The present invention claims priority of Chinese Patent Application No. 201510679909.9, filed on Oct. 19, 2015 and named after “Solar cell, preparation method thereof and solar cell module assembled thereof”, the contents of which are hereby incorporated as a reference.
The present invention relates to the technical field of solar cells, and more specifically to a solar cell and a solar module with such solar cells connected in series. The present invention also relates to a preparation method for the solar cell.
Solar energy is an inexhaustible energy source. It is estimated that solar energy irradiating onto the earth in a year is equivalent to heat generated by 1,370 billion tons of standard coal, and is about more than twenty thousand times energy generated by various energy sources In a year throughout the world at present. In China, solar resources can be utilized better in about ⅔ of regions, solar energy generation is free of regional limits, and a photovoltaic system can be modularized, can be mounted in a place close to power consumption as well as a region far away from a power grid, so that power transmission and power distribution cost can be reduced, and reliability of a power supply facility can be improved. At present, a small amount of material is used for a light absorption layer of a thin film solar cell, so that only a few microns are required by effective conversion of solar energy into electric energy by its inherent material property.
A semiconductor heterojunction solar cell is formed by two semiconductor materials with different energy band structures, energy bands can be bent or mutated on a contact interface, thereby forming a built-in electric field, to provide a condition for separating carriers generated by a photovoltaic effect in a semiconductor. Since there are various semiconductor materials, there are also multiple materials selected to form heterojunction solar cells. At present, semiconductor heterojunction solar cells mainly include amorphous silicon/monocrystalline silicon heterojunction cells, Indium Gallium Phosphide (InGaP)/Gallium Arsenide (GaAs) heterojunction cells, Cadmium Sulfide (CdS)/Cadmium Telluride (CdTe) heterojunction cells, organism heterojunction and Aluminum Gallium Arsenide (AlGaAs)/GaAs heterojunction cells and the like. An Epitaxial Lift-Off (ELO) technology implemented by a HydroFluoric (HF) acid is used to separate a GaAs epitaxial layer from a substrate, and a p-n layer is formed by contact between an n type doped base layer and a p+ type doped emitter layer. When light is absorbed near the p-n layer to generate electron-hole pairs, a built-in electric field in a heterojunction to drive holes to a p+ type doped side and move electrons to an n type doped side. Displacement of a photon-generated carrier forms an electric potential difference between the p+ type doping side and the n type doping side to achieve the photovoltaic effect. A GaAs thin film solar cell is a cell with highest photoelectric conversion efficiency in present thin film cells, has the characteristics of lightweight, flexibility and the like, has broad application prospect, may have high output power under a smaller illuminated area under the same condition due to its characteristic of high efficiency, and may be applied to a consumer solar product.
At present, a Metal Organic Chemical Vapor Deposition (MOCVD) method is mainly adopted to deposit cell layers on GaAs substrates to form photovoltaic devices, then an ELO technology is adopted to lift off the cell layers, N type electrode contacts are interconnected and P+ type electrode contacts are interconnected of a photovoltaic device to form a photovoltaic conversion module with higher current output, or the N type contacts and P type contacts are interconnected to form a photovoltaic conversion module with a higher output voltage. However, in a preparation process for a back contact type GaAs cell, a dry or a wet etching is required to anisotropically etch cylindrical grooves to further prepare contacts. Sidewall of the cylindrical grooves are perpendicular to the cell, and this is unfavorable for depositing and attaching a passivator to the sidewall of the cylindrical grooves in a subsequent passivation layer preparation process, so that it probably causes the problems of cavities, excessively small and nonuniform thicknesses of passivation layers attached to the sidewalls and the like, and the problem of anode and cathode short-circuit in an electrode contact preparation process is also easily brought. In addition, for achieving proper thicknesses of the passivation layers on the sidewalls of the cylindrical grooves, a longer time is required by cell surface passivation, so that a process time and the amount of a raw material used are increased. Moreover, excessive exposition of GaAs material layers increases a dark current, and for avoiding contact between base electrodes and P type AlGaAs, larger base electrode grooves are required, which further increases the dark current. Therefore, smaller base electrode grooves are required, but the smaller electrode grooves make it difficult to prepare the passivation layers on sidewalls of the grooves and difficult to prepare the base electrodes.
