CN102916061B - Micro-crystalline germanium and non-crystalline germanium heterogeneous absorption layer material with narrow band gap and application thereof - Google Patents

Abstract

A narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material is a multi-layer material prepared by a layer-by-layer cycle deposition method by alternately growing microcrystalline germanium films and amorphous germanium films. The thickness of the microcrystalline germanium film is The thickness of the amorphous germanium film is 20-50nm, and the thickness of the amorphous germanium film is 1-10nm, and then undergoes plasma treatment or chemical annealing treatment, so that the microcrystalline germanium film and the amorphous germanium film are deposited cyclically until a microcrystalline film with a total thickness of 50-1500nm is formed Germanium-amorphous germanium heterogeneous thin film; the narrow bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material can be used for wide-spectrum four-terminal stacked silicon-based thin film solar cells based on group IV thin film materials. The advantages of the present invention are: the spectral response range of thin-film solar cells can be extended to 1800nm, and a new type of wide-spectrum laminated solar cell based on Group IV thin-film materials can be obtained without increasing equipment costs, making full use of the solar energy. Spectrum, improve the photoelectric conversion efficiency of the battery.

Description

A kind of narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material and its application

【Technical field】

The invention relates to the technical field of silicon-based thin-film solar cells, in particular to a narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material and its application.

【technical background】

In the field of solar cells, silicon-based thin-film solar cells are a widely recognized low-cost technical route. Traditionally speaking, silicon-based thin-film solar cells refer to solar cells with thin-film materials such as amorphous silicon, microcrystalline silicon, silicon-germanium alloys, silicon-carbon alloys, and silicon-oxygen alloys as intrinsic absorbing layers, which generally have low raw material consumption. , Easy to prepare in a large area, low manufacturing cost and energy consumption, and the manufacturing process is non-toxic and pollution-free, and has gradually moved towards industrialization.

It is an effective way to improve the stable efficiency of silicon-based thin film solar cells by using absorbing layer materials with different band gaps to make multi-junction laminated cells. At present, the most common stack cell structure is amorphous silicon-microcrystalline silicon double junction stack, amorphous silicon-amorphous silicon germanium-amorphous silicon germanium and amorphous silicon-amorphous silicon germanium-microcrystalline silicon triple junction laminated structure, etc. In the above structure, the first layer, the second layer and the subsequent layers have decreasing band gaps, and each layer absorbs increasing wavelengths of the solar spectrum.

However, regardless of the cell structure, the theoretical bandgap of the bottom cell is not lower than 1.1eV, thus limiting the long-wave spectrum absorption of the solar cell to 1100nm, which can only utilize about 80% of the total radiation of the AM1.5 standard solar spectrum , resulting in a certain loss of light. Therefore, expanding the spectral absorption range has become the key to further improving the efficiency of silicon-based thin film solar cells.

【Content of invention】

The purpose of the present invention is to address the above existing problems, to provide a narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material and its application, the material can absorb wavelengths greater than 1100nm, and is applied to four-terminal stacks based on group IV thin film materials The multi-layer solar cell has a novel structure, which can expand the spectral response of the solar cell in the near-infrared region and maximize the use of the solar spectrum.

Technical scheme of the present invention:

A narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material is a multi-layer material prepared by a layer-by-layer cycle deposition method by alternately growing microcrystalline germanium films and amorphous germanium films. The thickness of the microcrystalline germanium film is It is 20-50nm, and its internal crystalline composition accounts for 40-80% of the volume of the total material, and the grain size is 15-40nm. After that, the thickness of the amorphous germanium film is 1-10nm, and then plasma treatment or chemical annealing treatment, so that the microcrystalline germanium thin film and amorphous germanium thin film are deposited cyclically until a microcrystalline germanium-amorphous germanium heterogeneous thin film with a total thickness of 50-1500nm is formed, which is a narrow bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer Material.

