DE102009050454A1 - Multi-junction-inverted metamorphous solar cell i.e. photovoltaic cell, for use in e.g. LED in aerospace application, has solar cell aligned regarding another solar-cell by considering lattice defect and exhibiting band gap - Google Patents

Abstract

The cell has an upper first solar sub-cell arranged adjacent to second solar-sub cell. A grading intermediate layer is provided adjacent to the first solar sub-cell. A third solar-sub cell possesses a first band gap, which is larger than second band gap. Another grading intermediate layer possesses third band gap, which is larger than the first band gap. A fourth solar-sub cell is provided adjacent to the latter layer. The fourth cell possesses fourth band gap, which is smaller than the first band gap. The fourth cell is aligned regarding the third solar-cell by considering lattice defect. An independent claim is also included for a method for manufacturing the solar cell.

Description

RIGHTS OF THE GOVERNMENT

The invention was made with government support under Contract Number FA9453-06-C-0345 of the US Air Force. The government has certain rights to this invention.

REFERENCE TO RELATED APPLICATIONS

This application is in relation to pending US Patent Application Serial No. 12 / 267,812 filed on Nov. 10, 2008.

This application is related to pending US Application Serial No. 12 / 258,190, filed October 24, 2008.

This application is related to pending US Application Serial No. 12 / 2253,051, filed October 16, 2008.

This application is related to pending US Application Serial No. 12 / 190,449, filed on August 12, 2008.

This application is related to pending US Application Serial No. 12 / 187,477, filed August 7, 2008.

This application is related to pending US Application Serial No. 12 / 218,582, filed July 18, 2008.

This application is related to pending US Application Serial No. 12 / 218,558, filed July 17, 2008.

This application is related to pending US Application Serial No. 12 / 123,864, filed May 20, 2008.

This application is related to pending US Application Serial No. 12 / 102,550, filed April 14, 2008.

This application is related to pending US Application Serial No. 12 / 047,842, filed March 13, 2008.

This application is related to pending US Application Serial No. 12 / 023,772, filed January 31, 2008.

This application is related to pending US Application Serial No. 11 / 956,069, filed December 13, 2007.

This application is related to pending US Serial Nos. 11 / 860,142 and 11 / 860,183, filed September 24, 2007.

This application is related to pending US Application Serial No. 11 / 836,402, filed August 8, 2007.

This application is related to pending US Application Serial No. 11 / 616,596 filed December 27, 2007.

This application is related to pending US Application Serial No. 11 / 614,332, filed December 21, 2006.

This application is related to pending US Application Serial No. 11 / 445,793, filed June 2, 2006.

This application is related to pending US Application Serial No. 11 / 500,053, filed August 7, 2006.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to the field of semiconductor devices and manufacturing methods, and devices such as multi-junction solar cells based on III-V semiconductor compounds including a metamorphic layer. Such devices are also known as inverted nietamorphic multijunction solar cells (solar cells with multiple pn junctions).

2. Description of Related Art

Solar power of photovoltaic cells, also referred to as solar cells, has been predominantly provided by silicon semiconductor technology. However, in recent years, the fabrication of III-V compound semiconductor multijunction solar cells for space applications has accelerated the development of this technology, not only for space applications but also for use in terrestrial solar power applications. Compared to silicon, III-V compound semiconductor multijunction devices have greater energy conversion efficiencies and generally have greater radiation resistance, although they tend to be more complicated to manufacture. Typical III-V compound semiconductor multijunction solar cells have energy efficiencies that exceed 27% with a sun, air mass 0 (AM0) exposure, whereas even the most efficient silicon technologies generally only achieve about 18% efficiency under comparable conditions. At a high solar concentration (eg, 500X), III-V compound semiconductor multijunction solar cells have energy efficiencies in terrestrial applications (at AM1, 5D) that exceed 37%. The high conversion efficiency of III-V compound semiconductor multi-junction solar cells, compared to silicon solar cells, is based in part on the ability to achieve spectral splitting of the incident radiation through the use of a plurality of photovoltaic zones or regions of different Band gap energies, and summation of the current from each of the zones.

Typical III-V compound semiconductor multi-junction solar cells are fabricated on a semiconductor wafer in vertical multi-junction structures. The individual solar cells or wafers are then arranged in horizontal arrangements, wherein the individual solar cells are connected to each other in a series electrical connection. The shape and structure of an array and also the number of cells containing the array are determined in part by the desired output voltage and the desired output current.

Inverted metamorphic solar cell structures based on III-V compound semiconductor layers, such as in MW Wanlass et al, Lattice Mismatched Approaches for High Performance, III-V Photovoltaic Energy Converters (Conference Proceedings of the 31st IEEE Photovoltaic Specialist Conference, Jan. 3-7, 2005, IEEE Press, 2005) are an important conceptual starting point for the development of future commercial high efficiency solar cells. The materials and structures for a number of different layers of the proposed and described cells of the cited citation result in a number of practical difficulties, which may be appropriate Refer to selection of materials and manufacturing steps.

Prior to the present invention, the prior art materials and fabrication steps were apparently inadequate to produce a commercially disruptive and energy efficient solar cell using commercially available fabrication processes to create an inverted metamorphic multi-junction cell structure.

SUMMARY OF THE INVENTION

Briefly and generally, the invention provides a multi-junction solar cell having an upper first solar subcell with a first bandgap; a second solar subcell adjacent to the first solar subcell and having a second bandgap less than the first bandgap; a first graded intermediate layer adjacent to the second solar subcell; wherein the first graded interlayer has a third bandgap greater than the second bandgap; and a third solar subcell adjacent to the first graded interlayer, the third subcell having a fourth bandgap less than the second bandgap such that the third subcell is lattice misaligned with respect to the second subcell mentioned; a graded intermediate layer adjacent to the third subcell; wherein the second graded interlayer has a fifth bandgap greater than the fourth bandgap; and a lower fourth solar subcell adjacent to said second graded interlayer, wherein said lower subcell has a sixth band gap that is less than the fourth bandgap such that said fourth subcell is lattice misaligned with respect to said third subcell.

According to another aspect of the present invention, there is provided a method of manufacturing a solar cell by providing a first substrate; Forming an upper first solar subcell having a first band gap on the first substrate; Forming or forming a second solar subcell adjacent to the first solar subcell and having a second bandgap less than the first bandgap; Forming a first graded interlayer adjacent the second solar subcell; wherein the first graded interlayer has a third bandgap greater than the second bandgap; Forming a third solar subcell adjacent to the first graded interlayer, the third subcell having a fourth bandgap smaller than the second bandgap such that the third subcell is lattice misaligned with respect to the second subcell; Forming a second graded intermediate layer adjacent to the third solar subcell; wherein the second graded interlayer has a fifth bandgap greater than the fourth bandgap; Forming or forming a lower fourth solar subcell adjacent to the second graded interlayer, the lower subcell having a sixth band gap that is less than the fourth bandgap such that the fourth subcell is grid misaligned with respect to the third subcell; Attaching a surrogate substrate on top of the fourth solar subcell; and removing the first substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its meaning fully appreciated by reference to the following detailed Description together with the attached drawings; in the drawing shows:

1 a graph showing the bandgap of certain binary materials and their lattice constants;

2 a cross section of the solar cell of the present invention after the initial stage of production, including the deposition of certain semiconductor layers on the growth substrate;

3 a cross-sectional view of the solar cell of 2 after the next sequence of processing steps;

4 a cross section of the solar cell of 3 after the next sequence of processing steps;

5 a cross-sectional view of the solar cell of 4 after the next sequence of processing steps;

6 a cross-sectional view of the solar cell of 5 after the next processing step;

7 a cross-sectional view of the solar cell of 6 after the next processing step in which a surrogate substrate is attached;

8A a cross-sectional view of the solar cell of 7 after the next processing step, in which the original substrate is removed;