To this end, the technical problem to be solved by the present invention is the problem that it is difficult to form a passivation layer on a sidewall due to the fact that an N type contact of an existing solar cell is cylindrical, and a solar cell and a solar cell module with such solar cells connected in series are further provided. A shape of the N type contact of the solar cell is changed to solve the problem that it is difficult to form the passivation layer on the sidewall, lower the process difficulty and reduce use of a passivation material.
The following technical solutions are adopted.
A solar cell comprises a window layer, a base layer, an emitter layer and a passivation layer which are provided in a stacking manner, wherein the solar cell further comprises an N type contact array and a P type contact arrays which is arranged at intervals, The N type contact penetrates through the emitter layer and the passivation layer, and the P type contact penetrates through the passivation layer, and
the solar cell further comprises an interface layer provided between the emitter layer and the passivation layer, the N type contact penetrates through the emitter layer, the interface layer and the passivation layer to expose the base layer, and the P type contact penetrates through the passivation layer to expose the interface layer.
A cross sectional area of open end of the N type contact is larger than its bottom cross sectional area.
The N type contact is inverted circular truncated cone-shaped.
An acute angle α formed by a sidewall of the N type contact and a horizontal plane are: 5°≤α≤85.
A sidewall passivation layer formed by extension of the passivation layer is provided on outer side of the sidewall of the N type contact.
Adjacent the N type contact array and the P type contact array form a contact array group, the number of the contact array groups is an even number, and the N type contact array and the P type contact array of the contact array group arranged on one side of a centerline of the solar cell form a mirror distribution with the P type contact array and the N type contact array of the contact array group on the other side of the centerline respectively.
Adjacent the N type contact array and the P type contact array form a contact array group, the number of the contact array groups is an odd number, and the N type contact array and the P type contact array arranged on one side of a centerline of the middle contact array group form a mirror distribution with the P type contact array and the N type contact array of the contact array group on the other side of the centerline respectively.
The N type contact arrays and the P type contact arrays are arranged at equal interval.
The solar cell is a gallium arsenide thin film solar cell.
The solar cell further comprises an Anti-Reflection coating provided on a side of the window layer, which the side is far away from the base layer.
A series-connected solar module comprises at least two solar cells, and an N type contact array and a P type contact array at corresponding positions of adjacent solar cells are serially electrically conducted.
The N type contact array and P type contact array at the corresponding positions of the adjacent solar cells are electrically conducted to be connected in series through an electrode connecting wires.
Each solar cell is arranged reversely in parallel with the adjacent solar cell.
Wherein, being arranged reversely in parallel refers to that the adjacent solar cell of the solar cell is obtained by rotating the solar cell 180°, two ends of the two cells may be aligned, and the two ends of the two cells may also not be aligned.
The N type contact array of the solar cell is electrically conducted with the P type contact array of the adjacent solar cell through an electrode connecting wire, and the P type contact array is electrically conducted with the N type contact array of the adjacent solar cell through an electrode connecting wire.
A preparation method of a solar cell comprises the following steps:
S1: a buffer layer, a release layer, a window layer, a base layer, an emitter layer and an interface layer are sequentially prepared on a substrate;
S2: inverted circular truncated cone-shaped grooves distributed in arrays penetrating through the interface layer and the emitter layer are formed in an etching manner, the base layer being at bottom of the inverted circular truncated cone-shaped groove an acute angle α formed by sidewall and a horizontal plane of the inverted circular truncated cone-shaped groove is: 5°≤α≤85°;
S3: a passivation layer is prepared on the basis of Step S2, an area reserved for an N type contact in the inverted circular truncated cone-shaped groove is covered by masking process, thereby forming a passivation layer on the interface layer and forming a sidewall passivation layer on the sidewall of the inverted circular truncated cone-shaped groove, and an inverted circular truncated cone-shaped base electrode groove is formed between the sidewall passivation layers and the base layer;
S4: an emitter electrode groove distributed in array penetrating through the passivation layer is formed in the etching manner, the interface layer is at bottom of the emitter electrode groove;
S5: the N type contacts is prepared in the inverted circular truncated cone-shaped base electrode groove, and the P type contact is prepared in the emitter electrode groove; and
S6: the substrate, the buffer layer and the release layer are lifted off, to obtain the solar cell.
