JP2013074277A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for improving conversion efficiency more.SOLUTION: An photoelectric conversion device 10 includes a photoelectric conversion layer 14 which absorbs light and generates a carrier, and a transparent conductive film 30 provided on the side of a light reception surface 16 of the photoelectric conversion layer 14. The transparent conductive film 30 is configured to generate photons more than incident photons, and to emit the generated photons toward the photoelectric conversion layer 14. The transparent conductive film is so configured that the energy of the generated photons is larger than a band gap of a semiconductor layer that the photoelectric conversion layer includes.

Description

  The present invention relates to a photoelectric conversion device suitable for a solar cell.

  2. Description of the Related Art Conventionally, so-called solar cells have been vigorously developed in various fields as photoelectric conversion devices that convert light energy into electrical energy. Solar cells are expected to be a new energy source because they can directly convert light from the sun, a clean and inexhaustible energy source, into electricity.

  In addition, a solar cell requires a pair of electrodes for taking out the generated electricity to the outside. Usually, these electrodes are provided on the surface that receives sunlight and the back surface on the opposite side.

  However, since sunlight does not enter the lower region of the electrode on the light receiving surface side, the region does not contribute to power generation. Therefore, the surface electrode contributes to a decrease in conversion efficiency. Therefore, a solar cell in which a pair of electrodes is formed on the back surface has been developed (see Patent Document 1).

JP 2007-59644 A

  By the way, the wavelength (energy) of light absorbed by the semiconductor layer depends on the band gap Eg of the material constituting the semiconductor layer. For example, when the material is crystalline silicon, the band gap Eg is about 1.1 eV, and light having energy smaller than the band gap Eg (light having a wavelength of about 1100 nm or more) does not contribute to power generation.

  Further, light having an energy hν larger than the band gap Eg (light having a wavelength of about 1100 nm or less) is absorbed by the semiconductor and generates carriers. At this time, energy corresponding to hν-Eg is released as heat. . Therefore, even if the light is on the short wavelength side, not all of the absorbed light energy is converted into electrical energy, and there is room for further improvement in the utilization efficiency of the light on the short wavelength side of sunlight. .

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for further improving the conversion efficiency.

  In order to solve the above problems, a photoelectric conversion device according to an aspect of the present invention includes a photoelectric conversion layer that absorbs light and generates carriers, and a transparent conductive film provided on a light-receiving surface side of the photoelectric conversion layer. Prepare. The transparent conductive film is configured to generate more photons than the number of incident photons and to emit the generated photons toward the photoelectric conversion layer.

  According to the present invention, further improvement in conversion efficiency can be realized.

It is the figure which showed typically the cross section of the photoelectric conversion apparatus which concerns on 1st Embodiment. It is a top view of the transparent conductive film seen from the arrow A direction shown in FIG. It is a top view of the transparent conductive film which concerns on 2nd Embodiment. It is a schematic diagram which shows the principal part of the photoelectric conversion apparatus which concerns on 2nd Embodiment. It is a schematic diagram which shows the layer structure of the photoelectric conversion apparatus which concerns on a modification.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate.

(First embodiment)
FIG. 1 is a diagram schematically showing a cross section of the photoelectric conversion device according to the first embodiment. It should be noted that the scales and shapes of each layer and each part shown in the following drawings are set for convenience of explanation, and are not interpreted in a limited manner unless otherwise specified.

  As shown in FIG. 1, the photoelectric conversion device 10 according to the present embodiment includes a photoelectric conversion layer 14 having a first semiconductor layer 12 exhibiting a first conductivity type. The photoelectric conversion layer 14 further includes a second semiconductor layer 20 and a third semiconductor layer 22 formed on the back surface 18 side opposite to the light receiving surface 16.

