A solar cell based on multi-quantum well structure and its preparation method

Abstract

The present invention discloses a solar cell based on a multi-quantum well structure and a preparation method thereof, wherein the solar cell based on the multi-quantum well structure comprises a substrate, a buffer layer, an n-GaN layer, an MQW absorption layer, a p-GaN composite layer and a current diffusion layer which are stacked in sequence, wherein the p-GaN composite layer comprises a p-GaN layer having a patterned concave region on the surface and a nanomaterial formed in the patterned concave region, wherein the nanomaterial is a nanometal or a quantum dot material. The present invention can further improve the energy conversion efficiency of the solar cell by arranging the nanomaterial in the patterned concave region, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and in particular to a solar cell based on a multi-quantum well structure and a preparation method thereof. Background Art

[0002] InGaN is a promising material for solar cell applications due to its good optical and electrical properties and adjustable bandgap energy from 0.7eV (InN) to 3.4eV (GaN), which can cover almost the entire solar spectrum. InGaN is also more resistant to proton radiation than silicon (Si) or other III-V materials such as GaAs and GaInP, and is mainly suitable for space solar cells without performance degradation. However, in order to obtain high conversion efficiency in InGaN solar cells, an InGaN absorber layer with a high indium (In) content is required to absorb the longer wavelength region of the solar spectrum. Currently, most InGaN-based solar cell systems use an InGaN / GaN multiple quantum well (MQW) structure, including an absorber layer with high crystalline quality and a high indium (In) content. However, since the thickness of the absorber layer in the InGaN / GaN MQW is limited to a few tens of nanometers, it is difficult to absorb all incident photons. In addition, for incident light with a longer wavelength, the absorption coefficient of InGaN is small, which will lead to a decrease in the external quantum efficiency in the longer wavelength region, thus resulting in limited energy conversion efficiency. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a solar cell based on a multi-quantum well structure and a preparation method thereof, which can further improve the energy conversion efficiency of the solar cell.

[0004] The technical solution adopted by the present invention is:

[0005] The present invention provides a solar cell based on a multi-quantum well structure, comprising a substrate, an n-GaN layer, a buffer layer, an MQW absorption layer, a p-GaN composite layer and a current diffusion layer which are stacked in sequence, wherein the p-GaN composite layer comprises a p-GaN layer with a patterned recessed area on the surface and a nanomaterial formed in the patterned recessed area, wherein the nanomaterial is a nanometal or a quantum dot material.

[0006] Preferably, the patterned recessed area is a micron-circular area.

[0007] Preferably, the p-GaN composite layer has a thickness of 150-200 μm.

[0008] Preferably, the nanometal includes at least one of nanosilver, nanogold, nanoindium, and nanometal alloy.

[0009] Preferably, the MQW absorption layer is any one of InGaN / GaN, InGaN / AlInGaN, and AlGaN / InGaN. More preferably, the MQW absorption layer is InGaN / GaN.

[0010] Preferably, the n-GaN layer comprises Si-doped n - GaN layer and Si heavily doped n + GaN layer.

[0011] Preferably, the current diffusion layer is an ITO layer, an IZO layer or an AZO layer.

[0012] Preferably, the substrate is made of sapphire, silicon carbide, gallium nitride or silicon.

[0013] Preferably, an ohmic contact structure is provided on the current diffusion layer and the n-GaN layer.

[0014] Furthermore, the ohmic contact structure is a single metal including but not limited to any one of Cr, Al, Ti, Pt, and Au, or a metal combination including but not limited to Cr / Au, Ti / Al / Au.

[0015] Preferably, the buffer layer comprises a low-temperature GaN buffer layer grown at 525-550°C and a high-temperature AlN buffer layer grown at 950-1100°C.

[0016] The present invention also provides a method for preparing the above-mentioned solar cell based on the multi-quantum well structure, comprising the following steps:

[0017] (1) preparing or obtaining a basic solar cell, wherein the basic solar cell comprises a substrate, a buffer layer, an n-GaN layer, an MQW absorption layer and a p-GaN layer stacked in sequence;

[0018] (2) preparing a SiO2 layer on the p-GaN layer and etching to expose a portion of the n-GaN layer;

[0019] (3) using a mask etching method to completely penetrate the SiO2 layer and partially penetrate the p-GaN layer to form a patterned recessed area;

[0020] (4) removing the SiO2 layer and forming a nano-metal or quantum dot material in the patterned recessed area;

[0021] (5) Prepare the current diffusion layer.