Preferably, Step S2 is: the inverted circular truncated cone-shaped groove etched by a dry etching or a wet isotropic etching;
Step S4 is: the emitter electrode groove is etched by a dry etching or a wet etching and
Step S6 is: after the substrate, the buffer layer and the release layer are lifted off, an Anti-Reflection coating is provided on a side of the window layer, which the side is far away from the base layer,
Alternately, Step S3 is: the passivation layer is formed on the interface layer, the sidewall passivation layer is formed on the sidewall of the inverted circular truncated cone-shaped groove, then the passivation layer at the bottom of the inverted circular truncated cone-shaped groove is removed by an etching process to expose the base layer for preparation of a base electrode, and the inverted circular truncated cone-shaped base electrode groove is formed between the sidewall passivation layers and the base layer.
Compared with a conventional art, the present invention has the following beneficial effects:
A purpose of the present invention is to provide a novel solar cell. The solar cell comprises the P type contact array and the N type contact array arranged at intervals, the N type contact is inverted circular truncated cone-shaped, and an acute angle α formed by the sidewall of the N type contact and the horizontal plane is: 5°≤α≤85°. Inner sidewall surfaces of the inverted circular truncated cone-shaped grooves form certain inclination angles with the base layer, so that difficulties in preparation of the sidewall passivation layer can be remarkably lowered. Meanwhile, implementing the inverted circular truncated cone-shaped base electrode prepared method may reduce surface defects caused by preparation of the base electrode groove, reduce a dark current of the cell and improve efficiency of the cell.
Furthermore, each solar cell of the present invention has the same structure, and during connection, the electrode contact (the P type contact) of the solar cell is connected with different contact (the N type contact) of an adjacent solar cell, and its N type contact connected with different contact (the P type contacts) of the adjacent solar cell, thereby forming series connections of GaAs photovoltaic devices. Such a preparation method avoids preparation of GaAs photovoltaic device units with two types of electrode contact layouts, and has the characteristics of simple structure and easiness for implementation.
For making it easier to comprehend the contents of the present invention clearly, the present invention will further be described below according to specific embodiments of the present invention and in combination with the drawings in detail, wherein
In the drawings: 1-substrate; 2-buffer layer; 3-release layer; 4-window layer; 5-base layer; 6-emitter layer; 7-interface layer; 8-passivation layer; 10-sidewall passivation layer; 12-N type contact; 13-P type contact; 14-electrode connecting wire; and 15-Anti-Reflection coating.
For making the purpose, technical solutions and advantages of the present invention more clearly, embodiments of the present invention will further be described below in combination with the drawings in detail.
As shown in
As another embodiment, the solar cell further comprises an interface layer 7 provided between the emitter layer 6 and the passivation layer 8, the N type contact 12 penetrates through the emitter layer 6, the interface layer 7 and the passivation layer 8 to expose the base layer 5, and the P type contact 13 penetrates through the passivation layer 8 to expose the interface layer 7.
A cross sectional area of open end of the N type contact 12 is larger than its bottom cross sectional area of the N type contact 12, the N type contact is preferably inverted circular truncated cone-shaped, an acute angle α formed by sidewall of the N type contact 12 and a horizontal plane is: 5°≤α≤85. A sidewall passivation layer 10 formed by extension of the passivation layer 8 is provided on outer side of the sidewall of the N type contact 12.
Furthermore, as shown in
The number of the contact array groups shown in
The N type contact 12 arrays and the P type contact 13 arrays can be arranged at unequal interval, may also be arranged at equal interval, and are preferably arranged at equal interval.
The solar cell of the present invention is a gallium arsenide thin film solar cell.
