EP2126980A2 - Heterojunction with intrinsically amorphous interface - Google Patents

Heterojunction with intrinsically amorphous interface

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Publication number
EP2126980A2
EP2126980A2 EP07857992A EP07857992A EP2126980A2 EP 2126980 A2 EP2126980 A2 EP 2126980A2 EP 07857992 A EP07857992 A EP 07857992A EP 07857992 A EP07857992 A EP 07857992A EP 2126980 A2 EP2126980 A2 EP 2126980A2
Authority
EP
European Patent Office
Prior art keywords
layer
doped
interface
sige
concentration
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Withdrawn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
EP07857992A
Other languages
German (de)
French (fr)
Inventor
Pere Roca I Cabarrocas
Jérôme DAMON-LACOSTE
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.)
Centre National de la Recherche Scientifique CNRS
Ecole Polytechnique
Original Assignee
Centre National de la Recherche Scientifique CNRS
Ecole Polytechnique
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Filing date
Publication date
Application filed by Centre National de la Recherche Scientifique CNRS, Ecole Polytechnique filed Critical Centre National de la Recherche Scientifique CNRS
Publication of EP2126980A2 publication Critical patent/EP2126980A2/en
Withdrawn legal-status Critical Current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 at least one potential-jump barrier or surface barrier
    • 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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PIN type
    • H01L31/077—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 at least one potential-jump barrier or surface barrier the potential barriers being only of the PIN type the devices comprising monocrystalline or polycrystalline materials
    • 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 at least one potential-jump barrier or surface barrier
    • 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 at least one potential-jump barrier or surface barrier 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 at least one potential-jump barrier or surface barrier 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
    • 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
    • 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 invention relates to the field of photovoltaic cells, and more particularly that of photovoltaic cells using heterojunctions.
  • This invention may in particular relate to cells comprising:
  • a rear contact layer of electrically conductive material located on the rear face of the central layer.
  • the contact layer may be for example a metal material or transparent conductive oxide - such NTO (acronym for "Indium Tin Oxide” for tin oxide and Indium).
  • This type of structure comprises a heterojunction consisting of the central layer and the rear contact layer.
  • Such a normally or heavily doped heterojunction suffers from poor interface quality due to poor passivation of the c-Si layer, as well as a too large barrier of potential at the interface, resulting in poor collection. carriers.
  • a deleterious effect is a significant loss of signal between the core layer and the back contact layer, which limits the efficiency of the cell.
  • Diffusion problems of metal elements of the front and rear contact layer of the cell may further occur during the formation of the ⁇ -Si: H layer.
  • An object of the invention is to provide new solutions to the problem of the quality of the interface between the c-Si and the rear contact layer on the rear face of the c-Si layer.
  • Another goal is to increase the feasibility of the back side.
  • Another objective of the invention is to increase the efficiency of photovoltaic cells with heterojunctions, to lower the costs, and / or to increase the conversion efficiency / cost ratio of the photovoltaic modules.
  • Another object of the invention is to limit the temperature of production of the cell.
  • a structure for photovoltaic applications comprising:
  • a first crystalline semiconductor material layer having a front face for receiving and / or emitting photons and a rear face; a rear contact made of conducting material situated on the side of the rear face; characterized in that it further comprises:
  • the second layer is doped or intrinsic
  • said crystalline semiconductor material is mono, poly or multicrystalline silicon (Si), and optionally Si is p-doped and ⁇ -SiGe: H is p-doped, or Si is doped n and ⁇ -SiGe: H is doped n;
  • the second layer further comprises carbon
  • the rear contact layer is made of a metallic material or a transparent conductive oxide, such as NTO; the concentration of Ge in the second layer varies gradually in the thickness thereof; the concentration of Ge in the second layer may vary progressively in the thickness thereof so as to be larger on the side of the rear contact layer and less important on the side of the first layer;
  • the structure further comprises a third layer of amorphous or polymorphous semiconductor material, possibly doped, on the front face of the first layer; the third layer is optionally hydrogenated amorphous Si or hydrogenated amorphous SiGe; the third layer is optionally n-doped if the first layer is p-doped, or the third layer is p-doped if the first layer is n-doped; the structure may further comprise a front contact layer of electrically conductive material and transparent on the third layer, the conductive material may be a transparent conductive oxide such as NTO; the second layer has a forbidden band between approximately 1, 2 and 1, 7 eV, and more particularly of the order of 1.5 eV;
  • the invention provides a method for producing a structure for photovoltaic applications, comprising the following steps: (a) providing a first crystalline semiconductor material layer having a front face for receiving and / or emitting photons and a face back ;
  • step (a) and / or (b) further comprises implantation of doping elements
  • step (b) is carried out at a temperature below or similar to 250 ° C .; step (b) is implemented so that the concentration of Ge in the second layer varies gradually in the thickness thereof; the concentration of Ge in the second layer can in particular gradually increase from the first layer;
  • the method further comprises a selection of the hydrogen concentration in the second layer in order to adjust the valence and conduction bands so as to obtain, respectively, discontinuities of valence bands and conduction bands determined at 1 interface with the first layer;
  • the second layer can be n-doped, the valence band discontinuity is sufficiently strong to provide a potential barrier able to push back holes of the interface and thus avoid recombination at the interface, and the discontinuity of conduction bands is low enough to minimize the blocking of electrons at the interface;
  • the second layer may be p-doped, the valence band discontinuity is small enough to minimize the locking of the holes at the interface, and the conduction band gap is strong enough to repel the interface electrons and avoid
  • the method further comprises selecting the concentration of germanium in the second layer so that the bandgap of the material of the rear portion of the second layer has a predetermined width;
  • the method further comprises forming a third layer of hydrogenated amorphous material, possibly doped, on the front face of the first layer, the third layer being made of an amorphous or polymorphic semiconductor material; optionally, the method includes training an electrically conductive and photon-transparent electrical contact layer on the third layer.
  • FIG. 1 represents a schematic cross-sectional view of a heterojunction structure, for photovoltaic application, according to the invention.
  • FIG. 2 represents an exemplary band diagram of the rear face of a p-type Si / Si-SiGe type c-Si heterojunction.
  • a heterojunctional structure 100 such as, for example, a photoelectric cell, comprises a doped doped crystalline (eg monocrystalline, polycrystalline or multicrystalline) active layer or substrate (10) and a layer of doped amorphous material having a difference in bandgap values and therefore discontinuities of bands between them.
  • a doped doped crystalline eg monocrystalline, polycrystalline or multicrystalline active layer or substrate (10)
  • a layer of doped amorphous material having a difference in bandgap values and therefore discontinuities of bands between them.
  • either the active layer 10 is n-doped and the amorphous layer 20 is p-doped or the active layer 10 is p-doped and the amorphous layer 20 is n-doped.
  • silicon and / or SiGe may be chosen to form these two layers 10 and 20.
  • This amorphous / crystalline heterojunction is performed so as to obtain a determined front face tension.
  • the active layer 10 may have a thickness of several micrometers or even several hundred micrometers. Its resistivity may be less than 20, 10 ohms or more particularly around 5 ohms or less.
  • the active layer 10 has a front face 1 and a rear face 2.
  • the front face 1 is intended to receive the photons (and / or to emit them).
  • the rear face 2 is intended to be connected to a rear electrical contact.
