KR101535281B1 - Method for manufacturing solar cell - Google Patents

Abstract

The present invention provides a method for manufacturing a solar cell which includes the steps of: forming a top cell made of semiconductor materials; forming a bottom cell which is electrically isolated from the top cell and generates a separate electromotive force; spraying a transparent layer on the bottom cell; and bonding the top cell to the bottom cell with the transparent layer. The transparent layer transmits the light inputted to the top cell without absorption or by minimizing the absorption. The bottom cell is made of semiconductor materials which are different from the semiconductor materials of the top cell. Therefore, the present invention extracts and uses an independent voltage at need through the solar cell which is electrically isolated.

Description

{Method for manufacturing solar cell}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a method of manufacturing a solar cell comprising a plurality of cells, and more particularly, to a method of manufacturing a solar cell which is electrically separated and generates a separate independent voltage.

As global low-carbon green energy development becomes an issue, researches on efficiency improvement of various green energy sources such as solar cell and application of automobiles and buildings are actively under way. In particular, solar cells are green energy devices that are currently being studied and developed most actively. Currently, solar photovoltaic research in the world is proceeding to form so-called multi-junction solar cells by forming multiple pn junctions in order to maximize solar efficiency.

However, multi-junction solar cells are less cost effective because each solar absorbing film grows into a costly epitaxy process. Referring to FIG. 1, a conventional multi-junction solar cell 100 has a GaInP / GaAs / Ge structure that is widely used today. Ge, which is the third battery 113, is a high-priced material compared to Si, but its solar collection efficiency drops and is used for epitaxial growth of GaAs and GaInP on the upper side. The multi-junction solar cell 100 grows GaAs and GaInP on the substrate by epitaxial processes, respectively, resulting in a high cost due to growth of each layer and a large number of epitaxial processes for forming PN junction / tunnel junctions. In order to increase the process efficiency of a solar cell including multiple junctions, Korean Unexamined Patent Application Publication No. 2008-0079058 proposes a separate process for independently fabricating and connecting a plurality of solar cell layers.

However, Korean patents still need to perform several processes according to multiple junctions, and do not consider the case where the lattice constants of the materials constituting the solar cell are different. Referring to FIG. 2, the lattice constant of Ge is similar to that of GaAs, and when GaAs is used as a semiconductor material before the sun, the layer adjacent to GaAs must be Ge. Therefore, the prior art has a limitation on the selection of semiconductor materials since materials having similar lattice constants are grown by an epitaxy process. In particular, Ge is often used because it has a disadvantage in that it involves a number of epitaxy processes, complicating the process and relatively low efficiency, but is similar to the lattice constants of the most commonly used GaAs and GaInP .

In addition, since a conventional solar cell absorbs energy of light corresponding to the band gap of each semiconductor layer and converts it into electricity to generate an electromotive force by connecting the semiconductor layers in series, the respective semiconductor layers are electrically (Tunnel junction) and a high-cost epitaxy process corresponding to the above-described structure.

Accordingly, the present invention proposes a manufacturing method for a solar cell capable of generating a plurality of independent voltages rather than a single voltage without being limited by a lattice constant in selecting a semiconductor material constituting a solar cell.

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a solar cell using materials having different lattice constants and band gap energies.

Another problem to be solved by the present invention is to provide a solar cell manufacturing method that provides independent electromotive force.

In one aspect of the present invention, the present invention provides a method of manufacturing a semiconductor device, comprising: forming an upper cell formed of a semiconductor material; Forming a lower cell electrically separated from the upper cell to generate a separate electromotive force; Applying a transparent layer to the lower battery; And bonding the upper cell to the lower cell to which the transparent layer is applied, wherein the transparent layer transmits light incident on the upper cell without absorbing or absorbing the lower cell, And the second electrode is formed of a semiconductor material different from the semiconductor material.

Preferably, the semiconductor material of the lower cell has a different lattice constant from the lattice constant of the semiconductor material of the upper cell.

