Classifications

• • 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
  • H01L31/0248—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 characterised by their semiconductor bodies
  • H01L31/0256—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 characterised by their semiconductor bodies characterised by the material
  • H01L31/0264—Inorganic materials
  • H01L31/028—Inorganic materials including, apart from doping material or other impurities, only elements of Group IV of the Periodic Table
• • 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
  • H01L31/0248—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 characterised by their semiconductor bodies
  • H01L31/036—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 characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
  • H01L31/0376—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 characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including amorphous semiconductors
  • H01L31/03762—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 characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including amorphous semiconductors including only elements of Group IV of the Periodic Table
• • 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
• • 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
• • 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
  • Y02E10/547—Monocrystalline silicon PV cells
• • 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

• the present invention relates to a heterojunction solar cell and to a production process for such a heterojunction solar cell.
• Solar cells are used to convert light into electrical energy.
• the solar cell In order to be able to spatially separate the charge carrier pairs generated by incident light in a solar cell substrate, the solar cell has various contiguous semiconductor regions, wherein the individual regions due to the energy band structure of the semiconductor materials used for the areas and / or due to the nature and concentration of introduced into the respective semiconductor material Have dopants different electrical properties. Due to these different electrical properties, an electrical potential difference arises at the interface between the different semiconductor regions, as a result of which the electrons and holes of the light-generated charge carrier pairs are spatially separated.
• homojunction solar cells generally exhibit
• RAK sis a single semiconductor substrate made of a semiconductor material, in which by local introduction of different dopants, the mutually adjacent different semiconductor regions are generated.
• a boron doped region having the p-type semiconductor may be adjacent to a phosphorus doped region having the n-type semiconductor, forming a pn junction at the interface, in turn in turn generates the necessary for the separation of the charge carrier potential difference.
• heterojunction solar cells have contiguous regions composed of different semiconductor materials. Since the valence bands and conduction bands of the different semiconductor materials are at different energy levels, so-called "band offsets" occur at the interface at which the different semiconductor materials adjoin one another, and in general also to a band bending which can bring about the potential difference desired for charge carrier separation This effect can be further supported by the fact that the individual semiconductor materials in turn can be doped, which leads to additional influences on the band bending.
• the semiconductor materials used for the formation of the heterojunction solar cell may differ on the one hand with regard to the chemical elements used for this purpose.
• layers of various semiconductor-forming elements such as silicon, germanium, gallium arsenide, etc.
• semiconductor materials of the same chemical elements but in different crystalline or amorphous structures may also be used.
• silicon depending on whether it is in the crystalline or in the amorphous state, may have very different electrical properties, that is, inter alia, the energy levels of the valence and conduction bands or their edges and the intervening band gap significantly can distinguish.
• FIG. 1 a shows a conventional heterojunction solar cell 101, in which an additional semiconductor layer, which is referred to here as a heterojunction layer 105, is deposited on an absorber layer 103 of crystalline silicon (c-Si) on a surface facing the incident light in use ,
• the heterojunction layer 105 is made of amorphous silicon (a-Si) and is doped to have the opposite semiconductor type of the absorber layer 103.
• the heterojunction layer 105 thus forms an emitter for the absorber layer 103.
• the desired potential difference for the separation of the charge carrier pairs is generated due to the band bends or band offsets occurring there.
• a further heterojunction layer 107 is deposited in the example shown. This has the same type of semiconductor as the absorber layer 103, but the doping concentration is higher, so that this heterojunction layer 107 can serve as a back-surface field (BSF).
• BSF back-surface field
• FIG. 1 b shows the location-dependent doping concentration C for the regions of the heterojunction solar cell 101 shown in FIG. 1 a.
• FIG. 1b is shown in such a way that the areas to be assigned to the individual layers 103, 105, 107 can be recognized directly by comparison with FIG. 1a.
• the change in the doping concentration C at the interfaces between the individual heterojunction layers 105, 107 and the absorber layer 103 is abrupt.
