DE102018203509A1 - Quadruple solar cell for room applications - Google Patents

Abstract

A multi-junction solar cell comprises: a growth substrate; a first solar subcell formed over or in the growth substrate; a graded interlayer deposited over the first solar subcell; and a series of layers of semiconductor material deposited over the graded interlayer, comprising a plurality of solar subcells including a second solar subcell arranged above and lattice matched with respect to the growth substrate and having a bandgap in the range of 0.9 to 1.8 eV and at least an upper solar subcell located above the second subcell and having an aluminum content above 30% in mole fraction and a bandgap in the range of 2.0 to 2.20 eV.

Description

Field of the invention

The present disclosure relates to solar cells and the fabrication of solar cells, and more particularly to the construction and specification of composition and bandgap of each of the four subcells in a quadruple solar cell based on III-V semiconductor interconnects to provide improved end-of-life Life "performance as may be predetermined for a predetermined space mission and the environment.

Description of related art

In this disclosure, the term "bandgap" of a solar subcell internally having different band gap layers is defined as the bandgap of the solar subcell layer in which the majority of the carriers are formed (such sublayer or sublayer is typically the one) p-type base semiconductor layer of the base / emitter-photovoltaic junction (junction) of such a subcell). In the case that such a layer in turn sublayers (sublaid) having different band gaps or band gaps (such as in the case of a base layer with a graded (location-dependent) composition and in particular a graded (location-dependent) band gap), the sublayer or the lower layer of these Solar cell with the lowest band gap should be provided to define the "band gap" of such a subcell. Apart from a solar subcell, more generally in a specially designed semiconductor region or zone (such as a metamorphic layer) in which the semiconductor region or sub-region has sub-layers or sub-regions with different band gaps (such as the case of a semiconductor zone) with a graded composition, and in particular a graded bandgap), the sublayer or subregion of this lower bandgap semiconductor region should be considered as defining the "band gap" of that semiconductor region.

In recent years, the high volume production of III-V compound semiconductor multi-junction solar cells has accelerated the development of such technology, compared to silicon solar cells, III-V compound semiconductors, multi-junction solar cells have greater energy conversion efficiencies and are generally more radiation resistant. although they tend to be more complex in order to be properly specified and manufactured. Typical, commercially available III-V compound semiconductors Multijunction solar cells have energy efficiencies exceeding 29.5% under "one sun", air mass 0 (AMO) illumination. The higher conversion efficiency (conversion efficiency) of the III-V compound semiconductor solar cells compared to silicon solar cells is based in part on the ability to spectrally split the incident radiation by using a plurality of series connected photovoltaic zones with different bandgap energies and summing the voltage at a given stream from each of the zones or regions.

In satellite or other space applications, the size, mass, and cost of the satellite power system are directly related to the power and energy conversion efficiency of the solar cells that are used. In other words, the size of the payload and the availability of on-board services are proportional to the amount of service provided. Because payload usage increases the amount of complexity associated with completing and shipments and applications for the next five, ten, twenty, or more years, the power-to-weight (W / kg) and power-to-area ( W / m ² ) ratios and the lifetime efficiency of a solar cell increasing more important. There is growing interest, not only performance per gram of weight and power area of the solar cell, and not only in the initial use, but also in the entire service life of the satellite system, or as a design description, with the amount of remaining power provided at the specified "end of the solar cell Life (EOL), which is affected by the exposure of the solar cell to radiation over time in the solar system's particular spatial environment, the period of the EOL being different for different missions and applications.

Typical III-V compound semiconductor solar cells are fabricated on a semiconductor wafer in vertical multijunction structures (multiple pn junction structures) or stacked on solar subcells, each subcell formed with appropriate semiconductor layers and having a pn photoactive junction. Each subcell or subcell is designed to convert photons into electrical current via different spectral or wavelength bands. After the collective light on the front the solar cell impinges and photons pass through the subcells, each subcell being constructed for photons in a wavelength band. After passing through a subcell, photons that are not absorbed and converted into electrical energy propagate to the next subcell where these photons are to be captured and converted into electrical energy.

The subcell that is closest to the incident sunlight is often referred to as the "top" or "top" subcell or, in some nomenclatures, the "first subcell" and has the largest band gap of all subcells, the Subcells below the first subcell are the "second", the "third", etc. subcells.

Another nomenclature for the identification of subcells is based on the context that the stacked sequence of solar subcells are grown epitaxially sequentially on a semiconductor substrate, one after the other. In this case, the first in or grown on the substrate may be referred to as the "first" subcell, and subsequent subcells sequentially grown, the "second," "third," and so on called subcell, with the last of these subcells in an upright arrangement "Uppermost" or "upper" subcell of the solar cell is called and has the largest band gap of all subcells.

