CN106098812B - A kind of solar cell and preparation method based on oxygen doping zinc telluridse nano-wire array - Google Patents

Abstract

The invention discloses a solar cell based on an oxygen-doped zinc telluride nanowire array, which is as follows from top to bottom: a nanowire array coated with zinc oxide/oxygen-doped zinc telluride/zinc telluride three-layer coaxial coating The top n-type AZO transparent conductive film, zinc oxide/oxygen-doped zinc telluride/zinc telluride three-layer coaxially coated nanowire array, PMDS support layer wrapped at the bottom of the nanowire and p-type doped high-conductivity single crystal Silicon layer substrate, using zinc oxide/oxygen-doped zinc telluride/zinc telluride three-layer coaxially coated nanowire array with intermediate band characteristics as the photoelectric absorption layer; in AZO transparent conductive film and p-type doped high The conductive monocrystalline silicon layer leads out the electrodes respectively.

Description

A solar cell based on oxygen-doped zinc telluride nanowire array and its preparation method

technical field

The invention relates to a solar cell structure with a nanowire absorbing layer and a preparation method thereof, belonging to the technical field of solar cells.

Background technique

Solar cells are photoelectric devices that convert solar energy into electrical energy by using the photovoltaic effect of photovoltaic semiconductor materials, and have been widely used in production and life. Existing solar cells are generally made of ultra-pure single-crystal silicon wafers, and the thickness of this very expensive material is required to be about 200um in order to absorb as much sunlight as possible, which makes the manufacturing process of silicon-based flat-panel solar cells very difficult. It is complicated, consumes a lot of energy, and costs high. Compared with traditional solar cells, intermediate-band solar cells achieve high-efficiency photoelectric conversion with a relatively simple structure, and the nanowire absorption layer with intermediate-band shortens the drift of carriers while maintaining the advantages of intermediate-band solar cells. The distance further increases the conversion efficiency of solar energy.

Traditional solar cells made of single crystal silicon wafers can only absorb photons larger than the forbidden band width of silicon (1.1eV), and the energy beyond the forbidden band width will be converted into heat energy in the form of electron-lattice interaction. Therefore, the theory predicts that the conversion efficiency of traditional silicon solar cells cannot exceed 32%. Intermediate-band solar cells use materials with intermediate-band properties such as high-mismatch alloys and quantum dots as solar cells for the absorbing layer. Taking the middle-band photovoltaic material of highly mismatched gold oxygen-doped zinc telluride (ZnTe:O, with a band gap of 2.25eV) as an example, the isoelectronic doping of oxygen forms a stable middle band in the forbidden band, and the energy level is located at 0.45eV below the bottom of the conduction band, which is located at 1.8eV. When exposed to sunlight, electrons can transition not only through the valence band-conduction band, but also through the valence band-intermediate band-conduction band, so photons with lower energy can also be used. Therefore, the conversion efficiency of intermediate solar cells is much higher than that of traditional solar cells. In addition, the transmittance of single crystal silicon is relatively high, so a silicon absorbing layer with a thickness of hundreds of microns is required to fully absorb photons. The absorption layer of the intermediate zone material generally has a lower transmittance, and the thickness of the absorption layer is on the order of hundreds of nanometers.

Compared with the absorbing layer of layered structure, the structural characteristics of nanowires make the average carrier drift distance shorter. The photogenerated carriers in the absorbing layer may undergo non-radiative recombination during the drift process. Shortening the drift distance of carriers in the absorbing layer is beneficial to reduce the probability of carrier recombination, thereby further increasing the photoelectric conversion efficiency of solar cells.

Contents of the invention

The object of the present invention is to propose a middle-zone solar cell structure in which the oxygen-doped zinc telluride nanowire array enhances the absorption. The light conversion efficiency has laid a solid foundation for the preparation of high-efficiency solar cells, and is expected to realize the development of next-generation solar cells in the direction of high efficiency and low cost.