• the substantially homogeneously doped absorber layer of the n-type semiconductor or p-type semiconductor adjacent to the likewise substantially homogeneously doped serving as an emitter layer heterojunction layer 105 of the corresponding opposite p-type semiconductor or n-type semiconductor and thus thus If a strong potential difference is formed, there is an abrupt transition from a doping of the one semiconductor type to a doping of the corresponding other type of semiconductor.
• FIG. 2 a shows another example of a conventional heterojunction solar cell 151.
• an absorber layer 153 and a heterojunction layer 155 serving as an emitter layer on the front side and a BSF layer on the back side are used Heterojunction layer 157 each stored an additional, intrinsic amorphous semiconductor layer 159, 161.
• the space charge zones or potential deflections arising at the junctions are widened in this way and the heavily doped heterojunction layers, which typically do not have very high carrier lifetimes, are spatially separated from the absorber volume by the non-doped or weakly doped intermediate layer.
• the heterojunction solar cell structure shown in Figure 2a when well prepared, has a higher surface passivation quality, which can result in a correspondingly higher open-clamp voltage than the solar cell structure of Figure 1 a Case is.
• the quality of the surface passivation increases with increasing thickness of the intrinsic layers 159, 161 of amorphous silicon. Typical thicknesses of such intrinsic layers 159, 161 are in the range of 0.5 nm to 10 nm.
• the observation that in the heterojunction solar cell structure shown in FIG. 2a, on the one hand, the open-terminal voltage is higher than in the structure shown in FIG. 1a, but on the other hand, the observed fill factor is lower, can be justified, inter alia, in the following way
• the intrinsic a-Si layer 159, 161 has a much higher electronic quality as the doped a-Si heterojunction layers 105, 155, 107, 157. That is, the recombination activity (in) of the intrinsic layer is lower than in the doped a-Si heterojunction layers.
• a heterojunction solar cell which comprises an absorber layer of silicon with a basic doping and at least one heterojunction layer of a doped semiconductor material, whose Band gap is different from that of the silicon of the absorber layer has.
• the absorber layer has at a boundary surface directed toward the heterojunction layer a doped layer whose doping concentration is higher than the basic doping concentration of the absorber layer.
• This first aspect of the present invention may be considered as based on the following idea:
• an absorber layer that is essentially homogeneously doped with respect to its basic doping no longer abruptly changes into a heterojunction layer, which in turn is essentially homogeneously doped, at its interface the doping concentration within the absorber layer changes towards the interface with the heterojunction layer, preferably continuously.
• the absorber layer there is therefore an increased dopant concentration near its surface.
• the optimum for the mode of action of a solar cell dopant concentration of the basic doping in the actual absorber is typically in the range of IxIO 14 Cm "3 to IxIO 16 Cm " 3 , but may also be lower, so that the absorber can in extreme cases also consist of intrinsic material.
• this comparatively heavily doped layer is selected to be low, for example, less than 2 ⁇ m, so that the recombination increased within the area due to the increased doping relatively low volume fraction of this layer on the total volume of the absorber provides no significant contribution to the total recombination in the absorber.
• the "field effect” resulting from the near-surface doping profile leads to one type of charge carrier, that is to say either the holes or the electrons, from surface defect states, as occur, for example, at the interface between the absorber layer and the heterojunction layer,
• This effect is also called “field effect passivation” and implies a physical description of the effective surface passivation based on an electric field.
• the surface-near high doping leads to a corresponding band bending, which causes a corresponding surface-near electric field, which in turn prevents a sort of charge carriers from reaching the surface and the recombination centers located there.
• the charge carriers generated within the absorber layer can largely no longer diffuse to the surface of the absorber due to the field effect which is caused by the near-surface heavy doping and recombine at the recombination centers located there.