  • the doped amorphous layer 20 is located on the side of the front face 1.
  • Oxide "for tin oxide and indium), may be provided on the amorphous layer 20.
  • screen printed metal patterns 80 on this contact layer before 30 may be provided on the amorphous layer 20.
  • an ⁇ -SiGe: H transition layer 50 is interposed between the active layer 10 and this rear contact layer 40.
  • this silicon-germanium layer may be of polymorphic material, thus of the type pmSiGe: H.
  • a deposition for example by PECVD, of the amorphous or polymorphic material is then performed on the rear face 2 of the active layer 10. More details on one or more deposition techniques may for example be found in "Hydrogenated amorphous silicon deposition processes" by Werner Lucas and Y. Simon Tsuo (Copyright 1993 by Marcel Dekker Inc. ISBN 0-8247-9146-0).
  • Such a transition layer 50 according to the invention makes it possible to passively pass the surface of the crystalline silicon, the amorphous or polymorphous silicon-germanium having properties that are suitable for reducing the presence of interface defects with, for example, an active layer 10. in c-Si.
  • transition layer 50 Another advantage of such a transition layer 50 is that the amorphous silicon-germanium alloys on the back of heterojunction cells have a gap width ("gap") less than amorphous silicon, and therefore closer to the forbidden band of the c-Si of the active layer 10. It will thus be typically, in the case where the active layer 10 is c-Si, an ⁇ -SiGe: H transition layer 50 having a potential barrier lower than ⁇ -Si: H, for equivalent deposits and thicknesses.
  • transition layer 50 in a-SiGe H
  • a transition layer 50 of a-Si: H while being closer to the electrical properties of the active layer 10, facilitating the transport of carriers of the active layer 10 to the rear contact layer 40, a transition layer 50 of a-Si: H.
  • a transition layer 50 of a-SiGe: H thus makes it possible to improve the rear-face contact made to extract the carriers of the structure 100.
  • the structure or cell 100 thus gains in yield and accuracy.
  • Another advantage of the invention lies in the possibility of easily varying the gap of the transition layer 50.
  • the transition layer 50 comprises three elements (Si, Ge and H) whose respective concentrations determine the gap, as well as the profile of the valence and conduction bands.
  • This concentration variation can be continuous by continuously varying the dosage of Ge precursors relative to the precursors of Si as it is deposited, or in stages by successively depositing layers which have Ge being constant in each of them but varying from one layer to another.
  • the concentration of Ge in the transition layer 50 may vary so as to be larger on the side of the rear contact layer 40 and less important on the active layer 10 side, in order to reduce progressively the gap of the transition layer 50 between the gap of the active layer 10 and that of the rear contact layer 40.
  • variation of the hydrogen content of the material can modify the distribution of the valence and conduction band discontinuities at the interface, without necessarily changing the value of the gap.
  • FIG. 2 illustrating the valence band discontinuities ⁇ E V and the conduction bands ⁇ E C existing at the interface between the c-Si on the one hand (left part of the band diagram) and the a-SiGe : H on the other hand (right part), one can realize that it is indeed possible to vary the value of the ⁇ E V and the value of ⁇ E C without modifying the difference of gap between the two materials (this difference being equal to the sum of ⁇ E V and ⁇ E C ).
  • an increase in the concentration of hydrogen in the transition layer 50 may make it possible to increase ⁇ E V while decreasing ⁇ E C and, conversely, a decrease in the concentration of hydrogen in the transition layer 50 can make it possible to decrease ⁇ E V while increasing ⁇ E C.
  • a prior selection of the hydrogen concentration in the transition layer 50 is therefore suitably done according to the invention, so as to adjust the valence and conduction bands of the transition layer 50 to obtain, respectively, discontinuities of valence and conduction bands determined at the interface with the active layer 10.
  • a hydrogen concentration for:
  • transition layer 50 is n-doped, obtain a sufficiently strong ⁇ E V to make a potential barrier able to push back the holes of the interface sufficiently to prevent them from recombining, and a sufficiently low ⁇ E C for limit the blocking of electrons at the interface; or
  • transition layer 50 is p-doped, obtain a sufficiently low ⁇ E V to minimize the potential barrier at the interface and thus facilitate the displacement of the holes towards the rear contact 40, and a ⁇ E C strong enough to produce a barrier potential to repel the electrons of the interface sufficiently to prevent them recombine.
  • the invention it is therefore possible to optimize the electrical interface quality on the rear face of the cell 100 by acting on the deposition parameters of the transition layer 50, and in particular by selecting the respective compositions in Ge and H special.
  • the invention thus offers an additional degree of freedom in backside band engineering of heterojunction cells.
  • the variation of the germanium and / or hydrogen content according to the invention makes it possible to change the nature and the properties of the amorphous material while not modifying the temperature of the deposit.
  • This adjustment of the repository parameters is therefore in no way constraining from a time (rise in temperature), energy and management point of view.
  • the invention makes it possible, for example, to obtain small bandgap widths for the amorphous semiconductor (between 1, 1 and 1, 7 eV, and more particularly of the order of 1.5 eV) and / or a quality of the material. amorphous deposited on the back without increasing the temperature too much (of the order of 250 ° C).
  • Another advantage of the invention is that, in order to obtain the same predetermined gap value, the deposition temperature of an ⁇ -SiGe: H layer (which is typically similar or less than 250 ° C.) is below the temperature. depositing an ⁇ -Si: H layer.
  • the thermal budget to provide is therefore easier to manage and less expensive.
  • this decrease in temperature with respect to the a-Si: H makes it possible to reduce the risks of diffusion in the semiconductors of the layers 10, 20, 50 of conducting elements (for example metallic) originating from the contact layers 30-40. which would clearly impair the operation of the cell 100.
  • the transition layer 50 is further doped p or n.
  • the structure 100 may for example comprise an active layer 10 of p-type crystalline silicon, an n-type layer 20 of a-Si: H on the front face 1 and a p-type layer 50 of a-SiGe: H on the rear face 2.
  • the doping element or elements may be chosen from: P, B, As, Zn, Al.
  • the structure 100 may for example comprise an active n-type crystalline silicon layer 10, a p-type layer 20 Si: H on the front face 1 and a layer 50 of the n type with a-SiGe: H on the rear face 2.
  • the doping element or elements may be chosen from: P, B, As, Zn 1 AI.
  • the rear-face embodiment 2 of a layer 50 made of a-SiGe: H having a doping of the same type as that of the active layer 10 in c-Si makes it possible to further reduce the carrier recombinations before the rear contact layer 40.
  • the other layers 40, 20, 50 of the structure 100 are deposited by techniques known per se, such as vapor phase deposition techniques or the like.
  • a field of application of this invention using amorphous silicon germanium relates to the energy sector, and in particular: the cells 100 can be used for the conversion of solar energy into electrical energy.
  • the cells 100 according to the invention are produced at a lower cost while having a greater efficiency.

Abstract

The invention relates to a structure (100) for photovoltaic applications including: a first layer (10) of a crystalline semiconductor material having a front face (1) for receiving and/or emitting photons and a back face (2); a back contact (40) of a conductive material provided on the side pf the back face (2); characterised in that it further comprises a second layer (50) of hydrogenated amorphous silicon-germanium (a-SiGe:H) between the back face (2) of the first layer (10) and the back contact (40). The invention also relates to a method for realising said structure (100).

