JP5291427B2 - Photovoltaic generator - Google Patents

Description

The present invention relates to a photovoltaic power generation device such as a solar cell or a wavelength-resolved spectrum analyzer photoreceiver.

  In general, in a solar cell as a photovoltaic generator, an incident photon having energy exceeding the band gap of a semiconductor is captured by a depletion layer (or i layer) of a pn junction (or pin junction), and an electron-hole pair is captured. And the electric charges (electrons and holes) are taken out to the two output terminals, and a potential difference equal to the above-mentioned band gap is generated between the output terminals.

  In a single-junction solar cell composed of a single cell of conventional single crystal silicon, polycrystalline silicon, amorphous silicon, or the like, the amount of incident photon energy exceeding the silicon band gap is not as shown in FIG. If the energy of the incident photon is smaller than the band gap of silicon, the incident photon itself is not captured and becomes a transmission loss. As a result, the energy conversion efficiency was low because the incomplete utilization and the transmission loss were large.

  In order to improve the energy conversion efficiency of solar cells, multi-junction solar cells in which a plurality of pn junction elements or pin junction elements (hereinafter referred to as cells) are connected in the vertical direction have been developed (see Patent Document 1, Patent). Literature 2, Patent Literature 3, Patent Literature 4).

  FIG. 10 is a perspective view of a conventional 3-junction solar cell made of InGaP / InGaAs / Ge. That is, in FIG. 10, a bottom cell 101 made of Ge, a middle cell 102 made of InGaAs, and a top cell 103 made of InGaP are joined in the vertical direction. In this case, a cell having a large light absorption end band gap (minimum energy that can be absorbed) is positioned on the upper side, and a cell having a small light absorption end band gap is positioned on the lower side, thereby increasing the energy conversion efficiency.

In the three-junction solar cell of FIG. 10, incident photons having a wavelength of 660 nm or less are absorbed and photoelectrically converted by the InGaP top cell 103 as shown in FIG. 11, but the portion exceeding the band gap of InGaP is incompletely used. In addition, incident photons having a wavelength of 890 nm to 2000 nm are absorbed by the Ge bottom cell 101 and photoelectrically converted together with the incomplete utilization of the InGaAs middle cell 102, but the portion exceeding the Ge bandgap becomes the incomplete utilization. Furthermore, incident photons themselves having a wavelength of 2000 nm or more are not captured, resulting in a transmission loss. As a result, the final incomplete use and transmission loss are smaller than in the case of the single junction solar cell of FIG. 11, and the energy conversion efficiency is improved.
JP 2004-296658 A JP 2004-319934 A JP 2004-327889 A JP 2007-324563 A

  However, in the conventional three-junction solar cell of FIG. 10, with the light coupling loss due to the increase in the number of stacked layers, the incomplete use amount and the transmission loss amount are small but still insufficient. There was a problem that it was still small.

  In addition, since the conventional three-junction solar cell in FIG. 10 has a large number of layers having different compositions, if the composition has a high vapor pressure, it must be baked and blown, and the growth temperature is greatly different. If the growth temperature of the top cell is higher than the growth temperature of the middle cell or the bottom cell, the middle cell or the bottom cell may be damaged. As a result, the manufacturing cost is high and the manufacturing is difficult.

  In the conventional three-junction solar cell of FIG. 10, if the number of cells is increased, the amount of incomplete use and transmission loss can be further reduced and the energy conversion efficiency can be improved, but the number of cells is increased. Further increases the number of layers, and is problematic in terms of manufacturing cost and manufacturing difficulty.

In order to solve the above-described problems, a photovoltaic power generation apparatus according to the present invention includes a substrate, a plurality of pn junction elements or pin junction elements having different band gaps formed laterally on the substrate, and the substrate. It is formed on, and and a GaN buffer layer having an uneven surface of the mountain-shaped inclination of the inclined angles corresponding to the respective band gaps, the pn junction element or the pin junction element is constituted by the InAlGaN layer having a composition corresponding to the bandgap The InAlGaN layer is formed on the GaN buffer layer . Since the plurality of pn junction elements or pin junction elements (cells) are arranged in the lateral direction of the substrate, a large number of cells having different band gaps can be arranged on the substrate, and as a result, energy conversion efficiency is improved. Moreover, since the number of stacked layers does not increase even if the number of cells increases, the manufacturing cost is reduced and the manufacturing is facilitated.

