CN101820007A - High-conversion rate silicon and thin film compound type multijunction PIN solar cell and manufacturing method thereof - Google Patents

Abstract

The invention provides a high-conversion rate silicon and thin film compound type multijunction PIN solar cell and a manufacturing method thereof. The silicon and thin film compound type multijunction structure can be adopted from relevant six materials to form the two-junction, three-junction, four-junction, five-junction or six-junction thin film solar cell. The manufacturing method adopts a double-face polishing process, an ion implantation process, a plasma-strengthened chemical vapor deposition process, a laser crystallization process, a plasma-doping process and a PECVD (Plasma Enhanced Chemical Vapor Deposition) transition laminate process to improve the interface performance among laminates, for example, reducing the interface resistance among the laminates and strengthening the crystallization performance of thin-film materials, and uses a hydrotreating process for keeping the performance stability of the material of each laminate and improving the light transmittance and the electrical conductivity of the transparent conducting thin-film materials and interfaces. The conversion rate of the cell can reach 25%-30%, and the cell has better stability.

Description

High conversion rate silicon crystal and thin film composite multi-junction PIN solar cell and manufacturing method thereof

technical field

The invention relates to a solar cell, especially a crystalline silicon and silicon-based thin-film solar cell structure and a manufacturing method thereof.

Background technique

Since the French scientist AE. Becquerel discovered the photoelectric conversion phenomenon in 1839, the first solar cell based on semiconductor selenium was born in 1883. RuSSell obtained the first solar cell patent (US.2,402,662) in 1946, and its photoelectric conversion efficiency was only 1%. It was not until 1954 that Bell Laboratories' research discovered that doped silicon-based materials have high photoelectric conversion efficiency. This research laid the foundation for the modern solar cell industry. In 1958, the Haffman Power Company of the United States installed the first solar panel on a satellite in the United States, and its photoelectric conversion efficiency was about 6%. Since then, the research and production of solar cells on monocrystalline silicon and polycrystalline silicon substrates have developed rapidly. In 2006, the output of solar cells has reached 2000 megawatts, the photoelectric conversion efficiency of monocrystalline silicon solar cells has reached 24.7%, and commercial products have reached 22.7%. %, the photoelectric conversion efficiency of polycrystalline silicon solar cells reaches 20.3%, and commercial products reach 15.3%.

On the other hand, Zhores Alferov of the Soviet Union developed the first GaAs-based high-efficiency III-V solar cells in 1970. Since MOCVD (metal organic chemical vapor deposition), the key technology for preparing III-V thin film materials, was not successfully developed until around 1980, the Applied Solar Cell Company in the United States successfully applied this technology in 1988 to prepare a photoelectric conversion efficiency of 17%. GaAs-based III-V solar cells. Afterwards, the doping technology of III-V materials with GaAs as the substrate and the preparation technology of multi-level tandem solar cells have been extensively researched and developed. The photoelectric conversion efficiency reached 19% in 1993 and 24% in 2000. %, reaching 26% in 2002, 28% in 2005, and 30% in 2007. In 2007, Emcore and SpectroLab, two major American III-V solar cell companies, produced high-efficiency III-V solar commercial products with a photoelectric conversion rate of 38%. These two companies occupy the global III-V solar cell market. 95%. Recently, the National Energy Institute of the United States announced that they have successfully developed a multi-stage tandem III-V solar cell with a photoelectric conversion efficiency as high as 50%. Because the substrate of this type of solar cell is expensive, and the cost of equipment and process is high, it is mainly used in the fields of aviation, aerospace, national defense and military industry.

The research and production of solar cells in foreign countries can be roughly divided into three stages, that is, there are three generations of solar cells.

The first generation of solar cells is basically represented by single-unit solar cells based on monocrystalline silicon and polycrystalline silicon. Focusing only on improving photoelectric conversion efficiency and large-scale production, there are problems such as high energy consumption, labor-intensive, unfriendly to the environment, and high cost. The price of electricity generated by it is about 5 to 6 times that of coal electricity; until 2007 , The output of the first generation of solar cells still accounts for 89% of the total solar cells in the world. Experts predict that the first generation of solar cells will be phased out in ten years and become history.

The second generation of solar cells is thin-film solar cells, which is a new technology developed in recent years. It focuses on reducing energy consumption and process costs in the production process. Experts call it a green photovoltaic industry. Compared with monocrystalline silicon and polycrystalline silicon solar cells, the amount of thin-film high-purity silicon is 1% of it. At the same time, low-temperature plasma-enhanced chemical vapor deposition deposition technology, electroplating technology, and printing technology are widely studied and applied to thin-film solar cells. Production of batteries. Due to the use of low-cost glass, stainless steel sheets, and polymer substrates as substrate materials, the production cost is greatly reduced, and it is beneficial to large-scale production. The materials of thin-film solar cells that have been successfully developed so far are: CdTe, whose photoelectric conversion efficiency is 16.5%, while commercial products are about 7%; CulnSe, whose photoelectric conversion efficiency is 19.5%, and commercial products are 11%; amorphous silicon and The photoelectric conversion efficiency of microcrystalline silicon is 8.3-15%, and that of commercial products is 7-13.3%. Has been applied to silicon-based thin-film solar cells. Experts predict that thin-film solar cells will become the mainstream product of solar cells in the world in the next 5 to 10 years due to their low cost, high efficiency and mass production capacity. The focus of research on thin-film solar cells is to develop high-efficiency, low-cost, and long-life photovoltaic solar cells. They should have the following characteristics: low cost, high efficiency, long life, abundant material sources, and non-toxic. Scientists are more optimistic about amorphous silicon thin film solar cells. At present, the thin-film solar cells that account for the largest share are amorphous silicon solar cells, usually pin structure cells, the window layer is boron-doped P-type amorphous silicon, followed by a layer of undoped i-layer, and then a layer of phosphorus-doped N-type amorphous silicon, and plated electrodes.