[0022] Preferably, step (4) is specifically as follows: preparing a metal layer in the patterned recessed area, then using a solvent to remove the SiO2 layer, and then using a rapid thermal annealing process or a furnace tube equipment to process the metal layer to form a nanometal; or preparing a quantum dot material in the patterned recessed area, and then removing the SiO2 layer.

[0023] The beneficial effects of the present invention are as follows: the present invention adopts a mature epitaxial growth process widely used in light-emitting diodes and laser diodes, and prepares nano-metal or quantum dot materials by patterning recessed areas in the p-GaN layer, which is easy to prepare.

[0024] The solar cell based on the multi-quantum well structure provided by the present invention has a patterned recessed area on the surface of the p-GaN layer and nano-metal or quantum dot particles are embedded in the patterned recessed area. Since the nano-metal is close to the MQW absorption layer, the local electric field near the MQW absorption layer can be enhanced to propagate scattered light to the MQW absorption layer, while enhancing the absorption capacity of short wavelengths, thereby improving the efficiency of the solar cell. In addition, the quantum dot material can effectively utilize the short-wavelength part of the solar energy spectrum, while increasing the surface photoconductivity effect and the filling factor of the solar cell on the surface of the component, thereby also improving the efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of a solar cell based on a multi-quantum well structure in Example 1;

[0026] Figure 2 This is a flow chart of the preparation of a solar cell based on a multi-quantum well structure in Example 1. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0028] Example 1

[0029] See also Figure 1 The present embodiment provides a solar cell based on a multi-quantum well structure, comprising a substrate 1, a GaN buffer layer 2, an n-GaN layer 3, an MQW absorption layer 4, a p-GaN composite layer and a current diffusion layer 8 stacked in sequence, wherein the substrate 1 is a sapphire substrate, the GaN buffer layer 2 is a low-temperature GaN buffer layer grown at 525-550°C, the n-GaN layer 3 comprises a 2-3 μm thick Si-doped n-GaN layer 4, and a p-GaN composite layer and a current diffusion layer 8. -GaN layer 31 and 10-20 nm thick Si heavily doped n + GaN layer 32, the MQW absorption layer 4 is 5 to 7 periods of In 0.17 Ga 0.83 N / GaN (3nm / 5nm) MQW absorption layer, the p-GaN composite layer includes a Mg-doped p-GaN layer 5 with a thickness of 200nm and a patterned recessed area on the surface and a nanometal 7b formed in the patterned recessed area, the current diffusion layer 8 is an ITO layer, and an ohmic contact structure 9 is also provided on the surface of the current diffusion layer 8 and the n-GaN layer 3. In this embodiment, the ohmic contact structure 9 uses Cr / Au.

[0030] See also Figure 2 This embodiment also provides a method for preparing the solar cell based on the multi-quantum well structure, comprising the following steps:

[0031] (1) Preparation of basic solar cells: A basic solar cell is prepared by using a metal organic chemical vapor deposition (MOCVD) system. The basic solar cell comprises a sapphire substrate 1 (0001), a buffer layer 2 grown on the sapphire substrate 1, and a Si-doped n-type silicon-doped ... - GaN layer 31, 10 to 20 nm thick Si heavily doped n + GaN layer 32, 5 to 7 periods of In 0.17 Ga 0.83 The N / GaN (3nm / 5nm) MQW absorption layer 4 and the top 200nm thick Mg-doped p-GaN layer 5 are composed. A 400-500nm thick SiO2 layer 6 is deposited on the top p-GaN layer 5 of the above-mentioned basic solar cell for etching mask. The buffer layer used in this embodiment is a low-temperature GaN buffer layer prepared by the following steps: the temperature is maintained in a specific range of 525℃~550℃, and after the temperature is stable, a low-flow trimethylgallium (TMGa) is loaded, the flow ratio of hydrogen and ammonia is maintained, and a low-temperature GaN buffer layer is grown on a sapphire substrate, with a trimethylgallium flow rate of 25sccm, a hydrogen flow rate of 25000sccm, and an ammonia flow rate of 25000sccm. The temperature time can be set to 3 minutes, and the thickness of the gallium nitride low-temperature buffer layer is about 20-30nm. (2) The polar surface is etched using an inductively coupled plasma (ICP) etching system until the n-GaN layer 3 is exposed. Due to the high etching selectivity between SiO2 and GaN, even after etching 400 to 500 nm deep to form the polar surface region, a SiO2 layer of about 200 to 300 nm thick is still retained.

