EP2223344A2 - Cellule solaire à contact arrière comportant des zones d'émetteur de côté arrière de grande surface et procédé de fabrication de la cellule solaire - Google Patents

Cellule solaire à contact arrière comportant des zones d'émetteur de côté arrière de grande surface et procédé de fabrication de la cellule solaire

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Publication number
EP2223344A2
EP2223344A2 EP08858742A EP08858742A EP2223344A2 EP 2223344 A2 EP2223344 A2 EP 2223344A2 EP 08858742 A EP08858742 A EP 08858742A EP 08858742 A EP08858742 A EP 08858742A EP 2223344 A2 EP2223344 A2 EP 2223344A2
Authority
EP
European Patent Office
Prior art keywords
regions
base
emitter
semiconductor substrate
solar cell
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08858742A
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German (de)
English (en)
Inventor
Nils-Peter Harder
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Institut fuer Solarenergieforschung GmbH
Original Assignee
Institut fuer Solarenergieforschung GmbH
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Filing date
Publication date
Application filed by Institut fuer Solarenergieforschung GmbH filed Critical Institut fuer Solarenergieforschung GmbH
Publication of EP2223344A2 publication Critical patent/EP2223344A2/fr
Withdrawn legal-status Critical Current

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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
    • H01L31/04—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
    • H01L31/068—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 homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H01L31/0682—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 homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells back-junction, i.e. rearside emitter, solar cells, e.g. interdigitated base-emitter regions back-junction 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
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells
    • H01L31/022441—Electrode arrangements specially adapted for back-contact solar 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
    • Y02E10/547—Monocrystalline silicon PV cells

Definitions

  • the present invention relates to a back-contact solar cell with large-area rear-side emitter regions and to a production method for such a back-contact solar cell.
  • Conventional solar cells have a front-side contact, that is, a contact disposed on a light-facing surface of the solar cell, and a back-side contact on a surface of the solar cell facing away from the light.
  • the largest volume fraction of a semiconductor light-absorbing substrate is of the semiconductor type (for example, p-type) contacted by the backside contact. This volume fraction is commonly referred to as the base, and the backside contacts are therefore commonly referred to as base contacts.
  • the backside contacts are therefore commonly referred to as base contacts.
  • In the area of the surface of the front side of the semiconductor substrate is a thin layer of the opposite type of semiconductor (for example, n-type). This layer is commonly referred to as an emitter and the contacts contacting them as emitter contacts.
  • the pn junction which is decisive for current collection, lies just below the front surface of the solar cell.
  • This position of the pn junction is particularly advantageous when using semiconductor material of poor to medium quality for efficient current collection, since the highest generation rate of charge carrier pairs is present on the light-facing side of the solar cell and thus the most light-generated (minority) charge carriers only have to travel a short distance to the pn junction.
  • both the base contacts and the emitter contacts lead due to their associated partial shading of the front to a loss of efficiency.
  • corresponding emitter regions must be formed on the rear side of the solar cell.
  • a solar cell in which both emitter regions and base regions are located on the side facing away from the light in use and in which both the emitter contacts and the base contacts are formed on the back, is referred to as a back contact solar cell.
  • the surface regions of the base regions provided on the rear-side surface should be arranged especially for solar cells whose current collector india pn junction is arranged exclusively on the back side of the solar cell that essentially do not contribute to the formation of the charge carrier-collecting pn junction, be as small as possible in order to influence the effectiveness of the current collection through the pn junction as little as possible negatively.
  • the procedure in this situation is that the largest surface portion of the back of the solar cell is provided with an emitter and extending therebetween only narrow base portions.
  • a semiconductor substrate 101 forms in its volume a base region, for example of the p-type semiconductor.
  • Emitter regions 105 are formed on a back surface 103.
  • the emitter regions 105 occupy the predominant portion of the rear-side surface 103.
  • linear regions are left open, at which base regions 107 of the semiconductor substrate 101 to the back surface 103 are sufficient. In the region of the rear surface, these base regions may have a stronger doping than the main volume of the base of the solar cell.
  • the entire backside surface 103 is covered with a dielectric passivation layer 109, which may have a low refractive index, so that it may serve, for example, as a back reflector for the solar cell, and may be formed of silicon dioxide, for example.
  • the passivation layer 109 has locally openings 111 through which emitter contacts 113 can contact the emitter regions 105.
