CN102723405A - Method for preparing double-faced growth efficient wide-spectrum absorption multi-junction solar cell - Google Patents

Abstract

The invention discloses a method for preparing double-sided growth high-efficiency broad-spectrum absorption multi-junction solar cells, which utilizes high aspect ratio dislocation trapping technology to realize InP epitaxy on GaAs materials and monolithic integration of GaAs-based and InP-based cells, specifically including The steps are as follows: (1) Form a dielectric film on the first surface of a double-sided polished GaAs substrate, and grow a lattice-matched GaAs/GaInP solar cell structure on the second surface; Protect the two sides, and then process and form a nanoscale dielectric mask pattern on the first side of the substrate; (3) grow and form an InP film on the first side of the substrate, and polish the InP film to a flatness reaching the epitaxial level; ( 4) Sequential growth on the first surface of the substrate to form an InGaAsP or InGaAsP/InGaAs solar cell structure and electrode contact layer; (5) Release the protection on the second surface of the substrate to obtain the target product. The invention has simple process, easy operation and high yield, and effectively solves the influence of lattice mismatch and thermal mismatch on the quality and performance of battery materials in heterogeneous multi-junction solar cells.

Description

Preparation method of double-sided growth high-efficiency broad-spectrum absorption multi-junction solar cells

technical field

The invention relates to a preparation method of a photovoltaic device, in particular to a preparation method of a double-sided growth high-efficiency broad-spectrum absorption solar cell.

Background technique

As a typical way of utilizing solar energy, solar cells have become an important development direction of renewable energy. Improving the efficiency of solar cells is one of the goals pursued by solar cells. III-V group compound semiconductors are ideal for solar cell materials due to their broad energy band structure. GaAs-based III-V group multi-junction cells have been the efficiency record holders and creators in the field of solar cells since their inception. According to the solar spectrum and the band relationship of III-V materials, GaAs-based lattice-matched GaInP/GaAs double-junction cells and InP-based lattice-matched InGaAsP/InGaAs double-junction cells can be reasonably designed to cover most of the sun with current matching. Spectrum, the experiment proves that the cell efficiency of this type of solar cell system can reach 43% by using a spectroscopic method. It is an ideal combination for realizing wide-spectrum high-efficiency solar cells. However, because the lattice mismatch between GaAs material and InP material reaches 3.8%, it is difficult to epitaxial high-quality InP material on GaAs by traditional methods. Therefore, in order to obtain efficient GaInP/GaAs/InGaAsP/InGaAs solar cells, wafer bonding is mostly used method to try to realize the quadruple-junction current-matched broad-spectrum absorption cell, however, on the one hand, wafer bonding involves a variety of processes (including layer transfer and chip lift-off technology), which reduces the success rate of the chip; on the other hand, GaAs materials and InP The direct bonding of materials has very high requirements on the cleanliness of the environment and equipment, and due to the difference in thermal expansion coefficient between the two, if the temperature difference in the post-bonding process or post-work is large, it will cause the warping of the material chip, and after bonding, the two If the series resistance between them is large, it will virtually increase the electrical loss of the four-junction battery; if metal bonding is used, the problem of balancing the series resistance and infrared optical absorption will be encountered.

Contents of the invention

The purpose of the present invention is to address the deficiencies in the prior art and provide a method for preparing double-sided growth high-efficiency broad-spectrum absorption multi-junction solar cells, which uses GaAs-based nanoscale patterning design to achieve high-quality epitaxy of GaAs-based InP materials , and then grow a lattice-matched InGaAsP/InGaAs solar cell on this basis, and grow a lattice-matched GaAs/GaInP solar cell on the other side of the GaAs substrate, and finally obtain a small lattice mismatch and thermal mismatch, It is a target product with good performance, and the preparation method is easy to operate and has a high yield rate, which is beneficial to improving the reliability and service life of the overall device.

In order to achieve the above-mentioned purpose of the invention, the preparation method of the double-sided growth high-efficiency broad-spectrum absorption multi-junction solar cell adopted in the present invention comprises the following steps:

(1) Forming a dielectric film on the first side of a double-sided polished GaAs substrate, and growing a lattice-matched GaAs/GaInP solar cell structure on the second side of the substrate;

(2) Protecting the second surface of the substrate, and then processing and forming a nanoscale dielectric mask pattern on the first surface of the substrate;

(3) growing and forming an InP thin film on the first surface of the substrate, and polishing the InP thin film until the flatness reaches the epitaxial level;

(4) sequentially growing an InGaAsP or InGaAsP/InGaAs solar cell structure and an electrode contact layer on the first surface of the substrate;

(5) Unprotecting the second surface of the substrate to obtain the target product.