The technical scheme for solving the problem of the present invention is: a solar cell based on an oxygen-doped zinc telluride nanowire array, from top to bottom: wrapped in a three-layer coaxial package of zinc oxide/oxygen-doped zinc telluride/zinc telluride n-type AZO transparent conductive film on the top of the coated nanowire array, zinc oxide/oxygen-doped zinc telluride/zinc telluride three-layer coaxial coated (vertical) nanowire array, PMDS support wrapped at the bottom of the nanowire layer and p-type doped high-conductivity single-crystal silicon layer substrate, using zinc oxide/oxygen-doped zinc telluride/zinc telluride three-layer coaxially coated vertical nanowire array with intermediate band characteristics as the photoelectric absorption layer ; The electrodes are respectively drawn out from the AZO transparent conductive film and the p-type doped high-conductivity single crystal silicon layer;

The oxygen-doped zinc telluride nanowire array has a height of 5-10 μm and a diameter of 100-300 nm, the oxygen diffusion doping concentration in the oxygen-doped zinc telluride is 1-5%, and the thickness of the diffusion layer is 20-100 nm; the zinc telluride The thickness is 10-50nm; zinc oxide, oxygen-doped zinc telluride, and zinc telluride form a coaxial coating structure, and zinc oxide is on the outermost layer; observed under a high-resolution field emission scanning electron microscope, each square micron The number of oxygen-doped ZnTe nanowires that can be observed on the substrate surface should be more than 2.

Preparation method: The physical vapor deposition of zinc oxide/oxygen-doped zinc telluride/zinc telluride three-layer coaxially coated nanowire arrays is completed in a multi-temperature zone tube furnace; the source of zinc telluride is powdered zinc telluride Crystal, placed upstream of the gas flow and located in the center of a zone heating section of a tube furnace; the substrate for depositing ZnTe nanowires is placed downstream of the ZnTe source and located in the center of a zone heating section or two heating sections During the deposition process, the temperature of multiple heating sections is raised at the same time to ensure that the temperature distribution in the tube furnace is uniform and constant, and to ensure that the evaporation source temperature is maintained at 780-900 ° C, the substrate temperature is maintained at 380-450 ° C, and the temperature is kept for 30-90 minutes , to prepare uniform and defect-free zinc telluride nanowires;

The catalyst gold or bismuth used for depositing zinc telluride is plated on the substrate used for depositing zinc telluride by electron beam evaporation or magnetron sputtering process, and then annealed to form particles with a diameter of 25-100nm; gas phase transport telluride The zinc transport gas uses high-purity nitrogen gas, the flow rate is precisely controlled by the gas flow meter at 50-200 sccm, and flows from the source of zinc telluride to the substrate; the surface of the substrate is at an angle of 50°-80° to the gas flow of zinc telluride transported in the gas phase ;

After the zinc telluride nanowires are deposited, the atmosphere in the tube furnace is replaced with a mixed gas of oxygen and nitrogen, the temperature is raised and maintained at 200-300° C., and the temperature is kept for 2-20 hours. A zinc oxide layer is formed on the surface of the zinc telluride nanowire, and oxygen diffuses into the zinc telluride lattice to form an oxygen-doped zinc telluride layer. The three form a zinc oxide/oxygen-doped zinc telluride/zinc telluride coaxial coating nanowire structure. The zinc oxide/oxygen-doped zinc telluride/zinc telluride coaxial coating nanowire array is prepared by annealing the zinc telluride nanowire array under a mixed atmosphere of oxygen and nitrogen.

The PDMS layer is prepared by an injection molding process, wrapping the bottom end of the oxygen-doped zinc telluride nanowire, and after injection molding, the top of the nanowire is exposed by oxygen ion etching; the thickness of the PDMS layer is based on the wrapped nanowire array.

The n-type AZO light-transmitting layer deposited by pulsed laser has a thickness of 2-10 μm, and the AZO layer wraps the top of the oxygen-doped ZnTe nanowire. The light transmittance of the AZO layer is above 85%, and the resistivity is 10 ^-4 Ω· cm level or lower.