Preferably, the semiconductor material of the lower cell has a band gap energy smaller than a band gap energy of the semiconductor material of the upper cell.

Preferably, the semiconductor material of the lower cell has a band gap energy of 1 eV to 1.1 eV.

Preferably, the semiconductor material of the lower cell is at least one of Si, GaSb, and InGaAs.

Preferably, the semiconductor material of the upper cell is a plurality of semiconductor materials having different band gap energies.

Preferably, the semiconductor material of the upper cell or the lower cell is formed through multiple bonding.

Preferably, the semiconductor material of the upper cell is a GaInP-based or GaAs-based compound.

Preferably, the forming of the upper cell comprises: forming a substrate; Generating an electromotive force and forming a second battery layer on one side of the substrate; And forming a first cell layer for generating an electromotive force in the second cell layer, wherein the semiconductor material of the second cell layer and the semiconductor material of the first cell layer are different from each other, And a manufacturing method thereof.

Preferably, the first cell layer is formed of a semiconductor material having a larger band gap energy than the semiconductor material of the second cell layer.

Preferably, at least one of the step of forming the first cell layer and the step of forming the second cell layer includes forming a trap prevention layer.

Preferably, the method may further comprise: forming a contact layer that forms a resistance junction with the first cell layer; And forming a first metal layer on the contact layer. ≪ RTI ID = 0.0 > [10] < / RTI >

Preferably, the method further comprises forming an antireflection film on the first metal layer.

Preferably, the method further comprises forming a second metal layer on the other surface of the substrate.

Preferably, the second metal layer is formed in a pattern that minimizes reflection of light incident on the first metal layer.

Preferably, the forming the lower battery includes: forming a third battery layer generating an electromotive force; And forming a third metal layer on one surface of the third battery layer.

Preferably, the third metal layer includes a pattern that minimizes reflection of light incident on the upper cell.

Preferably, the transparent layer is a material having transparency and insulating properties.

Preferably, the transparent layer is made of PMMA or PDMS.

Preferably, the PMMA transparent layer is prepared by dissolving PMMA in chloroform (CHCl ₃ ) at a weight ratio of 1.5 wt% and 3 wt%, respectively.

Preferably, the method further comprises: forming a transparent layer between the lower cell and the fourth cell layer, the fourth cell layer being electrically separated from the lower cell to generate a separate electromotive force; and ≪ / RTI >

The present invention has an effect that an independent voltage can be extracted and used as needed through an electrically separated solar cell.

Further, the present invention has the effect of expanding the selectivity of solar cell manufacturing by using various semiconductor materials without depending on the lattice constant.

In addition, the present invention has the effect of reducing the complexity of the processes required for bonding semiconductor materials by separating a specific cell layer of a solar cell.

1 is a view showing a configuration of a conventional multi-junction solar cell.
2 is a graph showing lattice constants and band gaps of solar cell semiconductor materials.
3 is a view showing a structure of a solar cell according to preferred embodiments of the present invention.
4 is a view showing a detailed view of a solar cell structure according to a preferred embodiment of the present invention.
5 is a view showing a detailed view of an upper cell of a solar cell structure according to a preferred embodiment of the present invention.
6 is a view illustrating a process of manufacturing a solar cell according to a preferred embodiment of the present invention.
7 is a view showing a mechanism of a trap prevention layer according to a preferred embodiment of the present invention.
8 is a view showing the reflectance of an antireflection film according to a thickness according to a preferred embodiment of the present invention.
9 is a graph showing the transmittance of a transparent layer according to a transparent layer material according to a preferred embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. In order to facilitate a thorough understanding of the present invention, the same reference numerals are used for the same means regardless of the number of the drawings.

3 is a view showing a structure of a solar cell according to preferred embodiments of the present invention. FIG. 3A illustrates a solar cell 300 that generates two parallel independent voltages in accordance with a preferred embodiment of the present invention, and FIG. 3B illustrates a method of generating three parallel independent voltages according to another preferred embodiment of the present invention. The battery 300 is shown.