8B a further cross section of the solar cell of 8A with the surrogate substrate at the bottom of the figure;

9 a simplified cross-sectional view of the solar cell of 8B after the next processing step;

10 a cross section of the solar cell of 9 after the next processing step;

11 a cross section of the solar cell of 10 after the next processing step;

12 a cross section of the solar cell of 11 after the next processing step;

13 a plan view of a wafer in which the solar cells are produced;

13B a plan view of the wafer from below, in which the solar cells are produced;

14 a cross section of the solar cell of 12 after the next processing step;

15 a cross section of the solar cell of 14 after the next processing step;

16 a cross section of the solar cell of 15 after the next processing step;

17 a plan view of the wafer 16 showing a surface view of the trench etched about the cell;

18A a cross section of the solar cell of 16 after the next processing step;

18B a cross section of the solar cell of 16 after the next processing step in a second embodiment of the present invention;

19 a cross-sectional view of the solar cell of 18 after the next processing step;

20 a graphical representation of the doping profile of base and emitter layers of a subcell in the metamorphic solar cell according to the invention;

21 Fig. 10 is a graph showing the current and voltage characteristics of the inverted multi-junction metamorphic solar cell according to the invention;

22 FIG. 4 is a graph illustrating the range of band gaps of various GaInAlAs materials as a function of the relative concentration of Al, In, and Ga; FIG.

23 a plot of the Ga mole fraction depending on the Al to In mole fraction in GaInAlAs materials necessary to achieve a constant 1.5 eV bandgap;

24 a plot of the molar fraction to lattice constant in GaInAlAs materials necessary to achieve a constant 1.5 EV bandgap.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Details of the present invention will now be described, including exemplary aspects and embodiments thereof. With reference to the drawings and the following description, it should be noted that the same reference numerals are used to refer to the same or functionally similar elements The description is intended to describe key features of exemplary embodiments in an extremely simplified schematic manner. In addition, it should be noted that the drawings do not show every feature of the actual embodiment, nor the relative dimensions of the illustrated elements, which are not drawn to scale.

The basic concept of fabricating an inverted metamorphic multi-junction (IMM) solar cell is to grow the subcell of the solar cell on a substrate in a "reversed" sequence. That is, the high bandgap subcells (ie, the subcell having bandgaps in the range of 1.8 to 2.1 eV) that are normally "up" on the subcells and are indicative of solar radiation become epitaxially grown on a semiconductor growth substrate, such as For example, GaAs or Ge grown and these subcells are therefore lattice matched to this substrate. One or more of the lower sub-band middle subcellular cells (i.e., the cells with band gaps in the range of 1.2 to 1.8 eV) can then be grown on the high band gap subcells.

At least one lower subcell is formed over the middle or middle subcell such that the at least one lower subcell is substantially lattice matched with respect to the growth substrate and such that at least one lower subcell has a third lower bandgap (ie, a bandgap in the range of 0.7 to 1 , 2 eV). A surrogate substrate or support substrate is then applied or provided over the bottom or substantially lattice mismatched lower subcell, and the growth semiconductor substrate is subsequently removed. (The growth substrate can subsequently be reused for the growth of a second and subsequent solar cells).

A variety of different features of the inverted multi-junction metamorphic solar cells are disclosed in the above-referenced related applications. Some or all of these features may be employed in the structures and processes associated with the solar cells of the present invention. However, the present invention is particularly directed to the fabrication of a four-junction inverted metamorphic solar cell having two distinct metamorphic layers, all grown on a single growth substrate. According to the present invention, the resulting construction comprises four sub-cells with band gaps in the range of 1.8 to 2.1 eV, 1.3 to 1.5 eV, 0.9 to 1.1 eV, and 0.6 to 0, respectively. 8 eV.

1 Figure 4 is a graphical representation of the bandgap or bandgap of certain binary materials and their lattice constants. The bandgap and lattice constants of ternary materials are arranged on the lines drawn between the typical associated binary materials (binary materials such as the ternary GaAlAs material located between the GaAs and AlAs points of the plot, where the bandgap of the ternary material is between 1.42 eV for GaAs and 2.16 eV for AlAs, depending on the relative size of the individual constituents Thus, depending on the desired bandgap, the material components of the ternary materials can be suitably selected for growth become.

The lattice constants and electrical properties of the layers of the semiconductor structure are preferably controlled by the specification of appropriate reactor growth temperatures and times and by the use of appropriate chemical composition and dopants. The use of a vapor deposition technique such as Organo Metallic Vapor Phase Epitaxy (OMVPE), Metal Organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy (MBE) or other vapor deposition techniques for reverse growth, the layers of the monolithic semiconductor structure forming the cell may be grown to the required thickness, elemental composition, dopant concentration.

2 Figure 12 illustrates the multi-junction solar cell according to the present invention after the sequential formation or formation of three sub-cells A, B and C on a GaAs growth substrate. In particular, here is a substrate 101 which is preferably gallium arsenide (GaAs) but may also be germanium (Ge) or other suitable material. For GaAs, the substrate is preferably a 15 ° cut substrate, ie the surface is 15 ° opposite the 100 ) Level to the ( 111 ) -A plane, as described in detail in U.S. Patent Application Serial No. 12 / 047,944, filed Mar. 13, 2008.

In the case of a Ge substrate, a seed layer (not shown) directly on the substrate 111 deposited. Further, on the substrate or over the nucleation layer (in the case of a Ge substrate) is a buffer layer 102 and an etch stop layer 103 still deposited. In the case of a GaAs substrate, the buffer layer is 102 preferably GaAs. In the case of a Ge substrate, the buffer layer is 102 preferably InGaAs. A contact layer 104 GaAs is then deposited on the layer 103 deposited and a window layer 105 AlInP is deposited over the contact layer. Subcell A, consisting of an n + emitter layer 106 and a p-type base layer 107 , then becomes epitaxial on the window layer 105 deposited. Subcell A is generally lattice matched to the growth substrate 101 ,

It should be noted that the multi-junction solar cell structure could be formed by any suitable combination of group III to V elements listed in the Periodic Table, taking into account lattice constants and bandgap requirements, where Group III comprises: boron (B) , Aluminum (Al), gallium (Ga), indium (In) and thallium (T). Group IV includes carbon (C), silicon (Si), and germanium (Ge) and tin (Sn). Group V includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi).

In the preferred embodiment, the emitter layer is 106 constructed from InGa (Al) P and the base layer 107 is made up of InGa (Al) P. The aluminum or Al term in parentheses in the mentioned formula means that Al is an optional ingredient, in this case in an amount of 0% to 30%. The doping profile of the emitter and base layers 106 and 107 according to the present invention is used in conjunction with 20 discussed.

The subcell A finally becomes the "upper" subcell of the inverted metamorphic structure after completion of the processing steps according to the present invention, which will be described later.

On top of the base layer 107 becomes a BSF or Back Surface Field (BSF) layer 108 (rear surface field layer 108 ), preferably p + AlGaInP, and used to reduce recombination loss.

The BSF layer 103 drives minority carriers from the zone near the base / BSF interface surface to minimize the effect of recombination loss. In other words: the BSF layer 18 reduces recombination loss at the back of solar subcell A, thereby reducing recombination in the base.

On top of the BSF layer 108 becomes a sequence of heavily doped p-type and n-type layers 109a and 109b , which form a tunnel diode, deposited, ie an ohmic circuit element, which connects the subcell A with the subcell B. The layer 109a is preferably composed of p ++ AlGaAs and the layer 109b is preferably composed of n +++ InGaP.

On top of the tunnel diode layers 109 becomes a window layer 110 deposited, preferably n + InGaP. The advantage of using InGaP as the material which the window layer 110 is that this material has a refractive index closely matched to the adjacent emitter layer 111 as more fully described in U.S. Application Serial No. 12 / 258,190, filed October 24, 2008. The window layer 110 used in subcell B causes the reduction of interface recombination loss. One skilled in the art will recognize that additional layers or an additional layer may be added or omitted in the cell structure without departing from the scope of the invention.

