated when the semiconductor film 901 absorbs sunlight, and the light energy is converted into electric energy by extracting the carriers to the outside with the electrodes 902 and 903. The upper electrode 902 is also provided with an auxiliary electrode 905.

  In the conventional solar cell 900 configured as described above, when the semiconductor film 901 is thin, the ratio of the irradiated sunlight transmitted without being absorbed by the semiconductor film 901 is increased. Only efficiency can be obtained.

  As a means for improving the photoelectric conversion efficiency, in the solar cell 910 described in Patent Document 1 shown in FIG. 6, the sunlight irradiated from an arbitrary direction is provided on the light receiving surface of the solar cell by providing a condensing unit. I try to irradiate. The solar cell 910 collects the sunlight incident on the semi-cylindrical light incident portion 913, sends it to the light guide path 912, and makes it enter the light receiving surface of the flat plate solar cell 911 from the light guide path 912. Yes.

  In the solar cell 910 having the above-described configuration, light incident from an arbitrary direction is configured to be collected by the light incident unit 913. Therefore, the direction of the light receiving surface is adjusted to be perpendicular to the irradiation direction. There is no need. Also, the sunlight received by the light incident portion 913 is sent to the light guiding path 912 and repeatedly incident on the light receiving surface of the flat plate solar cell 911, so that the light receiving efficiency of the solar cell 910 is improved.

  As another example of a conventional solar cell that improves the photoelectric conversion efficiency, a solar cell described in Patent Document 2 shown in FIG. 7 is also known. A solar cell 920 described in Patent Document 2 includes a thin film solar cell including a transparent conductive film 922, a photoelectric conversion layer 923, a transparent conductive film 924, and a first reflective layer 925 provided on one surface of a transparent substrate 921, and is transparent. A second reflection layer 926 and a condenser lens group 929 are provided on the other surface of the substrate 921.

In the solar cell 920 described in Patent Document 2, the light condensed by the condenser lens group 929 is incident on the transparent substrate 921 from the pinhole 927 provided in the second reflective layer 926, and this incident light is first reflected. It is configured to be confined between the layer 925 and the second reflective layer 926. In this manner, incident light is confined between the first reflective layer 925 and the second reflective layer 926, thereby increasing the amount of light applied to the thin film solar cell, thereby increasing the photoelectric conversion efficiency. .
JP 2000-22194 A JP 2003-46103 A

  However, in the conventional solar cell 900 as shown in FIG. 5, the conversion efficiency is such that light incident in a substantially film thickness direction is absorbed by the reflection film 903 until it is reflected once and emitted to the outside. Therefore, it is necessary to increase the thickness of the semiconductor film 901 in order to increase the photoelectric conversion efficiency. On the other hand, when the film thickness of the semiconductor film 901 is increased, the carrier trap probability in the meantime increases, which causes a decrease in photoelectric conversion efficiency. Therefore, in the conventional solar cell 900 as shown in FIG. 5, even if the thickness of the semiconductor film 901 is increased, the photoelectric conversion efficiency cannot be greatly improved. Moreover, since it is necessary to install a light-receiving surface perpendicular | vertical with respect to the incident direction of sunlight, there also exists a problem that a solar cell will enlarge.

  In the solar cell 910 described in Patent Document 1, specific characteristics such as a refractive index are not shown for the flat plate solar cell 911, the light guiding path 912, the light incident portion 913, and the like. It is not always possible to efficiently irradiate the light receiving surface 911. As an example, even if the light confined in the light guide path 912 is reflected by the light receiving surface of the flat plate solar cell 911 and returned to the light guide path 912 or is incident on the flat plate solar cell 911, it is not absorbed immediately. There is also a possibility that the rate of returning to the light guiding path 912 may be high.

  Furthermore, the solar cell 920 described in Patent Document 2 uses a large number of condensing lenses and is configured to be combined with a thin-film solar cell, but the focal point of the condensing lens coincides with the position of the pinhole 927. It is necessary to perform alignment with high accuracy. Since it is necessary to perform such alignment for each of a large number of lenses, there is a problem that the production efficiency is lowered and the cost is increased. Further, similarly to the solar cell 910 described in Patent Document 1, there is a possibility that incident light may be confined inside the transparent substrate 921 without being efficiently incident on the photoelectric conversion layer 923.