• the requirement for a very low surface recombination at the interface between the absorber layer and the heterojunction layer, as conventionally to be achieved mainly in that as few recombination centers as possible should exist both at the interface and within the heterojunction layer, which in turn achieves this can be that the heterojunction layer should be as defect-free - and thus slowly and costly - should be deposited or an additional intrinsic layer between the absorber layer and the heterojunction layer should be stored, can thus be reduced.
• heterojunction solar cells proposed here it seems possible in the case of the heterojunction solar cells proposed here to be able to omit the currently mostly integrated, interposed, stored intrinsic layer in conventional heterojunction solar cells, or at least make them thinner, without there being any deterioration in the electrical properties of the solar cell.
• This can contribute to the fact that the series resistance occurring in conventional heterojunction solar cells due to the interposed intrinsic layer would be eliminated or reduced, which can lead to an increase in the fill factor and thus the efficiency of the solar cell.
• heterojunction solar cell in which the heterojunction layer is designed as emitter and the absorber layer as a base, is located at the resulting pn junction forming space charge zone in which the electron and hole concentration correspond to each other, in the region of the interface between the absorber layer and the heterojunction layer.
• the interfacial defect states which occur virtually inevitably at this interface are therefore in the space charge zone which is particularly sensitive to recombination.
• the position of the pn junction is decoupled from that of the heterojunction.
• emitter is formed here not only by the heterojunction layer, but in addition by the introduced into the absorber layer close to the surface doped layer, which also forms part of the emitter in this particular embodiment.
• the actual pn junction is thus shifted to the defect-poor region of the absorber layer.
• the absorber layer can be any desired layer of silicon doped in a basic doping.
• the basic doping may be, for example, in a range of 10 16 cm -3 , but it may also be lower, in extreme cases even as low as, for example, 10 13 cm -3 so that intrinsic silicon can be assumed
• the absorber layer can also be provided as a silicon thin film
• the absorber layer has a thickness such that a significant portion of irradiated light, in particular sunlight, is absorbed within the absorber layer more than 5 microns, preferably more than 20 microns and, in the case of a silicon wafer, preferably more than 100 microns.
• the absorber layer can be doped with any desired dopants.
• the silicon of the absorber layer can be doped with boron, so that p-type silicon results.
• phosphorus can be doped to give n-type silicon.
• the absorber layer comprises crystalline silicon, also referred to as c-Si.
• crystalline silicon also referred to as c-Si.
• Different types of crystallinity can be used, such as monocrystalline, multicrystalline or polycrystalline silicon.
• Crystalline silicon has, for example, compared to amorphous silicon, a low density of impurities that could act as recombination centers, and thus has a high electronic quality.
• the heterojunction layer differs from the absorber layer, in particular with regard to the doped semiconductor material used for it.
• the bandgap of the semiconductor material of the heterojunction layer is different from that of the silicon of the absorber layer. This difference can be both in the size of the band gap and in the energetic position of the band gap, for example based on the Fermi energy level.
• the band gap of the heterojunction layer is greater than that of the absorber layer.
• the semiconductor material of the heterojunction may comprise both silicon, but with a different doping than the silicon of the absorber layer or with a different structure or crystallinity, or it may have completely different semiconductor materials such as germanium, gallium arsenide, etc.
• the heterojunction layer comprises amorphous silicon.
• the heterojunction layer is formed as an emitter layer with a doping opposite to the absorber layer, the use of amorphous silicon may have an advantageous effect on the open-terminal voltage of the solar cell.
• the formation of a BSF by means of a Heterojunction- layer of amorphous silicon may also act advantageously on the open-terminal voltage.
• One or more heterojunction layers may be provided on different sub-surfaces of the absorber layer.
• a heterojunction layer serving as an emitter may be arranged on a front side and / or alternatively on a rear side of the absorber layer.
• a heterojunction layer serving as BSF may be arranged on partial surfaces of the absorber layer.
• the thickness of the heterojunction layer can be substantially less than the thickness of the absorber layer and, for example, less than 1 .mu.m, preferably less than 100 nm and more preferably in the range of 5 to 50 nm.