On top of the window layer 110 the layers of subcell B are deposited: the n-type emitter layer 111 and the p-type base layer 112 , These layers are preferably InGaP or In _0.015 GaAs (for a Ge substrate or growth template) or InGaP and GaAs (for a GaAs substrate, respectively), although any other materials that meet the requirements of lattice constants and Band gap correspond. Thus, the subcell B may be constructed with a GaAs, GaInP, GaInAs, GaAsSb or GaInAsN emitter region or region and a GaAs, GaInAs, GaAsSb or GaInAsN base region. The doping profile of the layers 111 and 112 according to the present invention is used in conjunction with 20 discussed.

In the previously disclosed inverted metamorphic solar cell implementations, the center cell was a homostructure. In accordance with the present invention, similar to that disclosed in US Pat. 12 / 023,772, the middle subcell becomes a heterostructure with an InGaP emitter and its window is converted from InAlP to InGaP. This modification eliminated the refractive index discontinuity at the window / emitter interface and middle subcell window / emitter interface, respectively, as described in detail in US Patent Application Serial No. 12 / 258,190, filed October 24, 2008 In addition, the window layer 110 preferably doped three times as much as the emitter 111 to shift the Fermi level up closer to the conduction band and therefore to band-bend the window / emitter interface, with the result that the minority carriers are confined to the emitter layer.

In the preferred embodiment of the present invention, the middle subcell emitter has a band gap equal to that of the upper subcell emitter, and the third subcell emitter has a band gap greater than the band gap of the base subcell base. Therefore, following the fabrication of the solar cell and its implementation and operation, none of the emitter of the middle subcell B nor the third subcell C is exposed to absorbable radiation. Substantially all of the photons that represent absorbable radiation are absorbed by the bases of cells B and C, which have narrower band gaps than the emitters. The advantages of using heterojunction subcells are as follows: (i) the short wavelength response for both subcells improves and (ii) the mass of the radiation is more effectively absorbed and collected through the narrower bandgap base. The effect is that J _{sc is} increased.

At the top of cell B is a BSF layer 113 deposited, which performs the same function as the BSF layer 109 , The p ++ / n ++ tunnel diode layers 114a respectively. 114b are above the BSF layer 113 similar to the layers 109a and 109b and form an ohmic circuit element to connect subcell B to subcell C. The layer 114a is preferably composed of p ++ AlGaAs and the layer 114b is preferably made of n ++ InGaP.

A barrier or barrier layer 115 , preferably composed of n-type InGa (Al) P, is above the tunnel diode 114a / 114b deposited, to a thickness of about 1.0 micron. This barrier layer is intended to prevent threading dislocations from propagating, either opposite to the direction of growth in the middle and upper sub-cells B and C or in the direction of growth into the bottom or bottom subcell A, which is described in detail in copending U.S. Patent Application Serial No. 11 / 800,183, filed September 24, 2007.

A metamorphic layer (or graded interlayer) 116 is above the barrier layer 115 deposited using a wetting agent or surface treatment agent (surfactant). The layer 116 is preferably a compositionally graded series of InGaAlAs layers, preferably with monotonic varying lattice constants, so as to achieve a gradual transition in lattice constants in the semiconductor structure from subcell B to subcell C while minimizing the occurrence of screw dislocations. The band gap of the layer 116 is constant throughout the thickness, preferably approximately equal to 1.5 eV, or otherwise consistent with a value slightly greater than the band gap of the middle subcell B. The preferred embodiment of the graded interlayer may also be made as (In _x Ga _1-x ). _y Al _1-y As are selected, where x and y are selected so that the band gap of the intermediate layer remains constant at approximately 1.05 eV or at another suitable band gap value.

In the wetting agent-assisted growth of the metamorphic layer 116 becomes a suitable chemical element in the reactor during the growth of the layer 116 introduced to improve the surface characteristics of the layer. In the preferred embodiment, such element may be a dopant or a donor atom, such as selenium (Se) or tellurium (Te). Small amounts of Se or Te are thus in the metamorphic layer 116 installed and remain in the finished solar cell. Although Se or Te are preferred n-type dopant atoms, other non-isoelectric wetting agents may also be used.

Wetting agent-assisted growth results in a much smoother or planar surface. Because surface topography affects the bulk properties of the semiconductor material as it grows thicker and thicker, the use of wetting agents can minimize screw dislocations in the active regions or zones and improves overall solar cell efficiency.

As an alternative to using a non-isoelectronic surfactant, one can use an isoelectronic surfactant. The term "isoelectronic" refers to wetting agents such as antimony (Sb) or bismuth (Bi) because such elements have the same number of bonding electrons as the P atom of InGaP or As the As atom in InGaAlAs in the metamorphic buffer layer. Such Sb or Bi surfactants are not typically in the metamorphic layer 116 built-in.

In an alternative embodiment where the solar cell has only two subcells and the "middle" cell B is the uppermost or upper subcell in the final solar cell, the "upper" subcell B typically has a band gap of 1.8 to 1.9 eV would, the band gap of the inner layer would remain at a constant 1.9 eV.

In the inverted metamorphic structure described in the Wanlass et al reference cited above, the metamorphic layer consists of nine compositionally graded InGaP steps, each step layer having a thickness of 0.25 microns. Consequently has every layer at Wanlass et al a different band gap. In the preferred embodiment of the present invention, the layer is 116 constructed or composed of a plurality of layers of InGaAlAs, with monotonic changing lattice constants, each layer having the same band gap of approximately 1.5 eV.

The advantage of using a constant bandgap material, such as InGaAlAs, is that the arsenide-based semiconductor material is much easier to process, with the conventional commercial MOCVD reactors, where the small amount of aluminum is the radiation transparency of the metamorphic layers ensures.

Although the preferred embodiment of the present invention includes a plurality of layers of InGaAlAs for the metamorphic layer 116 For reasons of manufacturability and radiation transparency, other embodiments of the present invention may use different material systems to achieve a change in lattice constants from subcell B to subcell C. In this way, the system of Wanlass using compositionally graded InGaP is a second embodiment of the present invention. Other embodiments of the present invention can use continuously graded materials as opposed to graded graded materials. More generally, the graded interlayer may be composed of any of the As-PN-Sb based III-V compound semiconductors, taking into account the limitations of having an in-plane lattice parameter greater than or equal to the second solar cell and is smaller than or equal to the third solar cell, and with a bandgap energy is greater than that of the second solar cell.

In another embodiment of the present invention, an optional or optionally second barrier layer 117 above the InGaAlAs metamorphic layer 116 be isolated. The second barrier layer 117 will typically have a different composition than the composition of the barrier layer 115 and performs substantially the same function, namely, preventing the propagation of screw dislocations. In the preferred embodiment, the barrier layer is 117 n + type GaInP.

A window layer 118 , preferably composed of n + -type GaInP, then becomes over the barrier layer 117 (or directly over layer 116 in the absence of a second barrier layer). This window layer works to reduce the recombination loss in subcell "C". It will be understood by those skilled in the art that additional layers may be added or omitted in this cell structure without departing from the scope of the invention.

On top of the window layer 118 the layers of cell C are deposited: the n + emitter layer 119 and the p-type base layer 120 , These layers are preferably composed of n + -type InGaAs and n + -type InGaAs, respectively, or n + -type InGaP and p-type InGaAs for heterojunction subcells, although other suitable materials in accordance with lattice constants and band gap requirements may also be used , The doping profile of the layer 119 and 120 will be in contact with 20 discussed.

A BSF layer 121 , preferably consisting of InGaAlAs, is then deposited on top of the cell C, the BSF layer having the same function as the BSF layers 108 and 113 performs.