Wherein, step (1) specifically includes: forming a dielectric film with a thickness of more than 200 nm on the first surface of the double-sided polished GaAs substrate, and sequentially growing a GaAs solar cell-tunneling junction on the second surface of the substrate. - GaInP solar cell structure, cell window layer and electrode contact layer.

In step (2), the dielectric film is patterned by chemical and/or physical processing methods, so as to form a smooth and dense dielectric mask pattern, and completely expose the substrate surface corresponding to the bare area.

As one of the preferred solutions, the dielectric film may be selected from any one or more of SiO ₂ film, SiN film, Al ₂ O ₃ film and TiO ₂ film, but is not limited thereto.

In step (2), the pattern is first formed by chemical and/or physical processing methods, and then the pattern is transferred to the dielectric film by dry etching and/or wet etching process, thereby forming a smooth and dense dielectric film pattern, and making The substrate surface corresponding to the exposed area is completely exposed.

Preferably, in step (2), the second surface of the substrate is protected by at least one of coating organic photoresist and depositing a dielectric film.

Step (3) is specifically as follows: first, selectively grow InP material in the nano-grooves formed in the dielectric mask pattern on the first surface of the substrate, and suppress misfit dislocations in the dielectric nano-grooves until no dislocation InP material, and then polymerize the discrete InP material until an InP film is formed, and then polish it by chemical and/or physical methods to form an InP film with epitaxial level flatness.

In step (4), an InGaAsP solar cell or an InGaAsP solar cell-tunnel junction-InGaAs solar cell and an electrode contact layer are sequentially grown on the InP thin film formed on the first surface of the substrate.

As one of the preferred solutions, the contact layer in step (4) may use InP and/or InGaAs layers, but is not limited thereto.

Further, in step (5), after the protection of the second surface of the substrate is released, the formed multi-junction solar cell device is subjected to subsequent processing by using the universal III-V solar cell process, and the final target product is obtained.

Description of drawings

Fig. 1 is the structural representation of the double-sided polishing GaAs substrate that A side is deposited with dielectric film;

Fig. 2 is a schematic diagram of growing a GaAs/GaInP cell and an electrode contact layer on the B side of the GaAs substrate shown in Fig. 1;

FIG. 3 is a schematic diagram of protecting the B side of the GaAs substrate shown in FIG. 2 with a dielectric film or photoresist;

Figure 4 is a schematic diagram of the nanoscale patterned structure of the dielectric film on the A side of the GaAs substrate, in which Figures 4A-1 and 4A-2: straight groove shape; Figure 4B-1, 4B-2: square grid shape; Figure 4C-1, 4C -2: cylindrical; Fig. 4D-1, 4D-2: conical;

Fig. 5 is a schematic diagram of a dislocation-suppressed InP layer, a dislocation-free InP layer and an InP aggregation layer grown on the A-plane of a GaAs substrate;

Figure 6 is a schematic diagram of the polished InP thin film grown on the A side of the GaAs substrate;

Figure 7 is a schematic diagram of continuing to grow InGaAsP/InGaAs cells and electrode contact layers on the A side of the GaAs substrate;

Figure 8 is a schematic diagram of the structure of the device after removing the protective layer on the B side of the GaAs substrate

Figure 9 is a schematic diagram of the structure of a multi-junction solar cell device in an embodiment of the present invention, with electrode contact layer/GaInP (battery)/tunnel junction 1/GaAs (battery)/GaAs substrate/dielectric film nanoscale pattern grown on both sides /InP dislocation suppression layer/InP dislocation-free layer/InGaAsP (cell)/tunnel junction 2/InGaAs (cell)/electrode contact layer. the

Detailed ways

As mentioned above, the inventor in this case aims to provide a high-efficiency and broad-spectrum absorption multi-junction solar cell manufacturing process to address the shortcomings of the existing multi-junction solar cell manufacturing process. In a nutshell, the present invention applies nanopatterning technology to the epitaxy of GaAs-based InP materials (the lattice mismatch of the two reaches 3.81%, the thermal mismatch is small, and both are zinc blende cubic structures) (GaAs thermal expansion coefficient 5.73 *10 ^-6 ℃ ^-1 , thermal expansion coefficient of InP 4.6*10 ^-6 ℃ ^-1 , thermal expansion coefficient of Si 2.6*10 ^-6 ℃ ^-1 , thermal expansion coefficient of Ge 5.9*10 ^-6 ℃ ^-1 ), and The double-sided growth method is adopted in order not to affect the growth quality of each lattice matching material, so as to obtain GaInP/GaAs/InGaAsP/(InGaAs) wide-spectrum high-efficiency multi-junction cells.