Oxygen-doped zinc telluride has an intermediate band energy level, which can not only absorb photons larger than the energy band gap, but also absorb photons with lower energy through electronic transitions from the valence band to the intermediate band and from the intermediate band to the conduction band. At the same time, the nanowires The structure greatly shortens the drift distance of the photogenerated electron-hole pair under the action of the built-in electric field, reduces the recombination probability of the photogenerated electron-hole pair, and thus enhances the light absorption and conversion efficiency of the solar cell.

Beneficial effects: doped zinc telluride has an intermediate band energy level, which can absorb photons with high efficiency and generate electron-hole pairs; at the same time, the nanowire structure reduces the drift distance of photo-generated carriers and reduces the Therefore, the photoelectric conversion efficiency of this solar cell is much higher than that of traditional solar cells. The use of the intermediate band nanowires in the present invention can obtain higher photoelectric conversion efficiency compared with the commonly used film absorbing layer. Experiments show that the solar cell prepared by the above method has higher photoelectric conversion efficiency.

Description of drawings

Fig. 1 is a schematic structural diagram of a solar cell based on an oxygen-doped zinc telluride nanowire array; where A is a perspective view and B is a cross-sectional view.

Fig. 2 Schematic diagram of the principle of intermediate zone solar cells.

detailed description

Below in conjunction with accompanying drawing, the solar cell based on oxygen-doped zinc telluride nanowire array of the present invention and preparation method thereof are described in detail: 1, nanowire (array); 2, n-type AZO transparent conductive layer; 3, PMDS supporting layer ; 4, p-type high conductivity silicon substrate.

Referring to shown in Fig. 1, the solar cell based on oxygen-doped zinc telluride nanowire array of the present invention comprises: by zinc oxide/oxygen-doped zinc telluride/zinc telluride coaxial nanowire (array) 1, n-type AZO transparent Conductive layer 2, polydimethylsiloxane (polydimethylsilaxone, PMDS) support layer 3, p-type high-conductivity silicon substrate 4 composed of a solar cell structure; wherein the n-type AZO transparent conductive layer 2 wraps zinc oxide/oxygen-doped tellurium The top of the zinc oxide/zinc telluride coaxial nanowire 1 and forms a contact, the PMDS support layer wraps the bottom end of the zinc oxide/oxygen doped zinc telluride/zinc telluride coaxial nanowire 1, the zinc oxide/oxygen doped tellurium The zinc oxide/zinc telluride coaxial nanowire 1 is in contact with the p-type high conductivity silicon substrate 4, the n-type AZO transparent conductive layer 2 is grown on the surface of the PMDS support layer 3, the n-type AZO transparent conductive layer 2 and the p-type high conductivity The silicon substrate 4 is respectively connected to the electrodes during operation.

The working process of the present invention is as follows: the working process of the solar cell designed by the present invention is as follows: when sunlight irradiates the solar cell, the AZO transparent conductive layer 2 will transmit most of the sunlight to the surface formed by zinc oxide/oxygen-doped zinc telluride /ZnTe coaxial nanowire 1, the pin structure formed by the ZnTe layer of the nanowire, the oxygen-doped ZnTe layer and the ZnO layer will absorb photons and generate electron-hole pairs, and the electron-hole pairs are built in Under the action of an electric field, they drift towards zinc oxide and zinc telluride, respectively. When the electrodes are connected to the external circuit and conducted, electrons and holes are conducted through the AZO transparent conductive layer 2 and the p-type silicon substrate 4 to form a current in the external circuit.

The operation steps are as follows:

1) Preparation of catalyst

Electron beam evaporation or magnetron sputtering process is used to plate catalyst gold or bismuth on the silicon substrate used for depositing zinc telluride, and then anneal to form particles.

2) Preparation of ZnTe nanowire arrays

The substrate with the catalyst prepared in step 1) and the source of zinc telluride are placed in a multi-temperature zone tube furnace, and high-purity nitrogen is used as the transport gas, and the physical vapor deposition method is used to deposit on the silicon substrate with catalyst particles ZnTe nanowires.