Description

HETEROJONCTION A INTERFACE INTRINSEQUEMENT AMORPHE HETEROJUNCTION WITH INTRINSEALLY AMORPHOUS INTERFACE
L'invention concerne le domaine des cellules photovoltaïques, et plus particulièrement celui des cellules photovoltaïques utilisant des hétérojonctions.The invention relates to the field of photovoltaic cells, and more particularly that of photovoltaic cells using heterojunctions.
Cette invention peut en particulier concerner des cellules comprenant :This invention may in particular relate to cells comprising:
- une couche centrale en silicium cristallin (c-Si) dopé pour recevoir et/ou émettre des photons en face avant ;a central layer of crystalline silicon (c-Si) doped to receive and / or emit photons on the front face;
- éventuellement, une couche en silicium amorphe (a-Si) dopé située sur la face avant ; etoptionally, a layer of doped amorphous silicon (a-Si) located on the front face; and
- une couche de contact arrière, en matériau électriquement conducteur, située en face arrière de la couche centrale.- A rear contact layer of electrically conductive material, located on the rear face of the central layer.
La couche de contact peut être par exemple en un matériau métallique ou en oxyde conducteur transparent - tel NTO (acronyme anglo-saxon de « Indium Tin Oxide » pour Oxyde d'Etain et d'Indium).The contact layer may be for example a metal material or transparent conductive oxide - such NTO (acronym for "Indium Tin Oxide" for tin oxide and Indium).
Ce type de structure comprend une hétérojonction constituée de la couche centrale et de la couche de contact arrière.This type of structure comprises a heterojunction consisting of the central layer and the rear contact layer.
Une telle hétérojonction normalement ou fortement dopée souffre d'une mauvaise qualité d'interface liée à une mauvaise passivation de la couche de c-Si, ainsi que d'une trop grande barrière de potentiel à l'interface, ayant pour conséquence une mauvaise collecte des porteurs.Such a normally or heavily doped heterojunction suffers from poor interface quality due to poor passivation of the c-Si layer, as well as a too large barrier of potential at the interface, resulting in poor collection. carriers.
Un effet néfaste est une perte importante du signal entre la couche centrale et la couche de contact arrière, qui limite le rendement de la cellule.A deleterious effect is a significant loss of signal between the core layer and the back contact layer, which limits the efficiency of the cell.
Afin de diminuer ce problème, il est connu d'interposer entre le c-Si et la couche de contact arrière une couche en silicium amorphe hydrogéné (a- Si:H).In order to reduce this problem, it is known to interpose a layer of hydrogenated amorphous silicon (a-Si: H) between the c-Si and the rear contact layer.
Cependant, l'amélioration de la qualité d'interface reste insuffisante.However, the improvement of the interface quality remains insufficient.
Des problèmes de diffusion d'éléments métalliques de la couche de contact avant et arrière de la cellule peuvent en outre apparaître lors de la formation de la couche de a-Si:H. Un objectif de l'invention est d'apporter de nouvelles solutions au problème de la qualité de l'interface entre le c-Si et la couche de contact arrière, en face arrière de la couche de c-Si.Diffusion problems of metal elements of the front and rear contact layer of the cell may further occur during the formation of the α-Si: H layer. An object of the invention is to provide new solutions to the problem of the quality of the interface between the c-Si and the rear contact layer on the rear face of the c-Si layer.
Un autre objectif est d'augmenter la faisabilité de la face arrière. Un autre objectif de l'invention est d'augmenter le rendement de cellules photovoltaïques à hétérojonctions, de baisser les coûts, et/ou d'augmenter le rapport rendement de conversion/coût des modules photovoltaïques.Another goal is to increase the feasibility of the back side. Another objective of the invention is to increase the efficiency of photovoltaic cells with heterojunctions, to lower the costs, and / or to increase the conversion efficiency / cost ratio of the photovoltaic modules.
Un autre objectif de l'invention est de limiter la température de réalisation de la cellule.Another object of the invention is to limit the temperature of production of the cell.
Afin d'atteindre ces objectifs, l'invention propose, selon un premier aspect, une structure pour applications photovoltaïques, comprenant :In order to achieve these objectives, the invention proposes, according to a first aspect, a structure for photovoltaic applications, comprising:
- une première couche en matériau semiconducteur cristallin présentant une face avant pour recevoir et/ou émettre des photons et une face arrière ; - un contact arrière en matériau conducteur situé du côté de la face arrière ; caractérisée en ce qu'elle comprend en outre :a first crystalline semiconductor material layer having a front face for receiving and / or emitting photons and a rear face; a rear contact made of conducting material situated on the side of the rear face; characterized in that it further comprises:
- une deuxième couche en silicium-germanium amorphe hydrogéné (a- SiGe:H) entre la face arrière de la première couche et le contact arrière. D'autres caractéristiques optionnelles de cette structure selon l'invention sont les suivantes :a second layer of hydrogenated amorphous silicon-germanium (a-SiGe: H) between the rear face of the first layer and the rear contact. Other optional features of this structure according to the invention are the following:
- la deuxième couche est dopée ou intrinsèque ;the second layer is doped or intrinsic;
- ledit matériau semiconducteur cristallin est du silicium (Si) mono, poly ou multicristallin, et, optionnellement, le Si est dopé p et le a-SiGe:H est dopé p, ou le Si est dopé n et le a-SiGe:H est dopé n ;said crystalline semiconductor material is mono, poly or multicrystalline silicon (Si), and optionally Si is p-doped and α-SiGe: H is p-doped, or Si is doped n and α-SiGe: H is doped n;
- la deuxième couche comprend en outre du carbone ;the second layer further comprises carbon;
- la couche de contact arrière est en un matériau métallique ou en un oxyde conducteur transparent, tel NTO ; - la concentration en Ge dans la deuxième couche varie progressivement dans l'épaisseur de celle-ci ; la concentration en Ge dans la deuxième couche peut varier progressivement dans l'épaisseur de celle-ci de sorte à être plus importante du côté de la couche de contact arrière et moins importante du côté de la première couche ;the rear contact layer is made of a metallic material or a transparent conductive oxide, such as NTO; the concentration of Ge in the second layer varies gradually in the thickness thereof; the concentration of Ge in the second layer may vary progressively in the thickness thereof so as to be larger on the side of the rear contact layer and less important on the side of the first layer;
- la structure comprend en outre une troisième couche en matériau semiconducteur amorphe ou polymorphe, éventuellement dopée, sur la face avant de la première couche ; la troisième couche est éventuellement en Si amorphe hydrogéné ou en SiGe amorphe hydrogéné ; la troisième couche est éventuellement dopée n si la première couche est dopée p, ou la troisième couche est dopée p si la première couche est dopée n ; la structure peut comprendre en outre une couche de contact avant en matériau électriquement conducteur et transparent sur la troisième couche, le matériau conducteur pouvant être un oxyde conducteur transparent tel NTO ; - la deuxième couche présente une bande interdite entre environ 1 ,2 et 1 ,7 eV, et plus particulièrement de l'ordre de 1 ,5 eV ;the structure further comprises a third layer of amorphous or polymorphous semiconductor material, possibly doped, on the front face of the first layer; the third layer is optionally hydrogenated amorphous Si or hydrogenated amorphous SiGe; the third layer is optionally n-doped if the first layer is p-doped, or the third layer is p-doped if the first layer is n-doped; the structure may further comprise a front contact layer of electrically conductive material and transparent on the third layer, the conductive material may be a transparent conductive oxide such as NTO; the second layer has a forbidden band between approximately 1, 2 and 1, 7 eV, and more particularly of the order of 1.5 eV;
Selon un deuxième aspect, l'invention propose un procédé pour réaliser une structure pour applications photovoltaïques, comprenant les étapes suivantes : (a) fournir une première couche en matériau semiconducteur cristallin ayant une face avant pour recevoir et/ou émettre des photons et une face arrière ;According to a second aspect, the invention provides a method for producing a structure for photovoltaic applications, comprising the following steps: (a) providing a first crystalline semiconductor material layer having a front face for receiving and / or emitting photons and a face back ;
(b) former une deuxième couche par dépôt de silicium-germanium amorphe hydrogéné (a-SiGe:H) sur la face arrière de la première couche ; (c) former une couche de contact arrière en un matériau électriquement conducteur sur la deuxième couche.(b) forming a second layer by depositing hydrogenated amorphous silicon-germanium (a-SiGe: H) on the back side of the first layer; (c) forming a rear contact layer of an electrically conductive material on the second layer.