[0032] (3) A photoresist (PR) mask is used to pattern micron circles with a diameter of 2 μm and a period of 2 μm. The micron circle patterned area is then etched in the order of the SiO2 layer and the p-GaN layer. Only p-GaN holes with a depth of about 20 nm are retained by a reactive ion etching (RIE) system and ICP etching, and finally a micron circle patterned recessed area is formed in which the SiO2 layer 6 is completely penetrated and the p-GaN layer 5 is partially penetrated.

[0033] (4) A metal layer 7a is deposited on the above structure using a sputtering machine. In this embodiment, the metal layer 7a is an Ag thin film.

[0034] (5) The remaining SiO2 layer is then removed in a hydrogen fluoride (HF) solution, so that the metal layer 7a exists only in the etched micron-circle patterned recessed areas.

[0035] (6) The structure obtained in step (5) is annealed at 600° C. for 5 min in a nitrogen (N2) atmosphere using a rapid thermal annealer (RTA) to form nanometal 7b from the metal layer 7a. The uniform morphology and diameter (20 to 200 nm) of the nanometal particles can be optimized according to the thickness of the metal layer film to obtain better extinction efficiency.

[0036] (7) Finally, a 200 nm thick indium tin oxide (ITO) layer is deposited as a current diffusion layer 7, and an ohmic contact structure 9 is also provided on the surface of the current diffusion layer 8 and the n-GaN layer 3. In this embodiment, the ohmic contact structure 9 is Cr / Au (30 nm / 300 nm) for contact between n-type GaN and p-type GaN.

[0037] When the wavelength of the light source is closer to its surface plasmon resonance frequency, the intensity contrast will increase. The surface plasmon resonance frequency of the nano-silver particles made of the silver film in this embodiment is about 450nm, so it has a strong scattering ability relative to the short wavelengths in the solar spectrum. The thickness of the laid p-type gallium nitride (p-GaN) is usually 150 to 200 microns, and embedded in the p-GaN patterned recessed area, the nano-metal particles can be closer to the absorption layer indium gallium nitride (InGaN) to enhance the absorption capacity of short wavelengths and obtain higher light absorption efficiency. We only insert plasma Ag nanoparticles in the patterned recessed area for strong plasma interaction. The distance between the nano-metal particles and the absorption layer is very close, only about 20nm. In this embodiment, In is taken into account 0.17 Ga 0.83The band gap energy of N / GaN MQW (2.7eV) is estimated to occur in the target light absorption region below ~450nm. Ag nanoparticles produce plasma light scattering and local field enhancement near the MQW absorption layer, and the external quantum efficiency in the wavelength region is enhanced by matching the plasma resonance of Ag nanoparticles, resulting in improved Jsc and Voc.

[0038] This embodiment uses the simulation tool COMSOL to perform three-dimensional finite element method calculations on the prepared solar cell based on the multi-quantum well structure. The numerical simulation results show that the resonance of the localized surface plasmon can be adjusted by changing the size, shape and period of the nanoparticles to adjust its resonant wavelength. Similarly, the scattering effect can also be controlled to the desired wavelength by a similar method. Finally, the solar cell based on the multi-quantum well structure of this embodiment is integrated, and the overall energy conversion efficiency is improved with the help of the embedded silver nanoparticles.

[0039] In this embodiment, nano silver is used as an example for explanation. The nano metals actually used include but are not limited to nano silver, nano gold, nano indium, nano metal alloys, etc. In this embodiment, the buffer layer is used as an example for explanation. The buffer layer can also be a high temperature AlN buffer layer, which can be prepared by the following method: the temperature is maintained within a specific range of 950°C to 1100°C, and after the temperature is stable, a suitable flow of trimethylaluminum (TMA) is loaded, the flow ratio of hydrogen and ammonia is maintained, and a high temperature AlN buffer layer is grown on a sapphire substrate. The thickness of the aluminum nitride high temperature buffer layer is grown about 20 to 30 nm. Usually in the process of epitaxy of gallium nitride material (GaN), a buffer layer is first grown at a low temperature on the sapphire substrate before the growth of the epitaxial layer (epilayer), which can reduce the adverse effects on crystallinity caused by the difference in lattice constant and thermal expansion coefficient between the substrate and gallium nitride, thereby improving the electrical and optical properties of its epitaxial layer.