3) Preparation of ZnO/Oxygen-doped ZnTe/ZnTe coaxially coated nanowires

annealing the zinc telluride nanowires prepared in step 2) in a mixed atmosphere of oxygen and argon to obtain coaxially coated zinc oxide/oxygen doped zinc telluride/zinc telluride nanowires.

4) Inject PMDS

The zinc telluride nanowire array prepared in step 3) is wrapped with PMDS by using an injection molding process.

5) Oxygen ion etching

The top part of the PMDS in 4) is removed by oxygen ion etching, exposing the top of the oxygen-doped ZnTe nanowire array, and the bottom is still wrapped in the PMDS.

6) Prepare an n-type AZO transparent layer, transfer the p-type silicon substrate loaded with oxygen-doped zinc telluride nanowires prepared in step 5) to a pulsed laser deposition device, and prepare an AZO transparent conductive layer.

The preparation method of the solar cell based on the oxygen-doped zinc telluride nanowire array of the present invention more specifically comprises the following steps:

1) Catalyst preparation, using electron beam evaporation or magnetron sputtering process to plate catalyst gold or bismuth on the silicon substrate used for depositing zinc telluride, and then annealing to form particles with a diameter of 25 to 100 nm.

2) The preparation of the zinc telluride nanowire array, the substrate with the catalyst prepared in step 1) and the zinc telluride source are placed in a multi-temperature zone tube furnace, and the side of the substrate with the catalyst is facing the direction of the gas flow, that is, the substrate The plane and the direction of the pipe diameter form an angle of 50-80°. Vacuumize the furnace tube more than three times and fill it with high-purity nitrogen, then adjust the gas flow through a gas flow meter and keep it at 50-200 sccm. Then multiple temperature zones are heated up at the same time, so that the temperature at the zinc telluride source is maintained at a fixed temperature between 750-900°C, and the temperature at the substrate is maintained at 380-450°C. After 30-90 minutes of heat preservation, it is naturally cooled. The brick-red fuzz-like substance formed on the substrate is the zinc telluride nanowire array. The preferred substrate angle is 60°, the gas flow is 100 sccm, the zinc telluride source temperature is 780°C, the substrate temperature is 400°C, and the holding time is 60 minutes.

3) Preparation of zinc oxide/oxygen-doped zinc telluride/zinc telluride coaxially coated nanowires, the zinc telluride nanowires prepared in step 2) are kept at 100-300° C. for 10 days under a mixed gas atmosphere of nitrogen and oxygen. After ~20 hours, coaxially coated ZnTe nanowires were obtained. The preferred ratio of the mixed gas is nitrogen: oxygen (volume ratio) = 4:1, the preferred temperature is 250° C., and the time is 16 hours.

4) Injecting PMDS, wrapping the zinc telluride nanowire array prepared in step 3) with PMDS by using an injection molding process, the thickness of the PMDS layer is determined to be just enough to wrap the nanowire array.

5) Oxygen ion etching, using oxygen ion etching to remove the top part of the PMDS in 4), exposing the top of the oxygen-doped ZnTe nanowire array, and the bottom is still wrapped in PMDS.

6) Preparation of n-type AZO transparent layer

Transfer the p-type silicon substrate loaded with oxygen-doped zinc telluride nanowires prepared in step 5) to a pulsed laser deposition device, and excite the ^AZO target ⁵ ×10 ⁴ to 2×10 ⁵ times, the laser output energy is between 200 and 400 mJ, and the frequency is between 1 and 20 Hz, and an n-type AZO transparent conductive layer is prepared. The preferred oxygen pressure is 10 ^-4 Torr, the number of excitations is 8×10 ⁴ , the energy is 250 mJ, and the frequency is 10 Hz.

The above is only a specific embodiment of the present invention, but the scope of protection of the patent of the present invention is not limited thereto. Any person familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the patent of the present invention. , should be covered within the protection scope of the present invention.