  • the dielectric layer 109 has openings 115, through which base contacts 117 can contact the base regions 107 reaching locally up to the rear surface.
  • the emitter contacts 113 and the base contacts 117 are separated by narrow gaps 119 and thus electrically isolated.
  • the base contacts 117 are slightly narrower in this type of solar cell than the base regions 107 on the back surface 103. In this way it is ensured that even if the dielectric layer 109 is not perfectly electrically insulated, no unwanted short circuit to the emitter regions by the base contact 117 105 can be generated because the base contacts in the projection do not overlap with the emitter regions 105.
  • the emitter contacts 113 and the base contacts 117 are usually applied in conventional back-contact solar cells, as shown in FIG. 5, in a common method step, for example by vapor deposition or sputtering of metal, optionally with subsequent electroplating. and are thus substantially the same thickness.
  • the base contacts 117 are substantially narrower than the emitter contacts 113. Since both contacts 113, 117 must dissipate the same current, it follows that, by applying a metal layer thickness to the contacts, sufficient for efficient current drainage from the base through the base contacts , the emitter contacts are much thicker than required.
  • metal contacts for both the emitter and the base contacts may therefore be desirable to form the metal contacts for both the emitter and the base contacts in approximately the same width and thereby preferably make the metal contacts as wide as possible, so that with low metal layer thickness as low as possible electrical resistance of the metal contacts can be achieved.
  • the area ratios covered by the emitter contact 213 and the base contact 217 on the back surface of the semiconductor substrate 201, respectively, are substantially equal.
  • the base regions 207 extending between the emitter regions 205 to the back surface are narrower than the base contacts 217 contacting these regions.
  • the base contacts 217 extend laterally into regions where they overlap the emitter regions 205.
  • the dielectric layer 209 must be electrically insulated as well as possible.
  • the emitter regions adjacent the back surface of the solar cell can not be passivated sufficiently by conventional processes such as thermal oxidation.
  • a back contact solar cell and a method of manufacturing a back contact solar cell, in which the above-mentioned disadvantages of conventional back contact solar cells can be at least partially avoided.
  • a back-contact solar cell which, on the one hand, has good current-collecting properties due to the largest possible rear-side emitter and, on the other hand, the rear-side metal contacts can be applied in a favorable manner and preferably at the same time the risk of local short circuits caused by the metal contacts can be minimized or a surface passivation can be improved at the solar cell back.
  • This first aspect of the present invention may be considered to be based on the following idea: On the back surface of the semiconductor substrate, both emitter and base regions are formed, both of which can be electrically contacted by corresponding contacts on the back surface. Due to the fact that the emitter regions and the base regions overlap laterally in overlapping regions and the emitter regions can extend there deeper in the interior of the semiconductor substrate, while the base regions extend on the rear side surface of the semiconductor substrate Goals that appear contradictory to conventional back-contact solar cells are:
  • the base areas contacted by the base contacts may be formed on the rear side surface relatively wide or over a large area.
  • the base regions may occupy approximately the same or a slightly larger area of the back surface than the base contacts, so that it is not absolutely necessary to electrically insulate the base contacts from the substrate surface by a dielectric layer disposed thereunder.
  • the entire base region can be directly connected to the corresponding base contacts on its rear side surface without the need for undesirable short circuits.
  • the area fraction of the base regions on the rear side surface of the semiconductor substrate, and thus also the area fraction of the base contacts, can be approximately the same as the area fraction of the emitter adjoining regions or the emitter contacts adjoining the rear side surface.
  • both the emitter contacts and the base contacts can each be formed with the same thickness necessary to avoid substantial series resistance losses in the contacts.
  • the emitter regions and the base regions can be formed by means of two successive diffusion of dopants into the semiconductor substrate according to an embodiment to be described in more detail below become.
  • the emitter regions in a first diffusion step, can first be diffused, with small subregions in which the base regions subsequently to be produced on the back surface being in electrical contact with the base regions further inside the semiconductor substrate, either locally before the emitter diffusion be protected or the emitter areas then locally opened / removed at these locations.
  • the base regions can then be formed on the backside surface of the semiconductor substrate.