Amorphous silicon cells are generally formed by decomposing and depositing high-purity silane and other gases by PECVD (Plasma Enhanced Chemical Vapor Deposition) method. Such a manufacturing process can be continuously completed in multiple vacuum deposition chambers during production to achieve mass production. Due to the low deposition and decomposition temperature, thin films can be deposited on glass, stainless steel plates, ceramic plates, and flexible plastic sheets, which is easy for large-scale production and low cost. The structure of the amorphous silicon-based solar cell prepared on the glass substrate is: Glass/TCO/p-a-SiC:H/i-a-Si:H/n-a-Si:H/Al, and the amorphous silicon solar cell prepared on the stainless steel substrate The structure of silicon-based solar cells is: SS/ZnO/n-a-Si:H/i-a-Si(Ge):H/p-na-Si:H/ITO/Al.

The most effective way to improve cell efficiency is to maximize the light absorption efficiency of the cell. For silicon-based thin films, the use of narrow bandgap materials is an inevitable way. For example, the narrow bandgap material used by Uni-Solar is a-SiGe (amorphous silicon germanium) alloy, and their a-Si/a-SiGe/a-SiGe triple-junction laminated battery, small area battery (0.25cm ² ) efficiency It reaches 15.2%, the stable efficiency reaches 13%, the 900cm ² module efficiency reaches 11.4%, the stable efficiency reaches 10.2%, and the product efficiency reaches 7%-8%.

It is internationally recognized that amorphous silicon/microcrystalline silicon tandem solar cells are the next-generation technology of silicon-based thin-film batteries, an important technical approach to realize high-efficiency and low-cost thin-film solar cells, and a new industrialization direction of thin-film batteries. In 2005, the sample efficiencies of amorphous silicon/microcrystalline silicon laminated battery modules of Mitsubishi Heavy Industries and Zhongyuan Chemical Company reached 11.1% (40cm×50cm) and 13.5% (91cm×45cm) respectively. Japan's Sharp Corporation realized the industrial production of amorphous silicon/microcrystalline silicon stacked solar cells in September 2007 (25MW, efficiency 8%-8.5%), European Oerlikon (Olikon) company, American AppliedMaterials (applied materials company), It is also developing key manufacturing technologies for product-level amorphous silicon/microcrystalline silicon cells.

Domestically, Nankai University conducts research on microcrystalline silicon materials and amorphous silicon/microcrystalline silicon stacked batteries based on the national "10th Five-Year Plan", "11th Five-Year Plan" 973 Project and "11th Five-Year Plan" 863 Project. The efficiency of small-area microcrystalline silicon cells reaches 9.36%, the efficiency of amorphous silicon/microcrystalline silicon stacked cells reaches 11.8%, and the efficiency of 10cm×10cm modules reaches 9.7%. Now it is cooperating with Fujian Junshi Energy Company to carry out research and development of key equipment and battery manufacturing technology of square meter amorphous silicon/microcrystalline silicon laminated battery.

At present, silicon-based thin-film batteries mainly have three structures: single-junction or double-junction amorphous silicon batteries with glass as the substrate, amorphous silicon and microcrystalline silicon double-junction batteries with glass as the substrate, and amorphous silicon with stainless steel as the substrate. Crystalline silicon and amorphous germanium silicon alloy triple junction cells. Since each product has its unique advantages, these three battery structures will develop simultaneously in the future. The long-term development direction of silicon-based thin-film batteries is obvious. In addition to making full use of its unique advantages, it is mainly to overcome the problems in product development, production and sales. Silicon-based thin-film batteries need to further improve battery efficiency, and using microcrystalline silicon batteries as the bottom battery of multi-junction batteries can further improve battery efficiency and reduce light-induced degradation of batteries.

At present, the technical difficulties in the industrialization of microcrystalline silicon cells are the realization of high-speed deposition technology of microcrystalline silicon and the uniformity of large-area microcrystalline silicon-based thin film materials. If the technical problems of large-area and high-speed deposition of microcrystalline silicon can be solved in a relatively short period of time, it is expected that in the near future, multi-junction cells combining amorphous silicon and microcrystalline silicon will become the mainstay of silicon-based thin-film cells. product. Amorphous silicon and microcrystalline silicon multi-junction cells can be deposited on glass substrates or on flexible substrates. Both amorphous and microcrystalline silicon-based thin-film cells can be deposited on glass or flexible substrates. Silicon multi-junction cell structure.