Claims (3)

1. a kind of solar cell preparation method, it is characterized in that solar cell is based on oxygen doping zinc telluridse nano-wire array, from upper It is followed successively by under and：The n-type on the nano-wire array top that zinc oxide/oxygen doping zinc telluridse/three layers of zinc telluridse coaxially coats is wrapped up AZO transparent conductive film, zinc oxide/oxygen doping zinc telluridse/three layers of the zinc telluridse nano-wire array coaxially coated, parcel nano wire PMDS supporting layers and p types the doping height of bottom lead monocrystalline silicon layer substrate, utilize zinc oxide/oxygen doping with Intermediate Gray characteristic Three layers of nano-wire array coaxially coated of zinc telluridse/zinc telluridse are as photoelectric absorption layer；Mixed in AZO transparent conductive film and p types Miscellaneous height leads monocrystalline silicon layer difference extraction electrode；

Oxygen doping zinc telluridse nano-wire array is highly 5 ~ 10 μm, nanowire diameter 100-300nm, oxygen in oxygen doping zinc telluridse Diffusing, doping concentration is 1-5%, and thickness of diffusion layer is in 20 ~ 100nm；Zinc telluridse thickness is 10 ~ 50nm；Zinc oxide, oxygen doping telluride Zinc, zinc telluridse three form coaxial clad structure, and zinc oxide is in outermost layer；Per on square micron of substrate surface it is observed that oxygen Zinc telluridse number of nanowires is adulterated more than 2；

The physical vapour deposition (PVD) of zinc oxide/oxygen doping zinc telluridse/three layers of nano-wire array coaxially coated of zinc telluridse is in multi-temperature zone Completed in tube furnace；Zinc telluridse source is powdered zinc telluridse crystal, is placed in the upstream of air-flow and positioned at a temperature of tube furnace The center of area's bringing-up section；The substrate of deposition zinc telluridse nano wire is placed in the downstream in zinc telluridse source and is located at a warm area bringing-up section Between center or two bringing-up sections；Multiple bringing-up sections heat up to ensure that uniformity of temperature profile is permanent in tube furnace simultaneously in deposition process It is fixed, and ensure that source temperature maintains 780 ~ 900 DEG C, underlayer temperature maintains 380 ~ 450 DEG C, is incubated 30 ~ 90 minutes, prepares Go out uniform flawless zinc telluridse nano wire；

Zinc telluridse used catalyst gold or bismuth are deposited, by electron beam evaporation or magnetron sputtering technique, is plated in for depositing telluride On the substrate of zinc, then the annealed particle for forming 25 ~ 100nm of diameter；The carrier gas of vapor transportation zinc telluridse uses High Purity Nitrogen Gas, flow are accurately controlled in 50 ~ 200sccm by gas flowmeter, from zinc telluridse source stream to substrate；Substrate surface and vapor transportation The air-flow of zinc telluridse is in 50 ° ~ 80 ° angles；

After the deposition of zinc telluridse nano wire is completed, tubular type furnace atmosphere is replaced into the gaseous mixture of oxygen and nitrogen, heating is simultaneously 200 ~ 300 DEG C are maintained, insulation obtains oxygen doping zinc telluridse in 2 ~ 20 hours；Zinc oxide/oxygen doping zinc telluridse/zinc telluridse coaxially wraps Nano-wire array is covered to be prepared by annealing to zinc telluridse nano-wire array under the mixed atmosphere of oxygen and nitrogen.

2. solar cell preparation method according to claim 1, it is characterized in that PDMS layer is prepared by Shooting Technique, parcel In the bottom of oxygen doping zinc telluridse nano wire, after injection, the top of nano wire is exposed by oxygen rie；The thickness of PDMS layer Degree is defined by wrapping up nano-wire array.

3. solar cell preparation method according to claim 1, it is characterized in that saturating by the n-type AZO of pulsed laser deposition Photosphere thickness is 2 ~ 10 μm, and AZO layers wrap up the top of oxygen doping zinc telluridse nano wire, and the light transmittance of AZO layers is more than 85%, electricity Resistance rate is 10^-4Ω cm magnitudes are lower.