  • the so-called “emitter-push effect” can be used, in which in two successive process steps for the diffusion of dopants, for example in silicon, the second diffusion, even if of equal or greater strength, the first diffusion is not necessarily compensated or overcompensated since
  • the emitter-push effect can cause the dopants introduced during the first diffusion to diffuse further into the interior of the semiconductor substrate to produce the emitter regions, while the second diffusion can diffuse the dopants of the first diffusion
  • a structure can be achieved in which the emitter regions and the base regions have approximately the same dopant concentrations, but the emitter regions continue to be arranged in the interior of the semiconductor substrate are rdnet than the surface-arranged base portions, so that it may come to the desired overlap.
  • the emitter-push effect is particularly pronounced when the second diffusion is a phosphorus diffusion.
  • the overlapping structure can be achieved by first forming a deep emitter and subsequently producing shallower base regions in the region following base contacts to be generated, wherein the base regions are produced in such a way that the emitter doping originally contained in these regions is local is overcompensated.
  • the desired overlapping of the two regions can again occur.
  • dopants can also be introduced into the desired regions and depths by other methods, such as, for example, ion implantation, into the semiconductor substrate.
  • the structures according to the invention can also be produced by the application and structuring (or by structured application) of semiconductor layers by means of coating methods, for example expitaxy, hetero-epitaxy, or other coating methods.
  • the semiconductor substrate used for the back contact solar cell may be, for example, a monocrystalline or multicrystalline silicon wafer.
  • thin films of amorphous or crystalline silicon or of other semiconductive materials may also be used as the substrate.
  • the emitter regions may extend partially directly along the surface along the rear side surface of the semiconductor substrate, but parts of the emitter regions, in particular in the overlap regions, may not adjoin the surface directly, but may also extend somewhat deeper in the interior of the semiconductor substrate. These emitter regions which are "buried” in the interior can be in electrical contact with the regions of the emitter regions adjoining the rear side surface, so that they can also be contacted electrically therefrom by the emitter contacts.
  • the emitter regions can be formed by diffusing dopants into the semiconductor substrate be generated. For example, in a p-type semiconductor substrate, by locally diffusing phosphorus, an n-type emitter region can be formed. Alternatively, however, the emitter regions can also be produced by other methods, such as by ion implantation or alloying, so that a so-called homo-junction, that is a pn junction with oppositely doped regions of a same semiconductor base material, for example silicon, results.
  • the emitter regions can also be epitaxially deposited, for example vapor-deposited or sputtered on, so that, depending on the choice of material applied, homo- or so-called hetero junctions result, that is, pn junctions between a first semiconductor material of the basic semiconductor type and a second one Semiconductor material of an emitter semiconductor type called hetero-junctions when base and emitter semiconductors differ by more than just the line type (doping type).
  • a possible example is emitter regions of deposited or PECVD applied amorphous silicon (a-Si) on a semiconductor substrate made of crystalline silicon (c-Si).
  • the base regions can also be produced by means of one of the abovementioned production methods, although production by local in-diffusion of a dopant to form the base regions may be preferred.
  • the emitter regions and the base regions when viewed in a plan view of the rear side surface of the semiconductor substrate, may each have a comb-like structure, in each of which linear finger-like emitter regions adjoin adjacent linear finger-like base regions.
  • Such a nested structure is also referred to as "interdigitated”.
  • Both the emitter contacts and the base contacts can each be designed in the form of a local metallization, for example in the form of finger-like grids.
  • metals such as silver or aluminum may be deposited locally onto the base or emitter regions, for example, by vapor deposition or sputtering or by a printing process such as screen printing or dispensing, for example, through a mask or photolithography in the desired structure be applied.
  • an electrically insulating gap may be provided between the two. This result can also be achieved by a metal layer applied over the entire area, which is subsequently removed locally along the line of the desired contact separation.
  • An essential feature of the back contact solar cell according to the invention are the overlapping regions in which both a base region and an emitter region are located on the rear side of the semiconductor substrate in the projection onto the rear side surface.
  • the base region directly adjoins the backside surface, whereas the emitter region in this region is shifted further into the interior of the semiconductor substrate, whereby the emitter in this region can also be referred to as a "buried emitter.”