Further speaking, the process of the present invention may include the following steps:

(1) A dielectric film of a certain thickness is grown on the A side of the double-sided polished GaAs substrate;

(2) Use MOCVD or MBE to grow a lattice-matched solar cell GaAs/GaInP structure on the B side of the substrate;

(3) The surface B structure of the substrate is protected in a specific way, and the surface A of the substrate is patterned at the nanoscale to obtain a nanoscale patterned dielectric mask.

(4) Put the nano-patterned GaAs substrate back into the MOCVD or MBE equipment, and grow the InP dislocation suppression layer, the dislocation-free layer material and the InP aggregation layer material sequentially until the InP film is formed.

(5) Polish the InP film until an InP film with epitaxial level flatness is obtained, then put the substrate into MOCVD (or MBE), and continue to grow InGaAsP (or InGaAsP cells, tunneling junctions) according to the principle of multi-junction cell matching design. and InGaAs cells) solar cells, after the cell growth is completed, the electrode contact layer is finally grown.

(6) Remove the protective layer of the B-side structure of the multi-junction cell, and then prepare GaInP/GaAs/InGaAsP or GaInP/GaAs/InGaAsP/InGaAs high-efficiency broad-spectrum absorption multi-junction cells according to the universal III-V solar cell process .

In the aforementioned step 1, the A-side and B-side of the double-sided polished GaAs substrate are selected arbitrarily, just for easy marking, and the dielectric film can be SiO ₂ , SiNO, SiN, or Al ₂ O ₃ , TiO _{2 ,} etc. , and the growth method can be PECVD, thermal oxidation CVD, magnetron sputtering, electron beam evaporation and ALD, and the growth thickness depends on the requirements of subsequent nanoscale patterning and substrate protection, and should not be less than 50nm.

In the aforementioned step 2, MOCVD or MBE can be used to grow a lattice-matched solar cell GaAs/GaInP structure on the B side of the substrate. The B side refers to the side without a long dielectric film. GaAs/GaInP solar cells are grown sequentially. Junction solar cell design and existing growth conditions, sequentially grow GaAs solar cell-tunnel junction-GaInP solar cell structure and cell window layer and contact layer.

In the aforementioned step 3, the way to protect the B-surface structure of the substrate can be to use organic photoresist coating or dielectric film deposition protection, as long as the grown GaAs/GaInP battery structure is not protected from subsequent material growth and Process contamination is sufficient. The nanoscale patterning of the surface A of the substrate refers to patterning the dielectric film covered by the A surface according to the subsequent InP material growth requirements. The pattern formation method can be interference lithography, electron beam exposure, nano-press Printing, nanoball lithography, metal self-assembly, etc., and then transfer the pattern to the A-side dielectric film until the exposed area completely exposes the GaAs substrate. The transfer method can be dry etching, wet etching, or both. As long as the smooth and dense dielectric film pattern can be formed, and the exposed area completely exposes the GaAs substrate, the quality of the substrate is not damaged.

In the aforementioned step 4, the nanoscale patterned GaAs substrate is put back into the MOCVD or MBE equipment, firstly, the InP material is selectively grown in the nano-groove dielectric film, and misfit dislocations are suppressed in the dielectric nano-groove. Until a dislocation-free InP material is obtained, then the discrete InP material is polymerized until an InP film is formed.

In the foregoing step 5, the InP film is polished until an InP film with epitaxial level flatness is obtained, and then the substrate is placed in MOCVD (or MBE), and InGaAsP (or InGaAsP/ InGaAs) solar cells. Among them, InP thin film polishing can adopt various methods such as chemical mechanical polishing, chemical polishing, and ion beam polishing, as long as large-area epitaxial level flatness can be obtained. After polishing and cleaning, put the substrate B face up and continue to put it into the MOCVD (MBE) equipment, and grow InGaAsP solar cells or (InGaAsP-tunnel junction-InGaAs) on the polished InP film according to the design requirements of high-efficiency multi-junction cells The solar cell and the bottom electrode contact layer, which can be InP or InGaAs.