A solar cell designed for use in a spacecraft (such as a satellite, space station, or interplanetary research vehicle) has a sequence of subcells with compositions and bandgap optimized to provide maximum energy conversion efficiency for the AMO solar cell specification in space.

The radiation hardness of a solar cell is defined as how well the cell works after exposure to electrons or proton particle radiation, which is a characteristic of the room environment. A standard metric is the ratio of the end of life performance (or efficiency) divided by the beginning of the life or life performance (EOL / BOL) of the solar cell. The EOL fluence of electrons or protons, which can be different for different space missions or orbits. BOL performance is the performance parameter before exposure to particle irradiation.

An important mechanical or structural consideration is the choice of semiconductor layers for a solar cell and is the desirability of the adjacent layers of semiconductor material in the solar cell, that is, each layer of the crystalline semiconductor material that is deposited and grown to form a solar subcell has similar or Substantially similar crystal lattice constants or parameters.

There are advantages over using special elements in the composition of a layer which results in the enhancement of the stress associated with such a subcell and therefore possibly a greater power output and the deviation from the exact crystal lattice match with adjacent layers as a consequence of the inclusion of such Elements in the layer, which may result in a higher probability of damage resulting in lower production yields.

In this context, it should be noted that there is no strict definition of what is understood as two adjacent layers that are "lattice-matched" or have "lattice mismatch". For the purposes of this disclosure, "lattice mismatch" refers to two adjacently located materials or layers (with thicknesses greater than 100 nm) that have an "in-plane" lattice constant (in the growth plane) of materials in their fully unloaded state each other by less than 0.02% in the lattice constant (Applicant notes that this definition is considerably more stringent than that in, for example, US Pat U.S. Patent No. 8,962,993 proposed that suggests less than 0.6% lattice constant difference as "lattice mismatched" layers).

For many years, conventional wisdom has assumed that a monolithic tandem solar cell "... would best achieve the desired optical transparency and current conductivity between the upper and lower cells ... by lattice matching the upper cell material to the lower cell material. Misalignments in lattice constants create defects or dislocations in the crystal lattice where recombination centers can occur to cause the loss of photogenerated minority carriers, thus significantly degrading the photovoltaic quality of the device. More specifically, such effects reduce the open circuit voltage (V _oc ), the short circuit current (J _sc ), and the fill factor (FF), which represents the relationship or balance between current and voltage for the effective output "(Jerry M. Olseon, U.S. Patent No. 4,667,059 , "Current and lattice Matched Tandem Solar Celle").

Nonetheless, following the progress in multi-efficiency and higher efficiency solar cells with four or more subcells, it should be noted that: "lattice-matched designs are desiderably because they have proven reliability and because they are use less semiconductor material than metamorphic solar cells, which require relatively large buffer layers to make differences in the lattice constants of the various materials "(Rebecca Elizabeth Jones - Albertus et al. U.S. Patent No. 8,962,993 ).

The present disclosure proposes design features for multi-function solar cells that deviate from the conventional wisdom in order to increase the efficiency of the multi-junction solar cell in converting solar energy (or photons) into electrical energy and optimizing this efficiency at the "end of" Life "period.

Summary of the Revelation

Goals of the revelation

It is an object of the present disclosure to provide increased photo-conversion efficiency in a multi-junction solar cell, for space applications over the life of a photovoltaic power system.

It is a further object of the present disclosure to provide a multi-junction solar cell in which the composition of the sub-cells and their bandgaps are configured to optimize the efficiency of the solar cell under operating conditions of a predetermined high temperature (especially in the range of 40 to 70 ° C) when used in space at AMO a sun solar spectrum in a predetermined time (EOL) after the initial use such that time is at least one, five, ten, fifteen or twenty years and not maximized to the time of initial deployment (BOL).

It is another object of the present invention to provide a four-junction solar cell with four pn junctions (solar cell m) in which the average band gap divides every four cells, that is, the sum of the four-band distances of each subcell four is greater than 1.35 eV.

It is a further object of the present invention to provide a four junction solar cell in which the lower two sub-cells are lattice mismatched and in which the current through the bottom subcell is intentionally designed to be substantially larger than the current through the top three sub-cells measured at the " Beginning of life "or time of initial deployment.

Some implementations of the present disclosure may be incorporated or implemented with fewer aspects and features mentioned in the foregoing objects.