• the absorber layer differs from that used in conventional heterojunction solar cells, inter alia, in that additional dopants are introduced at an interface directed to the heterojunction layer, around a doped layer whose doping concentration is higher than that
• Basic doping concentration of the absorber layer to produce The more heavily doped layer is thus part of the absorber layer, but has a higher dopant concentration than the rest of the absorber layer.
• the dopant type and the dopant concentration can be selected such that the same type of semiconductor is established in the region of the doping profile as in the heterojunction layer.
• additional dopants can be introduced at the boundary layer between the absorber layer and the heterojunction layer in such a way that, for example, the homogeneous basic doping of the absorber layer is local in the region of Boundary is overcompensated and thus adjusts an emitter-like doping there.
• the heterojunction layer is formed, for example, as BSF with a doping corresponding to the absorber layer of the semiconductor type, only the basic doping of the absorber layer locally in the region of the boundary layer can be increased.
• the doped layer within the absorber layer has a maximum dopant concentration of between IxIO 17 Cm “3 and IxIO 20 Cm “ 3 , preferably of IxIO 18 Cm “3 and IxIO 19 Cm “ 3 .
• a maximum dopant concentration may result in charge carriers generated in the interior of the absorber layer due to the resulting field effect being kept away from the interface with the heterojunction layer.
• the dopant concentration is low enough that the additional charge carrier recombination, as it occurs in heavily doped semiconductor regions, is kept low, in particular the depth of the doping profile is kept low enough.
• the doped layer has a doping profile (23, 25) with a dopant concentration decreasing in a direction away from the interface.
• the doping is lower in a region further inside the absorber layer than further towards its surface.
• the doped layer has a doping profile as produced by diffusion processes.
• doping profiles are easy to produce using standard techniques in silicon wafers and, on the other hand, have long been proven in the production of homojunction solar cells because of their advantageous electronic properties.
• the doped layer has a depth of less than 3 ⁇ m, preferably less than 1 ⁇ m, and more preferably less than 0.5 ⁇ m.
• the doping profile can thus have a thickness or depth which is substantially less than the thickness of the absorber layer and which, furthermore, is preferably also less than the thickness of the heterojunction layer.
• the heterojunction layer directly adjoins the absorber layer.
• conventional heterojunction solar cells often have an intrinsic semiconductor layer interposed between the absorber layer and the heterojunction layer to reduce recombination losses at the interface between the two layers. Due to the doping profile proposed here in the interface-near region of the absorber layer and the field effect associated therewith, however, the proposed heterojunction solar cell can advantageously dispense with the provision of an additional layer of intrinsic semiconductor material without significant losses in the solar cell efficiency due to Interface recombination would come. It should be noted, however, that in addition a layer of intrinsic semiconductor material interposed between the heterojunction layer and the absorber layer may additionally be provided.
• a method for producing a heterojunction solar cell comprising the following steps: providing an absorber layer of silicon homogeneously doped substantially in a basic doping; Introducing dopants into the absorber layer to produce a doped layer whose doping concentration is higher than the base doping concentration of the absorber layer; and depositing a heterojunction layer of a doped semiconductor material whose bandgap differs from that of the silicon of the absorber layer at the surface of the absorber layer.
• substantially homogeneously doped silicon for the absorber layer can be understood in this case such that the silicon used as the base material for the absorber layer should not be intentionally provided with a doping profile, but it should not be ruled out that the dopant concentration locally varies slightly within the silicon used for the absorber layer, which is partially unavoidable, in particular due to external and intrinsic influences in the production of the silicon
• the dopant concentration within the substantially homogeneously doped silicon should not vary more than an order of magnitude.
• the dopants for producing the surface-near, more heavily doped layer within the absorber layer can be introduced in various ways. Preferably, the dopants are introduced by diffusion. For this purpose, dopants can be brought, for example in gaseous, liquid or solid form in the vicinity of the surface of the absorber layer and be superficially diffused at elevated temperatures in the material of the absorber layer.