The current commercial silicon-based thin-film solar cells are amorphous silicon thin-film solar cells. Since the energy gap of amorphous silicon is 1.7, it can only absorb solar energy with a wavelength of 400-500nm. Because of its low solar energy conversion efficiency, about 6%, the conversion rate of this silicon-based thin film solar cell needs to be improved

Although the technologies and background materials in the above aspects, it has been mentioned that materials with different energy gaps are used to expand the absorption spectrum of solar energy. But so far no one has used a series of six materials with different energy gaps to form a thin-film solar cell with a multi-junction multi-stacked PIN structure, and no one has developed a method for preparing such a thin-film solar cell with a multi-junction multi-stacked PIN structure. technology. Also no one has developed and prepared this high-conversion silicon crystal and thin film composite multi-junction multi-stacked PIN solar cell and its manufacturing method.

Contents of the invention

The technical problem to be solved by the present invention is to propose a high-conversion silicon crystal and thin film composite solar cell by combining monocrystalline silicon and polycrystalline silicon-based single-unit solar cells with silicon-based thin-film solar cells, aiming at the deficiencies in the prior art. A type multi-junction PIN solar cell and a manufacturing method thereof, the obtained cell has higher conversion efficiency and excellent stability.

One of the technical solutions of the present invention is that the structure of the high-conversion silicon crystal and thin-film composite multi-junction PIN solar cell is one of the following:

(1) Bottom electrode/n layer/i layer/p layer/intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n layer/i layer/p layer /intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/ p layer/intermediate reflection layer/n layer/i layer/p layer/TCO-Al/anti-reflection film;

(2) Bottom electrode/n layer/i layer/p layer/intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n layer/i layer/p layer /intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/ p-layer/TCO-Al/anti-reflection coating;

(3) Bottom electrode/n layer/i layer/p layer/intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n layer/i layer/p layer /intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/TCO-Al/anti-reflection film;

(4) Bottom electrode/n layer/i layer/p layer/intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n layer/i layer/p layer /intermediate reflective layer/n layer/i layer/p layer/intermediate reflective layer/n layer/i layer/p layer/TCO-Al/anti-reflection film;

(5) Bottom electrode/n layer/i layer/p layer/intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n layer/i layer/p layer /Intermediate reflection layer/n layer/i layer/p layer/TCO-Al/anti-reflection film;

(6) Bottom electrode/n layer/i layer/p layer/intermediate reflection layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/intermediate reflective layer/n layer/p layer/intermediate reflective layer/n layer/p layer/intermediate reflective layer/n layer/p layer/intermediate reflective layer/n layer/p layer/TCO- Al/anti-reflection coating;

(7) Bottom electrode/n layer/i layer/p layer/intermediate reflection layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/intermediate reflective layer/n layer/p layer/intermediate reflective layer/n layer/p layer/intermediate reflective layer/n layer/p layer/TCO-Al/antireflection film;

(8) Bottom electrode/n layer/i layer/p layer/intermediate reflection layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/TCO-Al/anti-reflection film;

(9) Bottom electrode/n layer/i layer/p layer/intermediate reflection layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/TCO-Al/anti-reflection film;

(10) Bottom electrode/n layer/i layer/p layer/intermediate reflection layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflection layer/n layer/p layer/intermediate reflection layer/n layer/p layer/TCO-Al/anti-reflection coating;

(11) Bottom electrode/n layer/i layer/p layer/intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n layer/p layer/TCO- Al/anti-reflection coating;

(12) Bottom electrode/n layer/i layer/p layer/intermediate reflection layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer//TCO-Al/anti-reflection film;

Wherein, the p layer, i layer and n layer are all selected from μc-Si _{1-x Gex} , A-Si _{1-x Gex} , μc-SiC, A-SiC, μc-Si, A-Si semiconductor One of the materials, the film layer between the TCO-Al layer and the adjacent intermediate reflective layer and between two adjacent intermediate reflective layers is a junction, and the semiconductor materials used in each film layer in each junction are the same and different due to doping And form a pin junction or pn junction; 0≤x≤1; "/" indicates the interface between the two layers; n- indicates an electronic (n-type) semiconductor, i- indicates an intrinsic semiconductor, and P- indicates a hole type ( P-type) semiconductor; A-indicates amorphous, μc-indicates microcrystalline.

The n ⁺ type silicon crystal layer can be a silicon crystal layer formed on an n-type silicon wafer by means of phosphorus (p) ion implantation and doping diffusion, and the P ⁺ silicon crystal layer can be formed by boron (B) ion implantation and doping Diffusion method is used to form a silicon crystal layer on an n-type silicon wafer, thereby forming the n ⁺ -type silicon crystal layer/n-type silicon wafer/p ⁺ -type silicon crystal layer.