  • Both regions can be very close to the back sides Surface area of the semiconductor substrate, in particular in view of the thickness of the semiconductor substrate which is usually large in comparison to the thickness of the emitter or base regions of, for example, a few micrometers, which may amount to approximately 200 ⁇ m in the case of a silicon wafer, however, the emitter region may, in particular in the overlap regions For example, the emitter region may extend to a depth of more than 1 ⁇ m, preferably more than 2 ⁇ m, below the back surface, whereas the base regions may be less than 1, for example m deep, for example, about 0.5 micro
  • the emitter areas do not extend along the finished solar cell in the process entire backside surface of the semiconductor substrate, but there are left small local areas therebetween, which do not have the emitter semiconductor type and which later serve for the electrical connection between the base areas formed on the back surface and the base areas inside the semiconductor substrate.
  • These connection regions in which either no corresponding emitter doping was effected during the generation of the emitter regions or in which a previously generated emitter doping was subsequently removed again, for example by etching away or by laser ablation, or by local overcompensation of the emitter doping by basic doping may be like a line, for example, parallel to the base contacts to be formed later, or punctiform.
  • the emitter regions extend along more than 60%, preferably more than 70%, even more preferably more than 80% and again more preferably more than 90%, of the backside surface of the semiconductor substrate and the base regions extend along more than 25%, preferably more than 40% and more preferably between 45% and 55% of the back surface of the semiconductor substrate.
  • the total area of the emitter regions facing the main volume and the base regions facing the cell back can add up to more than 100% of the backside surface of the semiconductor substrate.
  • an area of the back surface of the semiconductor substrate covered by the base contacts is between 70% and 100% of the area of the base regions on the back surface of the semiconductor substrate.
  • 70% to 100%, preferably 90% to 98%, of the area of the base regions may be covered by base contacts. Due to the large area of the base contacts that is possible in this way, low series resistances can be realized in these contacts.
  • the base contacts preferably do not protrude laterally beyond the underlying base regions to avoid any short circuits between the base contacts and the emitter regions adjacent the base regions.
  • a doping concentration in the base regions at the back surface of the semiconductor substrate is higher than at base regions inside the semiconductor substrate. This can result from the fact that the base regions on the rear-side surface are subsequently introduced into the semiconductor substrate during manufacture of the solar cell, for example, they are diffused. Such heavily doped superficial base regions can act as BSF (Back Surface Field).
  • BSF Back Surface Field
  • the doping concentration in the interior of the semiconductor substrate may be in the range of 1 x 10 14 cm “3 to 1 x 10 17 cm " 3
  • the Doping concentration in the base regions on the back surface may be greater than 1 x 10 18 cm "3 , preferably greater than 1 x 10 19 cm “ 3 may be.
  • planar p + n + transitions can act as zener diodes which can provide the function of a bypass diode for the solar cell.
  • a doping concentration in the base regions on the back surface of the semiconductor substrate is higher than in the emitter regions. This is especially true if the base regions are formed by local overcompensation of previously formed emitter regions.
  • an emitter region having a doping concentration of 5 ⁇ 10 18 cm -3 is produced, then in a partial region of the emitter region a base region having a doping concentration of, for example, more than 2 ⁇ 10 19 cm -3 can be obtained by overcompensating with dopants for the corresponding opposite Semiconductor type can be generated.
  • an area of the back surface of the semiconductor substrate contacted by the emitter contacts is less than 30%, preferably less than 20% relatively, more preferably less than 10% relative, of a surface in contact with the base contact Back surface of the semiconductor substrate.
  • the emitter contacts and the base contacts are approximately similar in area or equal in area, wherein ideally both the emitter contacts and the base contacts each approximately 50% of Cover back surface of the semiconductor substrate. Due to the fact that the two contact types are of approximately the same size in area, the series resistances effected in the contacts, which depend both on the lateral surface extent and on the thickness of the contacts, can also be approximately the same size.
  • Both types of contact can be made with the same thickness, but the thickness can be chosen so that the series resistance losses in the contacts are negligibly small. Even if the two contact types are generated in the same process step and thus automatically have the same thickness, none of the contact types has an excessively large thickness and no metal necessary for the production of the contacts is wasted.
  • portions in which base portions on the back surface of the semiconductor substrate contact base portions in the interior of the semiconductor substrate are formed as dot-shaped connection portions.
  • the connection regions interrupt the overlapping regions between the emitter regions and the base regions and can thus act as an electrical connection between the base contacts which contact the base regions and the base regions in the interior of the semiconductor substrate.