The p ++ / n ++ tunnel diode layers 122a respectively. 122b be above the BSF layer 121 similar to the layers 114a and 114b deposited and form an ohmic circuit element for connecting the subcell C with the subcell D. The layer 122a is preferably p ⁺⁺ InGaAlAs and the layer 122b preferably consists of n ++ - InGaAlAs.

3 shows a cross section of the solar cell of 2 after the next sequence or sequence of processing steps. A barrier or barrier layer 123 , preferably consisting of n-type GaInP is above the tunnel diode 122a / 122b deposited to a thickness of about 1.0 micron. Such a barrier layer is provided to prevent the propagation of screw dislocations, either opposite to the growth direction in the top and middle subcells A, B and C, or in a direction of growth into subcell D, in detail in copending US patent application Ser Serial No. 11 / 860,183, filed September 24, 2007.

A metamorphic layer (or graded interlayer) 124 is above the barrier layer 123 deposited using a wetting agent. The layer 124 is preferably a compositionally graded series of InGaAlAs layers, preferably with monotonic changing lattice constant, so as to achieve a gradual or gradual transition for the lattice constant in the semiconductor structure from subcell C to subcell D while minimizing the occurrence of screw dislocations. The band gap of the layer 124 is constant throughout the thickness, preferably approximately equal to 1.1 eV, or otherwise consistent with a value slightly greater than the bandgap of the middle subcell C. The preferred embodiment of the graded interlayer may also be made as (In _x Ga _{1). x} ) _y Al _1-y As are composed, with x and y selected so that the bandgap of the intermediate layer remains constant at approximately 1.1 eV or at another suitable bandgap.

In the wetting agent-assisted growth of the metamorphic layer 124 becomes a suitable chemical element in the reactor during the growth of the layer 124 introduced to improve the surface characteristics of the layer. In the preferred embodiment, such element may be a dopant or a donor atom, such as selenium (Se) or tellurium (Te). Small amounts of Se or Te are therefore in the metamorphic layer 124 installed and remain in the finished solar cell. Although Se or Te are the preferred n-type dopant atoms, other non-isoelectric wetting agents may also be used.

A window layer 125 , preferably consisting of n + -type InGaAlAs, is then over the layer 124 deposited (or over a second barrier layer, if any, disposed over the layer 124 ). This window layer works to reduce the recombination loss in the fourth subcell "D". One skilled in the art will recognize that additional layers may be added or omitted in the cell structure without departing from the scope of the present invention.

4 shows a cross section of the solar cell of 3 after the next sequence or sequence of processing steps. On top of the window layer 124 the layers of cell D are deposited: the n + emitter layer 124 and p-type base layer 127 , These layers are preferably composed of n + -type InGaAs or p-type InGaAs or n + -type InGaP and p-type InGaAs for a heterojunction subcell, although other suitable materials consistent with lattice constants and band gap requirements are also used can be. The doping profile of the layer 126 and 127 will be in contact with 20 discussed.

It is now up 5 Referenced. A BSF layer 128 , preferably consisting of p + -type InGaAlAs is then deposited on top of the cell D, the BSF layer having the same function as the BSF layers 108 . 113 and 121 exercises.

Finally, a high band gap possessing contact layer 129 , preferably consisting of p ++ type InGaAlAs on the BSF layer 128 deposited.

The composition of this contact layer 129 Placed on the bottom side (unexposed) of the lowest band gap photovoltaic cell (ie, subcell "D2 in the illustrated embodiment) in a multijunction photovoltaic cell, can be formulated to reduce the absorption of the light passing through the cell (i) the backside underlying ohmic metal contact layer (on the unexposed side) will also act as a mirror layer and (ii) the contact layer need not be selectively etched away to prevent absorption.

One skilled in the art will recognize that an additional layer or layers may be added or deleted in the cell structure without departing from the scope of the invention.

6 is a cross section of the solar cell of the 5 after the next processing step, in which a metal contact layer 123 over the p + semiconductor contact layer 122 is deposited. The metal is preferably a series of metal layers Ti / Au / Ag / Au.

The selected metal contact scheme is one having a planar interface with the semiconductor after heat treatment to activate the ohmic contact. This is done in such a way that, (1) a dielectric layer which separates the metal from the semiconductor need not be deposited and must be selectively etched in the metal contact regions, and (2) it reflects the contact layer mirror over the wavelength range of interest.

7 is a cross section of the solar cell of the 3 after the next processing step, in which an adhesive layer 13 over the metal layer 130 is deposited. The adhesive is preferably "Wafer Bond" (manufactured by Brewer Science, Inc. of Rolla, MO, USA).

In the next process or process step becomes a surrogate substrate 132 , preferably sapphire applied. Alternatively, the surrogate substrate may be GaAs, Ge or Si or other suitable material. The surrogate substrate is approximately 40 mils thick and is perforated 4 mm apart with holes about 1 mm in diameter to assist in the removal of the adhesive and substrate. An alternative to using an adhesive layer 131 is the eutectic or permanent connection of one suitable substrate (for example GaAs) with the metal layer 130 ,

8A is a cross-sectional view of the solar cell of 7 after the next step in which the original substrate is removed by a series of lapping or etching steps in which the substrate is removed 101 and the buffer layer 103 be removed. The selection of a particular etchant depends on the growth substrate.

8B is a cross section of the solar cell of the 8A , wherein the orientation of the surrogate substrate 132 at the bottom of the 4 is shown. The following figures in this application assume this orientation.

9 is a simplified cross section of the solar cell of 8B with only a few of the upper layers and lower layers over the surrogate substrate 132 are shown.

10 is a cross-sectional view of the solar cell of 9 after the next processing or process step in which the etch stop layer 103 is removed by an HCl / H ₂ O solution.

11 is a cross section of the solar cell of the 10 after the next sequence of process or process steps involving a photoresist mask (not shown) over contact layer 104 for the formation of the grid lines (grid conductor) 501 is placed. As described in detail below, the grid lines become 501 deposited by evaporation and patterned lithographically and over the contact layer 104 deposited. The mask is then followed by the finished metal grid lines 501 , as shown in the figures, lifted off.

As described in detail in U.S. Patent Application Serial No. 12 / 218,582, filed July 18, 2008, the grid lines are 501 preferably composed of Pd / Ge / Ti / Pd / Au, although other suitable materials may also be used. The disclosure of said patent application is to be regarded as included in the present application.

12 is a cross section of the solar cell 11 after the next processing step, where the grid lines are used as a mask, around the surface of the window layer 105 using a citric acid / peroxide etching mixture.

13A Fig. 10 is a plan view of a wafer in which four solar cells are implemented. The illustration of four cells is for illustrative purposes only and the present invention is not limited to any particular number of cells per wafer.

There are grid lines in each cell 501 (which in particular in the cross section in 9 shown), an interconnecting bus line or line 502 and a contact connection 503 , The geometry and number of grid and bus lines and the contact pad are to be understood as illustrative, and the present invention is not limited to the illustrated embodiment.

13B FIG. 12 is a bottom plan view of four solar cells according to FIG 13A ,

14 is a cross-sectional view of the solar cell of 12 after the next processing step, in which an anti-reflective (ARC) dielectric coating layer 130 over the entire surface of the bottom side of the wafer with the grid lines or lines 501 is applied.

15 is a cross-sectional view of the solar cell of 14 after the next process step according to the present invention, in which first and second ring channels 510 and 511 or part of the semiconductor structure to the metal layer 130 are etched down, using phosphide and arsenide etchants. These channels define a perimeter boundary between the cell and the remainder of the wafer, leaving behind a mesa structure that forms the solar cell. The in 15 shown cross-section is the one how to get it from the AA level according to 17 looks out. In a preferred embodiment, the channel is 510 much wider than the channel 511 ,

16 is a cross-sectional view of the solar cell of 15 after the next processing step, in which the channel 511 a metal etchant is exposed, and that part of the metal layer 130 , located at the bottom of the canal 511 , is removed. The depth of the channel 511 thereby becomes approximately the upper surface (upper side) of the adhesive layer 131 extends.