In the aforementioned step (6), the protective layer of the B-side structure of the multi-junction cell is removed, and then GaInP/GaAs/InGaAsP or GaInP/GaAs/InGaAsP/InGaAs high-efficiency wide Spectrally absorbing multi-junction cells.

The technical scheme of the present invention will be further described below in conjunction with a preferred embodiment and corresponding accompanying drawings:

The technological process of the present embodiment is as follows:

First, a layer of dielectric film is deposited on one side of the GaAs substrate, as shown in Figure 1, including the GaAs substrate 0 and the deposited dielectric film 1. The dielectric film can be SiO ₂ , SiN, SiNO, TiO ₂ , Al ₂ O as required ₃ , etc. The deposition thickness depends on the epitaxy requirements of the later nanoscale patterned substrate and the epitaxy protection requirements. The deposition equipment can be PECVD, thermal oxidation CVD, magnetron sputtering, electron beam evaporation, and atomic layer deposition.

Then GaAs cells, tunnel junctions, GaInP cells and electrode contact layers are sequentially deposited on the B side of the GaAs substrate using MOCVD or MBE equipment, as shown in FIG. 2 . The reference numerals 0 and 1 refer to the same components as in Figure 1, while the reference numeral 2 refers to the GaAs cell, 3 refers to the tunnel junction, 4 refers to the GaInP cell, 41 refers to the cell window layer Al(Ga)InP, 5 denotes an electrode contact layer. The thickness, doping type and concentration of the growth of each layer are determined according to the design of the high-efficiency multi-junction cell structure.

In order to not affect the B-side battery when the A-side battery structure is grown, the B-side battery is protected by a dielectric film or photoresist, as shown in Figure 3, where the reference numbers 0-5 refer to the same as the previous Figure 2, and the appended Figure 6 refers to the dielectric film deposited to protect the battery structure on side A, which can be SiO ₂ , SiN, SiNO, TiO ₂ , Al ₂ O ₃ , etc. The deposition equipment can be PECVD, thermal oxidation CVD, magnetron sputtering , electron beam evaporation and atomic layer deposition.

Then turn the above structure over, face A facing up, and conduct nano-patterning on the dielectric film 1. The patterned pattern can be one-dimensional deep groove shape (as shown in FIG. 4A ), two-dimensional deep groove shape ( 4B), two-dimensional cylindrical (as shown in FIG. 4C ), or two-dimensional conical (as shown in FIG. 4D ) and other patterns. The method of preparing graphics can be interference lithography, electron beam exposure, nanosphere lithography, nanoimprint metal self-assembly and other methods, and the graphics transfer method can be wet etching or reactive ion etching or inductively coupled plasma etching And mixed use of dry and wet etching.

After the nanoscale patterning process of the substrate A surface is completed, the InP layer is selectively grown on the surface of the substrate by MOCVD or MBE until the misfit dislocations are completely suppressed on the sidewall of the nanoscale patterned dielectric film, and then continue to grow InP until the InP exposes the dielectric nanostructure. As shown in Figure 5, the reference numerals 1-6 refer to the same components as those shown in Figures 4 and 3, while the reference numeral 81 refers to the grown InP mismatch layer, and threading dislocations are completely suppressed in the dielectric film Sidewall, as shown in this figure, the reference numeral 82 refers to the dislocation-free InP layer in the grown dielectric film, and the reference numeral 83 refers to the InP layer exposing the patterned dielectric film. In view of the fact that selective growth is anisotropic Growth, the InP surface has a certain crystal orientation, and the lateral growth is strengthened, and finally the InP layers are aggregated with each other to form a non-flat InP film.

The InP surface is polished to obtain an atomically flat InP surface, as shown in FIG. 6 . Wherein, reference numerals 1-6, 81 and 82 refer to components consistent with those indicated in FIG. 5, and reference numeral 84 refers to a polished InP film. The polishing method can be chemical mechanical polishing, chemical polishing, or a combination of the two.

The InGaAsP cell-tunnel junction-InGaAs cell-electrode contact layer is grown on the polished InP surface by MBE or MOCVD to complete the growth of the InGaAsP/InGaAs double junction cell. As shown in Figure 7, the components referred to by reference numerals 0-6, 81, 82, 83, and 84 are the same as those in Figure 6 above. The tunnel junction, 11 refers to the InGaAs cell, and 12 refers to the electrode contact layer.