  Further, the pn junction element or the pin junction element (cell) is connected in series between the two output terminals, and the photovoltaic power generation device functions as a solar cell.

  Furthermore, each of the pn junction element or the pin junction element (cell) has an independent output terminal, and the photovoltaic power generation device also functions as a wavelength-resolved spectrum analyzer photoreceiver.

  According to the present invention, a plurality of pn junction elements or pin junction elements (cells) having different band gaps are formed on the substrate in the lateral direction. The number of (cells) can be easily increased, and therefore the energy conversion efficiency can be easily increased.

  1A and 1B show a first embodiment of a photovoltaic power generation apparatus according to the present invention, where FIG. 1A is a plan view and FIG. 1B is a cross-sectional view. In addition, the photovoltaic generator of FIG. 1 acts as a solar cell.

  1, a plurality of cells 2-1, 2-2,..., 2-7 are formed on a sapphire substrate 1. Each of the cells 2-1, 2-2,..., 2-7 includes an n-type GaN buffer layer 21, an n-type InAlGaN layer 22, a p-type InAlGaN layer 23, a transparent electrode 24 made of ITO, ZnO, etc., an n-type GaN buffer. The n-side electrode 25 is formed on the layer 21, and the p-side electrode 26 is formed on the transparent electrode 24.

The cells 2-1, 2-2,..., 2-7 are connected in series between the two output terminals OUT ₁ and OUT ₂ . That is, the p-side electrode 26 of the cell 2-1 is connected to the n-side electrode 25 of the cell 2-2 by the bonding wire 3-1, and the p-side electrode 26 of the cell 2-2 is connected to the n-side of the cell 2-3. In the same manner, the p-side electrode 26 of the cell 2-6 is connected to the n-side electrode 25 of the cell 2-7 by the bonding wire 3-6. The bonding wire 3-0 connects the n-side electrode 25 of the cell 2-1 to the output terminal (pad) OUT ₁ , and the bonding wire 3-7 connects the p-side electrode 26 of the cell 2-7 to the output terminal (pad). Connected to OUT ₂ . The above bonding wires 3-1, 3-2,..., 3-6 may be connected by providing a wiring electrode pattern during the cell forming process.

  The compositions of the n-type InAlGaN layer 22 and the p-type InAlGaN layer 23 of each of the cells 2-1, 2-2,..., 2-7 are different, and therefore the band gaps are different. In addition, a depletion layer for trapping incident photons is formed between the n-type InAlGaN layer 22 and the p-type InAlGaN layer 23, but an i-type or undoped InAlGaN layer not intentionally added with impurities. May be formed.

  As described above, InAlGaN is used as the semiconductor material of each of the cells 2-1, 2-2,. This is because the utilization of sunlight is not sufficient in Si and Ge, and the utilization of sunlight is also insufficient in GaAlAs and InGaP compared to InAlGaN. That is, as shown in FIG. 2, it can be seen that when the composition of InAlGaN is varied, the range of change of the absorption edge band gap is larger than when the compositions of GaAlAs and InGaP are varied. In FIG. 2, when the main component of InAlGaN approaches InN, the absorption edge band gap corresponds to the photon energy in the infrared region, and when the main component of InAlGaN is InGaN, the absorption edge band gap is a photon in the visible region. When the main component of InAlGaN approaches AlN, the absorption edge band gap corresponds to the photon energy in the ultraviolet region.

  Next, the manufacturing method of the photovoltaic generator of FIG. 1 is demonstrated with reference to FIG. 3, FIG.

  First, referring to FIG. 3A, an n-type GaN buffer layer 21 having a thickness of about 2 μm to which Si is added is grown on a sapphire substrate 1 by metal organic chemical vapor deposition (MOCVD).