17 is a plan view of the wafer of 16 wherein the channels etched around the circumference of each cell 510 and 512 are shown.

18A is a cross-sectional view of the solar cell of 16 after the next processing step in a first embodiment of the invention, in which the surrogate substrate 132 suitably on a relatively thin layer 132a is diluted, by grinding, lapping or etching. In this embodiment, the thin layer forms 132a the carrier for the solar cells in applications where a cover glass is not is required, as is provided for the second embodiment, which will be described below. In such an embodiment, the electrical contact to the metal contact layer 130 through the channel 510 or by other structures.

18B is a cross-sectional view of the solar cell of 16 after the next processing step in a second embodiment of the invention, in which a cover glass 514 at the top of the cell with an adhesive 513 is attached. The cover glass 514 preferably covers the entire channel 510 but does not extend to the periphery of the cell near the channel 511 , Although the use of a cover glass is the preferred embodiment, it is not required for all implementations and additional layers or structures may also be used to provide additional support or environmental protection for the solar cell.

19 is a cross-sectional view of the solar cell of 18B after the next process step of the present invention, wherein the adhesive layer 131 , the surrogate substrate 132 and the peripheral part 512 of the wafer are completely removed, with the demolition in the zone of the channel 510 what happens is just the solar cell with the cover glass 514 (or other layers or structures) at the top leaves and the metal contact layer 130 at the bottom, which forms the back contact of the solar cell. The surrogate substrate is preferably removed by the use of the etchant EKC 922 , As noted above, the surrogate substrate has perforations across its surface that allow the etchant to pass through the surrogate substrate 132 can flow to allow its removal. The surrogate substrate can be used again in subsequent wafer processing operations.

20 FIG. 12 is a graphical representation of a doping profile in the emitter and base layers of one or more subcells of the inverse metamorphic multi-junction solar cell of the invention. FIG. The various doping profiles that are within the scope of the invention and the advantages of such doping profiles are described in detail in co-pending U.S. patent application Ser. No. 11 / 956,069, filed December 13, 2007, which is incorporated herein by reference in the disclosure of this application. The doping profiles shown therein are merely illustrative, and other more complicated profiles may be used, as will be apparent to those skilled in the art, without departing from the scope of the invention.

21 Fig. 12 is a graph illustrating the current and voltage characteristics of one of the test solar cells made according to the invention. In this test cell, the lower fourth subcell had a bandgap or band gap in the range of approximately 0.6 to 0.8 eV, and the third subcell had a bandgap in the range of approximately 0.9 to 1.1 eV, the second subcell had one Band gap in the range of approximately 1.35 to 1.45 eV and the upper subcell had a band gap in the range of 1.8 to 2.1 eV. The solar cell had an open circuit voltage (VOC) of approximately 3.265 volts, a short-flow current of approximately 16.26 mA / cm ² , a fill factor of approximately 82%, and an efficiency of 32.2% at one measurement.

22 Figure 12 is a graph illustrating the range of bandgaps of various GaInAlAs materials as a function of the relative concentration of Al, In and Ga. This diagram illustrates how to select a constant bandgap sequence of layers of GaInAlAs used in the metamorphic layer , can be designed by appropriately selecting the relative concentration of Al, In, and Ga to meet the different lattice constant requirements for each successive layer. However, regardless of whether 1.5 eV or 1.1 eV or another bandgap value is the desired constant bandgap, the graph illustrates a continuous curve for each bandgap and represents the incremental changes in component proportions as the lattice constant changes to reflect the band gap Layer to provide the required band gap and lattice constant.

23 FIG. 12 is a graph further illustrating the selection of a constant bandgap sequence of layers of GaInAlAs used in the metamorphic layer, showing the Ga mole fraction depending on the Al to In mole fraction in GaInAlAs materials. FIG necessary to obtain a constant 1.5 eV band gap.

24 Figure 4 is a graph further illustrating the selection of a constant bandgap sequence of layers of GaInAlAs using the metamorphic layer, depicting the mole fraction depending on the lattice constants in GaInAlAs materials necessary to achieve a constant 1.5 eV Band gap.

It will be appreciated that each of the elements described above, or two or more together, may find useful application in other types of designs that differ from the designs described above.

Although the preferred embodiment of the present invention uses a vertical stack of four subcells, the present invention can also be applied to stacks having fewer or more subcells, ie, two junction cells, three junction cells, five junction cells, and so on In the case of four or more junction cells, the use of more than one metamorphic grading layer may also be used.

In addition, although the present embodiment is configured with upper and lower electrical contacts, the subcells may alternatively be contacted by metal contacts on side conductive semiconductor layers between the cells. Such arrangements can be used to achieve 3-port, 4-port and generally n-port devices. The subcells may be connected between circuits that use these additional terminals such that the available photogenerated current density of each subcell can be effectively exploited, resulting in high efficiency for the multijunction cell, without contradicting the fact that the photogenerated current densities are typically different in the different subcells.

As mentioned above, the present invention may use an array of one or more or all of the homojunction cells or subcells, i. H. a cell or subcell in which the pn-junction is formed between a p-type semiconductor and an n-type semiconductor, both having the same chemical composition and the same bandgap, but only in the dopant Type and types, and one or more heterojunction cells or sub-cells can be provided. Subcell A with p-type and n-type InGaP is an example of a homojunction subcell. Alternatively, as specifically described in U.S. Patent Application Serial No. 12 / 023,772, filed January 31, 2008, the invention may use one or more or all of the heterojunction cells or subcells, i. H. a cell or subcell in which the pn junction is formed by a p-type semiconductor and an n-type semiconductor having different chemical compositions of the semiconductor material in the n-type regions and / or different bandgap or bandgap energies in the n-type p-type zones or regions, in addition to using different dopant species and the type of p-type and n-type regions forming the pn junction.

In some rows, a thin so-called intrinsic barrier layer ("intrinsic layer" or "i" layer) may be disposed between the emitter layer and the base layer with the same or different composition of both the emitter and base layers. The i-layer may cause the effect of suppressing the minority carrier recombination in the space charge region. Similarly, either the base layer or the emitter layer may also be intrinsically or unintentionally doped ("NID") over part or all of the thickness.

The composition of the window or BSF layers may use other semiconductor compounds, taking into account the requirements of lattice constants and bandgap, and these layers may include: AlInP, AlAs, AlP, AlGaInP, AlGaAsP, AlGaInAs, AlGaInPAs, GaInP, GaInAs, GaInPAs. AlGaAs, AlInAs, AlInPAs, GaAsSb, AlAsSb, GaAlAsSb, AlInSb, GaInSb, AlGaInSb, AlN, GaN, InN, GaInN, AlGaInN, GaInNAs, AlGaInNAs, ZnSSe, CdSSe, and similar materials falling within the scope of the present invention.

Although the invention has been illustrated and described as being in an inverted multi-junction metamorphic solar cell, it is not intended to limit the invention to the details shown, as various modifications and structural changes can be made without departing from the scope of the invention.

Although the description of this invention focuses primarily on solar cells or photovoltaic devices, those skilled in the art will recognize that other optoelectronic devices such as thermophotovoltaic (TPV) cells, photodetectors, and light emitting diodes (LEDs) have very similar structure, physical properties, and materials how to use photovoltaic devices, with some minor variations in doping and minority carrier lifetime. For example, photodetectors may use the same materials and structures as the photovoltaic devices described above, but possibly lower doping is used in terms of sensitivity rather than power production. On the other hand, LEDs with similar structures and materials can be made, but possibly with more doping, to shorten the recombination time, thus emphasizing the radiation lifetime for producing light rather than power. Thus, the present invention is also applicable to photodetectors and LEDs having structures, material compositions, and articles of manufacture with improvements as described above for the photovoltaic cells.