  Therefore, the present invention has been made to solve these problems, and makes it easy for the sunlight to enter the photoelectric conversion layer, and confine the light incident on the photoelectric conversion layer inside the photoelectric conversion layer to improve the photoelectric conversion efficiency. It aims at providing a high solar cell and a solar cell module.

  In the first aspect of the solar cell of the present invention, a transparent conductive film, a photoelectric conversion layer, and a reflective film are sequentially laminated on the surface excluding one end of the optical waveguide, and light incident from one end of the optical waveguide is A solar cell that performs photoelectric conversion by being absorbed by a photoelectric conversion layer, wherein a refractive index of the photoelectric conversion layer is larger than a refractive index of the transparent conductive film.

  Another aspect of the solar cell of the present invention is characterized in that the refractive index of the transparent conductive film is larger than the refractive index of the optical waveguide.

  Another aspect of the solar cell of the present invention is characterized in that a refractive index of the photoelectric conversion layer is at least one greater than a refractive index of the transparent conductive film.

  Another aspect of the solar cell of the present invention is characterized in that the photoelectric conversion layer has a refractive index of 3 or more.

  Another aspect of the solar cell of the present invention is characterized in that a condensing lens that condenses the light irradiated to one end of the optical waveguide and enters the optical waveguide is provided at one end of the optical waveguide. And

  Another aspect of the solar cell of the present invention is characterized in that the thickness of the photoelectric conversion layer is 100 times or less the diffusion length of carriers generated inside.

  A first aspect of the solar cell module of the present invention is characterized in that a plurality of the solar cells described above are arranged with the longitudinal direction of the optical waveguide aligned.

  As described above, according to the present invention, by making the refractive index of the photoelectric conversion layer larger than the refractive index of the transparent conductive film, it becomes easier for sunlight to enter the photoelectric conversion layer and also to enter the photoelectric conversion layer. It becomes possible to provide a solar cell and a solar cell module with high photoelectric conversion efficiency by confining the light inside.

  A solar cell and a solar cell module according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. In addition, about each structural part which has the same function, the same code | symbol is attached | subjected and shown for simplification of illustration and description.

  A solar cell according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1A is a perspective view showing the appearance of the solar cell 100, and FIG. 1B is a longitudinal sectional view showing the internal structure of the solar cell 100. The solar cell 100 of this embodiment uses a fiber 110 having a transparent conductive film 120 formed on the surface as a substrate, forms a photoelectric conversion layer 130 as a semiconductor film on the outer periphery of the transparent conductive film 120, and further performs photoelectric conversion. A reflective film 140 is formed on the outer periphery of the layer 130.

  The fiber 110 as a substrate is exposed at one end in the longitudinal direction so that sunlight can be input, and the other film is formed at the other end in the same manner as the outer peripheral portion. The transparent conductive film 120 is used as an inner electrode, and the reflective film 140 also serves as an outer electrode. Furthermore, in order to assist the transparent conductive film 120 as an inner electrode and lower the resistance value, the auxiliary electrode 160 is provided on the transparent conductive film 120 in a grid shape.

  The photoelectric conversion layer 130 is formed of a semiconductor layer and can have a structure in which a p-type semiconductor and an n-type semiconductor are stacked, or a PIN-type semiconductor can be used. As the photoelectric conversion layer 130, a silicon-based semiconductor can be used, or an organic-based semiconductor can be used.

  In the solar cell 100 of the present embodiment configured as described above, when sunlight 150 is input from one end of the fiber 110 to the inside thereof, it passes through the transparent conductive film 120 while passing through the inside of the fiber 110. It reaches the photoelectric conversion layer 130. Then, while passing through the photoelectric conversion layer 130, it is absorbed by the semiconductor and undergoes photoelectric conversion, but the light that has passed through the photoelectric conversion layer 130 without being absorbed and reached the reflective film 140 is reflected here. Return to the photoelectric conversion layer 130 again.

  The above structure is the same as the structure of a conventionally known solar cell, but in the solar cell 100 of the present embodiment, the refractive index is further defined for each of the transparent conductive film 120 and the photoelectric conversion layer 130. Thus, the sunlight 150 incident on the fiber 110 is efficiently utilized for photoelectric conversion. More preferably, the refractive index is also defined for the fiber 110.

