CN103594535A - Silicon nano wire quantum well solar cell and preparation method thereof - Google Patents

Abstract

The invention discloses a silicon nanowire quantum well solar cell, which comprises a Ti/Pd/Ag grid electrode, a transparent aluminum-doped zinc oxide (AZO) conductive layer film, an n ⁺ ohmic contact layer, and an n layer along the sunlight incident direction. , nc-Si:H/SiN _x superlattice quantum well, p ⁺ ohmic contact layer and Al back electrode, the solar cell adopts p-type silicon nanowire array to support nc-Si:H/SiN _x superlattice quantum well As well as the preparation method of the solar cell shown, the new solar cell has the advantages of "high light trapping, high efficiency, low cost and long life". A graded quantum well material is formed on the surface of the silicon nanowire array, which greatly improves the light trapping effect of the solar cell, and at the same time broadens the light absorption spectrum of the solar cell, forming a nearly full-spectrum nc-Si:H/SiN _x supercrystal Lattice quantum well solar cells.

Description

A kind of silicon nanowire quantum well solar cell and its preparation method

technical field

The invention relates to new energy technology fields such as nanotechnology and photovoltaic technology, and designs a new type of silicon nanometer that uses silicon nanowires as a support and deposits nc-Si:H and SiN _x on the silicon nanowires to form a superlattice quantum well material. wire solar cells.

Background technique

Traditional energy such as coal, oil, and natural gas will be exhausted. The environmental pollution they cause is very serious, such as water pollution, air pollution, dust pollution, etc., which seriously endanger people's health and living environment. Facing the global energy shortage crisis and the continuous deterioration of the ecological environment, countries all over the world are actively researching, developing and utilizing new energy sources. Renewable energy, especially solar energy, has attracted more and more attention. As an important way to utilize solar energy, photovoltaic applications have always been a research hotspot. The core device of solar photovoltaic power generation is the solar cell. From the comprehensive evaluation of energy conversion efficiency, production cost, device service life and practical application fields, Si-based solar cells undoubtedly have obvious advantages and have always occupied this leading position in development. Among Si-based solar cells, p-n junction single crystal Si solar cells have the highest conversion efficiency and the most mature technology. However, the production of such solar cells requires the consumption of a large amount of Si material. Therefore, how to realize Si-based solar cells with high conversion efficiency at a relatively low production cost has become an important issue before people.

At present, commercialized solar cells are mainly based on the first-generation monocrystalline silicon, polycrystalline silicon solar cells and the second-generation amorphous silicon thin-film solar cells. Among them, although the first-generation solar cells have high efficiency, the cost is also high; the second-generation solar cells are low in cost, but have disadvantages such as low efficiency, instability, toxic elements, and the need for rare metals. Therefore, in order to make solar energy accepted by more people, it is necessary to reduce the production cost of the first-generation silicon-based solar cells or increase the conversion efficiency of the second-generation silicon-based solar cells. Analysis of the problems existing in the first-generation and second-generation solar cells can be summarized into the following four main aspects: First, silicon-based materials are limited by the level of preparation technology, making it difficult to obtain expected structural and photoelectric properties, so As a result, the photovoltaic parameters of solar cells cannot meet the design indicators; second, the first and second generation solar cells require a separate light-trapping structure, and the effective pn junction area for photoelectric conversion is small; third, only a single band gap is used Photovoltaic materials make solar cells, because photons with energy less than this band gap cannot be absorbed, resulting in low energy loss, and the excess energy of photons greater than this band gap is dissipated in the form of heat energy, so that photon energy cannot be fully utilized; Fourth, in the current In the pn junction and pin type (p ⁺ -pinn ⁺ ) solar cells, a photon can only excite one electron-hole pair.