Features of the invention

All ranges of numerical parameters, as referred to in this disclosure, should be understood to include any and all subregions or "intervening generalizations". For example, a range of 1.0 to 2.0 eV for a band gap value should be understood to include any and all subregions starting with a minimum value of 1.0 eV or more and ending with a maximum value of 2.0 eV or less, for example 1.0 to 1.2 or 1.3 to 1.4 or 1.5 to 1.9 eV.

Briefly and in general, the present disclosure provides a multi-junction or multi-junction solar cell comprising: a growth substrate, a first solar subcell ( D ) formed over or in the growth substrate; a grading interlayer deposited over the first solar subcell; and a sequence of semiconductor material layers deposited over the grading interface comprising a plurality of solar subcells and including a second solar subcell ( C ) are arranged above and in lattice misalignment with respect to the growth substrate and with a band gap in the range of 0.9 to 1.8 eV, and with at least one upper solar subcell ( A ) disposed above the second subcell and having an aluminum content greater than 30% in mole fraction (mole fraction) and a Band gap in the range of 2.0 to 2.20 eV; wherein the graded interlayer is compositionally graded to conform to the growth substrate on one side and the second solar cell on the other side, constructed of any of the As, P, N, Sb based III- V compound semiconductors are subject to the constraints that the planar lattice parameter is greater than or equal to the growth substrate throughout its thickness; whenever the combination of the compositions and bandgaps of the solar cells is designed to maximize the efficiency of the solar cell at a predetermined time after the initial use when the solar cell is used in space at AMO and 1 MeV electron equivalent 5x10 ¹⁴ e / cm and at operating temperatures in the range of 40 to 70 ° C, wherein the predetermined time is at least five years and is referred to as End of Life (EOL).

It should be noted that in such a sequencing of the solar subcells, the inclusion requires at least three subcells, with the result that the multi-junction solar cell or multi-junction solar cell could be a triple, a quadruple, a five-fold (or multiple) multi-junction solar cell, ie a solar cell with 3, 4, 5 or more pn junctions.

In another aspect (and using terminology other than the terminology used in a previous paragraph to define and sequence the "first,""second,""third," and "fourth" sub-cells A or. B or. C or. D ), the present disclosure provides a four-junction solar cell comprising an upper first solar cell ( A ) constructed of a semiconductor material having a first band gap; a second solar subcell ( B ) adjacent to said first solar subcell and constructed of a second band gap semiconductor material and lattice matched with said upper first solar subcell; a third solar subcell ( C ) adjacent to said second solar subcell and constructed of a semiconductor material having a third bandgap smaller than said second bandgap and lattice matched with said second solar subcell; and a fourth solar subcell or bottom solar cell ( D ) adjacent to the third solar subcell and constructed of a semiconductor material having a fourth bandgap smaller than the third bandgap; wherein the average band gap of all four subcells (that is, the sum of the four band gaps of each subcell divided by four) is greater than 1.35 eV.

In another aspect, the present disclosure provides a space-qualified quadruple solar cell designed for operation at AMO and at 1 MeV electron equivalent fluence of at least 1 × 10 ¹⁴ e / cm ² , the solar cell having sub-cells, wherein a combination of the compositions and band gaps the subcell is designed to maximize the efficiency of the solar cell for a predetermined time after initial use when the solar cell is used in the room at operating temperatures in the range of 40 to 70 ° C, the predetermined time is at least five years and is referred to as the end of life (EOL). In particular, the solar cell has the following: an upper first solar subcell ( A ) composed of indium gallium aluminum phosphide and having a first band gap (bandgap, bandgap) in the range of 2.0 to 2.2 eV; a second solar subcell ( B ) adjacent to said first solar subcell and having an emitter layer composed of indium gallium phosphide or aluminum indium gallium arsenide, wherein a base layer made of aluminum indium gallium arsenide is provided and has a second band gap in the range of approximately 1.55 to 1.8 eV lattice-matched with the upper first solar subcell, wherein the emitter and base layers of the second solar subcell form a photoelectric junction; a third solar subcell ( C ) adjacent to said second solar subcell and constructed of indium gallium arsenide and having a third band gap smaller than said second solar subcell and lattice matched with said second solar subcell; and a fourth or bottom solar cell ( D ) adjacent to said third solar subcell and constructed of germanium and having a fourth bandgap of approximately 0.67 eV, the average bandgap of the solar cell (ie, the average or numerical sum of the bandgaps of each of the four subcells divided by four) being equal to or greater than 1.35 eV.