An application of the narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material for a wide-spectrum four-terminal stacked silicon-based thin-film solar cell based on group IV thin-film materials, the solar cell consists of a substrate, a metal electrode , transparent conductive electrode, n-type doped layer of the bottom cell, microcrystalline germanium-amorphous germanium heterogeneous absorption layer, p-type doped layer of the bottom cell, transparent conductive and gate line compound electrode, intermediate transparent insulating layer, Transparent conduction and gate line composite electrode, microcrystalline silicon battery, amorphous silicon germanium battery, amorphous silicon battery and transparent conduction and gate line composite electrode are superimposed, in which the n-type doping of the metal electrode, transparent conductive electrode, and bottom cell layer, microcrystalline germanium-amorphous germanium heterogeneous absorption layer, p-type doped layer of the bottom cell, and transparent conductive and gate line composite electrode constitute a thin-film solar cell with microcrystalline germanium-amorphous germanium heterogeneous material as the absorption layer The bottom end of the battery is used to absorb the long-wave solar spectrum in the 1100-1800nm band. Transparent conductive and grid line composite electrodes, microcrystalline silicon cells, amorphous silicon germanium cells, amorphous silicon cells, and transparent conductive and grid line composite electrodes constitute the traditional The silicon-based thin-film laminated top battery is used to absorb the solar spectrum in the 300-1100nm band. The bottom battery and the top battery each have battery poles and four lead-out terminals. There is a transparent insulating layer between the bottom battery and the top battery. Connected, the resistivity is higher than 1010Ωcm, the transmittance in the 1100-1800nm band is higher than 60%, and the refractive index is 1.5-3.0.

Working principle of the present invention:

A novel microcrystalline germanium-amorphous germanium heterogeneous absorption layer material prepared by a layer-by-layer deposition method has excellent photoelectric conversion capability. This is because the microcrystalline germanium material with a single composition accumulates grain boundary defects as the thickness increases during the growth process, and the large increase in the defect state density makes the carrier transport characteristics worse, and the material loses absorption. The ability to convert photons into electrons. Using the layer-by-layer deposition method, after depositing a certain thickness of microcrystalline germanium material, a thin layer of amorphous germanium is deposited, combined with a certain plasma treatment or chemical annealing treatment technology, which can effectively slow down the growth of grains and crossover. The grain boundary defects formed by the combination can achieve the purpose of passivating the grain boundary defects. In addition, the periodic microcrystalline germanium-amorphous germanium heterostructure is a multi-quantum well material. The amorphous germanium material with a band gap of 1.1eV constitutes a barrier for electrons and holes. By changing the thickness of the amorphous germanium layer , the band gap of the microcrystalline germanium-amorphous germanium heterogeneous absorption layer material can be adjusted to change between 0.70-1.10eV, so as to achieve the purpose of expanding the spectral response of the near-infrared region of the battery.

In order to give full play to the narrow bandgap advantage of the microcrystalline germanium-amorphous germanium heterogeneous absorber material and improve the conversion efficiency of the battery, we propose a novel four-terminal stacked battery structure design. The traditional structure of silicon-based thin-film stacked solar cells is that different sub-cells with band gaps ranging from wide to narrow absorb the solar spectrum from short-wave to long-wave respectively, and the sub-cells are connected in series in the form of tunnel junctions to realize current transmission. transport. However, if the narrow-bandgap microcrystalline germanium-amorphous germanium hetero-absorption layer material is directly used in a silicon-based thin-film stacked solar cell with a traditional structure, due to the limitation of the current matching principle of the stacked cell, the open circuit voltage is relatively low. It is impossible to really improve the conversion efficiency of the laminated battery under the premise. A novel four-terminal laminated battery structure is adopted, and the traditional n/p tunnel junction is replaced by an insulating transparent intermediate layer material to realize the physical connection and electrical separation of the top battery and the bottom battery, so that the top battery and the bottom battery can be separated. Absorbing the solar spectrum in the 300-1100nm and 1100-1800nm bands does not affect each other electrically and gets rid of the limitation of the current matching principle of laminated batteries; on the other hand, the transparent oxide insulating layer with low refractive index has the function of light management , plays the role of the middle reflective layer, selectively redistributes the incident light, reflects the suitable short-wavelength light back to the top cell, and at the same time ensures that the light suitable for the bottom cell can be effectively transmitted, and finally makes microcrystalline germanium- The advantage of the narrow bandgap of the amorphous germanium heterogeneous absorption layer material has been fully utilized.