  • the aforementioned dot-shaped connection regions are respectively arranged in lateral edge regions of the base regions on the back surface of the semiconductor substrate. Due to the fact that connecting regions are formed not in the middle, but in lateral edge regions of the base regions, the paths, the charge carriers, which are located in the interior of the Semiconductor substrate generated by light incident, must be reduced before they can flow through the connection areas through to the base contacts, reduced. This allows a reduced series resistance to be achieved within the base.
  • the base regions are phosphorus doped and the emitter regions are boron doped.
  • Such an embodiment makes it possible first to generate the emitter regions and then to diffuse the phosphorus-doped base regions and thereby to use the emitter-push effect, that is, to drive the boron doping previously generated in the emitter regions further into the interior of the semiconductor substrate. In this way, the overlapping areas can be generated in a procedurally simple manner.
  • the emitter regions essentially adjoin the backside surface only in the region of the emitter contacts.
  • the emitter regions extend substantially only where they are contacted by the emitter contacts, directly on the back surface of the solar cell, and in all other regions the emitter regions are buried deeper inside the solar cell and from the back surface
  • the overlapping areas in this embodiment extend laterally to just below the areas of the emitter areas contacted by the emitter contacts.
  • Substantially can be understood in this case as meaning that the regions of the emitter regions adjoining the backside surface are precisely down to manufacturing tolerances, ie to a few micrometers to a few hundred micrometers, depending on the manufacturing process, with the regions of the emitter contacts contacted by the emitter contacts Back surface match. At least in this embodiment, the area ratio of the regions of the emitter regions adjoining the backside surface should be be smaller than the area ratio of not adjacent to the back surface, ie buried, areas of the emitter areas.
  • a majority of the back surface is covered with base regions.
  • These base regions especially when dealing with n-type regions, can be better surface-passivated with established techniques such as thermal oxidation than p-type emitter regions.
  • At least some of the base regions are not in electrical contact with base contacts.
  • not all of the base regions on the back surface are in electrical contact with the base contacts, but some base regions are isolated from the base contacts.
  • These areas that are not directly contacted are also referred to as "floating" and can be passivated particularly well, especially if they are n-type areas.
  • a method for producing a solar cell in particular the above-described solar cell according to the invention, comprising the following process steps: providing a semiconductor substrate having a basic semiconductor type; Forming emitter regions along a backside surface of the semiconductor substrate, the emitter regions having an emitter semiconductor type opposite to the base semiconductor type; Forming base regions along the backside surface of the semiconductor substrate, the base regions having the base semiconductor type; Forming emitter contacts for electrically contacting the emitter regions; and forming base contacts for electrically contacting at least some of the base regions.
  • the emitter regions and the base regions are formed such that they overlap at least in overlap regions and the emitter regions in the overlap regions extend deeper into the semiconductor substrate than seen from the back surface the base areas.
  • the emitter regions and the base regions may be formed by various methods, for example, by local in-diffusion using, for example, masks or lithography, ion implantation, local alloying, epitaxial deposition of appropriate layers, whole-area deposition, and subsequent patterning, e.g. local removal, for example by means of laser ablation, etc.
  • the emitter and base contacts may also be formed by various methods, for example, by local vapor deposition using, for example, masks or lithography, or by screen printing or dispensing techniques. In general, all methods can be used which make it possible to form contacts locally, for example finger or grid-shaped, on a substrate back, including the possibility of applying full-area metal layers, which are subsequently patterned by local removal.
  • first the emitter regions having a first depth and a first doping concentration and then the base regions having a second depth and a second doping concentration are formed, wherein the first depth is greater than the second depth and wherein the first doping concentration is less than the second doping concentration.
  • initially a relatively weakly doped, deep emitter is formed, which can then be overcompensated locally by a more heavily doped, shallower base region.
  • deeper emitter regions can remain outside the overcompensated regions, so that the desired overlap region is formed.
  • the emitter regions are formed with a boron doping and subsequently the base regions are formed with a phosphorus doping.
  • the base regions it is not absolutely necessary for the base regions to be generated by overcompensating the emitter regions previously generated.
  • the emitter-push effect can be used, wherein during the diffusion of the phosphorus doping, the previously present there boron doping is pushed in front of him and forms a lower emitter region. Accordingly, the doping concentration in the base regions does not necessarily have to be larger than in the emitter regions.
  • At least some of the base regions are formed such that they are not in electrical contact with base contacts.