3A, the solar cell 300 of the present invention includes an upper cell 310, a lower cell 320, a transparent layer 330, and a terminal 340.

The upper cell 310 is formed of a semiconductor material and is formed of a semiconductor material different from the semiconductor material of the lower cell 320 and is electrically separated from the lower cell 320 to generate a separate upper voltage 350. The semiconductor material of the upper cell 310 may be at least one of GaInP and GaAs-based compounds.

The semiconductor material of the upper cell 310 may have a band gap energy different from that of the semiconductor material of the lower cell 320. [ The solar cell 300 receives light from the upper cell 310 and the light transmitted through the upper cell 310 is incident on the lower cell 320 through the transparent layer 330. The incident light is absorbed by the semiconductor material of the solar cell 300 along the wavelength band corresponding to the band gap energy of the semiconductor material. As shown in FIG. 1, incident light is sequentially absorbed around wavelengths of 1.8 eV, 1.4 eV and 1.1 eV, passing through GaInP, GaAs, and Si. Therefore, in order for the upper and lower batteries 310 and 320 to generate an electromotive force, the semiconductor material layer has a different band gap energy from the upper part to the lower part. It is reasonable.

The semiconductor material of the upper cell 310 may have a lattice constant different from that of the semiconductor material of the lower cell 320. [ Referring to FIGS. 1 and 2, in a solar cell manufactured by an epitaxy process, the lattice constants of the semiconductor materials of the bonded layers should be the same or similar. However, since the solar cell 300 according to the present invention can be electrically separated from the semiconductor material layer using the transparent layer 330, even if the solar cell 300 has semiconductor materials having different lattice constants, A semiconductor material having a band gap energy corresponding to < RTI ID = 0.0 > Referring to FIG. 2, the lattice constants of GaInP and GaAs bonded to each other are similar to each other, but the lattice constants of GaAs and Si separated by the transparent layer 330 are 5.4 and 5.6, respectively. Therefore, the solar cell 300 made of GaInP and GaAs can use Si having a band gap energy of 1 eV to 1.1 eV instead of Ge having a band gap energy of 0,7 eV by using the transparent layer 330 which is a bonding layer.

According to an embodiment of the present invention, the upper cell 310 may include a plurality of cell layers forming a bonding layer to generate one electromotive force. However, the upper cell 310 may include a transparent layer 330 internally, As shown in FIG.

The upper cell 310 may be formed of a single or a plurality of semiconductor material layers, and the single or multiple semiconductor material layers of the upper cell 310 may form a single or multiple cell layers. In this figure, the upper cell 310 is composed of a first cell layer 311 and a second cell layer 312.

The battery layer is a unit cell capable of generating one electromotive force (voltage). The cell layer is made of the same semiconductor material layer although there is a difference in doping concentration. 3, the GaInP semiconductor material layer is a (unit) cell generating an electromotive force of 1.8 eV, the GaAs semiconductor material layer is a (unit) cell generating an electromotive force of 1.4 eV, and the Si semiconductor material layer is 1.1 (unit) that generates an electromotive force of eV.

The first battery layer 311 and the second battery layer 312 have different band gap energies and have similar lattice constants. As described above, the band gap energy of the first cell layer 311 and the second cell layer 312 must be different from each other because the light of the wavelength band to be absorbed varies depending on the band gap energy of the semiconductor material. In addition, the lattice constants of the adjacent battery layers constituting the junction are similar in terms of process characteristics.

The lower cell 320 is formed of a semiconductor material and is formed of a semiconductor material different from the semiconductor material of the upper cell 310 and is electrically separated from the upper cell 310 to generate a separate lower voltage 360. The semiconductor material of the lower cell 320 may be at least one of Si, GaSb, and InGaAs.