D'autres caractéristiques optionnelles de ce procédé selon l'invention sont les suivantes : - l'étape (a) et/ou (b) comprend en outre une implantation d'éléments dopants;Other optional features of this method according to the invention are the following: step (a) and / or (b) further comprises implantation of doping elements;
- l'étape (b) est mise en œuvre à une température inférieure ou similaire à 2500C ; - l'étape (b) est mise en œuvre de sorte que la concentration en Ge dans la deuxième couche varie progressivement dans l'épaisseur de celle-ci ; la concentration en Ge dans la deuxième couche peut en particulier augmenter progressivement à partir de la première couche ;step (b) is carried out at a temperature below or similar to 250 ° C .; step (b) is implemented so that the concentration of Ge in the second layer varies gradually in the thickness thereof; the concentration of Ge in the second layer can in particular gradually increase from the first layer;
- le procédé comprend en outre une sélection de la concentration d'hydrogène dans la deuxième couche afin d'ajuster les bandes de valence et de conduction de sorte à obtenir, respectivement, des discontinuités de bandes de valence et de bandes de conduction déterminées à l'interface avec la première couche ; la deuxième couche peut être dopée n, la discontinuité de bande de valence est suffisamment forte pour réaliser une barrière de potentiel apte à venir repousser des trous de l'interface et éviter ainsi une recombinaison à l'interface, et la discontinuité de bandes de conduction est suffisamment faible pour minimiser le blocage des électrons à l'interface ; alternativement, la deuxième couche peut être dopée p, la discontinuité de bandes de valence est suffisamment faible pour minimiser le blocage des trous à l'interface, et la discontinuité de bandes de conduction est suffisamment forte pour repousser les électrons de l'interface et éviter ainsi une recombinaison à l'interface ;le procédé comprend en outre une sélection de la concentration de germanium dans la deuxième couche afin que la bande interdite du matériau de la partie arrière de la deuxième couche ait une largeur déterminée ;the method further comprises a selection of the hydrogen concentration in the second layer in order to adjust the valence and conduction bands so as to obtain, respectively, discontinuities of valence bands and conduction bands determined at 1 interface with the first layer; the second layer can be n-doped, the valence band discontinuity is sufficiently strong to provide a potential barrier able to push back holes of the interface and thus avoid recombination at the interface, and the discontinuity of conduction bands is low enough to minimize the blocking of electrons at the interface; alternatively, the second layer may be p-doped, the valence band discontinuity is small enough to minimize the locking of the holes at the interface, and the conduction band gap is strong enough to repel the interface electrons and avoid Thus, recombination at the interface, the method further comprises selecting the concentration of germanium in the second layer so that the bandgap of the material of the rear portion of the second layer has a predetermined width;
- le procédé comprend en outre la formation d'une troisième couche en matériau amorphe hydrogéné, éventuellement dopé, sur la face avant de la première couche, la troisième couche étant en un matériau semiconducteur amorphe ou polymorphe ; éventuellement, le procédé comprend la formation d'une couche de contact électrique en matériau électriquement conducteur et transparent aux photons, sur la troisième couche.the method further comprises forming a third layer of hydrogenated amorphous material, possibly doped, on the front face of the first layer, the third layer being made of an amorphous or polymorphic semiconductor material; optionally, the method includes training an electrically conductive and photon-transparent electrical contact layer on the third layer.
D'autres caractéristiques, buts et avantages de cette invention se comprendront mieux à la lecture de la description qui suit, non limitative, illustrée par la figure unique suivante :Other characteristics, aims and advantages of this invention will be better understood on reading the description which follows, which is nonlimiting, illustrated by the following single figure:
La figure 1 représente une vue schématique en coupe transversale d'une structure à hétérojonctions, pour application photovoltaïque, selon l'invention.FIG. 1 represents a schematic cross-sectional view of a heterojunction structure, for photovoltaic application, according to the invention.
La figure 2 représente un exemple de diagramme de bandes de la face arrière d'une hétérojonction c-Si de type P / a-SiGe de type P.FIG. 2 represents an exemplary band diagram of the rear face of a p-type Si / Si-SiGe type c-Si heterojunction.
Une structure à hétérojonction 100, telle que, par exemple, une cellule photoélectrique, comporte une couche active ou substrat 10 cristallin (e.g. monocristallin, polycristallin ou multicristallin) dopé et une couche en matériau amorphe dopé 20 présentant une différence de valeurs de bandes interdites et donc des discontinuités de bandes entre elles.A heterojunctional structure 100, such as, for example, a photoelectric cell, comprises a doped doped crystalline (eg monocrystalline, polycrystalline or multicrystalline) active layer or substrate (10) and a layer of doped amorphous material having a difference in bandgap values and therefore discontinuities of bands between them.
De préférence, soit la couche active 10 est dopée n et la couche amorphe 20 est dopée p soit la couche active 10 est dopée p et la couche amorphe 20 est dopée n.Preferably, either the active layer 10 is n-doped and the amorphous layer 20 is p-doped or the active layer 10 is p-doped and the amorphous layer 20 is n-doped.
On pourra par exemple choisir le silicium et/ou le SiGe pour constituer ces deux couches 10 et 20.For example, silicon and / or SiGe may be chosen to form these two layers 10 and 20.
Cette hétérojonction amorphe/cristallin est réalisée de sorte à permettre d'obtenir une tension en face avant déterminée.This amorphous / crystalline heterojunction is performed so as to obtain a determined front face tension.
La couche active 10 peut avoir une épaisseur de plusieurs micromètres voire de plusieurs centaines de micromètres. Sa résistivité peut être inférieure à 20, à 10 ohms ou plus particulièrement autour de 5 ohms ou moins.The active layer 10 may have a thickness of several micrometers or even several hundred micrometers. Its resistivity may be less than 20, 10 ohms or more particularly around 5 ohms or less.
La couche active 10 comporte une face avant 1 et une face arrière 2.The active layer 10 has a front face 1 and a rear face 2.