A series-connected solar cell module of the present invention comprises at least two solar cells shown In
As a preferred embodiment, the N type contact 12 array and P type contact 13 array at the corresponding positions of the adjacent solar cell are electrically conducted to be connected in series through an electrode connecting wire 14.
Specifically, the N type contact 12 array of the solar cell is electrically conducted with the P type contact 13 array of the adjacent solar cell through the electrode connecting wire 14, and the P type contact 13 array is electrically conducted with the N type contact 12 array of the adjacent solar cell through the electrode connecting wire 14.
As shown in
As shown in
Unless otherwise noted, the N type contact 12 array of the present invention refers to a column (or a row) formed by several N type contacts 12, and the P type contact 13 array refers to a column (or a row) formed by several P type contacts 13.
A preparation method for the solar cell comprises the following steps.
S1, as shown in
deposition of an Aluminum Arsenide (AlAs) release layer 3: deposition of the AlAs release layer 3 is performed on the GaAs buffer layer 2, wherein the release layer 3 comprising, but not limited to, an AlAs epitaxial material, the thickness range of release layer 3 is 5 nm-15 nm, such a thin release layer 3 is mainly used as a sacrificial layer, and an HF acid wet etching technology can be adopted, thereby separating the epitaxial layers subsequently deposited on the release layer from the buffer layer 2 and the GaAs substrate 1;
a window layer 4 deposition process: an AlGaAs semiconductor layer with a thickness of 10 nm-40 nm is deposited on the AlAs release layer 3 by an MOCVD method, wherein a proportion of Al:Ga is between 0.2:0.8 and 0.3:0.7, and the transparent window layer allows photons to directly penetrate through without absorption;
a base layer 5 deposition process: an n type III-V family compound material GaAs is deposited on the window layer 4, wherein the base layer 5, i.e., a GaAs layer, can be a single-crystal structure and can also be an n type doping material, wherein a doping concentration of an n type doped base layer 5 can range from 1×1016 cm−3 to 1×1019 cm−3, for example, 5×1017 cm−3, and a thickness of the base layer ranges from 400 nm to 4,000 nm;
an emitter layer 6 preparation process the emitter layer 6 is prepared on the base layer 5 by the MOCVD method, wherein the emitter layer 6 comprises any proper III-V family compound semiconductor capable of forming a heterojunction structure with the base layer 5, and for example, if the base layer is a GaAs material, the emitter layer 6 is an AlGaAs layer and is P type heavily doped with a doping concentration ranging from 1×1017 cm−3 to 1×1020 cm−3, for example, 5×1018 cm−3, a thickness of the emitter layer is between 150 nm and 450 nm, for example, 300 nm, and then the base layer 5 and the emitter layer 6 form a photoelectric absorption layer; and
an interface layer 7 preparation process: the interface layer 7 is prepared on the emitter layer 6 by the MOVCD method, wherein the interface layer 7 and the emitter layer are both AlGaAs layers, the interface layer 7 is P+ type heavily doped with a doping concentration ranging from 5×1017 cm−3 to 5×102 cm−3, for example, 1×1019 cm−3, a purpose of P+ type heavy doped can facilitate the formation of ohmic contact, and a thickness of the interface layer 7 is between 100 nm and 400 nm, for example, 200 nm.
In S2, inverted circular truncated cone-shaped grooves are prepared: inverted circular truncated cone-shaped grooves distributed in arrays penetrating through the interface layer 7 and the emitter layer 6 are etched by a dry etching or a wet isotropic etching, the base layer 5 is at bottom of the inverted circular truncated cone-shaped groove, an acute angles α formed by sidewall of the inverted circular truncated cone-shaped groove and a horizontal plane is: 5°≤α≤85°.