  The first semiconductor layer 12 according to the present embodiment is a single crystal n-type crystalline silicon layer, and has a refractive index of about 3.5 (when the wavelength of light is 1.1 μm). The refractive index varies depending on the carrier concentration and the wavelength of light. Moreover, the thickness of the photoelectric converting layer 14 is 100-150 micrometers. The form of the crystalline silicon layer may be single crystal, polycrystalline, microcrystalline, or a mixture.

The second semiconductor layer 20 has a second conductivity type having a polarity opposite to that of the first semiconductor layer 12. The second semiconductor layer 20 according to the present embodiment is a region (p ⁺ layer) having a high concentration of p-type impurities. The third semiconductor layer 22 has a first conductivity type that has the same polarity as the first semiconductor layer 12. The third semiconductor layer 22 according to the present embodiment is a region (n ⁺ layer) having a higher n-type impurity concentration than the first semiconductor layer 12.

  Note that in the photoelectric conversion device 10 according to the present embodiment, the first electrode 24 in contact with the second semiconductor layer 20 and the second electrode 26 in contact with the third semiconductor layer 22 are included in the photoelectric conversion layer 14. It is provided on the back surface 18 side. As a result, since incident light reaches the first semiconductor layer 12 without being blocked by the first electrode 24 and the second electrode 26, compared with the case where the electrode is provided on the light receiving surface 16 side of the photoelectric conversion layer 14. Thus, the power generation efficiency of the photoelectric conversion device 10 is improved.

  The electrode material is preferably aluminum (Al) or copper (Cu). When the electrode is formed of aluminum (Al), a vapor deposition method is preferable. On the other hand, when the electrode is formed of copper (Cu), a sputtering method or a plating method is preferable.

  A protective film (passivation film) 28 is laminated on the light receiving surface 16 side of the photoelectric conversion layer 14. A transparent conductive film 30 is laminated on the protective film 28, and an antireflection film 32 is further laminated so as to cover the transparent conductive film 30.

The transparent conductive film 30 is a transparent thin film having a low resistivity such as indium tin oxide (ITO) or zinc oxide (ZnO). In other words, the transparent conductive film 30 may be made of a material having a carrier density of 1.5 × 10 ²¹ [cm ⁻³ ] or less. As a result, more light passes through the transparent conductive film 30. The antireflection film 32 is preferably a nitride film.

  Next, the configuration of the transparent conductive film will be described. FIG. 2 is a top view of the transparent conductive film as seen from the direction of arrow A shown in FIG. The transparent conductive film 30 shown in FIG. 2 includes a transparent conductive region 30a integrated as a whole and a plurality of holes 30b formed in a lattice shape in the transparent conductive region 30a.

  The thickness of the transparent conductive film 30 is appropriately set according to the type of absorbed light targeted by the photoelectric conversion device 10 and the type of material constituting the photoelectric conversion layer. For example, when sunlight is used as a target, the thickness of the transparent conductive film 30 is preferably less than 500 nm so that normal light (wavelength of about 500 to 1100 nm) contributing to the conversion efficiency is transmitted as it is toward the photoelectric conversion layer 14. . As a result, light having a wavelength of approximately 500 nm or more is easily transmitted.

  The photoelectric conversion device 10 according to the present embodiment includes a photoelectric conversion layer 14 that absorbs light and generates carriers, and a transparent conductive film 30 provided on the light receiving surface 16 side of the photoelectric conversion layer 14.

  In the photoelectric conversion device 10 shown in FIG. 1, when the light L1 enters the transparent conductive region 30a of the transparent conductive film 30, it may be Compton scattered with carriers in the transparent conductive region 30a. The incident light L1 loses energy due to Compton scattering, and becomes light L2 having a long wavelength (low energy). On the other hand, the carriers in the transparent conductive region 30a form a charge distribution depending on the geometric shape of the transparent conductive film 30, and light L3 is emitted by the temporal change of the charge distribution. The transparent conductive film 30 is preferably adjusted in geometric shape so that the temporal change in the charge distribution is approximately the same as the frequency of light having a wavelength of about 1000 nm.

