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• • H—ELECTRICITY
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  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
  • H01L31/075—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PIN type, e.g. amorphous silicon PIN solar cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
  • H01L31/075—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PIN type, e.g. amorphous silicon PIN solar cells
  • H01L31/076—Multiple junction or tandem solar cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0216—Coatings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/042—PV modules or arrays of single PV cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
  • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
  • H01L31/072—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type
  • H01L31/0745—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells
  • H01L31/0747—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN heterojunction type comprising a AIVBIV heterojunction, e.g. Si/Ge, SiGe/Si or Si/SiC solar cells comprising a heterojunction of crystalline and amorphous materials, e.g. heterojunction with intrinsic thin layer
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
  • H01L31/20—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof such devices or parts thereof comprising amorphous semiconductor materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/548—Amorphous silicon PV cells

Definitions

• This invention relates to solar photovoltaic conversion devices, so- lar cells, especially thin- film silicon photovoltaic devices with improved performance due to the incorporation of (a) passivation layer (s) within the photoactive microcrystalline part of the device.
• FIG. 4A shows a tandem-junction silicon thin film solar cell as known in the art.
• a thin-film solar cell 50 generally includes a first or front electrode 42, one or more semiconductor thin-film p-i-n junctions (52-54, 51, 44-46, 43), and a second or back electrode 47, which are successively stacked on a substrate 41.
• the i-type layer 53, 45 which is a substantially intrinsic semiconductor layer, occupies the most part of the thick- ness of the thin-film p-i-n junction. Substantially intrinsic in this context is understood as "exhibiting essentially no resultant doping". Photoelectric conversion occurs primarily in this i-type layer; it is therefore also called absorber layer.
• solar cells or photoelectric (conversion) devices are characterized as amorphous (a-Si, 53) or microcrystalline ( ⁇ - ⁇ , 45) solar cells, independent of the kind of crystallinity of the adjacent p and n-layers.
• Microcrystalline layers are being understood, as common in the art, as layers comprising of a significant fraction of crystalline silicon - so called micro-crystallites - in an amorphous matrix.
• Stacks of p-i-n junctions are called tandem or triple junction photovoltaic cells.
• the crystallinity of the photoactive layer has to be chosen by considering that (for the standard PECVD- deposition conditions) on one hand, microcrystalline silicon layers have a better electronic quality (low defect density) when deposited close to the amorphous-microcrystalline silicon transition which results in a high open-circuit voltage (Voc) of the device.
• high current densities (Jsc) are obtained by increasing the crystallinity well over the amorphous-microcrystalline transition.
• the defect density in the i- ⁇ c-Si:H layer is not only related to its crystallinity. Additional defects are introduced when using rough front Transparent Conductive Oxide (TCO) layers as front electrode ("front TCO", front electrode) .
• TCO Transparent Conductive Oxide
• front TCO front electrode
• Such TCOs are used primarily for in- creasing the Jsc of thin- film silicon solar cells via the increase of the optical path of light within the device.
• the use of rough front TCOs leads usually to a decrease of the Voc and fill factor (FF) . This effect is attributed to the presence of additional morphology-related defects (zones of porous ⁇ - ⁇ -3 ⁇ : ⁇ ) which lead to a decrease in FF in Voc.
• the chosen device crystallinity of the ⁇ - ⁇ -3 ⁇ : ⁇ layer results from a compromise between high crystallinity for high Jsc and medium crystallinity for high Voc.
• Stand-of -the-art PECVD deposition tools and processes do not allow for an ideal ⁇ -3 ⁇ : ⁇ material with high crystallinity (high Jsc) and low defect density (high Voc) for the ⁇ - ⁇ -. ⁇ i- layer fabrication. But with a defect passivation layer, high crystallinity (high Jsc) and good Voc is possible with typical standard PECVD-deposition parameters.
• Figure 1 I (V) characteristics of Micromorph top-limited cells with varying passivation a-Si:H i-layers (tested thicknesses: 10, 50 and 150nm, rough LPCVD-ZnO substrate) .
• the reference cells have an average Voc of 1347 mV, Jsc of 12.2 mA/cm2 and FF of 70.2%.
• the cells passivated with 10 nm i-a:Si:H have the following average higher electrical performances of Voc: 1356 mV, Jsc of 12.4 mA/cm2 and FF of 72.4%.
• Figure 2 A and B Effect of the introduction of an a-Si:H passivation layer of varying thickness on the absolute values of the Voc and FF of the MM cells.
• Figure 3 Total External Quantum Efficiency (EQE) of a Micromorph tandem cell with a 10 nm passivation layer compared to a reference cell without a passivation layer.
• Fig. 4 A Prior Art - tandem junction thin film silicon photovoltaic cell. Thicknesses not to scale.