The semiconductor material of the lower cell 320 may have a band gap energy different from that of the semiconductor material of the upper cell 310. [ As described above, the incident light is partially absorbed by the upper cell 310 and then incident on the lower cell 320 through the transparent layer 330. The incident light is absorbed by the semiconductor material of the solar cell 300 along the wavelength band corresponding to the band gap energy of the semiconductor material. Therefore, in order for the lower cell 320 to generate an electromotive force, it is appropriate that each semiconductor material layer has different band gap energy from the upper part to the lower part, since the light of the once absorbed wavelength has no energy.

The semiconductor material of the lower cell 320 may have a different lattice constant from the lattice constant of the semiconductor material of the upper cell 310.

The lower cell 320 may be formed of a single or a plurality of semiconductor material layers, and the single or multiple semiconductor material layers of the lower cell 320 may form a single or multiple cell layers. In this figure, the lower battery 320 is composed of a third battery layer 313.

The third battery layer 313 and the first battery layer 311 and the second battery layer 312 have different band gap energies. The band gap energy of the third battery layer 313 and the first battery layer 311 and the second battery layer 312 are different from each other because the light of the wavelength band to be absorbed differs depending on the band gap energy of the semiconductor material, Should be different from each other. Even when the lower cell 320 includes a cell layer other than the third cell layer 313, it is preferable that the band gap energies of the respective cell layers are different from each other. The lattice constant of the third battery layer 313 may not be similar to the lattice constant of the first battery layer 311 and the second battery layer 312. However, when the lower cell 320 includes a cell layer other than the third cell layer 313, it is preferable that the cell layer adjacent to the third cell layer 313 has a similar lattice constant unless the transparent layer 330 is present .

The present invention results in an upper voltage 350 and a lower voltage 360, which are separate independent power sources. The upper voltage 350 is the electromotive force caused by the upper cell 310 and the lower voltage 360 is the electromotive force caused by the lower cell 320. [ The upper voltage 350 and the lower voltage 360 may be separately extracted and used. 3, since the electromotive force is caused by the upper voltage 350 or the lower voltage 360, it is equivalent to having two cells of 3.2 eV or 1.1 eV, respectively.

The terminal 340 is formed on the battery layer and extracts a voltage from the battery. The terminal 340 may be formed as a metal layer on the upper portion or the lower portion of the upper battery 310 and the lower battery 320.

Referring to FIG. 3B, the solar cell 300 of the present invention includes an upper cell 310, a first lower cell 321, a second lower cell 322, a transparent layer 330, and a terminal 340.

The solar cell 300 of FIG. 3B differs from FIG. 3A in that the lower cell 320 is composed of two stages. The lower cell 320 can be divided into two cells, that is, a first lower cell 321 and a second lower cell 322, with the transparent layer 330 as a boundary, and each lower cell is divided into a first lower voltage (361) and a second lower voltage (362).

The second lower battery 322 includes a fourth battery layer 314 made of a semiconductor material and the semiconductor material of the fourth battery layer 314 is different from the semiconductor material of the first through third battery layers, Preferably a semiconductor material having a band gap energy smaller than the band gap energy of the semiconductor material formed in the upper layer. The semiconductor material of the fourth battery layer 314 can be selected regardless of the lattice constant of the semiconductor material of the upper layer since the transparent layer 330 is bounded between the respective cells.

The solar cell 300 is not limited to the structure of FIG. 3A and FIG. 3B. The lower cell including the cell layer can be increased as necessary with the transparent layer 330 as a boundary, and the parallel independent voltage can be freely generated.

4 is a view showing a detailed view of a solar cell structure according to a preferred embodiment of the present invention.

Referring to FIG. 4, a detailed view of a semiconductor material layer constituting the solar cell 300 is shown.

The upper cell 310 includes a first cell layer 311, a second cell layer 312, a substrate 410, a contact layer 420, metal layers 431 and 432, and an anti-reflection layer 440.