  • so-called "floating" base regions can be formed, which can be passivated in particular in the case of n-type base regions.
  • the floating base regions can be electrically insulated from the base regions contacted by the base contacts by emitter regions or other insulating layers located therebetween.
  • FIG. 1 shows a cross-sectional representation of a back contact solar cell according to an embodiment of the present invention with overcompensated base regions.
  • FIG. 2 shows a cross-sectional representation of a back contact solar cell according to a further embodiment of the present invention with overlap regions generated by the emitter push effect.
  • FIG 3 shows a cross-sectional representation of a back contact solar cell according to a further embodiment of the present invention with connecting regions formed in edge regions of the base regions.
  • FIG. 4 shows a cut-out plan view of the rear side of the embodiment shown in FIG. 3.
  • Fig. 5 shows in cross-sectional representation a back contact solar cell according to another embodiment of the present invention, in which overlap areas come close to the emitter contacts.
  • 6 shows a cross-sectional representation of a back contact solar cell according to a further embodiment of the present invention with floating base regions.
  • Fig. 7 shows a back contact solar cell according to the prior art.
  • Fig. 8 shows another prior art back contact solar cell.
  • the back contact solar cell according to the invention shown in cross section in FIG. 1 has a semiconductor substrate 1 in the form of a silicon wafer. On the back surface 3 of the semiconductor substrate 1, both emitter regions 5 and base regions 7 are formed. Furthermore, a dielectric layer 9 made of silicon oxide or silicon nitride, which can serve for passivation of the surface of the semiconductor substrate and / or as a rear-side reflector, which, however, does not necessarily have to be electrically insulating, is located on the rear side surface 3. Over the dielectric layer 9 then the emitter contacts 11 and the base contacts 13 are formed. Both the emitter and the base contacts 11, 13 are in the form of elongated, finger-shaped, perpendicular to the plane extending contacts.
  • the emitter contact 11 contacts an emitter region 5 through line-shaped openings or through punctiform openings 15 arranged linearly adjacent to one another in the dielectric layer 9.
  • the width w e of the subregion of the emitter region 5 adjoining the back surface 3 is slightly greater than the width W E of the corresponding emitter contact 11. Accordingly, even if the dielectric layer 9 is not electrically insulating, no risk that the emitter contact 11 causes a short circuit to the adjacent base region 7.
  • a finger-shaped base contact 13 extends over the dielectric layer 9 and contacted by a linear opening or by linear successively arranged adjacent punctiform openings 17 the underlying base region 7.
  • the width W B of the base contact 13 is slightly smaller than the width Wb of the underlying base region 7, so that there is no risk of short circuits between metal contacts of one polarity and semiconductor regions of the other polarity, that is, for example, between base contacts and emitter regions.
  • emitter region 5 overlaps a base region 7 adjoining laterally therefrom.
  • This overlap region 19 is formed by initially diffusing emitter regions 5 having a relatively large depth t e into the rear side of semiconductor substrate 1 and subsequently to produce the illustrated back-contact solar cell the base regions 7 have been diffused with a smaller depth tb, wherein the diffusion of the base regions of the process parameters used therein, such as temperature and diffusion duration, is performed such that in the region of the base regions 7 overcompensation of the emitter doping previously present there occurs.
  • the overlapping regions 19 have a width w u which is slightly smaller than half the width W b of the base regions 7.
  • a gap acting as a connecting region 21 remains between the overlapping overlapping regions 19, at which the corresponding base region 7 with the interior of the semiconductor substrate 1 is in electrical contact and over which the majority charge carriers generated in the semiconductor substrate 1 can flow towards the base contact 13.
  • Fig. 2 embodiment of the back contact solar cell according to the invention agrees in most of its features with the embodiment shown in Fig. 1 match.
  • the main difference is the step-shaped transition 23 recognizable in the emitter region 5 at the edge of the overlapping region 19. This transition 23 is produced when the emitter-push effect is used during the generation of the emitter regions 5 and the base regions 7 and thus when the base region 7 diffuses the overlying emitter region 5 in the overlap region 19 is pushed deeper into the interior of the semiconductor substrate 1.
  • connection portion 21 which connects the disposed on the back surface 3 base portion 7 with the interior of the semiconductor substrate 1, not as in the figures 1 and 2 is shown approximately in the middle of the base region 7 is arranged.