A specific composition of the above battery structure is: bottom electrode/n-epi-Ge/i-gradient epi-Si _1-x Ge _x /p-epi-Si/intermediate reflection layer/n ⁺ type silicon crystal layer/n type Silicon wafer/p ⁺ type silicon crystal layer/intermediate reflection layer/n-μc-Si/i-μc-Si/p-μc-Si/intermediate reflection layer/nA-Si _1-x Ge _x /i-gradient A- Si _1-x Ge _x /pA-Si/intermediate reflector/nA-Si/iA-Si/pA-Si/intermediate reflector/n-μc-SiC/i-μc-SiC/p-μc-SiC/intermediate Reflective layer/nA-SiC/iA-SiC/pA-SiC/TCO-Al/anti-reflection film; among them, epi refers to epitaxial growth single crystal layer (epitaxy), such as n-epi-Ge refers to electronic type (n type) Semiconductor epitaxial growth of single crystal layer; "gradient" means that silicon germanium (Si _1-x Ge _x ) gradually changes from 1 to 0 by changing the value of x (0≤x≤1), while silicon germanium (Si _{1 -x} Ge _x ) changes from the (Ge) germanium layer - the gradient silicon germanium layer - to the silicon (Si) layer.

In the above structure, the PIN structure (n layer/i layer/p layer) may also be replaced by a PN structure (n layer/p layer).

In the above structure, the silicon wafer may be a single crystal silicon wafer or a polycrystalline silicon wafer.

In the above structure, the anti-reflection film may be a porous SiO ₂ film, or a nanofiber SiO ₂ film, or a SiO ₂ /TiO ₂ composite film or the like. Among them, the porous _SiO2 membrane can be selected from a porous _SiO2 membrane product with a porosity of 10-50% and a pore diameter of 50nm-1000nm; the nanofiber _SiO2 can be selected from a fiber diameter of 50nm-500nm and an aspect ratio of 1:5-1:10 Nanofiber SiO ₂ ; the SiO ₂ /TiO ₂ composite film can be single-layer composite or multi-layer composite, for example: TiO ₂ (145nm)/SiO ₂ (95nm) or TiO ₂ (15nm)/SiO ₂ (35nm) /TiO ₂ (150nm)/SiO ₂ (100nm) and so on.

In the above structure, the TCO-Al layer is a transparent conductive aluminum oxide film, and its technical parameters can be selected: the purity is above 99.9%, the visible light transmittance is greater than 90%; the resistivity is less than 1×10 ^-3 ohm cm, The thickness of the film is 50nm-5000nm; TCO (transparent conductive oxide film) can also be Ag, Ga, doped ZnO _x , ITO transparent conductive oxide film material, etc.; this layer can be prepared by PVD or sol, gel method.

In the above structure, the middle reflection layer is a film layer with good conductivity, which can be made of Ag or Al, Ga, doped ZnO _x , SiN _x , SiO _x , ITO and other materials, and can be made by PVD Or PECVD, or sol, gel method; a set of optional technical parameters for the film layer are: material purity greater than 99.9%, resistivity less than 1x10 ^-3 ohm cm, film thickness 50nm-5000nm. The intermediate reflection layer can allow long waves in a specific wavelength range to pass through and reflect short waves in a specific wavelength range.

The current of the multi-junction and multi-stacked PIN structure of the present invention has little change, and the voltage is increased by increasing the number of junctions, thereby improving the efficiency of the thin-film solar cell. Because the energy that can be used by a solar cell of a material is light energy in the spectral domain with a wavelength ratio of 1.24Eg (eV) (Eg is the energy gap width of the material). If the thin films of homogeneous and different bandgap materials are stacked, the light energy of a wider spectrum can be used, which can increase the light absorption efficiency of the solar cell; The electrical junction converts short-wavelength light energy into electrical energy; the use of narrow-band materials as the bottom electrical junction can convert ultra-long-wavelength light energy into electrical energy. Multi-junction multi-tandem solar cells have higher photoelectric conversion efficiency due to more fully utilizing the sunlight spectral domain. If in a multi-junction multi-stack solar cell, between the junctions with different energy gap widths, an intermediate reflective layer is added to gradually incident and total reflect the incident light of each wavelength band, increasing its optical path in the cell Therefore, the absorption of light by the solar cell is increased, and the conversion efficiency is improved.

The second technical solution of the present invention is that the high-conversion silicon crystal and thin film composite multi-junction PIN solar cell and its manufacturing method include:

Chemically or mechanically (CMP) double-sided polishing of n-type silicon wafers (monocrystalline or polycrystalline); then,

n-type silicon wafers (monocrystalline silicon wafers and polycrystalline silicon wafers) are cleaned; then,

Perform ion implantation on n-type silicon wafers (single crystal silicon wafers or polycrystalline silicon wafers) to form n ⁺ type silicon crystal layers/n type silicon wafers/p ⁺ type silicon crystal layers (i.e. n ⁺ -layer-n-type silicon wafers-p ⁺ -layer) structure;

Prepare TCO layer and anti-reflection film by conventional process;

PECVD (Plasma Enhanced Chemical Vapor Deposition Process), CVD (Chemical Vapor Deposition Process), Laser Crystallization Process, Plasma Doping Process and PECVD Process are used to prepare silicon-based thin films to obtain high-quality film layers and reduce the gap between layers. interface resistance;

The amorphous silicon or microcrystalline silicon film of the silicon-based film is generally deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition-plasma enhanced chemical vapor deposition) method, using hydrogen as the carrier gas, and using high-purity silane (SiH ₄ ) to decompose and deposit. become.