In S3, a passivation layer 8 preparation process: any proper passivation process can be adopted, for example, a Chemical Vapor Deposition (CVD) or plasma-enhanced chemical vapor deposited, an area reserved for N type contacts 12 in the inverted circular truncated cone-shaped groove is covered by a masking process, thereby forming the passivation layer 8 on the interface layer 7 and forming a sidewall passivation layer 10 on the sidewall of the inverted circular truncated cone-shaped groove, wherein the passivation layer 8 and the sidewall passivation layer 10 can comprise any nonconductive material, including, but not limited to, one or stacked structure of more of Silicon Nitride (SINx), Oxide Silicon (SiOx), Titanium Oxide (TiOx), Thallium Oxide (TaOx) and Zinc Sulfice (ZnS); and inverted circular truncated cone-shaped base electrode groove is formed between the sidewall passivation layers 10 and the base layer 5.
The passivation layer 8 can also be formed on the interface layer 7, the sidewall passivation layer 10 is formed on the sidewalls of the inverted circular truncated cone-shaped groove, and then the passivation layer at the bottom of the inverted circular truncated cone-shaped groove is removed by an etching process to expose the base layer 5 to form the inverted circular truncated cone-shaped base electrode groove.
In S4, emitter electrode grooves distributed in arrays penetrating through the passivation layer 8 are etched by a dry etching or a wet etching, the interface layer 7 is at bottom of the emitter electrode groove, a region of the P type contact 13 is reserved in the emitter electrode groove, the number of columns of the emitter electrode grooves along an X direction is the same with the number of columns of the inverted circular truncated cone-shaped base electrode grooves, and meanwhile, the emitter electrode grooves and the inverted circular truncated cone-shaped base electrode grooves are alternately distributed.
In S5, electrode contacts preparation: the N type contact 12 is prepared in the inverted circular truncated cone-shaped base electrode groove, and the P type contact 13 is prepared in the emitter electrode groove. The N type contact 12 and the P type contact 13 can be proper metal or metal alloy conducting materials and should not pierce the semiconductor layer of a photoelectric device during preparation. In addition, the material of the N type contact may preferably be applicable at a relatively low metallization process temperature (for example, between 150° C. and 200° C.). For example, Palladium (Pd) don't react with GaAs, so that the N type contact 12 and the P type contact 13 can be formed by a Palladium/Germanium (Pd/Ge) alloy. Therefore, GaAs photovoltaic device units may be formed. A preparation method of the N type contact 12 and the P type contact 13 comprises, but not limited to, a vacuum evaporation, a photoresist, a photolithography, a screen printing and a sputtering, so that deposition is performed only at the positions of the N type contact 12 and the P type contact 13. These methods all involve the same system, wherein a part requiring no contacts is protected.
In S6, an epitaxial lift off process of GaAs photovoltaic device units: each epitaxial layer subsequently deposited on the release layer is separated from the buffer layer 2 and the GaAs substrate 1 by a HF acid wet etching technology, result in lifting off and forming the GaAs photovoltaic device units. An Anti-Reflection coating 15 is configured on the window layer 4, and the Anti-Reflection coating comprises any material allowing light to pass through and prevent the light from being reflected on its surface, including one or any combination of Magnesium Fluoride (MgF2), Silicon Dioxide (SiO2), Zinc Sulfice (ZnS), Titanium Dioxide (TiO2) and Silicon Nitride (SiN). Any proper method (for example, the sputtering method) may be adopted to coat the Anti-Reflection coating on the window layer 4. In addition, pre coating Anti-Reflection coating, the window layer 4 can be roughened or texturized by a wet etching or a dry etching. The window layer 4 can be roughened or texturized to provide different angles at an interface between the Anti-Reflection coating and the window layer 4 (these layers with different refractive indexes), then the incident angle of some photons is excessively high according to the Snell's Law, as a result more incident photons can be transmitted into the window layer 4 rather than being reflected at the interface between the Anti-Reflection coating and the window layer 4, so that transmittance of the photons is improved.
Obviously, the above mentioned embodiments are only examples listed for clear description and not intended to limit the implementation modes. Those of ordinary skilled in the art may further make variations or modifications in other different forms on the basis of the descriptions made above, and not all the implementation modes are required to be exhausted herein. Apparent variations or modifications derived therefrom still fall within the scope of protection of the present invention.
Number | Date | Country | Kind |
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201510679909.9 | Oct 2015 | CN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/CN2016/101975 | 10/13/2016 | WO | 00 |