  For example, 3.1 eV (400 nm) light L1 is incident on the transparent conductive film 30 and is Compton scattered with carriers to become 1.6 eV light L2, and the remaining 1.5 eV energy is transferred on the surface of the transparent conductive region 30a. Of kinetic energy. Then, when the movement of the carriers is stopped by the hole 30b, it becomes 1.5eV light L3 and enters the first semiconductor layer 12 (note that energy loss due to energy transfer is not considered here). .

  The light L2 and the light L3 incident on the first semiconductor layer 12 can each generate a pair of carriers (electrons and holes). As described above, the transparent conductive film 30 according to the present embodiment is configured to generate more photons than the number of incident photons and to emit the generated photons toward the photoelectric conversion layer 14. .

  Therefore, compared to the case where one photon having a high energy (short wavelength) is incident on the semiconductor layer, the case where two photons having a lower energy (long wavelength) than the incident light is incident on the semiconductor layer. The number of carriers generated in the photoelectric conversion layer 14 increases. That is, power generation efficiency can be improved.

  The transparent conductive film 30 is preferably configured such that the energy of photons generated based on incident light is larger than the band gap Eg of the semiconductor layer included in the photoelectric conversion layer 14. Thereby, the light of the energy which is not absorbed by the photoelectric converting layer 14 decreases.

(Second Embodiment)
FIG. 3 is a top view of the transparent conductive film according to the second embodiment. The transparent conductive film 34 shown in FIG. 3 is provided in the same region as the transparent conductive film 30 in the photoelectric conversion device 10 according to the first embodiment shown in FIG.

  In the transparent conductive film 34, a plurality of island-shaped conductive regions 34a having gaps g are arranged in a lattice pattern. The island-shaped conductive regions 34a are spaced apart so as not to conduct each other. In order to form the island-shaped conductive region 34a, a mask pattern in consideration of the shape of the island-shaped conductive region 34a may be used for patterning. Further, when the island-shaped conductive region 34a is small in size and thickness, the island-shaped portion may be formed by film formation by sputtering. The behavior of light incident on the transparent conductive film 34 thus configured will be described below.

  FIG. 4 is a schematic diagram illustrating a main part of the photoelectric conversion device according to the second embodiment. The photoelectric conversion device 40 includes a photoelectric conversion layer 14 and a transparent conductive film 34 provided on the light receiving surface 16 side of the photoelectric conversion layer 14. Since the transparent conductive film 34 has a plurality of island-shaped conductive regions 34a having gaps g, one island-shaped conductive region 34a is opposed to each other with the coil L and the gap g. The conductive region can be considered as a capacitor C.

Therefore, the transparent conductive film 34 thus configured can be considered as a circuit having a resonance frequency f (= 1 / [2π · [CL] ^1/2 ]). Therefore, by optimizing C and L, the kinetic energy of the carrier that receives a part of the energy of the light incident on the transparent conductive film 34 is emitted as light having a desired frequency.

  As described above, the transparent conductive film 34 according to the present embodiment can generate more photons than the number of incident photons, and can emit the generated photons toward the photoelectric conversion layer 14.

  Next, a modification of the photoelectric conversion device including the above-described transparent conductive film will be described. FIG. 5 is a schematic diagram illustrating a layer structure of a photoelectric conversion device according to a modification.

  The photoelectric conversion device 42 includes an antireflection film 44, a transparent conductive film 46, a surface glass plate 48, a first electrode layer 50, a semiconductor layer 52, a transparent conductive film 54, and a second electrode layer 56 from the light receiving side. The first electrode layer 50, the semiconductor layer 52, the transparent conductive film 54, and the second electrode layer 56 are sequentially stacked on the surface glass plate 48 while being subjected to known laser patterning. A filler 58 and a back glass plate 60 are laminated on the second electrode layer 56.

  A transparent conductive film 46 is laminated on the light receiving surface 62 side of the front glass plate 48, and an antireflection film 44 is further laminated so as to cover the transparent conductive film 46.