Without further analysis, the above description may fully illustrate the present invention by utilizing current knowledge to readily provide adaptation for various applications without omitting features that are in a fair manner essential characteristics of the general or generic art from the standpoint of the art pertain to particular aspects of this invention such that such adaptations are within the scope and meaning of the equivalence of the following claims.

• 1. Eine Multijunction-Solarzelle, die Folgendes aufweist: eine obere erste Solarsubzelle mit einem ersten Bandabstand; eine zweite Solarsubzelle benachbart zu der ersten Solarsubzelle mit einem zweiten Bandabstand kleiner als der erste Bandabstand; eine erste gradierte Zwischenschicht benachbart zu der zweiten Solarsubzelle, wobei die erste gradierte Zwischenschicht einen dritten Bandabstand besitzt, der größer ist als der zweite Bandabstand; und eine dritte Solarsubzelle benachbart zu der ersten gradierten Zwischenschicht, wobei die dritte Subzelle einen vierten Bandabstand besitzt, der größer ist als der zweite Bandabstand derart, dass die dritte Subzelle gitterfehlangepasst bezüglich der zweiten Subzelle ist; eine zweite gradierte Zwischenschicht benachbart zu der dritten Subzelle, wobei die zweite gradierte Zwischenschicht einen fünften Bandabstand besitzt, der größer ist als der vierte Bandabstand; und und eine untere vierte Solarsubzelle benachbart zu der zweiten gradierten Zwischenschicht, wobei die untere Subzelle einen sechsten Bandabstand besitzt, der kleiner ist als der vierte Bandabschnitt derart, dass die vierte Subzelle gitterfehlausgerichtet ist bezüglich der dritten Subzelle.
• 2. Die Multijunction-Solarzelle nach 1, wobei die erste gradierte Zwischenschicht zusammensetzungsmäßig gradiert ist, um die Gitteranpassung der zweiten Subzelle auf der einen Seite und der dritten Subzelle auf der anderen Seite vorzusehen.
• 3. Die Multijunction-Solarzelle nach 1, wobei die zweite gradierte Zwischenschicht zusammensetzungsmäßig gradiert ist, um die dritte Subzelle auf einer Seite und die untere vierte Subzelle auf der anderen Seite gitteranzupassen.
• 4. Die Multijunction-Solarzelle nach 1, wobei die erste gradierte Zwischenschicht zusammengesetzt ist aus irgendeinem der folgenden Verbindungshalbleiter: As-P-N-Sb-basierende III–V-Verbindungshalbleiter, und zwar unter Berücksichtigung der Einschränkungen eines „in-plane”-Gitterparameters größer oder gleich dem der zweiten Subzelle und kleiner als oder gleich dem der dritten Subzelle und mit einer Bandabstandsenergie größer als die der zweiten Subzelle und der dritten Subzelle.
• 5. Die Multijunction-Solarzelle nach 1, wobei die zweite gradierte Zwischenschicht aufgebaut ist aus irgendeinem der folgenden Verbindungshalbleiter: As-P-N-Sb-basierende III–V-Verbindungshalbleiter, wobei dies unter Berücksichtigung der folgenden Einschränkungen geschieht: Der „in-plane”-Gitterparameter ist größer oder gleich dem der dritten Subzelle und kleiner oder gleich dem der unteren vierten Subzelle (Bodensubzelle) mit einer Bandabstandsenergie größer als der der dritten Subzelle und der der vierten Subzelle.
• 6. Die Multijunction-Solarzelle nach 1, wobei die ersten und zweiten gradierten Zwischenschichten aufgebaut sind aus (In_xGa_1-x)_yAl_1-yAs, wobei x und y derart ausgewählt sind, dass der Bandabstand jeder Zwischenschicht konstant über deren gesamte Dicke verbleibt.
• 7. Die Multijunction-Solarzelle nach 6, wobei der Bandabstand der ersten gradierten Zwischenschicht konstant bei 1,5 eV verbleibt.
• 8. Die Multijunction-Solarzelle nach 6, wobei der Bandabstand der zweiten gradierten Zwischenschicht konstant bei 1,1 eV verbleibt.
• 9. Die Multijunction-Solarzelle nach 1, wobei die obere Subzelle aus einer InGaP-Emitterschicht und einer InGaP-Basisschicht besteht, wobei die zweite Subzelle aufgebaut ist aus einer InGaP-Emitterschicht und einer GaAs-Basisschicht, wobei die dritte Subzelle aufgebaut ist aus einer InGaP-Emitterschicht und einer InGaAs-Basisschicht und wobei schließlich die am Boden befindliche untere vierte Subzelle aufgebaut ist aus einer InGaAs-Basisschicht und einer InGaAs-Emitterschicht, und zwar gitterangepasst mit der Basis.
• 10. Die Multijunction-Solarzelle nach 1, wobei die untere vierte Subzelle einen Bandabstand im Bereich von annähernd 0,6 bis 0,8 eV besitzt, wobei die dritte Subzelle einen Bandabstand im Gereicht von annähernd 0,9 bis 1,1 eV besitzt, wobei die zweite Subzelle einen Bandabstand im Bereich von annähernd 1,35 bis 1,45 eV besitzt und wobei die obere Subzelle einen Bandabstand im Bereich von 1,8 bis 2,1 eV besitzt.
• 11. Ein Verfahren zur Herstellung einer Solarzelle, wobei Folgendes vorgesehen ist: Vorsehen eines ersten Substrats; Ausbilden einer oberen ersten Solarsubzelle mit einem ersten Bandabstand auf dem ersten Substrat; Formen oder Bilden einer zweiten Solarsubzelle benachbart zu der ersten Solarsubzelle und mit einem zweiten Bandabstand, der kleiner ist als der erste Bandabstand; Formen oder Bilden einer ersten gradierten Zwischenschicht benachbart zu der zweiten Solarsubzelle; wobei die erste gradierte Zwischenschicht einen dritten Bandabstand besitzt, der größer ist als der zweite Bandabstand; Formen oder Ausbilden einer dritten Solarsubzelle benachbart zu der ersten gradierten Zwischenschicht, wobei die dritte Subzelle einen vierten Bandabstand besitzt, der kleiner ist als der zweite Bandabstand derart, dass die dritte Subzelle gitterfehlangepasst ist bezüglich der zweiten Subzelle; Ausbilden einer zweiten gradierten Zwischenschicht benachbart zu der dritten solaren Subzelle; wobei die zweite gradierte Zwischenschicht einen fünften Bandabstand aufweist, der größer ist als der erwähnte vierte Bandabstand; Formen oder Bilden einer unteren vierten Solarsubzelle benachbart zu der zweiten gradierten Zwischenschicht, wobei die untere Subzelle einen sechsten Bandabstand besitzt, der kleiner ist als der erwähnte vierte Bandabstand derart, dass die vierte Subzelle bezüglich der dritten Subzelle gitterfehlangepasst ist; Anbringen eines Surrogatsubstrats oben auf der vierten Subzelle; und Entfernen des ersten Substrats.
• 12. Verfahren nach 11, wobei die untere vierte Subzelle einen Bandabstand im Bereich von 0,6 bis 0,8 eV besitzt, die dritte Subzelle einen Bandabstand im Bereich von 0,9 bis 1,1 eV aufweist, die zweite Subzelle einen Bandabstand im Bereich von 1,35 bis 1,45 eV besitzt, und wobei schließlich die erste Subzelle einen Bandabstand im Bereich von 1,8 bis 2,1 eV besitzt.
• 13. Ein Verfahren nach 11, wobei das erste Substrat aufgebaut ist aus GaAs oder Ge und das Surrogatsubstrat aufgebaut ist aus Saphir, GaAs, Ge oder Si.
• 14. Verfahren nach 11, wobei die erste gradierte Zwischenschicht zusammensetzungsmäßig gradiert ist, um die zweite Subzelle auf einer Seite und die dritte Subzelle auf der anderen Seite Gitter anzupassen, und wobei die zweite gradierte Zwischenschicht zusammensetzungsmäßig gradiert ist, um die Gitteranpassung zur dritten Subzelle auf der einen Seite und zur vierten Bodensubzelle auf der anderen Seite vorzusehen.
• 15. Verfahren nach 11, wobei die erste gradierte Zwischenschicht aufgebaut ist aus irgendeinem der As-P-N-Sb-basierenden III–V-Verbindungshalbleiter, und zwar unter Berücksichtung der folgenden Einschränkung: dass ein „In-Ebene”-Gitterparameter vorliegt, der größer ist oder gleich ist dem der zweiten Subzelle und kleiner als oder gleich dem der dritten Subzelle und mit einer Bandabstandsenergie, die größer ist als die der zweiten Subzelle und der dritten Subzelle.
• 16. Verfahren nach 11, wobei die zweite gradierte Zwischenschicht aufgebaut ist aus irgendeinem der As-P-N-Sb-basierenden III–V-Verbindungshalbleiter mit den folgenden Einschränkungen: dass deren In-Ebene-Gitterparameter größer oder gleich dem der dritten Subzelle ist und kleiner als oder gleich dem der vierten oder Bodensubzelle und mit einer Bandabstandsenergie größer als der dritten Subzelle und der vierten Subzelle.
• 17. Verfahren nach 11, wobei die ersten und zweiten gradierten Zwischenschichten aufgebaut sind aus (In_xGa_1-x)_yAl_1-yAs, wobei x und y derart ausgebildet sind, dass der Bandabstand jeder Zwischenschicht über deren gesamte Dicke hinweg konstant verbleibt.
• 18. Verfahren nach 11, wobei der Bandabstand der ersten gradierten Zwischenschicht konstant bei 1,5 eV verbleibt und der Bandabstand der zweiten gradierten Zwischenschicht konstant bei 1,1 eV bleibt.
• 19. Verfahren nach 11, wobei die erste Subzelle aufgebaut ist aus einer InGaP-Mittelschicht und einer InGaP-Basisschicht, wobei die zweite Subzelle aufgebaut ist aus InGaP-Mittelschicht und einer GaS-Basisschicht, wobei schließlich die dritte Subzelle aufgebaut ist aus einer InGa-Mittelschicht und einer InGaAs-Basisschicht und wobei die vierte Bodensubzelle aufgebaut ist aus InGaS-Basisschicht und einer InGaS-Mittelschicht gitterangepasst an die Basisschicht.
• 20. Verfahren zur Herstellung einer Solarzelle, wobei Folgendes vorgesehen ist: Vorsehen einer ersten Substratschicht; Abschalten auf dem ersten Substrat einer ersten Sequenz von Schichten aus Halbleitermaterial, die erste und zweite Solarzellen bilden; Abschalten auf den ersten und zweiten Solarzellen einer ersten gradierten Zwischenschicht; Abschalten auf der ersten gradierten Zwischenschicht eine zweite Folge von Schichten von Halbleitermaterial einschließlich einer zweiten gradierten Zwischenschicht und dritten und vierten Solarzellen; Anbringen und Verbinden bzw. Verkleben eines Surrogatsubstrats oben auf der Sequenz von Schichten; und Entfernen des ersten Substrats.