After patent retrieval, silicon nanowire/amorphous silicon heterojunction solar cell (CN101262024A) patent and a new structure silicon nanowire solar cell (CN101369610A) patent use wet etching process to prepare silicon nanowire array, and use PECVD technology in the Amorphous silicon is grown on p-type monocrystalline silicon nanowires to form pn and pin structures respectively, and then ITO transparent conductive film is prepared by magnetron sputtering, and finally Ti/Pd/Ag is deposited on the surface of ITO conductive film by mask method As the front electrode, a metal aluminum film is deposited on the back of the p-type silicon substrate, and after sintering, it is used as the back electrode to make a silicon nanowire solar cell. Nc - Si:H / SiN _x superlattice quantum well solar cell (CN102157594 A) patent uses PECVD layer-by-layer deposition technology to deposit materials with different components, and prepares a planar p ⁺ ohmic contact layer and p layer on the TCO transparent electrode , nc-Si: H/SiN _x superlattice quantum well layer, n layer, n ⁺ ohmic contact layer and ZnO/Al back electrode quantum well solar cell.

Silicon nanowire/amorphous silicon heterojunction solar cell (CN101262024A) patent and a new structure silicon nanowire solar cell (CN101369610A) patent only use amorphous silicon materials with a single band gap to make solar cells, because the energy is smaller than this band gap The photons in the band gap cannot be absorbed, resulting in low-energy loss, while the excess energy of the photons larger than the band gap is lost in the form of heat energy, resulting in the photon energy not being fully utilized. The Nc - Si:H / SiN _x superlattice quantum well solar cell (CN102157594 A) patent adopts the traditional planar cell structure, which not only has a relatively high surface reflectivity, but also has a limited effective photoelectric conversion area that can receive light. The very long carrier transport distance between the upper and lower electrodes of the battery leads to very low carrier collection efficiency.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention utilizes the unique optical and electrical characteristics of one-dimensional nanowires, as well as the obvious influence on the efficiency and spectral response of solar cells to improve the performance of solar cells, increase efficiency, and the band of nano-silicon A nc-Si:H/SiN _x superlattice quantum well nanowire solar cell supported by silicon nanowires was prepared by combining the gap tunability and the good barrier properties of polysilicon nitride.

Silicon nanowire quantum well solar cells are followed by Ti/Pd/Ag grid electrode, transparent aluminum-doped zinc oxide (AZO) conductive layer film, n ⁺ ohmic contact layer, n layer, nc-Si:H/ SiN _x superlattice quantum well, p-type silicon nanowire array, p ⁺ ohmic contact layer and Al back electrode. The thickness of each monolayer of Nc-Si is controlled at 9±0.5 nm, and the period is 45±5 nm; the thickness of each monolayer of _SiNx is controlled at 9±0.5 nm, and the period is 45±5 nm.

The silicon nanowires of this cell play the role of trapping light, supporting the nc-Si:H/SiN _x superlattice quantum well layer and expanding the area of the effective photoelectric conversion region, while the radial transport of photogenerated carriers greatly reduces its transport The distance improves the collection efficiency.

In the superlattice quantum well material in the battery, the extremely thin nc-Si layer acts as a quantum well layer that confines carriers, and the optical bandgap of the nc-Si:H thin film forms a transition structure along the incident direction of sunlight in turn, expanding Improve the absorption spectrum of solar cells to light, improve the total amount of light absorption and absorption efficiency; at the same time maintain the low cost advantages of the second-generation thin film cells.

A method for preparing silicon nanowire quantum well solar cells using electroless metal-assisted etching technology to prepare silicon nanowire arrays; using layer-by-layer plasma chemical vapor deposition technology to alternately prepare nc-Si/SiN _x supercrystals on silicon nanowire arrays Lattice quantum well; use plasma chemical vapor deposition technology to prepare n ⁺ ohmic contact layer, n layer on nc - Si/SiNx superlattice quantum well; use atomic layer deposition technology to prepare transparent aluminum-doped zinc oxide (AZO) conductive layer film; Use atomic layer deposition technology to deposit transparent aluminum-doped zinc oxide (AZO) conductive layer film on the n ⁺ layer; use mask method to prepare Ti/Pd/Ag grid electrode, which is located on the transparent AZO conductive film layer; use plasma chemistry Prepare the p ⁺ ohmic contact layer on the back of the silicon wafer with silicon nanowire arrays by vapor deposition technology; prepare the Al back electrode on the p ⁺ ohmic contact layer on the back of the silicon wafer by sputtering technology; perform solar panel etching and packaging Subsequent process.