The band gap energy of the first cell layer 311 and the second cell layer 312 is higher than that of the third cell layer 313 and the band gap energy of the first cell layer 311 is higher than that of the second cell layer 312 It is higher than that. In this figure, GaInP is used for the first battery layer 311, GaAs is used for the second battery layer 312, and Si is used for the third battery layer 313. The solar cell 300 of the present invention, however, Various semiconductor materials can be used if only the band gap energy differences are matched. The first cell layer 311, the second cell layer 312, and the third cell layer 313 include semiconductor materials bonded in n-type and p-type depending on the doping material and concentration. Preferably, the first cell layer 311 and the second cell layer 312 are formed of a pn junction or an np junction, and are formed only of an np junction or a pn junction. For example, if the first cell layer 311 is n-GaInP and p-GaInP, the second cell layer 312 can be formed of n-GaAs and p-GaAs and can not be formed in the form of p-GaAs and n-GaAs . If the first cell layer 311 is p-GaInP and n-GaInP, the second cell layer 312 becomes p-GaAs and n-GaAs and can not be formed in the form of n-GaAs and p-GaAs. In this figure, the first battery layer 311 and the second battery layer 312 formed by the np junction are shown, but the present invention is not limited thereto.

The transparent layer 330 is positioned between the upper cell 310 and the lower cell 320 to bond the two. The transparent layer 330 allows light incident from the upper cell 310 to pass through the lower cell 320.

The metal layers 431 to 434 constitute voltage terminals. The metal layers 431 to 434 include a first metal layer 431, a second metal layer 432, a third metal layer 433, and a fourth metal layer 434. The first metal layer 431 is formed on the contact layer 420 formed on the first battery layer 311 and the second metal layer 432 is formed on the lower side of the substrate 410 while the third metal layer 433 is formed on the third battery layer 313, and a fourth metal layer 434 is formed under the third battery layer 313. The first metal layer 431 and the second metal layer 432 form terminals of the upper battery 310 and the third metal layer 433 and the fourth metal layer 434 form terminals of the lower battery 320.

The metal layers 431 to 434 may have a certain pattern. The pattern may have a pattern such that the light incident on the upper cell 310 minimizes the reflection. In this pattern, incident light increases photons reaching the lower battery 320, thereby increasing the energy efficiency and stably supplying the voltage. Preferably, the patterns of the metal layers 431 to 434 may be aligned with each other and have the same spacing. In other words, the pattern interval of the first metal layer (431) (L ₁₎ and a second pattern spacing of the metal layer 432 (L ₂₎ is the same, and the pattern interval of the second metal layer 432 to each other (L ₂₎ and third The pattern intervals L ₃ of the metal layers 433 are preferably equal to each other. It is preferable that the pattern of the first metal layer 431, the pattern of the second metal layer 432, and the pattern of the third metal layer 433 are all aligned at the same position. If all the pattern intervals (L ₁ , L ₂ , L ₃ ) of the respective metal layers are the same and the same, the incident light can reach the lower battery 320 without reflection of light.

The antireflection film 440 prevents reflection of light incident on the solar cell 300. When the light is incident through the upper cell 310, the light is incident through the anti-reflection film 440. The antireflection film 440 reduces the amount of light reflected outside or reflected from the outside of the solar cell 300 immediately before incidence.

FIG. 5 is a view showing a detailed view of an upper cell 310 of a solar cell structure according to a preferred embodiment of the present invention, and FIG. 7 is a view showing a mechanism of a trap prevention layer according to a preferred embodiment of the present invention.

Referring to FIG. 5, the cell layer includes a trap prevention layer 510 and a tunnel junction (TJ). This figure shows the trap barrier layer 510 and the tunnel junction layer reflecting the optimum conditions.

The tunnel junction layer allows as much electrons and holes as possible to move between the first cell layer 311 and the second cell layer 312. Since it is necessary to move as much electron holes as possible in the tunnel junction layer, it is preferable to perform high concentration doping to minimize the tunneling distance.