[0040] Example 2

[0041] This embodiment provides a solar cell based on a multi-quantum well structure, which is the same as that in Embodiment 1, except that the nanomaterial formed in the patterned recessed area is a quantum dot material, which can be CdS, CdSe quantum dots, etc. These nano-sized materials can absorb short-wavelength light and efficiently convert it into visible light, thereby improving the efficiency of the solar cell.

[0042] The preparation method of the solar cell based on the multi-quantum hydrazine structure is the same as the preparation steps (1)-(5) in Example 1, except that step (4) is to deposit the quantum dot material on the structure formed in step (3) using a sputtering machine. Since the quantum dot material itself is a nanomaterial, there is no need to perform rapid thermal annealing (RTA) treatment on it. Finally, the power diffusion layer is deposited and the ohmic contact structure is prepared.

[0043] In this embodiment, the quantum dot material deposition can also utilize the spin coating technology to spin-coat the quantum dots onto the surface structure to form a quantum solar cell device.

Claims

1. A solar cell based on a multi-quantum well structure, It is characterized in that The invention comprises a substrate, a buffer layer, an n-GaN layer, an MQW absorption layer, a p-GaN composite layer and a current diffusion layer which are stacked in sequence, wherein the p-GaN composite layer comprises a p-GaN layer with a patterned concave region on the surface and a nano material formed in the patterned concave region, wherein the nano material is a nano metal or a quantum dot material; the thickness of the p-GaN composite layer is 150 to 200 μm; the patterned concave region is a micron circle region; the buffer layer is a low-temperature GaN buffer layer grown at 525 to 550° C. or a high-temperature AlN buffer layer grown at 950 to 1100° C.; the n-GaN layer comprises a Si-doped n-GaN layer; - GaN layer and Si heavily doped n + GaN layer; The solar cell is prepared by a preparation method comprising the following steps: (1) preparing or obtaining a basic solar cell, wherein the basic solar cell comprises a substrate, a buffer layer, an n-GaN layer, an MQW absorption layer and a p-GaN layer stacked in sequence; (2) Preparing SiO on the p-GaN layer 2 layer, etching to expose a portion of the n-GaN layer; (3) Using mask etching method to make SiO 2 The p-GaN layer is fully penetrated and the p-GaN layer is partially penetrated to form a patterned recessed area; (4) Removal of SiO 2 A layer is formed to form a nano-metal or quantum dot material in the patterned recessed area; (5) Prepare the current diffusion layer.

2. The solar cell based on the multi-quantum well structure according to claim 1, It is characterized in that The nano-metal includes at least one of nano-silver, nano-gold, nano-indium, and nano-metal alloy.

3. The solar cell based on the multi-quantum well structure according to claim 1, It is characterized in that The MQW absorption layer is any one of InGaN / GaN, InGaN / AlInGaN, and AlGaN / InGaN.

4. A solar cell based on a multi-quantum well structure according to any one of claims 1 to 3, It is characterized in that The current diffusion layer is an ITO layer, an IZO layer or an AZO layer.

5. A solar cell based on a multi-quantum well structure according to any one of claims 1 to 3, It is characterized in that The substrate is made of sapphire, silicon carbide, gallium nitride or silicon.

6. A solar cell based on a multi-quantum well structure according to any one of claims 1 to 3, It is characterized in that An ohmic contact structure is arranged on the current diffusion layer and the n-GaN layer.

7. The solar cell based on the multi-quantum well structure according to claim 6, It is characterized in that The ohmic contact structure is a single metal or a combination of metals.

8. The solar cell based on the multi-quantum well structure according to claim 1, It is characterized in that Step (4) is specifically: preparing a metal layer in the patterned recessed area, and then removing SiO 2 layer, and then use a rapid thermal annealing process or a furnace tube device to process the metal layer to form a nanometal; or prepare a quantum dot material in the patterned concave area, and then remove SiO 2 layer.

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