Essential features of the invention are summarized as follows:

• A multi-junction solar cell comprising: an upper first solar subcell having a first band gap; a second solar subcell adjacent the first solar subcell having a second bandgap smaller than the first bandgap; a first graded interlayer adjacent the second solar subcell, the first graded interlayer having a third bandgap greater than the second bandgap; and a third solar subcell adjacent to the first graded interlayer, the third subcell having a fourth bandgap greater than the second bandgap such that the third subcell is lattice mismatched with respect to the second subcell; a second graded interlayer adjacent the third subcell, the second graded interlayer having a fifth bandgap greater than the fourth bandgap; and a lower fourth solar subcell adjacent to the second graded interlayer, the lower subcell having a sixth bandgap smaller than the fourth band portion such that the fourth subcell is grid misaligned with respect to the third subcell.
• 2. The multi-junction solar cell of claim 1, wherein the first graded interlayer is compositionally graded to provide lattice matching of the second subcell on one side and the third subcell on the other side.
• 3. The multi-junction solar cell of 1, wherein the second graded interlayer is compositionally graded to lattice match the third subcell on one side and the bottom fourth subcell on the other side.
• 4. The multijunction solar cell of Figure 1, wherein the first graded interlayer is composed of any of the following compound semiconductors: As-PN-Sb based III-V compound semiconductors, taking into account the limitations of an in-plane lattice parameter greater or equal to that of the second subcell and less than or equal to the third subcell and having a band gap energy greater than that of the second subcell and the third subcell.
• 5. The multijunction solar cell of 1, wherein the second graded interlayer is constructed of any of the following compound semiconductors: As-PN-Sb based III-V compound semiconductors, with the following limitations: the in-plane Grid parameter is greater than or equal to that of the third subcell and less than or equal to the lower fourth subcell (bottom subcell) having a bandgap energy greater than that of the third subcell and that of the fourth subcell.
• 6. The multijunction solar cell of 1, wherein the first and second graded interlayers are composed of (In _x Ga _{1-x) y} Al _1-y As, wherein x and y are selected such that the band gap of each interlayer constant over their entire thickness remains.
• 7. The multijunction solar cell of Figure 6, wherein the bandgap of the first graded interlayer remains constant at 1.5 eV.
• 8. The multijunction solar cell of Figure 6, wherein the bandgap of the second graded interlayer remains constant at 1.1 eV.
• 9. The multijunction solar cell of claim 1, wherein the upper subcell consists of an InGaP emitter layer and an InGaP base layer, wherein the second subcell is constructed of an InGaP emitter layer and a GaAs base layer, the third subcell being composed of a InGaP emitter layer and InGaAs base layer, and finally, the bottom bottom fourth sub-cell is composed of InGaAs base layer and InGaAs emitter layer, lattice-matched with the base.
• 10. The multijunction solar cell of 1, wherein the lower fourth subcell has a band gap in the range of approximately 0.6 to 0.8 eV, the third subcell having a band gap of approximately 0.9 to 1.1 eV, wherein the second subcell has a band gap in the range of approximately 1.35 to 1.45 eV, and wherein the upper subcell has a band gap in the range of 1.8 to 2.1 eV.
• 11. A method of manufacturing a solar cell, comprising: providing a first substrate; Forming an upper first solar subcell having a first band gap on the first substrate; Forming or forming a second solar subcell adjacent to the first solar subcell and having a second bandgap less than the first bandgap; Forming or forming a first graded intermediate layer adjacent to the second solar subcell; wherein the first graded interlayer has a third bandgap greater than the second bandgap; Forming or forming a third solar subcell adjacent the first graded interlayer, the third subcell having a fourth bandgap less than the second bandgap such that the third subcell is lattice mismatched with respect to the second subcell; Forming a second graded intermediate layer adjacent to the third solar subcell; wherein the second graded interlayer has a fifth bandgap greater than said fourth bandgap; Forming or forming a lower fourth solar subcell adjacent to the second graded interlayer, the lower subcell having a sixth bandgap less than said fourth bandgap such that the fourth subcell is lattice mismatched with respect to the third subcell; Attaching a surrogate substrate on top of the fourth subcell; and removing the first substrate.
• 12. The method of 11, wherein the lower fourth subcell has a band gap in the range of 0.6 to 0.8 eV, the third subcell has a band gap in the range of 0.9 to 1.1 eV, the second subcell has a band gap in the Range of 1.35 to 1.45 eV, and finally, the first subcell has a band gap in the range of 1.8 to 2.1 eV.
• 13. A method according to 11, wherein the first substrate is composed of GaAs or Ge and the surrogate substrate is composed of sapphire, GaAs, Ge or Si.
• 14. The method of claim 11, wherein the first graded interlayer is compositionally graded to match the second subcell on one side and the third subcell on the other side, and wherein the second graded interlayer is compositionally graded to match the lattice match to the third subcell one side and the fourth bottom subcell on the other side.
• 15. The method of 11, wherein the first graded interlayer is constructed of any of the As-PN-Sb based III-V compound semiconductors, with the following constraint: that an in-plane lattice parameter is larger is equal to or equal to that of the second subcell and less than or equal to that of the third subcell and having a band gap energy greater than that of the second subcell and the third subcell.
• 16. The method of 11, wherein the second graded interlayer is constructed of any of the As-PN-Sb based III-V compound semiconductors with the following constraints: their in-plane lattice parameter is greater than or equal to the third subcell and smaller as or equal to that of the fourth or bottom subcell and with a band gap energy greater than the third subcell and the fourth subcell.
• 17. The method according to 11, wherein the first and second graded interlayers are composed of (In _x Ga _{1-x) y} Al _1-y As, where x and y are formed such that the band gap of each interlayer constant over their entire thickness remains.
• 18. The method of 11, wherein the band gap of the first graded interlayer remains constant at 1.5 eV and the band gap of the second graded interlayer remains constant at 1.1 eV.
• 19. The method of claim 11, wherein the first subcell is made up of an InGaP middle layer and an InGaP base layer, wherein the second subcell is made up of InGaP middle layer and a GaS base layer, finally the third sub cell is made up of an InGaP Middle layer and an InGaAs base layer and wherein the fourth bottom subcell is constructed of InGaS base layer and an InGaS middle layer lattice-matched to the base layer.
• 20. A method of manufacturing a solar cell, comprising: providing a first substrate layer; Turning off on the first substrate a first sequence of layers of semiconductor material forming first and second solar cells; Switching off on the first and second solar cells of a first graded intermediate layer; Turning off on the first graded interlayer a second series of layers of semiconductor material including a second graded interlayer and third and fourth solar cells; Attaching and bonding a surrogate substrate on top of the sequence of layers; and removing the first substrate.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• MW Wanlass et al, Lattice Mismatched Approaches for High Performance, III-V Photovoltaic Energy Converters (Conference Proceedings of the 31st IEEE Photovoltaic Specialist Conference, Jan. 3-7, 2005, IEEE Press, 2005). [0023]
• Wanlass et al. [0080]