• the heterojunction layer can then be deposited on the surface of the absorber layer, particularly where the additional dopants were previously introduced.
• This can be achieved by any of various coating or epitaxy techniques, such as chemical vapor deposition (CVD), in particular Plasma Enhanced CVD (PECVD), Physical Vapor Deposition (PVD), or Liquid Phase Epitaxy (LPE). liquid phase epitaxy) happen.
• CVD chemical vapor deposition
• PECVD Plasma Enhanced CVD
• PVD Physical Vapor Deposition
• LPE Liquid Phase Epitaxy
• Fig. Ia shows in cross-section a conventional heterojunction solar cell.
• FIG. 1b shows the doping profile of the heterojunction solar cell shown in FIG.
• FIG. 2 a shows in cross-section a further conventional heterojunction solar cell with integrated intrinsic semiconductor layers.
• FIG. 2b shows the doping profile of the heterojunction solar cell shown in FIG. 2a.
• FIG. 3a shows a cross-sectional representation of a heterojunction solar cell according to an embodiment of the present invention.
• FIG. 3b shows the doping profile of the heterojunction solar cell shown in FIG. 3a.
• FIG. 4 a shows a cross-sectional representation of a heterojunction solar cell according to a further embodiment of the present invention with integrated intrinsic semiconductor layers.
• FIG. 4b shows the doping profile of the heterojunction solar cell shown in FIG. 4a.
• Fig. 3a shows a heterojunction solar cell 1 according to an embodiment of the present invention.
• An absorber layer 3 made of crystalline silicon is, as shown schematically in the diffusion profile shown in FIG. 3b, doped in a central region 21 in a homogeneous p-type manner. In areas close to the surface, a doped layer 23, 25 having a doping profile is additionally introduced.
• the dopant concentration C decreases in each case away from the boundary surface 13, 15 of the absorber layer 3 and toward the interior of the absorber layer 3.
• 3b (and 1b, 2b and 4b) is to be understood as showing the doping concentration of one type (for example n-type) to the left of the center of the graph and to the right of the center of the Graphene the doping concentration of the other type.
• the doping type is opposite to the doping type in the central region 21 in FIGS. 3 and 3b in the front region 23 and thus has emitter-like properties compared to the base-like central region 21.
• the doping type in the rear region 25 corresponds to that of the central region 21, so that a BSF-like region is formed there.
• the homogeneously doped central region 21 can already be doped with boron during the production of the absorber, for example in the form of a crystalline silicon wafer, whereas the additional doped regions 25, 23 can be produced by subsequent in-diffusion of additional boron or phosphorus. Substantially non-doped absorbers can also be used.
• Heterojunction- layers 5, 7 are attached to both the front and on the back. These layers each have a substantially homogeneous doping concentration, the doping type of the respective Heterojunction- layer 5, 7 corresponds to that doping type, as it prevails at the respective interface of the absorber layer 3, to which the heterojunction layer 5, 7 is attached.
• the dopant concentration within the front-side, emitter-like heterojunction layer 5 is substantially greater than the surface dopant concentration within the adjacent region 23 of the doping profile introduced into the absorber layer 3. The same applies to the arranged at the back, base-like heterojunction layer. 7
• an additional intrinsic layer 9 is interposed in the front between the absorber layer 3 and the emitter-like heterojunction layer 5. Furthermore, an additional intrinsic layer 11 is interposed between the absorber layer 3 and the base-like heterojunction layer 7 on the rear side.
• the intrinsic layers 9, 11 can contribute to a further reduction of recombination losses in the region of the transition from the absorber layer 3 to one of the heterojunction layers 5, 7.
• due to the additional doping profile provided by the absorber layer 3 and the field effect caused thereby its positive influence is likely to be lower than in the case of conventional heterojunction solar cells, as illustrated, for example, in FIG. 2a.

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