The silicon nanowire array adopts the electroless silver plating assisted etching method, and the etching solution is an HF acid aqueous solution containing AgNO ₃ , wherein the concentration of HF acid is 3-5 mol/L, and the concentration of AgNO ₃ is 0.01 -0.05 mol/L, etch at 20-50°C for 10-60min; rinse with deionized water, etch with KOH aqueous solution with a concentration of 0.1-1 mol/L for 10-60s, and finally use Rinse with deionized water and blow dry with nitrogen gas.

The diameter and period of the nano-arrays prepared by the electroless silver-plating-assisted etching method are 50-200 nm and 350-650 nm, respectively.

^Nc - Si / SiN _x superlattice quantum well, n ⁺ ohmic contact layer, p ⁺ ohmic contact layer are alternately deposited layer by layer; Control the crystal grain size of nc-Si:H at 2-3 nm with a DC bias voltage of 200V; adjust the RF power from 50 W to 250 W to control the crystal composition of nc-Si:H, and prepare the optical bandgap from the inside to the outside in turn Small to large quantum well materials; the thickness of Nc - Si and SiN _x is controlled by controlling the film growth time, and the thickness of each single layer is controlled at 9 ± 0.5 nm, and the period is 45 ± 5 nm.

nc - Si:H / SiN _x superlattice quantum well materials were alternately deposited layer by layer by PECVD.

The deposition conditions used were background vacuum at 1.6×10 ^-4 Pa, RF power at 50-250W (frequency at 13.56MHz), deposition temperature at 300°C, DC bias at 200V, and reaction pressure at 200Pa.

The hydrogen dilution ratio of the silane used is 5%, and both hydrogen and nitrogen are 99.9999% high-purity gases. The hydrogen dilution ratio [SiH ₄ ]/[SiH+H ₂ ] of the silane used is 5%; the p ⁺ type silicon film is prepared by PECVD method, and the boron doping rate β ₁ =B/Si=10%; the n Type silicon film, phosphorus doping rate β ₂ =B/Si=5%; use PECVD method to prepare n ⁺ type silicon film, phosphorus doping rate β ₃ =B/Si=10%.

A transparent aluminum-doped zinc oxide (AZO) conductive layer film is deposited on the n ⁺ layer by atomic layer deposition technology. The aluminum content in aluminum-doped zinc oxide (AZO) is 0.86%, the deposition temperature is 200°C, and the deposition thickness is 30-70nm .

Prepare the Al back electrode on the p ⁺ ohmic contact layer on the back of the silicon wafer by sputtering technology, the background vacuum before sputtering is 1.6×10 ^-4 Pa, the gas flow rate is 80-100ml/min, and Ar is used as the protective gas .

The novel solar cell structure provided by the invention has the advantages of "high light trapping, high efficiency, low cost and long life". A graded quantum well material is formed on the surface of the silicon nanowire array, which greatly improves the light trapping effect of the solar cell, and at the same time broadens the light absorption spectrum of the solar cell, forming an approximately full-spectrum nc-Si:H/SiN _x supercrystal Lattice quantum well solar cells. And it has an obvious quantum effect, and can produce multiple excitation properties, that is, one photon can generate multiple electron-hole pairs.

Adopting the technical solution of the invention, the silicon nanowire quantum well solar cell with a novel structure has strong light absorption capacity, high photoelectric conversion efficiency, long service life and low cost.