The advantages and beneficial effects of the present invention are: research and development and preparation of a new type of absorber material for thin film solar cells, that is, a periodic narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorber material based on grain boundary passivation technology, The material has the characteristics of low defect state density, and the bandgap can be continuously adjusted between 0.70-1.10eV, which can extend the spectral response range of thin-film solar cells to 1800nm, realize broad-spectrum absorption, and can effectively utilize AM1.5 solar energy 95% of the total radiation of the spectrum; this material is used in a wide-spectrum four-terminal laminated battery based on group IV thin film materials, which can give full play to the narrow bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material in expanding the spectral response range advantages, and is compatible with the traditional silicon-based thin-film stack cell technology, so that the two can be organically combined, and a new wide-spectrum solar cell based on group IV thin-film materials can be obtained without increasing equipment costs, making full use of The solar spectrum improves the photoelectric conversion efficiency of the battery.

【Description of drawings】

Fig. 1 is a schematic diagram of the structure of a narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material.

In the picture: 1. Microcrystalline germanium material i1 2. Amorphous germanium material i2

3. Microcrystalline germanium material i1 4. Amorphous germanium material i2

5. Microcrystalline germanium material i1 6. Amorphous germanium material i2

7. Microcrystalline germanium material i1 8. Amorphous germanium material i2

9. Microcrystalline germanium material i1 10. Amorphous germanium material i2

11. Microcrystalline germanium material i1 12. Amorphous germanium material i2

13. Microcrystalline germanium material i1 14. Amorphous germanium material i2

15. Microcrystalline germanium material i1 16. Amorphous germanium material i2

17. Microcrystalline germanium material i1 18. Amorphous germanium material i2

19. Microcrystalline germanium material i1 20. Amorphous germanium material i2

21. Microcrystalline germanium material i1 22. Amorphous germanium material i2

23. Microcrystalline germanium material i1 24. Amorphous germanium material i2

25. Microcrystalline germanium material i1 26. Amorphous germanium material i2

Fig. 2 is a schematic diagram of the structure of a wide-spectrum four-terminal laminate battery based on group IV thin film materials.

In the figure: 27. Substrate 28. Metal electrode 29. Transparent conductive electrode 30. N-type doped layer of bottom cell 31. Narrow band gap microcrystalline germanium-amorphous germanium heterogeneous absorption layer 32. P-type bottom cell Doped layer 33. Transparent conductive and grid line composite electrode 34. Transparent insulating layer 35. Transparent conductive and grid line composite electrode 36. Microcrystalline silicon battery 37. Amorphous silicon germanium battery 38. Amorphous silicon battery 39. Transparent conductive and grid compound electrode

【Detailed ways】

Example:

A narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material, as shown in Figure 1, is a multi-layer material that is alternately grown by microcrystalline germanium thin films and amorphous germanium thin films prepared by a layer-by-layer cyclic deposition method, Among them, the microcrystalline germanium films 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, and 25 were prepared by plasma-assisted reactive thermal CVD technology, that is, the chemical reaction between germane and hydrogen was deposited on the The temperature is 250-350°C, the gas volume flow percentage is: germane accounts for 0.1-2%, hydrogen is the balance, the thickness of the microcrystalline germanium film is 45nm, and its internal crystal composition accounts for 60% of the volume of the whole material. , with a grain size of 30nm and a band gap of 0.7-0.8eV; amorphous germanium films 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, and 26 use plasma-enhanced chemical vapor phase Prepared by deposition technology, the reaction gas is pure germane, the reaction temperature is 250-300°C, the film thickness is 5nm; the total thickness of the microcrystalline germanium-amorphous germanium heterogeneous film is 650nm.

The narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material is used in a wide-spectrum four-terminal stacked silicon-based thin-film solar cell based on group IV thin-film materials. The solar cell consists of a substrate 27, a metal electrode 28, a transparent conductive Electrode 29, n-type doped layer 30 of the bottom cell, microcrystalline germanium-amorphous germanium heterogeneous absorption layer 31, p-type doped layer 32 of the bottom cell, transparent conductive and gate line composite electrode 33, transparent insulating layer 34. Transparent conductive and gate line composite electrode 35, microcrystalline silicon battery 36, amorphous silicon germanium battery 37, amorphous silicon battery 38 and transparent conductive and grid line composite electrode 39 are superimposed to form, wherein metal electrode 28, transparent conductive electrode 29 , the n-type doped layer 30 of the bottom cell, the microcrystalline germanium-amorphous germanium heterogeneous absorption layer 31, the p-type doped layer 32 of the bottom cell, and the transparent conductive and gate line composite electrode 33 are composed of microcrystalline germanium-amorphous germanium The bottom cell of the thin-film solar cell with amorphous germanium heterogeneous material as the absorbing layer is used to absorb the long-wave solar spectrum in the 1100-1800nm band, transparent conductive and gate line composite electrode 35, microcrystalline silicon cell 36, amorphous silicon germanium cell 37. Amorphous silicon battery 38 and transparent conduction and gate line composite electrode 39 constitute a traditional silicon-based thin film laminated top battery, which is used to absorb the solar spectrum in the 300-1100nm band. The bottom battery and the top battery each have battery poles and are arranged There are four lead-out terminals 28, 33, 35, 39, the bottom cell and the top cell are connected by a transparent insulating layer 34, the resistivity is higher than ¹⁰¹⁰ Ωcm, the transmittance in the 1100-1800nm band is higher than 60%, and the refraction The rate is 1.5-3.0.

The material of the intermediate transparent insulating layer involved in this embodiment is a hydrogenated amorphous silicon oxide material, which is prepared by plasma-enhanced chemical vapor deposition technology, that is, it is prepared by the chemical reaction of silane, carbon dioxide and hydrogen at a deposition temperature of 200°C, with a thickness of 500nm, the refractive index is 2.0-2.5. The microcrystalline silicon cell 37, the amorphous silicon germanium cell 38 and the amorphous silicon cell 39 are prepared by plasma-enhanced chemical vapor deposition technology, and the traditional stacked silicon-based thin-film solar cells obtained in series can achieve a conversion efficiency of 12-13%. Combined with the bottom cell, the conversion efficiency of the four-terminal stacked cell based on group IV thin film materials can reach 13-14%.

Claims (2)

1. A narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorption layer material is characterized in that: it is a multilayer material grown alternately by microcrystalline germanium thin films and amorphous germanium thin films prepared by layer-by-layer circulation deposition method, The thickness of the microcrystalline germanium film is 20-50nm, the volume percentage of the internal crystalline composition of the microcrystalline germanium film is 40-80%, the grain size is 15-40nm, and the thickness of the deposited amorphous germanium film is 1-10nm. Then perform plasma treatment or chemical annealing, so that the microcrystalline germanium film and the amorphous germanium film are deposited cyclically until a microcrystalline germanium-amorphous germanium heterogeneous film with a total thickness of 50-1500nm is formed, which is narrow-bandgap microcrystalline germanium - Amorphous germanium heterogeneous absorber layer material. 2. the application of a narrow-bandgap microcrystalline germanium-amorphous germanium heterogeneous absorber material as claimed in claim 1, characterized in that: it is used for wide-spectrum four-terminal stacked silicon-based thin-film solar cells based on group IV thin-film materials , the solar cell consists of a substrate, a metal electrode, a transparent conductive electrode, an n-type doped layer of the bottom cell, a microcrystalline germanium-amorphous germanium heterogeneous absorption layer, a p-type doped layer of the bottom cell, a transparent conductive layer and Composite grid line electrode, intermediate transparent insulating layer, transparent conductive and grid line composite electrode, microcrystalline silicon battery, amorphous silicon germanium battery, amorphous silicon battery and transparent conductive and grid line composite electrode are superimposed, in which the metal electrode, transparent conductive The electrode, the n-type doped layer of the bottom cell, the microcrystalline germanium-amorphous germanium heterogeneous absorption layer, the p-type doped layer of the bottom cell, and the transparent conductive and gate line composite electrode are composed of microcrystalline germanium-amorphous germanium The bottom cell of thin-film solar cells with heterogeneous materials as the absorbing layer, used to absorb the long-wave solar spectrum in the 1100-1800nm band, transparent conductive and grid line composite electrodes, microcrystalline silicon cells, amorphous silicon germanium cells, amorphous silicon cells The traditional silicon-based thin-film laminated top cell is composed of a transparent conductive and grid line composite electrode, which is used to absorb the solar spectrum in the 300-1100nm band. The battery and the top battery are connected by a transparent insulating layer, the resistivity is higher than 10 ¹⁰ Ω·cm, the transmittance in the 1100-1800nm band is higher than 60%, and the refractive index is 1.5-3.0.