The amorphous or microcrystalline Si _1-x Ge _x thin film is generally formed by reaction decomposition and deposition using SiH ₄ and GeH ₄ as reaction precursors and H ₂ as carrier gas.

The amorphous or microcrystalline SiC thin film is generally formed by reaction decomposition and deposition using SiH ₄ and CH ₄ as reaction precursors and H ₂ as carrier gas.

The silicon-rich silicon oxide intermediate reflection layer film is generally formed by reaction decomposition and deposition using SiH ₄ and NO ₂ as reaction precursors and H ₂ as carrier gas.

The P-type and N-type silicon-based thin films are generally realized by doping with PH ₃ (N-type) and B ₂ H ₆ (P-type) plasma.

The plasma enhanced chemical vapor deposition temperature is 200°C-400°C.

The single crystal epitaxial thin film of Si _1-x Ge _x is deposited by chemical vapor deposition process using SiH ₄ and GeH ₄ as reaction precursors, H ₂ as carrier gas, and a reaction temperature of 600°C-1000°C.

Hydrogenation treatment is carried out on the silicon-based film layer to maintain the stability of the material properties of each film layer and improve the light transmittance and conductivity of the transparent conductive film material and the interface.

These thin film materials can also be prepared by HD-PECVD.

In the manufacturing method of the present invention, silicon wafer (monocrystalline silicon wafer or polycrystalline silicon wafer) is carried out cleaning process in two steps:

In the first step, wash with a solution of HCl:H ₂ O ₂ :H ₂ O=10:1:50 at 60°C-70°C for 5 minutes-10 minutes;

In the second step, wash with a solution of NH ₄ OH: _{H 2} O ₂ :H ₂ O=10:1:50 at 60°C-70°C for 5 minutes-10 minutes; finally wash with water.

In the manufacturing method of the present invention, the laser crystallization process uses a XeCl excimer laser with a wavelength of 308nm, and by controlling the output power, step speed and time of the laser, recrystallization of amorphous Si, Si _1-x Ge _x , and SiC is formed Microcrystalline, and even form single crystal-like Si, Si _1-x Ge _x , SiC films.

In the manufacturing method of the present invention, the PECVD hydrogenation process adjusts the volume ratio of hydrogen and nitrogen and the energy of the plasma to hydrogenate the film at a temperature of 100°C-400°C to enhance the stability of the film material; the hydrogen and The volume ratio of nitrogen is 10-100 times (ie hydrogen volume: nitrogen volume=10-100).

The present invention adopts PECVD or HD-PECVD (Plasma Enhanced Chemical Vapor Deposition-High Density Plasma Enhanced Chemical Vapor Deposition) film deposition process, plasma doping process, laser crystallization process and hydrogenation treatment process to successfully prepare high-quality Amorphous (A) and microcrystalline (μc) Si and SiGe, SiC thin films. The energy gap widths of these materials are shown in Table 1.

Table 1 Energy gap width of amorphous (A) and microcrystalline (μc) Si, SiGe and SiC thin film materials

Material Energy gap width (ev) Material Energy gap width (ev) A-Si _1-x Ge _x 1.3-1.7 µc-Si ~1.2 μc-Si _1-x Ge _x 0.7-1.2 A-SiC ~2.1 A-Si ~1.7 μc-SiC ~1.8

Therefore, we can combine the above six materials to broaden the energy spectrum absorption width of silicon-based thin-film solar cells, so as to improve the photoelectric conversion rate of silicon-based thin-film solar cells. The absorption energy spectrum range of various materials is shown in Fig. 1.

The method of the present invention prepares amorphous and microcrystalline Si, and the properties of SiGe and SiC thin films are shown in Table 2.

Table 2 Properties of amorphous and microcrystalline Si, SiGe and SiC films

Technical Parameters a-Si _1-x Ge _x mc-Si _1-x Ge _x p,n-(a,μc) _-SiCx Darkroom conductivity Ω-cm) ^-1 ~10 ^-8 < ^10-7 ~10 ^-5 -10 ^-6 activation energy ~0.7 ~0.5 Optical energy gap (eV) (300k) 1.5-1.7 ~0.9 1.8-2.1 Spin density (cm ^-3 ) <10 ¹⁷ <10 ¹⁷ From the migration speed μ _τ (cm ² /V) ＞10 ^-7 (600nm) ＞10 ^-7 (600nm) Absorption coefficient (cm ^-1 ) ＞10 ³ (800nm) ＞10 ³ (800nm) ＞10 ⁴ (400nm)

From the above, it can be known that the present invention is a high-conversion silicon crystal and thin-film composite multi-junction PIN solar cell and its manufacturing method. The conversion efficiency of multi-junction series thin-film solar cells can reach 25-30%, and it has better stability. properties; the present invention adopts laser crystallization process, plasma doping process and PECVD transition layer process to improve the interface performance between each layer, reduce the interface resistance between each laminated layer and enhance the crystallization performance of thin film material, and use hydrogenation treatment process to maintain Stabilize the performance of each layer of material and improve the light transmittance and conductivity of the transparent conductive film material and interface.