ここで、ｎ１、ｎ２はそれぞれファイバ１１０と透明導電膜１２０の屈折率を表す。 In the solar cell 100 of the present embodiment, when the sunlight 150 incident on the fiber 110 reaches the boundary with the transparent conductive film 120, the refractive index of the transparent conductive film 120 is set so as to easily enter the transparent conductive film 120 side. It is larger than the refractive index of the fiber 110. That is, since light easily passes from the smaller refractive index to the larger refractive index, the solar cell 100 of the present embodiment defines the following relationship for the refractive indices of the fiber 110 and the transparent conductive film 120. .

Here, n1 and n2 represent the refractive indexes of the fiber 110 and the transparent conductive film 120, respectively.

ここで、ｎ３は光電変換層１３０の屈折率を表す。このように、ファイバ１１０、透明導電膜１２０、及び光電変換層１３０のそれぞれの屈折率を（式１）と（式２）で規定することで、ファイバ１１０に入射された太陽光が光電変換層１３０に到達しやすくすることができる。 In this embodiment, the light incident on the transparent conductive film 120 is easily incident on the photoelectric conversion layer 130 side when the light reaches the boundary with the photoelectric conversion layer 130 next time. The following relationship is defined for each of the refractive indexes 130 and 130.

Here, n3 represents the refractive index of the photoelectric conversion layer 130. As described above, the refractive index of each of the fiber 110, the transparent conductive film 120, and the photoelectric conversion layer 130 is defined by (Expression 1) and (Expression 2), so that the sunlight incident on the fiber 110 is converted into the photoelectric conversion layer. 130 can be easily reached.

  The light incident on the photoelectric conversion layer 130 is partially absorbed by the semiconductor and subjected to photoelectric conversion, while the light that has reached the reflection film 140 without being absorbed is reflected here and returns to the photoelectric conversion layer 130 again. . A part of the light is again absorbed by the semiconductor and photoelectrically converted, but the light that has not been absorbed reaches the boundary with the transparent conductive film 120. Here, since the refractive index of the photoelectric conversion layer 130 is larger than the refractive index of the transparent conductive film 120, the ratio of light that is reflected without entering the transparent conductive film 120 and returns to the photoelectric conversion layer 130 again becomes high. . In particular, when the incident angle to the boundary with the transparent conductive film 120 is large, the light is totally reflected without entering the transparent conductive film 120 side.

  By defining the refractive index based on (Equation 1) and (Equation 2) as described above, the light incident on the photoelectric conversion layer 130 side is confined between the transparent conductive film 120 and the reflective film 140. This increases the rate at which photoelectric conversion is performed by being absorbed by the semiconductor in the photoelectric conversion layer 130, that is, the photoelectric conversion efficiency is increased. A state in which light is confined between the transparent conductive film 120 and the reflective film 140 is schematically shown in FIG. Here, a state in which the light 151 is confined between the transparent conductive film 120 and the reflective film 140 is shown.

  A part of the light 152 reflected by the reflective film 140 and reaching the boundary with the transparent conductive film 120 is incident on the transparent conductive film 120 side, but as shown in FIG. From the relationship of the respective refractive indexes of the conductive film 120 (Equation 1), the light is reflected at the boundary with the fiber 110 and returns to the transparent conductive film 120 side. The light that has returned to the transparent conductive film 120 side is further incident on the photoelectric conversion layer 130 side, and is absorbed in the photoelectric conversion layer 130 and contributes to increasing the rate at which photoelectric conversion is performed.

  As described above, in the solar cell 100 of the present embodiment, the ratio of light incident on the photoelectric conversion layer 130 is increased between the transparent conductive film 120 and the reflective film 140 and leaked to the transparent conductive film 120 side. Light can also be easily reflected back at the boundary with the fiber 110 and returned to the photoelectric conversion layer 130 again, so that light can be absorbed in the photoelectric conversion layer 130 and the photoelectric conversion efficiency can be increased. It becomes.