Description of drawings

Fig. 1 is a schematic diagram of preparing silicon nanowire arrays by electroless silver plating assisted etching method in the present invention.

Fig. 2 is a comparison chart of the reflectivity of the silicon nanowire array and the reflectivity of the polished silicon wafer.

Fig. 3 is a schematic diagram of energy loss analysis of a solar cell.

Fig. 4 is a schematic diagram of the bandgap of the nanowire nc-Si:H/ _SiNx superlattice quantum well cell of the present invention.

Fig. 5 is a schematic diagram of the structure of a single nanowire of the novel solar cell of the present invention.

Fig. 6 is a SEM top view of the prepared silicon nanowire array.

Fig. 7 is a SEM top view after depositing nc-Si:H/ _SiNx superlattice quantum well, n layer, n+ ohmic contact layer and AZO layer on the surface of the nanowire.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

As shown in Fig. 5, Al/p ⁺ /p/nc-Si:H/SiN _x superlattice quantum wells /n/n ⁺ / A new type of solar cell with AZO structure, the silicon nanowire quantum well solar cell is followed by Ti/Pd/Ag grid electrode, transparent aluminum-doped zinc oxide (AZO) conductive layer film, n+ ohmic contact layer, n layer, nc-Si:H/SiN _x superlattice quantum well, p-type silicon nanowire array, p ⁺ ohmic contact layer and Al back electrode. The thickness of each monolayer of Nc-Si is controlled at 9±0.5 nm, and the period is 45±5 nm; the thickness of each monolayer of _SiNx is controlled at 9±0.5 nm, and the period is 45±5 nm.

As shown in FIG. 2 , the comparison chart of the reflectance of the silicon nanowire array and the reflectance of the polished silicon wafer, that is, the solar cell adopting the technical solution of the present invention, adopts the silicon nanowire as the supporting structure to enhance the light trapping effect. Increasing p ⁺ and n ⁺ is to reduce the contact resistance between the semiconductor material and the metal electrode and increase the short-circuit current; the optical band gap of nc-Si:H in nc-Si:H/SiN _x is adjustable, thus forming nc-Si:H The decreasing optical bandgap from outside to inside can effectively expand the spectral absorption range and increase the effective photoelectric conversion area.

Preparation method of silicon nanowire quantum well solar cell:

1. Cleaning of silicon wafers: clean with acetone and alcohol ultrasonic vibration (room temperature for 10 minutes); soak in 5% wt HF acid solution for 3 minutes, and then use NH ₃ ·H ₂ O:H ₂ O ₂ :H ₂ O=1 :1:5(V/V/V) Incubate at 80°C for 30 min; rinse the surface of the sample with deionized water.

2. Preparation of silicon nanowire arrays: as shown in Figure 1, the samples were placed in HF/AgNO ₃ mixed aqueous solution, in which HF 5 mol/L, AgNO ₃ 0.02 mol/L, etched at 45°C for 15 min. Put the sample in a mixed solution of HNO ₃ : H ₂ O = 1:1 (V:V) and keep it warm at 50°C for 30 minutes to remove the silver and silver fluoride on the surface of the silicon wafer, and then rinse it with deionized water repeatedly. The sample was etched in an aqueous KOH solution with a concentration of 0.5 mol/L for 45 seconds, then rinsed repeatedly with deionized water, and dried with nitrogen at room temperature, as shown in Figure 6. SEM top view of the line array.