• Fig. 4 B Embodiment according to the invention with passivation layer. Thicknesses not to scale.
• the present invention comprises introducing a defect -passivation layer 55 in or adjacent to the microcrystalline i- layer 45 of a PV cell 60 (bottom cell in a Micromorph tandem cell) .
• This additional passivation layer 55 includes an a-Si:H i-layer which is optically transparent to the light impinging on it (i.e.
• top limited Micromorph cells were prepared on as grown rough TCO' s (LPCVD-ZnO) .
• the reference devices 50 for comparison offers a top pin a-Si:H cell 51 with an i- layer 53 thickness of 250 nm and a bottom ⁇ -3 ⁇ : ⁇ cell 43 with a photoactive i-layer 45 of 2000 nm with a medium crystallinity (bulk Raman crystallinity measured with a 780nm laser: 50-55%) .
• the passivated devices 60 have identical i-layer thicknesses for the top and bottom cells, except that the deposition of the ⁇ -3 ⁇ : ⁇ i-layer 45 was followed by the deposition of a fully amorphous i-layer 55 (passivation layer) of varying thickness, according to the invention.
• the passivated devices 60 show improved electrical performances (see Figure 1) . This is the indication that the detrimental effect of some of the defects of the underlying microcrystalline silicon layer has been thus mitigated.
• recombination centres such as dangling bonds can be efficiently passivated with a-Si:H and the corresponding decreased recombination of photocarriers leads to an increased Voc, FF and total (top plus bottom sub cells) Jsc (measured by EQE) as observed in our illustrative example.
• the detrimental effect of the morphology- induced defects, namely growth-related defects, is as well reduced by the introduction of the passivation layer at the end of the ⁇ - ⁇ -3 ⁇ : ⁇ layer growth.
• the relative gain in efficiency obtained by the introduction of the amorphous passivation layer at the end of the microcrystalline i- layer is about 5%.
• the appropriate thickness of the passivation layer has to be chosen by considering its effect on the Voc and FF of the cell, as depicted in Figure 1. This figure indicates that a certain thickness of the passivation layer is needed for a simultaneously increased value of FF and Voc. However, when the passivation layer is too thick, a double diode behaviour appears in the I (V) curve which decrease considerably the device performances.
• Figure 2 shows the limitations gain vs. layer thickness.
• silicon-based passivation i-layers than pure a-Si:H can be used as well, alloys such as a-SiC:H, a-Si:0:H or a-SiN:H etc...
• TCO roughness has to be chosen for each TCO roughness according to their conductivity and optical transparency in the wave- length range from 650nm-1100nm.
• this passivation layer is not mandatory to apply this passivation layer at the end of the deposition of the intrinsic microcrystalline layer.
• This layer can be applied at varying locations during the intrinsic mi- crocrystalline layer growth, provided that the subsequent crystalline layer has the adequate crystallinity . It is also possible to introduce more than one passivation layer (s) during the growth of the microcrystalline i- layer.
• a passivation layer according to the invention can be prepared as follows.
• a PECVD process chamber as known in the art (e. g. KAI-M commercially available from Oerlikon Solar) the following process parameter have been used.
• Substrate size was about 500 x 400 mm 2 .
• a high-quality a-Si:H passivation layer is achievable with a pressure between 0.1-2mbar, preferably 0.2-0.5mbar, a power between 5- 500W (2.5mW/cm 2 - 250m /cm 2 substrate size), preferably 30-100W
• Process temperature was chosen between 100°-250°C, preferably around 200°C.
• a process pressure of 1-5 mbar, a power between 100- 600W and a ratio between hydrogen and silane of 10:1 to 200:1 can be applied.
• the deposition rate depends on the process tool used; process duration will therefore vary until the layer thickness accord- ing to the invention between 5nm-50nm has been achieved.
• Photovoltaic cell 60 comprising a substrate 31, a front or first electrode 42 of transparent conductive oxide and at least one p-i-n junction 43 comprising microcrystalline silicon, said p-i-n junction 43 comprising a first sub-layer 44 comprising silicon and a n-dopant and a second sub-layer 46 comprising silicon and a p-dopant and a third sub-layer 45 comprising essentially intrinsic microcrystalline silicon, wherein at least one passivation layer 45 comprising essentially intrinsic amorphous silicon is arranged a) between the micro- crystalline intrinsic sub-layer 45 and n-doped silicon layer 46 or b) as a layer embedded in the microcrystalline intrinsic sub-layer 45 or c) both.
• Passivation layer 45 has a thickness of 5nm-200nm, preferably 10-50nm.
• Passivation layer 55 may be realized with essentially intrinsic silicon or silicon compounds/alloys such as a-SiC:H, a-Si:0:H or a- SiN:H or alike.
• a process for depositing a passivation layer 55 in a photovoltaic thin film solar cell comprises introducing in a PECVD process chamber exhibiting a substrate to be treated a gas mixture comprising silane and hydrogen, establishing either a process pressure between 0.1-2mbar, preferably 0.2-0.5mbar, a RF power (40 MHz or more) be- tween 5-500W, preferably 30-100W, and a ratio between hydrogen and silane of 1:1;
• a method for manufacturing a photovoltaic thin film silicon solar cell comprising:

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• 2011
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