Description of drawings

Figure 1 is an energy spectrum depicting amorphous, microcrystalline and crystalline silicon (Si), amorphous and microcrystalline (or epitaxial single crystal) silicon germanium (SiGe) and amorphous and microcrystalline silicon carbide (SiC) absorption range;

Figure 2 is a schematic diagram of the film layer structure and preparation process of a high-conversion silicon crystal and thin film composite multi-junction PIN solar cell according to an embodiment of the present invention, and the battery is a single-junction six-layer pin Structural thin-film solar cells.

Detailed ways

Example 1: A high-conversion silicon crystal and thin film composite multi-junction PIN solar cell, the structure is: bottom electrode/n-epi-Ge/i-gradient epi-Si _1-x Ge _x /p-epi-Si /intermediate reflective layer/n ⁺ type silicon crystal layer/n type silicon wafer/p ⁺ type silicon crystal layer/intermediate reflective layer/n-μc-Si/i-μc-Si/p-μc-Si/intermediate reflective layer/ nA-Si _1-x Ge _x /i-gradient A-Si _1-x Ge _x /pA-Si/intermediate reflector/nA-Si/iA-Si/pA-Si/intermediate reflector/n-μc-SiC /i-μc-SiC/p-μc-SiC/intermediate reflection layer/nA-SiC/iA-SiC/pA-SiC/TCO-Al/anti-reflection coating.

Embodiment 2: A kind of preparation method of silicon crystal and thin film composite type multi-junction PIN solar cell with high conversion rate, comprises the following steps:

1. Chemically or mechanically (CMP) double-sided polishing of n-type silicon wafers (single crystal silicon wafers or polycrystalline silicon wafers), and then,

2. After cleaning the n-type silicon wafer (monocrystalline silicon wafer or polycrystalline silicon wafer), carry out P or B ion implantation to the n-type silicon wafer (monocrystalline silicon wafer or polycrystalline silicon wafer) to form "n ⁺ type silicon crystal layer/ n-type silicon wafer/p ⁺ -type silicon layer"structure;

3. Use PECVD to form a silicon-rich silicon oxide or TCO intermediate reflection layer film;

4. On the front side of n-type silicon wafer (single crystal silicon wafer or polycrystalline silicon wafer), deposit boron (B) doped p-type Si by CVD method, i-gradient μc or epi Si _1-x Ge _x film and Phosphorus (P) doped n-type Ge, and plated Al electrodes by PVD method;

5. On the opposite side of the n-type silicon wafer (single crystal silicon wafer or polycrystalline silicon wafer), deposit phosphorus (P) doped n-μc-Si thin film, I-μc-Si thin film and boron (B) doped by PECVD method p-type μc Si; or use PECVD method to deposit amorphous A-SiC thin film, then laser crystallize to form microcrystalline μc-SiC thin film, and use PECVD hydrogenation treatment;

6. Form silicon-rich silicon oxide or TCO intermediate reflection layer film by PECVD method;

7. Deposit phosphorus (P) doped amorphous n-type A-Si _1-x Ge _x film (1>x>0 uniform transition) and IA-Si _1-x Ge _x film (1>x>0 by PECVD method) 0 uniform over) and boron (B) doped p-type A-Si film, and treated with PECVD hydrogenation;

8. Form silicon-rich silicon oxide or TCO intermediate reflection layer film by PECVD method;

9. Deposit phosphorus (P) doped amorphous n-type A-Si thin film by PECVD method, I-A-Si thin film and boron (B) doped p-type A-Si thin film, and use PECVD hydrogenation treatment;

10. Form silicon-rich silicon oxide or TCO intermediate reflection layer film by PECVD method;

11. Deposit phosphorus (P) doped microcrystalline n-type μc-SiC film, I-μc-SiC film and boron (B) doped p-type μc-SiC film by PECVD method, or deposit amorphous A by PECVD method -SiC thin film, then laser crystallized to form microcrystalline μc-SiC thin film, and hydrogenated by PECVD;

12. Form a silicon-rich silicon oxide or TCO intermediate reflection layer film by PECVD method;

13. Deposit phosphorus (P) doped amorphous n-type A-SiC film, I-A-SiC film and boron (B) doped p-type A-SiC film by PECVD method, and use PECVD hydrogenation treatment;

The films in the above-mentioned relevant steps can also be deposited by HD-PECVD method, and treated with PECVD hydrogenation;

14. Use PVD method to prepare ZnO, ZnO:Ag, and Al thin films (or prepare them by sol-gel method), then dry them, and then heat them at 400°C for 1 minute to 10 minutes in a hydrogen-containing atmosphere; and use PVD method to plate Al electrode;

15. Use PVD or sol-gel method to plate anti-reflection film, which can be porous SiO ₂ or nanofiber SiO ₂ , SiO ₂ /TiO ₂ composite film structure.