3. Preparation of nc - Si / SiN _x superlattice quantum wells. Fabrication of nc - Si / SiN _x superlattice quantum wells alternately on silicon nanowire arrays by layer-by-layer plasma chemical vapor deposition; fabrication of n ⁺ on nc - Si / SiN _x superlattice quantum wells by plasma chemical vapor deposition The ohmic contact layer is an n layer; the p+ ohmic contact layer is prepared on the back of a silicon chip with a silicon nanowire array by using plasma chemical vapor deposition technology. By layer-by-layer alternate deposition, the grain size of nc-Si:H is controlled at 2-3 nm through a fixed DC bias voltage of 200v. As shown in Figure 4, and by adjusting the RF power from 50 W to 250 W, and controlling the nc-Si:H crystal composition, the quantum well materials with optical band gaps from small to large are prepared from the inside to the outside. The thickness of Nc-Si and _SiNx is controlled by controlling the film growth time, and the thickness of each monolayer is controlled at 9 ± 0.5 nm with a period of 45 ± 5 nm.

The hydrogen dilution ratio of the silane used is 5%, and both hydrogen and nitrogen are 99.9999% high-purity gases. The hydrogen dilution ratio [SiH ₄ ]/[SiH+H ₂ ] of the silane used is 5%; the p ⁺ type silicon film is prepared by PECVD method, and the boron doping rate β ₁ =B/Si=10%; the n Type silicon film, phosphorus doping rate β ₂ =B/Si=5%; use PECVD method to prepare n+ type silicon film, phosphorus doping rate β ₃ =B/Si=10%.

4. Transparent aluminum-doped zinc oxide (AZO) conductive layer film. A transparent aluminum-doped zinc oxide (AZO) conductive layer film is deposited on the n+ layer by atomic layer deposition technology. The aluminum content in aluminum-doped zinc oxide (AZO) is 0.86%, the deposition temperature is 200°C, and the deposition thickness is 30-70nm. As shown in Figure 7, it is a SEM top view after depositing nc-Si:H/SiN _x superlattice quantum wells, n layer, n ⁺ ohmic contact layer and AZO layer on the surface of the nanowire.

5. The upper and lower electrodes are grown by magnetron sputtering technology.

6. Interface defect handling

After each layer of silicon film was deposited by PECVD, the film was subjected to hydrogen passivation treatment for 5 minutes to reduce surface carrier recombination.

7. Battery etching and packaging

The surface average reflectance of the prepared new nanowire quantum well solar cell can reach 2.2% in the 300 nm-1100 nm band, and the cell efficiency can break through the limit efficiency (27%) of traditional silicon-based solar cells, which can approximate full-spectrum solar cells.

As shown in Figure 3, the new solar cell has the advantages of "high light trapping, high efficiency, low cost and long life". A graded quantum well material is formed on the surface of the silicon nanowire array, which greatly improves the light trapping effect of the solar cell, and at the same time broadens the light absorption spectrum of the solar cell, forming an approximately full-spectrum nc-Si:H/SiN _x supercrystal Lattice quantum well solar cells. And it has an obvious quantum effect, and can produce multiple excitation properties, that is, one photon can generate multiple electron-hole pairs.

Claims (10)

1. a silicon nanowires quantum well solar cell, is followed successively by Ti/Pd/Ag grid electrode, transparent Al-Doped ZnO (AZO) membrane of conducting layer, n along sunlight incident direction ⁺ohmic contact layer, n layer, nc-Si:H/SiN _xsuperlattice quantum well, p ⁺ohmic contact layer and and Al back electrode, it is characterized in that, described solar cell adopts p-type silicon nanowire array to support nc-Si:H/SiN _xsuperlattice quantum well.

2. a kind of silicon nanowires quantum well solar cell according to claim 1, is characterized in that, every thickness in monolayer of nc-Si is controlled at 9 ± 0.5 nm, and the cycle is 45 ± 5 nm.

3. a kind of silicon nanowires quantum well solar cell according to claim 1, is characterized in that SiN _xevery thickness in monolayer be controlled at 9 ± 0.5 nm, the cycle is 45 ± 5 nm.