Trapping layer 510 prevents trapping of electron holes at the interface between the pn junctions present in each cell layer. The trap prevention layer 510 may be a back-surface-field (BSF) or a window layer. At both ends of the pn junction, heterogeneous materials are bonded and the defect concentration is high, so that there is a high possibility that electron holes are trapped at the interface. Referring to FIG. 7, the trap prevention layer 510 formed at both ends of the pn junction allows the electron holes to be reflected without coming to the interface. The trap preventing layer 510 may be formed by adjusting the band gap through the doping concentration change.

6 is a view illustrating a process of manufacturing a solar cell according to a preferred embodiment of the present invention.

Referring to FIG. 6, a manufacturing process of the solar cell 300 is shown. The manufacturing process includes forming the upper cell 310, forming the lower cell 320, and aligning and combining the upper cell 310 and the lower cell 320. In this figure, for ease of explanation, the illustration of the trap preventing layer 510 and the tunnel junction layer TJ is omitted.

The substrate 410 of the upper cell 310, the second cell layer 312, the first cell layer 311, and the contact layer 420 are sequentially formed. In detail, a P-GaAs substrate 410 is prepared, and p-GaAs, n-GaAs, p-GaInP, and n-GaInP are formed on the substrate 410 through a single ultra-high vacuum epitaxy process equipment It grows. The contact layer 420 is in ohmic contact with the first metal layer 431. The contact layer 420, which is n-GaAs, is removed by selective etching (step (a)). When a photoresist (PR) is applied (step (b)), and exposure and development (development) are performed, a pattern is formed (step (c)). Thereafter, the first metal layer 431 is deposited through a vacuum deposition process (step (d)).

The first metal layer 431 is patterned when the photoresist is removed through a lift-off process (step (e)). Since the contact layer 420 of n-GaAs forms an ohmic contact, it is advantageous in terms of energy efficiency that the portion not in contact with the first metal layer 431 is removed. The contact layer 420 is partially removed using a selective etching solution (step (f)). The anti-reflection film 440 is deposited on the contact layer 420 and the first metal layer 431 on the upper cell 310 to minimize the reflection of the incident light. A second metal layer 432 having the same pattern as that of the first metal layer 431 on the upper cell 310 is also formed under the upper cell 310. At this time, the lower pattern second metal layer 432 of the upper cell 310 is deposited at the same position as the upper pattern, so that light passing through the upper cell 310 is not reflected by the lower pattern (step g). The completed upper cell 310 is bonded to the lower cell 320 made of Si with the transparent layer 330 interposed therebetween. The upper cell 310 is bonded to the lower cell 320 made of Si and the first metal layer 431, the second metal layer 432 and the third metal layer 433 Position and spacing are the same. At this time, the third metal layer 433 of the lower battery 320 should be formed in advance by a process such as lift-off or etching (step (h)).

8 is a view showing the reflectance of an antireflection film according to a thickness according to a preferred embodiment of the present invention.

Referring to FIG. 8, there is shown a graph showing the reflectance of the incident light to the antireflection film 440.

The reflection of incident light should be minimized. Preferably, the incident light is required to transmit through the surface of the upper cell 310 without reflection. Therefore, it is important that the antireflection film 440 located on the surface of the upper cell 310 transmits the incident light without reflecting it as much as possible, thereby enhancing the efficiency of the solar cell 300. Since the reflected light does not contribute to forming the electron holes of the solar cell 300, the amount of the reflected light must be minimized.

When light is vertically incident and the antireflection film 440 is a single layer, the reflectance of light is minimized when the thickness of the antireflection film 440 is a quarter wavelength of the incident light. The light reflected from the upper surface and the lower surface of the antireflection film 440 is interfered with. The refractive index of the antireflection film 440 having a reflectance of 0 can be obtained from the following formula (1).