In some embodiments, the fourth subcell is germanium.

In some embodiments, the second subcell has a band gap of approximately 1.73 eV, and the upper first subcell has a band gap of approximately 2.10 eV.

In some embodiments, the upper first solar subcell has a band gap of approximately 2.05 to 2.10 eV, the second solar subcell has a band gap in the range of 1.55 to 1.73 eV; and the third solar subcell has a band gap in the range of 1.15 to 1.41 eV.

In some embodiments, the upper first solar subcell has a band gap of approximately 2.10 and the second solar subcell has a band gap of approximately 1.73 eV; and the third solar subcell has a bandgap in the range of 1.41 eV.

In some embodiments, the upper first solar subcell has a band gap of approximately 2.10, the second solar subcell has a band gap of approximately 1.65 eV; and the third solar subcell has a bandgap of 1.3 eV.

In some embodiments, the upper first solar subcell has a band gap of approximately 2.05, the second solar subcell has a band gap of approximately 1.55 eV; and the third solar subcell has a bandgap of 1.2 eV.

In some embodiments, the first solar subcell has a band gap of 2.05 eV.

In some embodiments, the band gap of the third solar subcell is less than 1.41 eV, and larger than that of the fourth subcell.

In some embodiments, the third solar subcell has a band gap in the range of 1.15 to 1.35 eV.

In some embodiments, the third solar subcell has a band gap in the range of 1.1 to 1.2 eV.

In some embodiments, the third solar subcell has a band gap of approximately 1.2 eV.

In some embodiments, the upper first subcell is constructed of indium gallium aluminum phosphide; the second solar subcell comprises an emitter layer composed of indium gallium phosphide or aluminum indium gallium arsenide, and a base layer is composed of aluminum indium gallium arsenide; the third solar subcell is composed of indium gallium arsenide; and the fourth subcell is constructed of germanium.

In some embodiments, a distributed Bragg reflector (DBR) layer is further provided adjacent to and between the third and fourth solar cell or bottom solar cell and further arranged so that light may enter and pass through the third solar cell and at least a portion thereof are reflected back into the third solar subcell through the DBR layer.

In some embodiments, the DBR layer is constructed of a plurality of alternating layers of lattice-matched materials with discontinuities in their respective refractive indices.

In some embodiments, the differences in refractive indices between alternate layers of the DBR layer are maximized to reduce the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines the stopband and its clipping wavelength.

In some embodiments, the DBR layer comprises a first DBR layer composed of a plurality of p-type In _z Al _x Ga _{1 -xz} As sublayers, and a second DBR layer is disposed over the first DBR layer and has a composition of a plurality of p-type In _w Al _y Ga _{1 -yx} As sublayers, where 0 <x <1, 0 <y <1, 1 <z <0 and y is greater than x, such that the first and second DBR Layers are compositionally different, whereby the reflection bandwidth of the DBR layer is increased.

In some embodiments, the selection of the composition of the sub-cells and their bandwidths maximizes the high temperature efficiency (in the range of 40 to 70 ° C) when applied in space at a predetermined time after the initial use (referred to as the beginning of Life or (BOL), this predetermined time being called end-of-life (EOL) and being at least five years.

In some embodiments, the top or top first subcell is constructed of a base layer of (In _x Ga ₁ -x) _1-y Al _y P, where x 0.505 and y is 0.142, corresponding to a band gap of 2.10 eV and an emitter layer of (In _x Ga _1-x ) - _y Al _y P, where x is 0.505 and y is 0.107, corresponding to a band gap of 2.05 eV.

In some embodiments, an intermediate layer (or "grading interlayer") is further disposed between the third subcell and the fourth or bottom solar cell, the interlayer being compositionally graded to match the third solar subcell on one side and the fourth or bottom solar cell on the other side and constructed from any one of the following: As, P, N, Sb based on III-V compound semiconductors, according to the constraints of having the in-plane lattice parameter greater than or equal to that of the fourth or bottom solar cell, and bandgap energy larger than that of the fourth solar subcell.

In some embodiments, the graded interlayer is compositionally graded with between one and four stages to lattice fit the third solar cell on one side and the fourth or bottom solar cell on the other side, constructed of In _x Ga _1-x As or (In _x Ga _1-x ) _y Al _1-y As where 0 <x <1, 0 <y <1 and where x and y are selected such that the band gap is in the range of 1.15 to 1.41 eV through its entire thickness.

In some embodiments, the graded interlayer has a constant band gap in the range of 1.15 to 1.41 eV or 1.2 to 1.35 eV or 1.25 to 1.30 eV.