La face avant 1 est destinée à recevoir les photons (et/ou à émettre ceux-ci). La face arrière 2 est destinée à être raccordée à un contact électrique arrière.The front face 1 is intended to receive the photons (and / or to emit them). The rear face 2 is intended to be connected to a rear electrical contact.
La couche amorphe dopée 20 se situe du côté de la face avant 1.The doped amorphous layer 20 is located on the side of the front face 1.
Une couche de contact avant 30 en matériau métallique, ou en oxyde conducteur transparent tel que NTO (acronyme anglo-saxon de « Indium TinA front contact layer 30 of metallic material, or transparent conductive oxide such as NTO (acronym for "Indium Tin")
Oxide » pour Oxyde d'Etain et d'Indium), peut être prévue sur la couche amorphe 20. Eventuellement, on peut trouver des motifs en métal sérigraphiés 80 sur cette couche de contact avant 30.Oxide "for tin oxide and indium), may be provided on the amorphous layer 20. Optionally, one can find screen printed metal patterns 80 on this contact layer before 30.
Une couche de contact arrière 40 en matériau métallique, ou en un oxyde conducteur transparent tel que NTO, est par ailleurs prévue du côté de la face arrière 2 de la couche active 10.A rear contact layer 40 made of metallic material, or a transparent conductive oxide such as NTO, is also provided on the side of the rear face 2 of the active layer 10.
Selon l'invention, une couche de transition 50 en a-SiGe:H est interposée entre la couche active 10 et cette couche de contact arrière 40.According to the invention, an α-SiGe: H transition layer 50 is interposed between the active layer 10 and this rear contact layer 40.
En alternative, cette couche de silicium-germanium peut être en matériau polymorphe donc de type pmSiGe :H.As an alternative, this silicon-germanium layer may be of polymorphic material, thus of the type pmSiGe: H.
Pour fabriquer une telle couche de transition 50, un dépôt, par exemple par PECVD, du matériau amorphe ou polymorphe est alors effectué en face arrière 2 de la couche active 10. Plus de précisions sur une ou plusieurs techniques de dépôt pourront par exemple être trouvées dans « Hydrogenated amorphous silicon déposition processes » de Werner Luft et Y. Simon Tsuo (Copyright 1993 de Marcel Dekker Inc. ISBN 0-8247-9146-0).To manufacture such a transition layer 50, a deposition, for example by PECVD, of the amorphous or polymorphic material is then performed on the rear face 2 of the active layer 10. More details on one or more deposition techniques may for example be found in "Hydrogenated amorphous silicon deposition processes" by Werner Luft and Y. Simon Tsuo (Copyright 1993 by Marcel Dekker Inc. ISBN 0-8247-9146-0).
Une telle couche de transition 50 selon l'invention permet de très bien passiver la surface du silicium cristallin, le silicium-germanium amorphe ou polymorphe ayant des propriétés adaptés pour diminuer la présence de défauts d'interface avec, par exemple, une couche active 10 en c-Si.Such a transition layer 50 according to the invention makes it possible to passively pass the surface of the crystalline silicon, the amorphous or polymorphous silicon-germanium having properties that are suitable for reducing the presence of interface defects with, for example, an active layer 10. in c-Si.
Un autre avantage d'une telle couche de transition 50 est que les alliages de silicium-germanium amorphes en face arrière de cellules à hétérojonctions ont une largeur de bande interdite (« gap ») moindre que le silicium amorphe, et donc plus proche de la bande interdite du c-Si de la couche active 10. On aura ainsi typiquement, dans le cas où la couche active 10 est en c-Si, une couche de transition 50 en a-SiGe:H ayant une barrière de potentiel inférieure à du a-Si:H, pour des dépôts et des épaisseurs équivalents.Another advantage of such a transition layer 50 is that the amorphous silicon-germanium alloys on the back of heterojunction cells have a gap width ("gap") less than amorphous silicon, and therefore closer to the forbidden band of the c-Si of the active layer 10. It will thus be typically, in the case where the active layer 10 is c-Si, an α-SiGe: H transition layer 50 having a potential barrier lower than α-Si: H, for equivalent deposits and thicknesses.
Avec une couche de transition 50 en a-SiGe:H, on peut donc : - aussi bien, voire mieux, passiver la face arrière 2 de la couche activeWith a transition layer 50 in a-SiGe: H, one can thus: - as well, or even better, passivate the rear face 2 of the active layer
10,10
- tout en se rapprochant davantage des propriétés électriques de la couche active 10, facilitant ainsi le transport des porteurs de la couche active 10 vers la couche de contact arrière 40, qu'une couche de transition 50 en a-Si:H.- while being closer to the electrical properties of the active layer 10, facilitating the transport of carriers of the active layer 10 to the rear contact layer 40, a transition layer 50 of a-Si: H.
Une couche de transition 50 en a-SiGe:H permet donc d'améliorer le contact en face arrière réalisé pour extraire les porteurs de la structure 100. La structure ou cellule 100 gagne donc en rendement et en précision. Un autre intérêt de l'invention réside dans la possibilité de faire varier facilement le gap de la couche de transition 50.A transition layer 50 of a-SiGe: H thus makes it possible to improve the rear-face contact made to extract the carriers of the structure 100. The structure or cell 100 thus gains in yield and accuracy. Another advantage of the invention lies in the possibility of easily varying the gap of the transition layer 50.
En effet, la couche de transition 50 comprend trois éléments (Si, Ge et H) dont les concentrations respectives déterminent le gap, ainsi que le profil des bandes de valence et de conduction.Indeed, the transition layer 50 comprises three elements (Si, Ge and H) whose respective concentrations determine the gap, as well as the profile of the valence and conduction bands.
En particulier, une augmentation du contenu en germanium des couches d'a-SiGe:H diminue la valeur du gap.In particular, an increase in the germanium content of the α-SiGe: H layers decreases the value of the gap.
Or, il peut être très utile de pouvoir ainsi contrôler précisément ce gap. On pourra ainsi faire en sorte d'obtenir des valeurs médianes entre les propriétés électriques de la couche active 10 et de la couche de contact arrière 40. Optionnellement, on pourra faire en sorte de faire varier progressivement la concentration en Ge dans l'épaisseur de la couche de transition 50. Cette variation de concentration peut être continue en faisant varier continûment le dosage des précurseurs du Ge par rapport aux précurseurs du Si au fur et à mesure du dépôt, ou par paliers en déposant successivement des couches qui ont des concentrations en Ge étant constantes dans chacune d'elles mais variant d'une couche à une autre. Ainsi, dans certaines conditions il pourra être avantageux que la concentration en Ge dans la couche de transition 50 varie de sorte à être plus importante du côté de la couche de contact arrière 40 et moins importante du côté de la couche active 10, afin de réduire progressivement le gap de la couche de transition 50 entre le gap de la couche active 10 et celui de la couche de contact arrière 40.However, it can be very useful to be able to precisely control this gap. It will thus be possible to obtain median values between the electrical properties of the active layer 10 and the rear contact layer 40. Optionally, it will be possible to make sure to gradually vary the concentration of Ge in the thickness of the the transition layer 50. This concentration variation can be continuous by continuously varying the dosage of Ge precursors relative to the precursors of Si as it is deposited, or in stages by successively depositing layers which have Ge being constant in each of them but varying from one layer to another. Thus, under certain conditions it may be advantageous for the concentration of Ge in the transition layer 50 to vary so as to be larger on the side of the rear contact layer 40 and less important on the active layer 10 side, in order to reduce progressively the gap of the transition layer 50 between the gap of the active layer 10 and that of the rear contact layer 40.