Claims (15)

A multi-junction solar cell, comprising: an upper first solar subcell having a first band gap; a second solar subcell adjacent the first solar subcell having a second bandgap smaller than the first bandgap; a first graded interlayer adjacent the second solar subcell, the first graded interlayer having a third bandgap greater than the second bandgap; and a third solar subcell adjacent to the first graded interlayer, the third subcell having a fourth bandgap greater than the second bandgap such that the third subcell is lattice mismatched with the second subcell; a second graded interlayer adjacent the third subcell, the second graded interlayer having a fifth bandgap greater than the fourth bandgap; and and a lower fourth solar subcell adjacent to the second graded interlayer, the lower subcell having a sixth bandgap less than the fourth band portion such that the fourth subcell is lattice misaligned with respect to the third subcell. The multi-junction solar cell of claim 1, wherein the first graded interlayer is compositionally graded to provide lattice matching of the second subcell on one side and the third subcell on the other side. The multi-junction solar cell of claim 1, wherein the second graded interlayer is compositionally graded to lattice match the third subcell on one side and the bottom fourth subcell on the other side. The multi-junction solar cell of claim 1, wherein the first graded interlayer is composed of any of the following compound semiconductors: As-PN-Sb based III-V compound semiconductors, taking into account the limitations of an in-plane grating parameter greater than or equal to equal to that of the second subcell and less than or equal to that of the third subcell and having a band gap energy greater than that of the second subcell and the third subcell. The multi-junction solar cell of claim 1, wherein the second graded interlayer is constructed of any of the following compound semiconductors: As-PN-Sb based III-V compound semiconductors, with the following limitations: the in-plane Lattice parameter is greater than or equal to the third subcell and less than or equal to the lower fourth subcell (bottom subcell) having a band gap energy greater than that of the third subcell and that of the fourth subcell. The multi-junction solar cell of claim 1, wherein the first and second graded interlayers are composed of (In _x Ga _1-x ) _y Al _1-y As, where x and y are given such that the bandgap of each interlayer is constant over its entire length Thickness remains. The multi-junction solar cell of claim 6, wherein the band gap of the first graded interlayer remains constant at 1.5 eV. The multi-junction solar cell of claim 6, wherein the bandgap of the second graded interlayer remains constant at 1.1 eV. The multi-junction solar cell according to claim 1, wherein the upper subcell consists of an InGaP emitter layer and an InGaP base layer, wherein the second subcell is constructed of an InGaP emitter layer and a GaAs base layer, the third subcell being constructed of InGaP Emitter layer and an InGaAs base layer, and finally, the bottom fourth lower subcell is made up of an InGaAs base layer and an InGaAs emitter layer, lattice-matched with the base. The multi-junction solar cell of claim 1, wherein the lower fourth subcell has a band gap in the range of approximately 0.6 to 0.8 eV, the third subcell having a band gap of approximately 0.9 to 1.1 eV, wherein the second subcell has a band gap in the range of approximately 1.35 to 1.45 eV, and wherein the upper subcell has a band gap in the range of 1.8 to 2.1 eV. A method of manufacturing a solar cell, comprising: providing a first substrate; Forming an upper first solar subcell having a first band gap on the first substrate; Forming or forming a second solar subcell adjacent to the first solar subcell and having a second bandgap less than the first bandgap; Forming or forming a first graded intermediate layer adjacent to the second solar subcell; wherein the first graded interlayer has a third bandgap greater than the second bandgap; Forming or forming a third solar subcell adjacent to the first graded interlayer, wherein the third subcell has a fourth bandgap smaller than the second Band gap such that the third subcell is lattice mismatched with respect to the second subcell; Forming a second graded intermediate layer adjacent to the third solar subcell; wherein the second graded interlayer has a fifth bandgap greater than said fourth bandgap; Forming or forming a lower fourth solar subcell adjacent to the second graded interlayer, the lower subcell having a sixth bandgap less than said fourth bandgap such that the fourth subcell is lattice mismatched with respect to the third subcell; Attaching a surrogate substrate on top of the fourth subcell; and removing the first substrate. The method of claim 11, wherein the lower fourth subcell has a band gap in the range of 0.6 to 0.8 eV, the third subcell has a band gap in the range of 0.9 to 1.1 eV, the second subcell has a band gap in the range of 1.35 to 1.45 eV, and finally, the first subcell has a band gap in the range of 1.8 to 2.1 eV. The method of claim 11, wherein the first graded interlayer is constructed of any one of the As-PN-Sb based III-V compound semiconductors, with the following constraint: that there is an in-plane lattice parameter that is larger or equal to that of the second subcell and less than or equal to that of the third subcell and having a band gap energy greater than that of the second subcell and the third subcell. The method of claim 11, wherein the second graded interlayer is constructed of any of the As-PN-Sb based III-V compound semiconductors with the following constraints: their in-plane lattice parameter is greater than or equal to the third subcell and less than or equal to that of the fourth or bottom subcell and having a band gap energy greater than the third subcell and the fourth subcell. The method of 11, wherein the first and second graded interlayers are composed of (In _x Ga _1-x ) _y Al _1-y As, where x and y are formed so that the band gap of each interlayer remains constant throughout its thickness.

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