  • two such connection regions 21 are provided, which are each provided in edge regions 25 of the base regions 7 and preferably do not form long lines extending parallel to the metal contacts, but particularly preferably represent punctiform connection regions.
  • majority charge carriers which are generated in the interior of the semiconductor substrate 1 in a region above the emitter regions 5, that is to say between two laterally adjacent base regions 7, can flow out through the connection regions 21 provided in the edge region 25 to the base contact 13, instead of as in FIGS in the Fign. 1 and 2 shown embodiments up to the provided in the middle of the base portion 7 connecting portion 21 to flow over a longer path before they can flow to the base contact 13. Accordingly, this series resistance losses can be reduced.
  • connecting regions 21 are only punctiform in this embodiment, there is also an electrical contact which is located centrally above the base contacts 13 arranged regions of the emitter regions 5 to the standing with the emitter contacts 11 in electrical contact regions of these emitter regions 5. Apart from the small recesses in the connecting regions 21 thus substantially the entire surface of the solar cell may be covered with an emitter 5, so that charge carriers very efficiently can be collected.
  • FIG. 5 shows an embodiment in which the emitter regions 5 adjoin the rear side surface 3 only in the region of the emitter contacts 11.
  • the emitter regions 5 are buried deeper in the interior of the solar cell and separated from the back surface 3 by base regions 7 located therebetween.
  • These base regions 7 are in turn covered by a dielectric layer 9, preferably a thermal oxide, and are therefore very well surface-passivated.
  • FIG. 6 shows an embodiment in which some of the base regions 7 are not in electrical contact with base contacts 13. These "floating" base regions 7 'are isolated from the contacted base regions 7 by parts of the emitter regions 5.
  • the floating base regions 7' can be passivated very well by a dielectric layer 9 deposited thereon.

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Abstract

L'invention concerne une cellule solaire à contact arrière et un procédé de fabrication de celle-ci. La cellule solaire à contact arrière comporte un substrat à semi-conducteurs (1) dont la surface du côté arrière (3) présente des zones d'émetteur (5) mises en contact par des contacts d'émetteur (11), et des zones de base (7) mises en contact par des contacts de base (13). Les zones d'émetteur (5) et les zones de base se chevauchent au moins dans des zones de chevauchement. Vues depuis la surface du côté arrière de la cellule solaire, dans les zones de chevauchement (19), les zones d'émetteur (5) s'étendent plus profondément dans le substrat à semi-conducteur (1) que les zones de base. De ce fait, une grande partie de la surface du côté arrière du substrat à semi-conducteurs peut être recouverte d'un émetteur collectant les porteurs de charge, cet émetteur étant toutefois au moins partiellement enfoui dans le substrat à semi-conducteurs (1), de telle manière que les contacts de base (13) ne risquent pas de provoquer un court-circuit avec les zones d'émetteur enfouies (5).
EP08858742A 2007-12-11 2008-11-28 Cellule solaire à contact arrière comportant des zones d'émetteur de côté arrière de grande surface et procédé de fabrication de la cellule solaire Withdrawn EP2223344A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE102007059487 2007-12-11
DE102008030880A DE102008030880A1 (de) 2007-12-11 2008-06-30 Rückkontaktsolarzelle mit großflächigen Rückseiten-Emitterbereichen und Herstellungsverfahren hierfür
PCT/EP2008/066445 WO2009074469A2 (fr) 2007-12-11 2008-11-28 Cellule solaire à contact arrière comportant des zones d'émetteur de côté arrière de grande surface et procédé de fabrication de la cellule solaire

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EP2223344A2 true EP2223344A2 (fr) 2010-09-01

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US (1) US20110023956A1 (fr)
EP (1) EP2223344A2 (fr)
JP (1) JP2011507246A (fr)
AU (1) AU2008334769A1 (fr)
CA (1) CA2708616A1 (fr)
DE (1) DE102008030880A1 (fr)
WO (1) WO2009074469A2 (fr)

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AU2008334769A1 (en) 2009-06-18
CA2708616A1 (fr) 2009-06-18
DE102008030880A1 (de) 2009-06-18
WO2009074469A2 (fr) 2009-06-18
WO2009074469A3 (fr) 2009-09-24
US20110023956A1 (en) 2011-02-03
JP2011507246A (ja) 2011-03-03

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