In some embodiments, either (i) have the emitter layer; or (ii) the base layer and emitter layer of the upper first solar subcell have a different lattice constant to the lattice constant of the second solar subcell.

In some embodiments, each subcell has an emitter region and a base region, and further one or more of the top or top subcells have a doping doping base region that is exponentially adjacent to 1 x 10 ¹⁵ atoms per cubic centimeter to pn junction to 4 × 10 ¹⁸ atoms per cubic centimeter adjacent to the adjacent layer at the back of the base zone and an emitter zone having a doping grading immediately adjacent to approximately 5 × 10 ¹⁸ atoms / cubic centimeter in the emitter zone of the adjacent subcell layer extends to 5 × 10 ¹⁸ atoms per cubic centimeter in the emitter zone adjacent to the pn junction.

In some embodiments, at least one of the upper sub-layers of the grading interlayer has a larger lattice constant than the adjacent layers of the semiconductor body with respect to the upper sub-layer of the grading interlayer disposed above the grading interlayer.

In some embodiments, the difference in lattice constants between the adjacent third and fourth or bottom subcells is in the range of 0.1 to 0.2 angstroms.

In some embodiments, a first threading dislocation prevention layer is further provided. provided with a thickness in the range of 0.10 to 1.0 microns and disposed over the fourth or bottom solar cell and below the grading intermediate layer.

In some embodiments, a second threading dislocation prevention layer is further provided having a thickness in the range of 0.10 to 1.0 micron and constructed of InGa (Al) P, wherein the second threading dislocation prevention layer or layer is provided A yarn displacement barrier layer is disposed above and directly adjacent to said grading intermediate layer to reduce the propagation of threading dislocations, wherein said second threading dislocation preventing layer has a composition comprising It is different from a composition of the first threading dislocation prevention layer and different from the adjacent grading intermediate layer.

According to another aspect of the present disclosure, there is provided a method of manufacturing a four-junction solar cell, wherein a germanium substrate forming a first subcell is provided; Growing on the germanium substrate a series of layers of semiconductor material using a semiconductor deposition process to form a solar cell having a plurality of subcells, including a second subcell disposed over the germanium substrate and lattice mismatched thereto and having a bandgap of 1.41 eV or less , a third Subcell located above the second subcell and with a band gap in the range of approximately 1.55 to 1.8 eV and an upper subcell located above the third subcell and with a band gap in the range of 2.0 to 2.15 eV.

In some embodiments, additional layer (s) in the cell structure may be added or omitted without departing from the scope of the invention.

In some implementations of the present disclosure, fewer of the mentioned aspects and features mentioned in the above abstracts may be incorporated or implemented.

list of figures

• 1 ist eine graphische Darstellung des BOL-Wertes des Parameters E_g/q-V_OC bei 28 °C aufgetragen gegenüber dem Bandabstand von bestimmten binären Materialien definiert entlang der x-Achse.
• 2 ist eine Querschnittsansicht der Solarzelle eines ersten Ausführungsbeispiels einer Vierfach-Solarzelle nach mehreren Herstellungsstufen einschließlich der Abscheidung bestimmter Halbleiterschichten auf dem Wachstumssubstrat bis zu der Kontaktschicht, und zwar gemäß der vorliegenden Offenbarung;
• 3 ist eine graphische Darstellung des Dotierprofils in den Basis- und Emitterschichten einer Subzelle in der Solarzelle gemäß der Offenbarung der vorliegenden Erfindung.
• 4A ist eine Querschnittsansicht eines zweiten Ausführungsbeispiels einer Vierfach-Solarzelle nach mehreren Herstellungsstufen einschließlich des Wachstums bestimmter Halbleiterschichten auf dem Wachstumssubstrat bis zur Kontaktschicht, und zwar gemäß der vorliegenden Offenbarung;
• 4B ist eine Querschnittsansicht eines dritten Ausführungsbeispiels einer Vierfach-Solarzelle nach mehreren Herstellungsstufen einschließlich des Wachstums bestimmter Halbleiterschichten auf dem Wachstumssubstrat bis zu der Kontaktschicht, und zwar gemäß der vorliegenden Offenbarung;
• 5 ist eine Querschnittsansicht eines vierten Ausführungsbeispiels einer Vierfach-Solarzelle nach mehreren Herstellungsstufen einschließlich der Stufen des Wachstums bestimmter Halbleiterschichten auf dem Wachstumssubstrat bis zu der Kontaktschicht, und zwar ausgeführt gemäß der vorliegenden Offenbarung;
• 6 ist eine Querschnittsansicht der Solarzelle der vorliegenden Offenbarung implementiert in einer CIC und angebracht auf einer Paneele oder Platte.
• 7 ist eine graphische Darstellung des Bandabstandes bestimmter binärer Materialien und ihrer Gitterkonstanten; und
• 8 ist eine Vergrößerung eines Teils der graphischen Darstellung der 7 und veranschaulicht unterschiedliche Verbindungen von GalnAs und GalnP mit unterschiedlichen Proportionen von Gallium und Indium und dem Ort der speziellen Verbindungen der graphischen Darstellung.