De plus, la variation du contenu en hydrogène du matériau peut modifier la répartition des discontinuités de bande de valence et de conduction à l'interface, sans pour autant que la valeur du gap en soit nécessairement modifiée.In addition, the variation of the hydrogen content of the material can modify the distribution of the valence and conduction band discontinuities at the interface, without necessarily changing the value of the gap.
En référence à la figure 2, illustrant les discontinuités de bande de valence ΔEV et de bandes de conduction ΔEC existant à l'interface entre le c- Si d'une part (partie gauche du diagramme de bandes) et le a-SiGe:H d'autre part (partie droite), on peut se rendre compte qu'il est effectivement possible de faire varier la valeur du ΔEV et la valeur du ΔEC sans pour autant modifier la différence de gap entre les deux matériaux (cette différence étant égale à la somme de ΔEV et de ΔEC).With reference to FIG. 2, illustrating the valence band discontinuities ΔE V and the conduction bands ΔE C existing at the interface between the c-Si on the one hand (left part of the band diagram) and the a-SiGe : H on the other hand (right part), one can realize that it is indeed possible to vary the value of the ΔE V and the value of ΔE C without modifying the difference of gap between the two materials (this difference being equal to the sum of ΔE V and ΔE C ).
En particulier, une augmentation de la concentration d'hydrogène dans la couche de transition 50 pourra permettre d'augmenter ΔEV tout en diminuant ΔEC et, à l'inverse, une diminution de la concentration d'hydrogène dans la couche de transition 50 pourra permettre de diminuer ΔEV tout en augmentant ΔEC.In particular, an increase in the concentration of hydrogen in the transition layer 50 may make it possible to increase ΔE V while decreasing ΔE C and, conversely, a decrease in the concentration of hydrogen in the transition layer 50 can make it possible to decrease ΔE V while increasing ΔE C.
Une sélection préalable de la concentration d'hydrogène dans la couche de transition 50 est donc avantageusement faite de façon appropriée selon l'invention, de sorte à ajuster les bandes de valence et de conduction de la couche de transition 50 pour obtenir, respectivement, des discontinuités de bandes de valence et de conduction déterminées à l'interface avec la couche active 10. En particulier, on peut choisir une concentration d'hydrogène pour :A prior selection of the hydrogen concentration in the transition layer 50 is therefore suitably done according to the invention, so as to adjust the valence and conduction bands of the transition layer 50 to obtain, respectively, discontinuities of valence and conduction bands determined at the interface with the active layer 10. In particular, it is possible to choose a hydrogen concentration for:
- si la couche de transition 50 est dopée n, obtenir un ΔEV suffisamment fort pour réaliser une barrière de potentiel apte à repousser les trous de l'interface suffisamment pour éviter qu'ils s'y recombinent, et un ΔEC suffisamment faible pour limiter le blocage des électrons à l'interface ; ouif the transition layer 50 is n-doped, obtain a sufficiently strong ΔE V to make a potential barrier able to push back the holes of the interface sufficiently to prevent them from recombining, and a sufficiently low ΔE C for limit the blocking of electrons at the interface; or
- si la couche de transition 50 est dopée p, obtenir un ΔEV suffisamment faible pour minimiser la barrière de potentiel à l'interface et faciliter ainsi le déplacement des trous vers le contact arrière 40, et un ΔEC suffisamment fort pour réaliser une barrière de potentiel apte à repousser les électrons de l'interface suffisamment pour éviter qu'ils s'y recombinent.if the transition layer 50 is p-doped, obtain a sufficiently low ΔE V to minimize the potential barrier at the interface and thus facilitate the displacement of the holes towards the rear contact 40, and a ΔE C strong enough to produce a barrier potential to repel the electrons of the interface sufficiently to prevent them recombine.
Plus de précisions concernant l'influence du taux d'hydrogène sur la répartition des discontinuités de bandes pourront par exemple être trouvées dans la publication de Chris G. Van de WaIIe intitulée « Band discontinuities at heterojuctions between crystalline and amorphous silicon » (Journal of Vacuum Science & Technology B, Vol.13, p.1635-1638 (1995)).Further details concerning the influence of the hydrogen content on the distribution of the discontinuities of bands can be found, for example, in the publication of Chris G. Van de WaIIe entitled "Band discontinuities and heterojuctions between crystalline and amorphous silicon" (Journal of Vacuum Science & Technology B, Vol.13, p.1635-1638 (1995)).
On peut donc, selon l'invention, optimiser la qualité électrique d'interface en face arrière de la cellule 100 en jouant sur les paramètres de dépôt de la couche de transition 50, et en particulier en sélectionnant les compositions respectives en Ge et en H particulières. L'invention offre donc un degré de liberté supplémentaire dans l'ingénierie de bandes des faces arrière des cellules à hétérojonctions.According to the invention, it is therefore possible to optimize the electrical interface quality on the rear face of the cell 100 by acting on the deposition parameters of the transition layer 50, and in particular by selecting the respective compositions in Ge and H special. The invention thus offers an additional degree of freedom in backside band engineering of heterojunction cells.
De plus, la variation du contenu en germanium et/ou en hydrogène selon l'invention permet de changer la nature et les propriétés du matériau amorphe tout en ne modifiant pas la température du dépôt. Cet ajustement de paramètres du dépôt n'est donc en rien contraignant d'un point de vue temps (de montée en température), énergie et gestion.In addition, the variation of the germanium and / or hydrogen content according to the invention makes it possible to change the nature and the properties of the amorphous material while not modifying the temperature of the deposit. This adjustment of the repository parameters is therefore in no way constraining from a time (rise in temperature), energy and management point of view.
L'invention permet par exemple d'obtenir de faibles largeurs de bande interdite pour le semiconducteur amorphe (entre 1 ,1 et 1 ,7 eV, et plus particulièrement de l'ordre de 1 ,5 eV) et/ou une qualité du matériau amorphe déposé en face arrière sans trop augmenter la température (de l'ordre de 250° C).The invention makes it possible, for example, to obtain small bandgap widths for the amorphous semiconductor (between 1, 1 and 1, 7 eV, and more particularly of the order of 1.5 eV) and / or a quality of the material. amorphous deposited on the back without increasing the temperature too much (of the order of 250 ° C).
Un autre intérêt de l'invention est que, pour obtenir une même valeur de gap prédéterminée, la température de dépôt d'une couche en a-SiGe:H (qui est typiquement similaire ou inférieure à 2500C) est inférieure à la température de dépôt d'une couche en a-Si:H.Another advantage of the invention is that, in order to obtain the same predetermined gap value, the deposition temperature of an α-SiGe: H layer (which is typically similar or less than 250 ° C.) is below the temperature. depositing an α-Si: H layer.
Pour illustration, le tableau donne des correspondances entre gaps et températures, pour différentes concentrations de Ge :For illustration, the table gives correspondences between gaps and temperatures, for different concentrations of Ge:
Par conséquent, la formation d'une telle couche de a-SiGe:H est plus économique en temps et en énergie que la formation d'une couche de a- Si:H. Therefore, the formation of such a? -SeGe: H layer is more economical in time and energy than the formation of a? -Si: H layer.