  Next, referring to FIG. 3B, a resist layer 21 a is applied on the n-type GaN buffer layer 21. On the other hand, a mold 21b having a concavo-convex surface having a chevron slope is prepared. This crest-shaped inclination changes in the lateral direction at intervals of 20 nm to several μm, but the pitch and the inclination angle of the crest-shaped inclination are designed in accordance with the spread of the output spectrum of the prism or diffraction grating described later. The mold can be formed of glass or resin instead of the metal material of the mold 21b.

  In the state of FIG. 3B, the mold 21b is lowered to the resist layer 21a, and the uneven surface of the mold 21b is transferred to the resist layer 21a, resulting in the state of FIG. Instead of the imprint technique using the mold 21b, a concavo-convex surface may be formed on the resist layer 21a by photolithography, that is, exposure development using a metal mask.

Next, in the state of FIG. 3C, the resist layer 21a and the n-type GaN buffer layer 21 are etched back by a reactive ion etching (RIE) method using Cl ₂ gas. As a result, the resist layer 21a The uneven surface is transferred to the surface of the n-type GaN buffer layer 21.

  Next, referring to FIG. 4B, an n-type InAlGaN layer 22 to which Si is added and a p-type InAlGaN layer 23 to which Mg is added on an n-type GaN buffer layer 21 having an uneven surface formed by MOCVD. Grow. In this case, the band gaps of the InAlGaN layers 22 and 23 change according to the inclination angle θ of the mountain-shaped inclination of the n-type GaN buffer layer 21. That is, as shown in FIG. 5, when the mountain-shaped inclination angle θ is changed, the In ratio of InAlGaN changes and the light absorption edge band gap can be changed. In addition, since the film thickness of the InAlGaN layers 22 and 23 becomes smaller as the mountain-shaped inclination angle θ becomes larger, the light absorption edge band gap shows a larger change when InAlGaN is used as a well layer of a quantum well structure. Further, an i-type or undoped InAlGaN layer to which no impurity is intentionally added may be formed between the n-type InAlGaN layer 22 and the p-type InAlGaN layer 23.

  Next, referring to FIG. 4C, a transparent electrode 24 made of ITO or ZnO is formed on the entire surface.

  Next, although not shown, the n-type GaN buffer layer 21 is exposed by photolithography and etching, and then an n-side electrode 25 is formed on the exposed portion of the n-type InAlGaN layer 22, and the p-type electrode is formed on the transparent electrode 24. The side electrode 26 is formed. Further, the transparent electrode 24, the p-type InAlGaN layer 23, and the n-type InAlGaN layer 22 are cut by the laser cutting method in the first direction of the sapphire substrate 1, and the cells 2-1, 2-2,. Separate on the substrate 1 (see FIG. 1). Next, the sapphire substrate 1 is cut by a laser scribing method in a second direction orthogonal to the first direction at the left end of the cell 2-1 and the right end of the cell 2-7. Finally, the bonding wires 3-0, 3-1,..., 3-7 are applied to the n-side electrode 25 and the p-side electrode 26 of the cells 2-1, 2-2,. The unit is completed. Of course, an example in which a unit is composed of seven cells is shown, but the unit is not limited to seven. The cell size and the number of cells in the unit may be changed according to the output voltage and the convenience of the spectroscopic unit. In addition to the laser scribing method, a point scribing method using diamond points may be used.

  When the photovoltaic power generation apparatus of FIG. 1 is used as a solar cell, an optical unit having a spectroscopic function is added as shown in FIGS. As shown in FIG. 6, the optical unit includes a convex lens 4a that collects sunlight and a columnar triangular prism 5b that separates the collected light. On the other hand, as shown in FIG. 7, the optical unit has a convex lens 4b that collects sunlight and a reflective diffraction grating 5b that separates the collected light. Thereby, a wide range of sunlight is dispersed, and the dispersed light is incident on the cells 2-1, 2-2,..., 2-7 having a band gap corresponding to the energy, and as a result, Energy conversion efficiency can be improved. An artificial light source may be used instead of sunlight. Further, the reflection type diffraction grating 5b in FIG. 7 may be a transmission type diffraction grating.