Then remove the material protection layer of surface A, as shown in FIG. 8 .

Finally, the GaInP/GaAs/GaAs (substrate)/InGaAsP/InGaAs four-junction tandem cell is prepared according to the universal III-V solar cell process, as shown in Figure 9, wherein the reference numeral 13 refers to the InGaAs ohmic contact electrode, attached The reference numeral 14 refers to the ohmic contact electrode of GaAs material, and the references of other numerals are the same as those in FIG. 7 above.

The above description and the embodiments shown in the drawings should not be interpreted as limiting the design concept of the present invention. Those who have the same knowledge in the technical field of the present invention can improve and change the technical idea of the present invention in various forms, and such improvements and changes should be understood as belonging to the protection scope of the present invention.

Claims (10)

1. the preparation method of the efficient wide range absorption of a two-sided growth multijunction solar cell is characterized in that this method comprises the steps:

(1) on first of the GaAs of twin polishing substrate, form deielectric-coating, and the GaAs/GaInP solar battery structure of the formation lattice match of on second of said substrate, growing;

(2) said substrate second face is protected, on first of said substrate, be processed to form nanoscale medium mask pattern again;

(3) growth forms the InP film on first of said substrate, and said InP film polishing to evenness is reached the extension level;

(4) on first of said substrate successively growth form InGaAsP or InGaAsP/InGaAs solar battery structure and contact electrode layer;

(5) releasing obtains target product to second protection of said substrate.

2. the efficient wide range of two-sided growth according to claim 1 absorbs the preparation method of multijunction solar cell; It is characterized in that; Step (1) is specially: on first of the GaAs of twin polishing substrate, form the deielectric-coating of thickness more than 50nm, and on second of said substrate successively growth form GaAs solar cell-tunnel junctions-GaInP solar battery structure, battery Window layer and contact electrode layer.

3. the efficient wide range of two-sided growth according to claim 1 absorbs the preparation method of multijunction solar cell; It is characterized in that; Be said deielectric-coating to be carried out patterned in the step (2) through chemistry and/or physical refining processes; Thereby form smooth compact medium mask pattern, and the substrate surface corresponding with exposed area exposed fully.

4. absorb the preparation method of multijunction solar cell according to the efficient wide range of each described two-sided growth among the claim 1-3, it is characterized in that said deielectric-coating is selected from SiO at least ₂Film, SiNO film, SiN film, Al ₂O ₃Film and TiO ₂In the film any one.

5. the efficient wide range of two-sided growth according to claim 3 absorbs the preparation method of multijunction solar cell; It is characterized in that; Be at first to form pattern in the step (2) through chemistry and/or physical refining processes; Then adopt dry etching and/or wet-etching technology with design transfer to deielectric-coating, thereby form smooth compact medium film figure, and the substrate surface corresponding with exposed area exposed fully.

6. absorb the preparation method of multijunction solar cell according to the efficient wide range of claim 1 or 5 described two-sided growths; It is characterized in that, be to adopt at least a mode that applies in organic photoresist and the deposition medium film that second face of said substrate is protected in the step (2).

7. the efficient wide range of two-sided growth according to claim 1 absorbs the preparation method of multijunction solar cell; It is characterized in that; Step (3) is specially: selective growth InP material in the nanometer ditch in the medium mask pattern on being formed at first of said substrate at first is suppressed at misfit dislocation in the medium nanometer ditch, up to obtaining dislocation-free InP material; Then with the InP material polymerization of separation; Until forming the InP film, polish with chemistry and/or physical method thereafter, form InP film with extension level evenness.

8. the efficient wide range of two-sided growth according to claim 1 absorbs the preparation method of multijunction solar cell; It is characterized in that, be growth InGaAsP solar cell or InGaAsP solar cell-tunnel junctions-InGaAs solar cell and contact electrode layer on the InP film that is formed on first of the said substrate successively in the step (4).

9. according to the preparation method of claim 1 or the efficient wide range absorption of 8 described two-sided growths multijunction solar cell, it is characterized in that contact layer described in the step (4) is InP and/or InGaAs layer.

10. the efficient wide range of two-sided growth according to claim 1 absorbs the preparation method of multijunction solar cell; It is characterized in that; In the step (5) after the protection of removing second of said substrate; Also adopt pervasive III-V II-VI group solar cell technology that the multijunction solar cell device that forms has been carried out subsequent treatment, the final goal product.

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