Le budget thermique à prévoir est donc plus simple à gérer et moins coûteux. De plus, cette diminution en température par rapport au a-Si:H permet de diminuer les risques de diffusion dans les semiconducteurs des couches 10, 20, 50 d'éléments conducteurs (par exemple métalliques) provenant des couches de contact 30-40, qui nuiraient clairement au fonctionnement de la cellule 100. Eventuellement, la couche de transition 50 est de plus dopée p ou n. La structure 100 peut par exemple comprendre une couche active 10 en silicium cristallin de type p, une couche 20 de type n en a-Si:H en face avant 1 et une couche 50 de type p en a-SiGe:H en face arrière 2. Le ou les éléments dopants peuvent être choisis parmi : P, B, As, Zn, Al. Alternativement, la structure 100 peut par exemple comprendre une couche active 10 en silicium cristallin de type n, une couche 20 de type p en a-Si:H en face avant 1 et une couche 50 de type n en a-SiGe:H en face arrière 2. Le ou les éléments dopants peuvent être choisis parmi : P, B, As, Zn1 AI. La réalisation en face arrière 2 d'une couche 50 en a-SiGe:H ayant un dopage du même type que celui de la couche active 10 en c-Si permet de diminuer encore les recombinaisons de porteurs avant la couche de contact arrière 40.The thermal budget to provide is therefore easier to manage and less expensive. In addition, this decrease in temperature with respect to the a-Si: H makes it possible to reduce the risks of diffusion in the semiconductors of the layers 10, 20, 50 of conducting elements (for example metallic) originating from the contact layers 30-40. which would clearly impair the operation of the cell 100. Optionally, the transition layer 50 is further doped p or n. The structure 100 may for example comprise an active layer 10 of p-type crystalline silicon, an n-type layer 20 of a-Si: H on the front face 1 and a p-type layer 50 of a-SiGe: H on the rear face 2. The doping element or elements may be chosen from: P, B, As, Zn, Al. Alternatively, the structure 100 may for example comprise an active n-type crystalline silicon layer 10, a p-type layer 20 Si: H on the front face 1 and a layer 50 of the n type with a-SiGe: H on the rear face 2. The doping element or elements may be chosen from: P, B, As, Zn 1 AI. The rear-face embodiment 2 of a layer 50 made of a-SiGe: H having a doping of the same type as that of the active layer 10 in c-Si makes it possible to further reduce the carrier recombinations before the rear contact layer 40.
Les autres couches 40, 20, 50 de la structure 100 sont déposées par des techniques connues en soi, telles que des techniques de dépôt en phase vapeur ou autres.The other layers 40, 20, 50 of the structure 100 are deposited by techniques known per se, such as vapor phase deposition techniques or the like.
Un domaine d'application de cette invention utilisant du silicium- germanium amorphe concerne le secteur énergétique, et en particulier : les cellules 100 peuvent être utilisées pour la conversion d'énergie solaire en énergie électrique.A field of application of this invention using amorphous silicon germanium relates to the energy sector, and in particular: the cells 100 can be used for the conversion of solar energy into electrical energy.
Comme expliqué auparavant, les cellules 100 selon l'invention sont réalisées à moindre coût tout en ayant un rendement plus grand. As explained above, the cells 100 according to the invention are produced at a lower cost while having a greater efficiency.

Claims

REVENDICATIONS
1. Structure (100) pour applications photovoltaïques, comprenant :A structure (100) for photovoltaic applications, comprising:
- une première couche (10) en matériau semiconducteur cristallin présentant une face avant (1 ) pour recevoir et/ou émettre des photons et une face arrière (2) ;- a first layer (10) of crystalline semiconductor material having a front face (1) for receiving and / or emitting photons and a rear face (2);
- un contact arrière (40) en matériau conducteur situé du côté de la face arrière (2) ; caractérisée en ce qu'elle comprend en outre :- a rear contact (40) of conductive material located on the side of the rear face (2); characterized in that it further comprises:
- une deuxième couche (50) unique en silicium-germanium amorphe hydrogéné (a-SiGe:H) entre la face arrière (2) de la première couche (10) et le contact arrière (40).a second single layer (50) of hydrogenated amorphous silicon-germanium (a-SiGe: H) between the rear face (2) of the first layer (10) and the rear contact (40).
2. Structure (100) selon la revendication précédente, caractérisée en ce que la deuxième couche (50) est dopée ou intrinsèque.2. Structure (100) according to the preceding claim, characterized in that the second layer (50) is doped or intrinsic.
3. Structure (100) selon l'une des revendications précédentes, caractérisée en ce que ledit matériau semiconducteur cristallin est du silicium3. Structure (100) according to one of the preceding claims, characterized in that said crystalline semiconductor material is silicon
(Si) mono, poly ou multicristallin.(Si) mono, poly or multicrystalline.
4. Structure (100) selon la revendication précédente, caractérisée en ce que le Si est dopé p et le a-SiGe:H est dopé p, ou le Si est dopé n et le a- SiGe:H est dopé n. 4. Structure (100) according to the preceding claim, characterized in that the Si is p-doped and the a-SiGe: H is p-doped, or the Si is doped n and the a-SiGe: H is doped n.
5. Structure (100) selon l'une des revendications précédentes, caractérisée en ce que la deuxième couche (50) comprend en outre du carbone.5. Structure (100) according to one of the preceding claims, characterized in that the second layer (50) further comprises carbon.
6. Structure (100) selon l'une des revendications précédentes, caractérisée en ce que la couche de contact arrière (40) est en un matériau métallique ou en un oxyde conducteur transparent, tel NTO.6. Structure (100) according to one of the preceding claims, characterized in that the rear contact layer (40) is a metal material or a transparent conductive oxide, such as NTO.
7. Structure (100) selon l'une des revendications précédentes, caractérisée en ce que la concentration en Ge dans la deuxième couche (50) varie progressivement dans l'épaisseur de celle-ci. 7. Structure (100) according to one of the preceding claims, characterized in that the Ge concentration in the second layer (50) varies gradually in the thickness thereof.
8. Structure (100) selon l'une des revendications 5 et 6 combinée avec la revendication 7, caractérisée en ce que la concentration en Ge dans la deuxième couche (50) varie progressivement dans l'épaisseur de celle-ci de sorte à être plus importante du côté de la couche de contact arrière (30) et moins importante du côté de la première couche (10).8. Structure (100) according to one of claims 5 and 6 combined with claim 7, characterized in that the Ge concentration in the second layer (50) varies gradually in the thickness thereof so as to be greater on the side of the rear contact layer (30) and less important on the side of the first layer (10).
9. Structure (100) selon l'une des revendications précédentes, caractérisée en ce qu'elle comprend en outre une troisième couche (20) en matériau semiconducteur amorphe ou polymorphe, éventuellement dopée, sur la face avant de la première couche. 9. Structure (100) according to one of the preceding claims, characterized in that it further comprises a third layer (20) of amorphous or polymorphous semiconductor material, possibly doped, on the front face of the first layer.