  In the photovoltaic power generation apparatus of FIG. 1, seven cells 2-1, 2-2,..., 2-7 are connected in series, but the present invention is not limited to seven cells. .

  8A and 8B show a second embodiment of the photovoltaic power generation apparatus according to the present invention, where FIG. 8A is a plan view and FIG. 8B is a cross-sectional view. Note that the photovoltaic power generation apparatus of FIG. 8 acts as a wavelength-resolved spectrum analyzer light receiver.

In FIG. 8, the n-side electrode 25 and the p-side electrode 26 of each of the cells 2-1, 2-2,..., 2-7 are independently output terminals OUT ₁₁ , OUT ₇₂ ; OUT ₂₁ , OUT ₂₂ ; _Acts as ₇₁ and OUT ₇₂ . As a result, since the light quantity corresponding to each band gap can be detected, it can act as a wavelength-resolved spectrum analyzer light receiver. In FIG. 8, the optical units shown in FIGS. 6 and 7 can be added as necessary.

1 shows a first embodiment of a photovoltaic power generation apparatus according to the present invention, where (A) is a plan view and (B) is a cross-sectional view. It is a graph which shows the change range of the light absorption edge band gap of the semiconductor with respect to a sunlight spectrum. It is sectional drawing explaining the photovoltaic generator production | generation apparatus of FIG. It is sectional drawing explaining the photovoltaic generator production | generation apparatus of FIG. It is a graph which shows the relationship between the crest-shaped inclination angle in FIG. 1, and the light absorption edge band gap of InAlGaN. It is a figure which shows the 1st example which added the optical unit to the photovoltaic generator of FIG. It is a figure which shows the 2nd example which added the optical unit to the photovoltaic generator of FIG. 2nd Embodiment of the photovoltaic generator which concerns on this invention is shown, (A) is a top view, (B) shows sectional drawing. It is a graph which shows the solar energy density explaining the energy conversion efficiency of the conventional single junction type solar cell. It is a perspective view which shows the conventional 3 junction type solar cell. It is a graph which shows the solar energy density explaining the energy conversion efficiency of the conventional 3 junction type solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2-1, 2-2, ..., 2-7 ... Cell 3-0, 3-1, ..., 3-7 ... Bonding wire 4a, 4b ... Convex lens 5a ... Columnar triangular prism 5b ... Reflective diffraction Lattice 21 ... n-type GaN buffer layer 21a ... resist layer 21b ... mold 22 ... n-type InAlGaN layer 23 ... p-type InAlGaN layer 24 ... transparent electrode 25 ... n-side electrode 26 ... p-side electrode 101 ... bottom cell 102 ... middle cell 103 ... Top cell

Claims (9)

A substrate,
A plurality of pn junction elements or pin junction elements having different band gaps formed laterally on the substrate ;
A GaN buffer layer formed on the substrate, and having a concavo-convex surface with an inclined angle corresponding to each band gap ,
Each pn junction element or pin junction element is composed of an InAlGaN layer having a composition corresponding to each band gap,
The InAlGaN layer is a photovoltaic generator formed on the GaN buffer layer .   The photovoltaic generator according to claim 1, wherein a band gap of the pn junction element or the pin junction element changes in a lateral direction of the substrate.   The photovoltaic generator according to claim 1, wherein the pn junction element or the pin junction element is connected in series between two output terminals.   The photovoltaic generator according to claim 1, wherein each of the pn junction element or the pin junction element has an independent output terminal. Furthermore, an optical unit having a spectroscopic function is provided,
The photovoltaic generator according to claim 1, wherein the pn junction elements or pin junction elements are arranged in accordance with an output spectrum of the optical unit. The optical unit is
A condenser lens;
The photovoltaic generator according to claim 5 , further comprising: a light dispersion element that splits light collected by the condenser lens to generate the output spectrum. The photovoltaic generator according to claim 6 , wherein the condenser lens includes a convex lens. The photovoltaic generator according to claim 6 , wherein the light dispersing element includes a prism. The photovoltaic generator according to claim 6 , wherein the light dispersion element includes a diffraction grating.

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