  Since the solar cell 100 of this embodiment forms each layer which comprises a solar cell in the circumference | surroundings using the fiber 110 as a board | substrate, the light from the transparent conductive film 120 side is not reflected by the boundary with the fiber 110 When leaking to the fiber 110 side, the light passes through the fiber 110, enters the transparent conductive film 120 from the opposite side, and further enters the photoelectric conversion layer 130 to be used for photoelectric conversion.

  As described above, in the solar cell 100 of the present embodiment, the sunlight 150 incident from one end of the fiber 110 can be multiple-reflected inside the solar cell 100 and can be photoelectrically converted by the photoelectric conversion layer 130. By defining the refractive index of each layer constituting 100 based on (Equation 1) and (Equation 2), it is possible to confine incident light in the photoelectric conversion layer 130 as much as possible so that it can be easily absorbed. In comparison, the photoelectric conversion efficiency can be significantly increased.

  As the solar cell 100 of this embodiment, for example, a glass substrate is used as the fiber 110 and a glass substrate is used. For example, ITO (indium bell oxide) is used as the transparent conductive film 120, and the photoelectric conversion layer 130 is a silicon-based semiconductor layer. In this case, the refractive indexes of the glass substrate can be about 1.5, the ITO can be about 2.0, and the silicon-based semiconductor layer can be about 3.5, and the sun can be formed so as to satisfy the above (Formula 1) and (Formula 2). The battery 100 can be configured. As the reflective film 140 of the outer electrode, a metal film such as silver or aluminum having a high reflectance can be used.

  In general, since light absorption is proportional to the length of a path through which light passes, it is preferable to increase the width of the photoelectric conversion layer in the incident direction in a conventional solar cell. However, if the width of the photoelectric conversion layer is increased, the probability that carriers are trapped before reaching the electrode is increased, and the photoelectric conversion efficiency may be lowered. In the solar cell 100 of the present embodiment, since the incident light is configured to be multiple-reflected inside, even if the path length during one pass through the photoelectric conversion layer 130 is short, the photoelectric conversion layer 130 It is possible to realize high photoelectric conversion efficiency by repeatedly passing.

  Therefore, in the solar cell 100 of this embodiment, it is possible to make the photoelectric conversion layer 130 thin without reducing the photoelectric conversion efficiency. By making the photoelectric conversion layer 130 thinner, the distance between the transparent conductive film 120 of the inner electrode and the reflective film 140 of the outer electrode is shortened, thereby reducing the carrier path in the photoelectric conversion layer 130 and reducing the trap probability. It becomes possible to make it. That is, it becomes possible to increase the photoelectric conversion efficiency of the solar cell 100 by reducing the resistance (internal resistance) between the electrodes. The film thickness of the photoelectric conversion layer 130 is preferably 100 times or less the diffusion length of carriers generated inside.

  As a manufacturing method of the solar cell 100 of the present embodiment, a glass fiber is used as the fiber 110 to form a transparent glass substrate, and a ZnO electrode can be formed on the transparent conductive film 120 thereon by sputtering to about 200 nm. Alternatively, it is possible to form an ITO film when drawing the glass fiber.

As a method for manufacturing the photoelectric conversion layer 130, a method in which a p-type silicon film, an i-type silicon film, and an n-type silicon film are sequentially formed using plasma CVD can be used. A mixed gas of SiH ₄ and H ₂ is used as a source gas. When a p-type film is formed, a small amount of B ₂ H ₆ is mixed with the source gas, and when an n-type film is formed, a small amount of PH ₃ is added. Can be used as a mixture. In this case, the thickness of each semiconductor film can be, for example, 20 nm for the p-type film, 100 nm for the i-type film, and 20 nm for the n-type film. As a method for forming the reflective film 140 on the photoelectric conversion layer 130, for example, Ag or aluminum can be formed by sputtering.

  As described above, in the solar cell 100 of the present embodiment, the refractive index of each layer is defined based on (Equation 1) and (Equation 2), so that the sunlight 150 incident from the fiber 110 can be converted into the photoelectric conversion layer 130 as much as possible. It becomes possible to achieve high photoelectric conversion efficiency by confining the material inside and facilitating absorption. In addition, since the thickness of the photoelectric conversion layer 130 can be reduced without reducing the photoelectric conversion efficiency, the internal resistance between the electrodes can be reduced to further increase the photoelectric conversion efficiency. .