10. Structure (100) selon la revendication précédente, caractérisée en ce que la troisième couche (20) est en Si amorphe hydrogéné ou en SiGe amorphe hydrogéné.10. Structure (100) according to the preceding claim, characterized in that the third layer (20) is hydrogenated amorphous Si or hydrogenated amorphous SiGe.
11. Structure (100) selon la revendication 4 combinée à la revendication 10, caractérisée en ce que la troisième couche (20) est dopée n si la première couche (10) est dopée p, ou la troisième couche (20) est dopée p si la première couche (10) est dopée n.11. Structure (100) according to claim 4 combined with claim 10, characterized in that the third layer (20) is n-doped if the first layer (10) is p-doped, or the third layer (20) is p-doped. if the first layer (10) is doped n.
12. Structure (100) selon l'une des trois revendications précédentes, caractérisée en ce qu'elle comprend en outre une couche de contact avant (30) en matériau électriquement conducteur et transparent sur la troisième couche (20).12. Structure (100) according to one of the three preceding claims, characterized in that it further comprises a front contact layer (30) of electrically conductive material and transparent on the third layer (20).
13. Structure (100) selon la revendication précédente, caractérisée en ce que la couche de contact avant (30) est en un oxyde conducteur transparent, tel I1ITO.13. Structure (100) according to the preceding claim, characterized in that the front contact layer (30) is a transparent conductive oxide such as ITO I 1.
14.Structure (100) selon l'une des revendications précédentes, caractérisée en ce que la deuxième couche (50) présente une bande interdite entre environ 1 ,2 et 1 ,7 eV, et plus particulièrement de l'ordre de 1 ,5 eV.14.Structure (100) according to one of the preceding claims, characterized in that the second layer (50) has a band gap between about 1, 2 and 1, 7 eV, and more particularly of the order of 1, 5 eV.
15. Procédé pour réaliser une structure (100) pour applications photovoltaïques, comprenant les étapes suivantes : (a) fournir une première couche (10) en matériau semiconducteur cristallin ayant une face avant (1 ) pour recevoir et/ou émettre des photons et une face arrière (2) ;Process for producing a structure (100) for photovoltaic applications, comprising the following steps: (a) providing a first layer (10) of crystalline semiconductor material having a front face (1) for receiving and / or emitting photons and a back face (2);
(b) former une deuxième couche (50) par dépôt de silicium-germanium amorphe hydrogéné (a-SiGe:H) sur la face arrière (2) de la première couche (10) ;(b) forming a second layer (50) by deposition of hydrogenated amorphous silicon-germanium (a-SiGe: H) on the rear face (2) of the first layer (10);
(c) former une couche de contact arrière (40) en un matériau électriquement conducteur sur la deuxième couche (50).(c) forming a rear contact layer (40) of an electrically conductive material on the second layer (50).
16. Procédé selon la revendication précédente, caractérisé en ce que l'étape (a) et/ou (b) comprend en outre une implantation d'éléments dopants.16. Method according to the preceding claim, characterized in that step (a) and / or (b) further comprises implantation of doping elements.
17. Procédé selon l'une des deux revendications précédentes, caractérisé en ce que l'étape (b) est mise en œuvre à une température inférieure ou similaire à 2500C.17. Method according to one of the two preceding claims, characterized in that step (b) is carried out at a temperature below or similar to 250 0 C.
18. Procédé selon l'une des trois revendications précédentes, caractérisé en ce que l'étape (b) est mise en œuvre de sorte que la concentration en Ge dans la deuxième couche (50) varie progressivement dans l'épaisseur de celle-ci.18. Method according to one of the three preceding claims, characterized in that step (b) is implemented so that the concentration of Ge in the second layer (50) varies gradually in the thickness thereof .
19. Procédé selon la revendication précédente, caractérisé en ce que la concentration en Ge dans la deuxième couche (50) augmente progressivement à partir de la première couche (10).19. Method according to the preceding claim, characterized in that the Ge concentration in the second layer (50) increases gradually from the first layer (10).
20. Procédé selon l'une des cinq revendications précédentes, caractérisé en ce qu'il comprend en outre une sélection de la concentration d'hydrogène dans la deuxième couche (50) afin d'ajuster les bandes de valence et de conduction de sorte à obtenir, respectivement, des discontinuités de bandes de valence et de bandes de conduction déterminées à l'interface avec la première couche (10).20. Method according to one of the five preceding claims, characterized in that it further comprises a selection of the hydrogen concentration in the second layer (50) in order to adjust the valence and conduction bands so as to obtaining, respectively, discontinuities of valence bands and conduction bands determined at the interface with the first layer (10).
21. Procédé selon la revendication précédente, caractérisé en ce que :21. Method according to the preceding claim, characterized in that:
- la deuxième couche (50) est dopée n, en ce que la discontinuité de bandes de valence est suffisamment forte pour réaliser une barrière de potentiel apte à venir repousser des trous de l'interface et éviter ainsi une recombinaison à l'interface, et en ce que la discontinuité de bandes de conduction est suffisamment faible pour minimiser le blocage des électrons à l'interface ;the second layer (50) is n-doped, in that the discontinuity of valence bands is sufficiently strong to provide a potential barrier able to push back holes in the interface and thus avoid a recombination at the interface, and in that the conduction band discontinuity is sufficiently small to minimize electron blockage at the interface;
- la deuxième couche (50) est dopée p, en ce que la discontinuité de bandes de valence est suffisamment faible pour minimiser le blocage des trous à l'interface, et en ce que la discontinuité de bandes de conduction est suffisamment forte pour repousser les électrons de l'interface et éviter ainsi une recombinaison à l'interface.the second layer (50) is doped with p, in that the valence band discontinuity is sufficiently small to minimize the locking of the holes at the interface, and in that the conduction band discontinuity is sufficiently strong to repel the holes; electrons from the interface and thus avoid recombination at the interface.
22. Procédé selon l'une des revendications 15 à 21 , caractérisé en ce qu'il comprend en outre une sélection de la concentration de germanium dans la deuxième couche (50) afin que la bande interdite du matériau constituant la partie arrière de la deuxième couche (50) ait une largeur déterminée.22. Method according to one of claims 15 to 21, characterized in that it further comprises a selection of the germanium concentration in the second layer (50) so that the bandgap of the material constituting the rear portion of the second layer (50) has a determined width.
23. Procédé selon l'une des revendications 15 à 22, caractérisé en ce qu'il comprend en outre la formation d'une troisième couche (30) en matériau amorphe hydrogéné, éventuellement dopé, sur la face avant (1 ) de la première couche (10), la troisième couche (30) étant en un matériau semiconducteur amorphe ou polymorphe.23. Method according to one of claims 15 to 22, characterized in that it further comprises the formation of a third layer (30) of hydrogenated amorphous material, optionally doped, on the front face (1) of the first layer (10), the third layer (30) being an amorphous or polymorphic semiconductor material.
24. Procédé selon la revendication précédente, caractérisé en ce qu'il comprend la formation d'une couche de contact électrique (30) en matériau électriquement conducteur et transparent aux photons, sur la troisième couche (20). 24. Method according to the preceding claim, characterized in that it comprises the formation of an electrical contact layer (30) of electrically conductive material and transparent to photons, on the third layer (20).
EP07857992A 2006-12-20 2007-12-20 Heterojunction with intrinsically amorphous interface Withdrawn EP2126980A2 (en)

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