Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F10/00—Individual photovoltaic cells, e.g. solar cells
  • H10F10/10—Individual photovoltaic cells, e.g. solar cells having potential barriers
  • H10F10/17—Photovoltaic cells having only PIN junction potential barriers
  • H10F10/174—Photovoltaic cells having only PIN junction potential barriers comprising monocrystalline or polycrystalline materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F10/00—Individual photovoltaic cells, e.g. solar cells
  • H10F10/10—Individual photovoltaic cells, e.g. solar cells having potential barriers
  • H10F10/16—Photovoltaic cells having only PN heterojunction potential barriers
  • H10F10/164—Photovoltaic cells having only PN heterojunction potential barriers comprising heterojunctions with Group IV materials, e.g. ITO/Si or GaAs/SiGe photovoltaic cells
  • H10F10/165—Photovoltaic cells having only PN heterojunction potential barriers comprising heterojunctions with Group IV materials, e.g. ITO/Si or GaAs/SiGe photovoltaic cells the heterojunctions being Group IV-IV heterojunctions, e.g. Si/Ge, SiGe/Si or Si/SiC photovoltaic 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.

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• 2006
  • 2006-12-20 FR FR0655711A patent/FR2910711B1/fr not_active Expired - Fee Related
• 2007
  • 2007-12-20 US US12/520,309 patent/US20090308453A1/en not_active Abandoned
  • 2007-12-20 JP JP2009542077A patent/JP5567345B2/ja not_active Expired - Fee Related
  • 2007-12-20 WO PCT/EP2007/064373 patent/WO2008074875A2/fr not_active Ceased
  • 2007-12-20 EP EP07857992A patent/EP2126980A2/de not_active Withdrawn

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