The invention can be better and more fully understood by referring to the following detailed description when considered in conjunction with the drawing.

• 1 is a plot of the BOL value of the parameter E _g / qV _OC plotted against 28 ° C versus the bandgap of certain binary materials defined along the x -Axis.
• 2 FIG. 12 is a cross-sectional view of the solar cell of a first embodiment of a quadruple solar cell after a plurality of fabrication steps including deposition of certain semiconductor layers on the growth substrate to the contact layer, in accordance with the present disclosure; FIG.
• 3 Figure 3 is a graphical representation of the doping profile in the base and emitter layers of a subcell in the solar cell according to the disclosure of the present invention.
• 4A FIG. 12 is a cross-sectional view of a second embodiment of a quadruple solar cell after several stages of fabrication, including growth of certain semiconductor layers on the growth substrate to the contact layer, in accordance with the present disclosure; FIG.
• 4B FIG. 10 is a cross-sectional view of a third embodiment of a quadruple solar cell after multiple stages of fabrication, including growth of certain semiconductor layers on the growth substrate to the contact layer, in accordance with the present disclosure; FIG.
• 5 Fig. 12 is a cross-sectional view of a fourth embodiment of a quadruple solar cell after several stages of manufacture, including the steps of growing certain semiconductor layers on the growth substrate to the contact layer, carried out in accordance with the present disclosure;
• 6 FIG. 12 is a cross-sectional view of the solar cell of the present disclosure implemented in a CIC and mounted on a panel. FIG.
• 7 is a graphical representation of the bandgap of certain binary materials and their lattice constants; and
• 8th is an enlargement of part of the graphical representation of 7 and illustrates different compounds of GalnAs and GalnP with different proportions of gallium and indium and the location of the specific compounds of the graph.

Description of the Preferred Embodiment

A variety of different features of the multiple solar cells are disclosed in related applications of the user. Some, many, or all such features may be employed in the structures and methods associated with "upright" metamorphic multijunction solar cells of the present disclosure. In particular, however, the present disclosure is directed to the fabrication of a multiple solar cell grown on a single growth substrate comprising, in one embodiment, the two lower sub-cells, that is, the fourth and third sub-cells are lattice mismatched. More specifically, in some embodiments, the present disclosure relates to quadruple direct bandgap solar cells in the range of 2.0 to 2.15 eV (or higher) for the top last subcell, and (i) 1.65 to 1 , 8 eV and (ii) 1.41 eV or less for the second and third subcell, respectively, and 0.6 to 0.8 eV indirect band gap for the fourth bottom subcell.

The present disclosure provides a non-conventional quadruple or four-junction construction (with three lattice growth-matched sub-cells that are lattice mismatched with the fourth or bottom subcell or the Ge substrate) resulting in surprisingly significant enhancement performance, and although compared to the traditional triple solar cell, despite the substantial current mismatch existing between the top three junctions and the bottom-ge junction, that is, the four sub-cells. This performance gain is especially realized at high temperature and high exposure to space radiation by suggesting the use of high bandgap semiconductors which are inherently more resistant to radiation and temperature, in particular the problem of ensuring continued adequate efficiency and power output during the process entire mission and especially at the end of life.

Another way of characterizing the present disclosure is that in some embodiments of a quadruple solar cell, the average bandgap of all four subcells (that is, the sum of the four bandgaps of each subcell divided by four) is greater than 1.35 eV.

In some embodiments, the fourth subcell is germanium, whereas in other embodiments the fourth subcell is InGaAs, GaAsSb, InAsP, InAlAs or SiGeSn, InGaAsN, InGaAsNSb, InGaAsNBi, InGaAsNSbBi, InGaSbN, InGaBiN, InGaSbBiN, or other III-V or II-VI. Compound semiconductor material is.

Another descriptive aspect of the present disclosure is to characterize the fourth bottom subcell as having a direct band gap greater than 0.75 eV.