4. a preparation method for silicon nanowires quantum well solar cell, is characterized in that, adopts electroless plated metal auxiliary etch technology to prepare silicon nanowire array; Utilize successively PCVD technology on silicon nanowire array, alternately to prepare nc-Si/SiN _xsuperlattice quantum well; Utilize PCVD technology at nc-Si/SiN _xon superlattice quantum well, prepare n ⁺ohmic contact layer, n layer; Adopt technique for atomic layer deposition to prepare transparent Al-Doped ZnO (AZO) membrane of conducting layer; Utilize technique for atomic layer deposition to be deposited on n ⁺deposit transparent Al-Doped ZnO (AZO) membrane of conducting layer on layer; Utilize mask method to prepare Ti/Pd/Ag grid electrode, be positioned on transparent AZO conductive membrane layer; Utilize PCVD technology to have the silicon chip back side of silicon nanowire array to prepare p long ⁺ohmic contact layer; Utilize sputtering technology at the p at the back side of silicon chip ⁺on ohmic contact layer, prepare Al back electrode; Carry out solar panel etching and encapsulation subsequent technique.

5. the preparation method of a kind of silicon nanowires quantum well solar cell according to claim 4, is characterized in that, silicon nanowire array adopts electroless deposition of silver auxiliary etch method, and etching solution is for containing AgNO ₃hF aqueous acid, wherein the amount of substance concentration of HF acid is 3-5 mol/L, AgNO ₃amount of substance concentration be 0.01-0.05 mol/L, etching 10-60min under 20-50 ℃ of condition; After rinsing well with deionized water, by amount of substance concentration, be the KOH aqueous solution etching 10-60s of 0.1-1 mol/L again, finally with deionized water, rinse well, and dry up with nitrogen.

6. the preparation method of a kind of silicon nanowires quantum well solar cell according to claim 5, is characterized in that, diameter and the cycle of nano-array prepared by employing electroless deposition of silver auxiliary etch method are respectively 50-200 nm and 350-650 nm.

7. the preparation method of a kind of silicon nanowires quantum well solar cell according to claim 4, is characterized in that nc-Si/SiN _xsuperlattice quantum well, n ⁺ohmic contact layer, p ⁺ohmic contact layer adopts successively alternating deposit; Sedimentary condition is base vacuum 1.6 * 10 ^-4pa, depositing temperature, at 300 ℃, adopts the fixedly grain size of direct current (DC) bias 200V control nc-Si:H to remain on 2-3 nm; Regulate radio-frequency power 50 W-250 W to control nc-Si:H crystalline state compositions, prepare optical band gap quantum-well materials from small to large successively from the inside to the outside; Nc-Si and SiN _xthickness by controlling the film growth time, control, every thickness in monolayer is controlled at 9 ± 0.5 nm, the cycle is 45 ± 5 nm.

8. according to the preparation method of a kind of silicon nanowires quantum well solar cell described in claim 4-to 7 any one, it is characterized in that the hydrogen thinner ratio [SiH of silane used ₄]/[SiH+H ₂] be 5%; Utilize PECVD method to prepare p ⁺type silicon thin film, boron doping rate β ₁=B/Si=10%; Utilize PECVD method to prepare N-shaped silicon thin film, phosphorus doping rate β ₂=B/Si=5%; Utilize PECVD method to prepare n ⁺type silicon thin film, phosphorus doping rate β ₃=B/Si=10%.

9. the preparation method of a kind of silicon nanowires quantum well solar cell according to claim 4, is characterized in that, utilizes technique for atomic layer deposition to be deposited on n ⁺deposit transparent Al-Doped ZnO (AZO) membrane of conducting layer on layer, in Al-Doped ZnO (AZO), aluminium content is 0.86%, and depositing temperature is 200 ℃, and deposit thickness is 30-70nm.

10. the preparation method of a kind of silicon nanowires quantum well solar cell according to claim 4, is characterized in that, utilizes sputtering technology at the p at the back side of silicon chip ⁺on ohmic contact layer, prepare Al back electrode, before sputter, base vacuum is 1.6 * 10 ^-4pa, importing gas flow is 80-100ml/min, employing Ar is protective gas.

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