(1)

(One)

(where n ₁ is the refractive index of the antireflection film, n ₀ is the refractive index of air, and n _s is the refractive index of the solar cell semiconductor material)

The reflectance of the antireflection film 440 having the thickness and the refractive index obtained by the formula (1) at a specific wavelength is 0, but the wavelength of the incident light is varied, so that the reflectivity of light of a wavelength other than the specific wavelength increases. In order to reduce the reflectivity to zero at a wide wavelength band, it is necessary to form a multilayer antireflection film 440 that is not a single layer. In order to use multiple layers, particularly a double layer, the thickness of each of the two layers is 1/4 of the desired wavelength, and the refractive index of each layer is obtained as shown in the following equation (2).

(2)

(2)

(where n _{1 and} n ₂ are the refractive index of the antireflection film, n ₀ is the refractive index of air, and n _s is the refractive index of the solar cell semiconductor material)

Therefore, the antireflection film 440 of the double film can remarkably reduce the reflectance to a wide wavelength band as compared with the antireflection film 440 of the single film.

9 is a graph showing the transmittance of a transparent layer according to a transparent layer material according to a preferred embodiment of the present invention.

Referring to FIG. 9, absorbance of PMMA (poly methyl methacrylate) in the material of the transparent layer 330 is shown.

The transparent layer 330 needs a buffer layer having transparency in order to adhere the GaAs layer and the Si layer and to reach the Si surface in the long wavelength region that is not absorbed by the GaAs layer. The transparent layer 330 must have insulating property to cut off the electrical flow between the upper cell 310 and the lower cell 320 and must adhere between the upper cell 310 and the lower cell 320, Should have. The transparent layer 330 is preferably made of a material having transparency and insulation.

PMMA (poly methyl methacrylate) or PDMS (poly di methyl siloxane) is used as a material for satisfying the requirements of transparency, insulation and adhesiveness of the transparent layer 330. PMMA exhibits low absorbance in the 300900 region.

According to an embodiment of the present invention, the PMMA transparent layer 330 is formed by mixing PMMA having a molecular weight of 350 / mole and chloroform (CHCl ₃ ) dissolved in a weight ratio of 1.5 wt.% And 3 wt.% And a stirrer at room temperature for 4 hours . The PMMA transparent layer 330 is formed and the PMMA transparent layer 330 is formed between the upper cell 310 and the lower cell 320. When the upper cell 310 is mounted on the lower cell 320, (320).

The transmittance of the PMMA transparent layer 330 is shown in Table 1 below. The transmittance was measured by dividing the PMMA / GaAs layer coated with 1.5 wt% and 3 wt% PMMA thin films, respectively. 1.5wt.% PMMA / GaAs has a transmittance of 55.5% T, and 3wt.% PMMA / GaAs has a transmittance of 40.1% T. When the incident direction of the light is reversed in the order of GaAs / PMMA layers, the transmittance of the layer with the weight ratio of 1.5 wt.% And 3 wt.% Is 54.5% T and 41.6% T, similar to PMMA / GaAs.

Sample Transmittance (% T, at 1000) GaAs 50.4 1.5 wt.% PMMA / GaAs 55.5 GaAs / 1.5 wt.% PMMA 54.5 3.0 wt.% PMMA / GaAs 40.1 GaAs / 3.0 wt.% PMMA 41.6

From the results in [Table 1], it is confirmed that GaAs as a short-wavelength light-absorbing layer and Si as a long-wavelength light-absorbing layer can be bonded by using a PMMA transparent polymer solution. It is also confirmed that the PMMA thin film does not greatly affect the light transmittance in GaAs. Further, when the light passing through the GaAs is absorbed in the Si layer, the PMMA thin film serves as an antireflection film 440, thereby contributing to efficient absorption of light.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that the present invention can be changed.