The indirect bandgap of germanium at room temperature is about 0.66 eV, with the direct band gap of germanium at room temperature being 0.8 eV. The experts usually refer to the "bandgap" of germanium as 0.67 eV, since this is lower than the direct band gap value of 0.8 eV.

The mention that "the fourth or bottom subcell has a direct bandgap greater than 0.75 eV", therefore, explicitly means to include germanium as a potential semiconductor for the fourth or bottom subcell, although other semiconductor material may also be used.

More particularly, the present disclosure intends to provide a relatively simple and reproducible teaching that uses non-inverted processing associated with the production of inverted metamorphic multijunction solar cells, and is suitable for use in the high volume production environment the various semiconductor layers are grown on a growth substrate in a MOCVD reactor and subsequently the processing steps are defined and selected to minimize any physical damage to the quality of the deposited layers, thereby achieving a relatively high yield of operable solar cells and the specifications will be reached at the end of the manufacturing process.

As suggested above, incremental improvements in the design of the multiple solar cells are made in view of the requirement of diversity of new space missions and application requirements. In addition, although such improvements may be relatively small quantitative modifications in the composition or bandgap of particular subcells, such small parametric changes (such as 0.1 to 0.5 eV in the bandgap specification of the upper first subcell or third subcell ) provide substantial improvements in efficiency that specifically addresses the "problems" identified in association with existing commercial multi-junction solar cells, and provides a "solution" that provides an "inventive step" in the art Represents the construction process.

One aspect of the present disclosure relates to the use of aluminum in the upper subcell active layers in a multiple solar cell. The effects of increasing the amounts of aluminum as a constituent element in an active layer of a subcell affect photovoltaic device performance. A measure of the "quality" or "goodness" of a solar cell junction is the difference between the band gap of the semiconductor material in that subcell or junction and the V _oc or open circuit voltage of the same junction. The smaller the difference, the higher the V _{oc of} the solar cell junction relative to the band gap, and the better the performance of the device. V _oc is very sensitive to the semiconductor material quality, so that the smaller E _g / q - V _{oc of} a device, the higher the quality of the material in the device. There is a theoretical limit to this difference, known as the Shockley-Queisser boundary. This is the best that can be provided for a solar cell junction under a given concentration of light and a given temperature.

The experimental data obtained for single-junction (AI) GalnP solar cells indicate that increasing the Al content of this "junction" (corresponding to the top or top subcell) results in a larger V _oc - E _g / q difference , which indicates that the material quality of the "junction" decreases with increasing Al content. 1 shows this effect. The three compositions mentioned in the figure are all lattice-matched to the GaAs, but have a different Al composition. The addition of AI increases the band gap of the junctions, but increases V _oc - E _g / q. Thus, we conclude that the addition of Al to the semiconductor material degrades the material such that a solar cell device made of this material does not work as well as a junction with less Al.

As for the multi-junction solar cell device of the present disclosure, it shows 2 a cross-sectional view of a first embodiment of a quadruple solar cell 200 after several stages of manufacture, including the growth of certain semiconductor layers on the growth substrate up to the contact layer 322 according to the present disclosure.

As in the illustrative example of 2 shows the fourth or bottom subcell D a growth substrate 300 formed of p-type germanium ("Ge"), which also serves as a base layer. A metal back contact element 350 shaped at the bottom of the base layer 300 sees an electrical contact to the multi-junction solar cell 200 in front. The soil subcell D further includes, for example, a highly doped n-type Ge emitter layer 301 on, and an n-type indium gallium arsenide ("InGaAs") nucleation layer 302 , The nucleation layer is deposited over the base layer and the emitter layer is formed in the substrate by the fusion of dopants into the Ge substrate, thereby forming the n-type Ge layer 301 is formed. Highly doped p-type aluminum indium gallium arsenide ("AIGaAs") and heavily doped n-type gallium arsenide ("GaAs") tunnel junction layers 300 . 303 may be deposited over the nucleation layer to provide a low resistance path between the bottom fourth subcell and the third subcell.

In some embodiments, distributed Bragg reflector (DBR) layers are 305 adjacent to and between the tunnel diode 303 . 304 the, fourth or bottom subcell D and the third solar subcell C grew up. The DBR layers 305 are arranged so that light enters and through the third Solarsubzelle or subcell C and at least part of it back into the third solar subcell C can be reflected, through the DBR layers 305 , In the embodiment shown in FIG 2 are the distributed Bragg reflector (DBR) layers 305 especially between the third solar cell C and the tunnel diode layers 304 . 303 arranged; In other embodiments, the distributed Bragg reflector (DBR) layers are disposed between tunnel diode layers 304 . 303 and buffer layer 302 ,

For some embodiments, the distributed Bragg reflector (DBR) layers 305 be constructed from a variety of alternating layers 305a to 305z lattice-matched materials with discontinuities in their respective refractive indices. For certain embodiments, the difference in the calculation indexes between alternating layers is maximized to reduce the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines the stopband and its limiting wavelength.