The conversion efficiency of this high-conversion silicon crystal and thin-film composite multi-junction PIN solar cell is expected to reach 25%-30%, and has good stability.

In the above-mentioned thin-film solar cell manufacturing process flow:

a. Chemical and mechanical (CMP) double-sided polishing of n-type silicon wafers (single crystal silicon wafers or polycrystalline silicon wafers);

b. The n-type silicon wafer (single crystal silicon wafer or polycrystalline silicon wafer) cleaning process is carried out in two steps:

In the first step, wash with a solution of HCl:H ₂ O ₂ :H ₂ O=10:1:50 at 60°C-70°C for 5 minutes-10 minutes;

In the second step, wash with a solution of NH ₄ OH: _{H 2} O ₂ :H ₂ O=10:1:50 at 60°C-70°C for 5 minutes-10 minutes, and finally wash with water;

c. Laser crystallization treatment process: use XeCl excimer laser with a wavelength of 308nm, by controlling the output power, step speed and time of the laser, recrystallize amorphous Si, Si _{1-x Gex} , SiC to form microcrystals, and even form Single crystal-like Si, Si _1-x Ge _x , SiC film;

d. PECVD hydrogenation treatment process: By adjusting the ratio of hydrogen and nitrogen (10-100 times) and the energy of the plasma, the film is hydrogenated at a certain temperature (100°C-400°C) to enhance the stability of the film material .

Claims (19)

1. high conversion silicon wafer and film composite type are tied the PIN solar cell more, it is characterized in that, its structure is following one of all kinds of:

(1) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/TCO-Al/ antireflective coating;

(2) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/TCO-Al/ antireflective coating;

(3) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/TCO-Al/ antireflective coating;

(4) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/TCO-Al/ antireflective coating;

(5) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/i layer/p layer/middle reflector/n layer/i layer/p layer/TCO-Al/ antireflective coating;

(6) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/TCO-Al/ antireflective coating;

(7) hearth electrode/n layer/i layer/p layer/middle reflector n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/TCO-Al/ antireflective coating;

(8) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/TCO-Al/ antireflective coating;

(9) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/TCO-Al/ antireflective coating;

(10) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/p layer/middle reflector/n layer/p layer/TCO-Al/ antireflective coating;

(11) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺Type silicon layer/middle reflector/n layer/p layer/TCO-Al/ antireflective coating;

(12) hearth electrode/n layer/i layer/p layer/middle reflector/n ⁺Type silicon layer/n type silicon wafer/p ⁺The type silicon layer //the TCO-Al/ antireflective coating;

Wherein, described p layer, i layer, n layer all are to be selected from μ c-Si _1-xGe _x, A-Si _1-xGe _x, a kind of in μ c-SiC, A-SiC, μ c-Si, the A-Si semi-conducting material, rete between the reflector is a knot between tco layer and the adjacent middle reflector and in the middle of adjacent two, and the used semi-conducting material of each rete is identical and form pin knot or pn knot because of the difference of mixing in every knot; 0≤x≤1; Interface between "/" expression is two-layer; N-represents N-type semiconductor, and i-represents intrinsic semiconductor, and P-represents P-type semiconductor; A-represents noncrystal, and μ c-represents crystallite.

2. tie the PIN solar cell according to described high conversion silicon wafer of claim 1 and film composite type more, it is characterized in that, its a kind of composition is: hearth electrode/n-epi-Ge/i-gradient epi-Si _1-xGe _xReflector/n in the middle of the/p-epi-Si/ ⁺Type silicon layer/n type silicon wafer/p ⁺Reflector/n-A-Si in the middle of type silicon layer/middle reflector/n-μ c-Si/i-μ c-Si/p-μ c-Si/ _1-xGe _x/ i-gradient A-Si _1-xGe _xReflector in the middle of reflector in the middle of reflector in the middle of the/p-A-Si//n-A-Si/i-A-Si/p-A-Si//n-μ c-SiC/i-μ c-SiC/p-μ c-SiC//n-A-SiC/i-A-SiC/p-A-SiC/TCO-Al/ antireflective coating;

Wherein, epi is meant the epitaxial growth single crystalline layer; Gradient is meant Si _1-xGe _xValue by changing x is from 1 graded to 0 progressively, and Si _1-xGe _xThen from Ge germanium layer-gradient silicon germanide layer-change to Si layer, 0≤x≤1.

3. tie the PIN solar cell according to claim 1 or 2 described high conversion silicon wafers and film composite type more, it is characterized in that, describedly use the PN junction structure of forming by n layer/p layer to substitute by the PIN structure that the n layer/i layer/p layer is formed.

4. tie the PIN solar cell according to claim 1 or 2 described high conversion silicon wafers and film composite type more, it is characterized in that described silicon wafer can be monocrystalline silicon piece or polysilicon chip.