  In addition, by reducing the thickness of the photoelectric conversion layer 130, it is possible to reduce the amount of the semiconductor film used and reduce the cost. The solar cell 100 of this embodiment can use either a silicon-based semiconductor or an organic-based semiconductor as the photoelectric conversion layer 130. In particular, when an organic solar cell is used, high photoelectric conversion efficiency can be realized by selecting a material satisfying the above (Formula 1) and (Formula 2). The effect of configuring the refractive index of each layer constituting the solar cell 100 so as to satisfy (Equation 1) and (Equation 2) can be obtained more significantly with respect to organic solar cells and solar cells with large internal resistance.

  The solar cell which concerns on another embodiment of this invention is demonstrated below using FIG. The solar cell 200 of this embodiment is characterized in that a condensing lens 210 is provided at one end of a fiber 110 that receives sunlight 150. By providing such a condensing lens 210 at one end of the fiber 110, the sunlight is irradiated from an oblique direction with respect to the axial direction of the fiber 110, and this is condensed and efficiently incident on the fiber 110. It becomes possible.

  Next, the solar cell module which concerns on embodiment of this invention is demonstrated below using FIG. The solar cell module 300 of the present embodiment is configured by arranging a plurality of solar cells 100 vertically and horizontally. One end of the fiber 110 for allowing the solar light of each solar cell 100 to enter is all aligned in the same direction, and the photoelectric conversion efficiency substantially equal to that of each solar cell 100 can be realized.

  In addition, the description in this Embodiment shows an example of the solar cell and solar cell module which concern on this invention, and is not limited to this. The detailed configuration and detailed operation of the solar cell and the solar cell module in the present embodiment can be appropriately changed without departing from the spirit of the present invention.

It is the perspective view and sectional drawing which show the solar cell which concerns on embodiment of this invention. It is a figure which shows typically the state by which the light is confine | sealed between a transparent conductive film and a reflecting film. It is sectional drawing which shows the solar cell which concerns on another embodiment of this invention. It is a perspective view which shows the solar cell module which concerns on embodiment of this invention. It is the perspective view and sectional drawing which show an example of the conventional solar cell. It is a perspective view which shows another example of the conventional solar cell. It is sectional drawing which shows another example of the conventional solar cell.

Explanation of symbols

100, 200, 900, 910, 920 Solar cell 110 Fiber 120, 922, 924 Transparent conductive film 130, 923 Photoelectric conversion layer 140 Reflective film 150, 151, 152 Light 160 Auxiliary electrode 901 Semiconductor film 902, 903 Electrode 904 Glass substrate 911 Flat solar cell 912 Light guide path 913 Light incident portion 921 Transparent substrate 925, 926 Reflective layer 927 Pinhole 929 Condensing lens group

Claims (7)

A transparent conductive film, a photoelectric conversion layer, and a reflective film are sequentially laminated on the surface excluding one end of the optical waveguide, and the solar that performs photoelectric conversion by absorbing light incident from one end of the optical waveguide by the photoelectric conversion layer A battery,
The solar cell, wherein a refractive index of the photoelectric conversion layer is larger than a refractive index of the transparent conductive film. The solar cell according to claim 1, wherein a refractive index of the transparent conductive film is larger than a refractive index of the optical waveguide. The solar cell according to claim 1 or 2, wherein a refractive index of the photoelectric conversion layer is at least one greater than a refractive index of the transparent conductive film. The solar cell according to claim 1 or 2, wherein a refractive index of the photoelectric conversion layer is 3 or more. The condensing lens which condenses the light irradiated to the one end of the said optical waveguide, and injects into the said optical waveguide is provided in the one end of the said optical waveguide. The Claim 1 or Claim 2 characterized by the above-mentioned. Solar cell. The film thickness of the said photoelectric converting layer is 100 times or less of the diffusion length of the carrier produced | generated inside. The solar cell of Claim 1 or Claim 2 characterized by the above-mentioned. A solar cell module, wherein a plurality of the solar cells according to any one of claims 1 to 6 are aligned with the longitudinal direction of the optical waveguide aligned.

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