  The 1st electrode layer 50 is formed on the surface on the opposite side to the light-receiving surface 62 of the surface glass plate 48, and has electroconductivity and translucency. As the first electrode layer 50 according to the present embodiment, a transparent conductive oxide (TCO) is used, and in particular, zinc oxide (ZnO) having high light transmittance, low resistance, and low cost is used. Used.

  The semiconductor layer 52 generates charges (electrons and holes) by incident light from the first electrode layer 50 side. As the semiconductor layer 52, for example, an amorphous (amorphous) silicon semiconductor layer having a pin junction or a pn junction as a basic structure, or a single layer or a stacked body of a microcrystalline silicon semiconductor layer can be used. The semiconductor layer 52 according to the present embodiment is configured by laminating an amorphous silicon semiconductor and a microcrystalline silicon semiconductor from the first electrode layer 50 side. Note that in this specification, the term “microcrystal” means not only a complete crystal state but also a state partially including an amorphous state.

  The transparent conductive film 54 is formed on the semiconductor layer 52. For the transparent conductive film 54, a transparent conductive oxide (TCO) such as zinc oxide (ZnO) is used. The transparent conductive film 54 prevents the semiconductor layer 52 and the second electrode layer 56 from being alloyed, and the connection resistance between the semiconductor layer 52 and the second electrode layer 56 can be reduced.

  The second electrode layer 56 is formed on the transparent conductive film 54. A reflective metal such as silver (Ag) is used for the second electrode layer 56. The transparent conductive film 54 and the second electrode layer 56 of one photoelectric conversion device 42 are in contact with the first electrode layer 50 of another adjacent photoelectric conversion device 42. Thereby, one photoelectric conversion device 42 and the other photoelectric conversion device 42 are electrically connected in series.

  Also in the amorphous photoelectric conversion device 42 configured as described above, the power generation efficiency can be improved by providing the transparent conductive film 46 similar to that of the first embodiment or the second embodiment.

  As another modification of the photoelectric conversion device, the transparent conductive film that is the same as that in the first embodiment or the second embodiment is used on the light-receiving surface side even in a configuration in which amorphous silicon and single crystal silicon are stacked. It is possible to improve the power generation efficiency by providing it.

  As described above, the present invention has been described with reference to the above-described embodiments. However, the present invention is not limited to the above-described embodiments, and the configurations of the embodiments are appropriately combined or replaced. Those are also included in the present invention. Further, it is possible to appropriately change the combination and processing order in each embodiment based on the knowledge of those skilled in the art and to add various modifications such as various design changes to each embodiment. Embodiments to which is added can also be included in the scope of the present invention.

  DESCRIPTION OF SYMBOLS 10 Photoelectric conversion apparatus, 12 1st semiconductor layer, 14 Photoelectric conversion layer, 16 Light-receiving surface, 30 Transparent electrically conductive film, 30a Transparent electrically conductive area | region, 30b Hole, 32 Antireflection film, 34a Island-like electrically conductive area | region.

Claims (5)

A photoelectric conversion layer that absorbs light and generates carriers;
A transparent conductive film provided on the light receiving surface side of the photoelectric conversion layer,
The transparent conductive film is configured to generate more photons than the number of incident photons, and to emit the generated photons toward the photoelectric conversion layer.   2. The photoelectric conversion device according to claim 1, wherein the transparent conductive film is configured such that energy of generated photons is larger than a band gap of a semiconductor layer included in the photoelectric conversion layer.   The photoelectric conversion device according to claim 1, wherein the transparent conductive film has a plurality of holes penetrating in the thickness direction.   3. The photoelectric conversion device according to claim 1, wherein the transparent conductive film includes a plurality of island-shaped conductive regions that are spaced from each other and arranged in a lattice pattern.   The photoelectric conversion device according to any one of claims 1 to 4, wherein the transparent conductive film has a thickness of less than 500 nm.

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