5. tie the PIN solar cell according to claim 1 or 2 described high conversion silicon wafers and film composite type more, it is characterized in that described antireflective coating is porous SiO ₂Film, or nanofiber SiO ₂Film, or SiO ₂/ TiO ₂Composite membrane; Described porous SiO ₂Film is selected porosity 10%-50% for use, the porous SiO of aperture 50nm-1000nm ₂The film product; Described nanofiber SiO ₂Select fibre diameter 50nm-500nm, draw ratio 1: 5-1 for use: 10 nanofiber SiO ₂Described SiO ₂/ TiO ₂Composite membrane is the compound or MULTILAYER COMPOSITE of individual layer.

6. tie the PIN solar cell according to claim 1 or 2 described high conversion silicon wafers and film composite type more, it is characterized in that described TCO-Al is the electrically conducting transparent aluminum oxide film, purity is more than 99.9%, and visible light transmissivity is greater than 90%; Resistivity is less than 1 * 10 ^-3Ohmcm, film thickness 50nm-5000nm.

7. tie the PIN solar cell according to claim 1 or 2 described high conversion silicon wafers and film composite type more, it is characterized in that, described in the middle of the reflector be conductive film layer, its material purity is greater than 99.9%, resistivity is less than 1x10 ^-3Ohmcm, film thickness 50nm-5000nm.

8. described high conversion silicon wafer of claim 1 and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that it comprises:

N type silicon wafer is carried out chemistry or mechanical twin polishing; Then,

N type silicon wafer is cleaned; Then,

N-type silicon wafer is carried out ion inject, form n ⁺Type silicon layer/n type silicon wafer/p ⁺The structure of type silicon layer;

Prepare tco layer, antireflective coating with common process;

Adopt PECVD, the CVD depositing operation, laser crystallization technology, plasma doping technology and HD-PECVD prepare silica-base film, to obtain high-quality rete and to reduce interface resistance between each lamination.

9. described according to Claim 8 high conversion silicon wafer and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that the amorphous silicon membrane of described silica-base film or microcrystalline silicon film adopt the PECVD method, use high purity silane, hydrogen is carrier gas, decomposes deposition and forms.

10. tie the manufacture method of PIN solar cell more according to the described high conversion silicon wafer of claim 9 and film composite type, it is characterized in that the amorphous of described silica-base film or crystallite Si _1-xGe _xFilm adopts SiH ₄And GeH ₄Be reaction precursor, H ₂Be carrier gas, the reaction decomposes deposition forms.

11. tie the manufacture method of PIN solar cell according to the described high conversion silicon wafer of claim 9 and film composite type more, it is characterized in that the amorphous of described silica-base film or crystallite SiC film adopt SiH ₄And CH ₄Be reaction precursor, H ₂Be carrier gas, the reaction decomposes deposition forms.

12. tie the manufacture method of PIN solar cell according to the described high conversion silicon wafer of claim 9 and film composite type more, it is characterized in that the reflector film adopts SiH in the middle of the Si oxide of the Silicon-rich of described silica-base film ₄And NO ₂Be reaction precursor, H ₂Be carrier gas,, the reaction decomposes deposition forms.

13. tie the manufacture method of PIN solar cell according to the described high conversion silicon wafer of claim 9 and film composite type more, it is characterized in that the N-type silica-base film of described silica-base film adopts PH ₃Plasma doping and forming, P-type silica-base film adopts B ₂H ₆Plasma doping and forming.

14. according to Claim 8 or 9 described high conversion silicon wafers and film composite type tie the manufacture method of PIN solar cell more, it is characterized in that described PECVD depositing temperature is 200-400 ℃.

15. described according to Claim 8 high conversion silicon wafer and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that the Si of described silica-base film _1-xGe _xSingle crystal epitaxial film adopt the CVD depositing operation, use SiH ₄And GeH ₄Be the reaction precursor,, H ₂Be carrier gas, reaction temperature is 600-1000 ℃ and deposits.

16. described according to Claim 8 high conversion silicon wafer and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that, prepare described silica-base film with the alternative PECVD of HD-PECVD technology, CVD depositing operation.

17. described according to Claim 8 high conversion silicon wafer and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that, described n type silicon wafer is cleaned in two steps carried out:

The first step is used HCl: H ₂O ₂: H ₂O=10: 1: 50 solution cleaned 5 minutes-10 minutes at 60 ℃-70 ℃;

In second step, use NH ₄OH: H ₂O ₂: H ₂O=10: 1: 50 solution cleaned 5 minutes-10 minutes at 60 ℃-70 ℃; Last water cleans up.

18. described according to Claim 8 high conversion silicon wafer and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that, described laser crystallization technology uses wavelength to be 308nm XeCl excimer laser, by the control output power of laser, stepping rate and time, make amorphous Si, Si _1-xGe _x, the SiC recrystallization forms crystallite, forms the Si of class monocrystalline even, Si _1-xGe _x, the SiC film.

19. described according to Claim 8 high conversion silicon wafer and film composite type are tied the manufacture method of PIN solar cell more, it is characterized in that, the PECVD hydrogenation process is by adjusting the volume ratio and the isoionic energy of hydrogen and nitrogen, under 100 ℃ of-400 ℃ of temperature, film is carried out hydrogenation treatment, with the stability of enhanced film material; The volume ratio of described hydrogen and nitrogen is 10-100 times.

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