300: Solar cell
310: upper battery
320:
330: transparent layer
340: terminal
350: upper voltage
360: lower voltage

Claims (21)

Forming an upper cell including a first metal layer and a second metal layer, which are formed of a semiconductor material and constitute a voltage terminal for extracting an upper voltage; And
Forming a lower electrode having a third metal layer and a fourth metal layer, which are electrically separated from the upper electrode to generate a separate electromotive force and constitute a voltage terminal for extracting a lower voltage;
Applying a transparent layer to the lower battery; And
And bonding the upper cell to the lower cell to which the transparent layer is applied,
The transparent layer transmits light incident on the upper cell without absorbing or minimizing absorption,
Wherein the first metal layer, the second metal layer, and the third metal layer have a pattern,
Wherein the lower battery is formed of a semiconductor material different from the semiconductor material of the upper battery
Wherein the solar cell is a solar cell. The method according to claim 1,
Wherein the semiconductor material of the lower cell has a different lattice constant from the lattice constant of the semiconductor material of the upper cell
Wherein the solar cell is a solar cell.
The method according to claim 1,
Wherein the semiconductor material of the lower battery has a band gap energy smaller than a band gap energy of the semiconductor material of the upper battery
Wherein the solar cell is a solar cell.
The method of claim 3,
The semiconductor material of the lower cell has a band gap energy of 1 eV to 1.1 eV
Wherein the solar cell is a solar cell.
The method according to claim 1,
The semiconductor material of the lower cell is at least one of Si, GaSb, and InGaAs
Wherein the solar cell is a solar cell.
The method according to claim 1,
The semiconductor material of the upper cell is a plurality of semiconductor materials having different band gap energies
Wherein the solar cell is a solar cell.
The method according to claim 1,
The semiconductor material of the upper cell or the lower cell is formed through multiple bonding
Wherein the solar cell is a solar cell.
The method according to claim 1,
The semiconductor material of the upper cell is a compound of GaInP and GaAs series
Wherein the solar cell is a solar cell.
The method according to claim 1,
The step of forming the upper cell
Forming a substrate;
Generating an electromotive force and forming a second battery layer on one side of the substrate; And
And forming a first battery layer for generating an electromotive force in the second battery layer,
The semiconductor material of the second battery layer and the semiconductor material of the first battery layer are different from each other
Wherein the solar cell is a solar cell.
10. The method of claim 9,
Wherein the first cell layer is formed of a semiconductor material having a larger band gap energy than the semiconductor material of the second cell layer
Wherein the solar cell is a solar cell.
10. The method of claim 9,
Forming at least one of the step of forming the first battery layer and the step of forming the second battery layer includes forming a trap prevention layer
Wherein the solar cell is a solar cell.
10. The method of claim 9,
Forming a contact layer that forms a resistance junction in the first cell layer; And
And forming a first metal layer on the contact layer
Wherein the solar cell is a solar cell.
13. The method of claim 12,
And forming an anti-reflection film on the first metal layer
Wherein the solar cell is a solar cell.
13. The method of claim 12,
And forming a second metal layer on the other surface of the substrate
Wherein the solar cell is a solar cell.
delete The method according to claim 1,
The step of forming the lower battery
Forming a third battery layer that generates an electromotive force; And
And forming a third metal layer on one surface of the third battery layer
Wherein the solar cell is a solar cell.
delete The method according to claim 1,
The transparent layer is a material having transparency and insulating properties
Wherein the solar cell is a solar cell.
The method according to claim 1,
The transparent layer may be made of PMMA or PDMS
Wherein the solar cell is a solar cell.
20. The method of claim 19,
The PMMA transparent layer was prepared by dissolving PMMA in chloroform (CHCl ₃ ) at a weight ratio of 1.5 wt% and 3 wt%
Wherein the solar cell is a solar cell.
The method according to claim 1,
A fourth cell layer electrically separated from the lower cell to generate a separate electromotive force, and a transparent layer formed between the lower cell and the fourth cell layer
Wherein the solar cell is a solar cell.

Images