For some embodiments, the distributed Bragg reflector (DBR) layers include 305a to 305z a first DBR layer composed of a plurality of p-type In _z / Al _x Ga _{1 -xz} As layers and a second DBR layer disposed over the first DBR layer and constructed of a plurality of p-type In _w / Al _y Ga _1-yw As layers with w between 0 and 1, x between 0 and 1, y between 0 and 1 and z between 0 and 1 and where y is greater than x.

Although the present disclosure is the DBR layer 305 arranged between the third and fourth subcell, in some embodiments, the DBR layers may be disposed between the first and second subcell and / or between the second and third subcell, and / or between the third and fourth subcell.

In the example shown the 2 indicates the third subcell C a highly doped p-type aluminum indium gallium arsenide ("AlInGaAs") back surface field ("BSF") layer 306 , a p-type InGaAs base layer 307 and higher doped n-type indium gallium arsenide ("InGaAs") emitter layer 308 and a heavily doped n-type indium aluminum phosphide ("AllnP ₂ ") or indium gallium phosphide ("GalnP") window layer 309 on. The InGaAs base layer 307 the subcell C For example, it can contain approximately 1.5% In. Other Compositions or compositions may also be used. The base layer 307 is above the BSR layer 306 Shaped after the BSF layer over the DBR layers 305 is deposited.

The window layer 309 is on the emitter layer 308 the third subcell C deposited. The window layer 309 in the third subcell C also helps reduce recombination losses and improves the passivation of the cell surface of the underlying junctions. Before the deposition of the layers of the subcell B can heavily doped n-type InGaP and p-type AlGaAs (or other suitable comopositions) tunnel junctions 310 . 311 over the subcell C be deposited.

The second subcell B has a highly doped p-type aluminum indium gallium arsenide ("AlInGaAs") back surface field ("BSF") layer 312 , a p-type AlInGaAs base layer 313 , a highly doped n-type indium gallium phosphide ("InGaP ₂ ") or AlInGaAs layer 314 and also a highly doped n-type indium gallium aluminum phosphide ("AIGaAIP") window layer 315 on. The emitter layer 314 For example, the second subcell B may include approximately 50% In. Other compositions may also be used.

Before the deposition of the layers of the upper first subcell A can heavily doped n-type InGaP and p-type AlGaAs tunnel junction layers 316 . 317 are deposited over the second subcell B.

In the illustrated example, the upper or uppermost first subcell A a highly doped p-type indium aluminum phosphide ("InAlP ₂ ") BSF layer 318 , a p-type InGaAlP base layer 319 , a highly doped n-type InGaAlP emitter layer 320 and a heavily doped n-type InAlP ₂ window layer 321 on. The base layer 319 the first subcell A is above the BSF layer 318 after the BSF layer 318 Shaped, isolated.

After the cap or contact layer 322 is deposited, the grid lines are formed via evaporation and lithographic patterning and deposition over the cap or contact layer 23 ,

In some embodiments, at least one of the first, second, or third solar subcells has graded doping, that is, the level of doping changes from one surface to the other through the thickness of the base layer. In some embodiments, grading during doping is exponential. In some embodiments, grading or grading during doping is incremental and monotonic.

In some embodiments, the emitter of at least one of the second, third or fourth solar subcells ( C or. D or. A ) also a graded doping, that is, the level of doping varies from one surface to the other through the thickness of the emitter layer. In some embodiments, gradation during doping is linearly or monotonically decreasing.

As a specific example, the doping profile of the emitters and base layers in FIG 3 to illustrate where the amount of doping is shown in the emitter zone and the base zone of the subcell. N-type dopants include silicon, selenium, sulfur, germanium or tin. P-type dopants include silicon, zinc, chromium or germanium.

In the example of 3 have one or more subcells ( C . B or A ) has a base region with a doping grading that increases and a value in the range of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ free carriers per cubic centimeter adjacent to the pn junction to a value in the range of 1 × 10 ¹⁶ to 4 × 10 ¹⁸ free carrier per cubic centimeter adjacent to the adjacent layer at the rear end of the base, and an emitter zone has a gradation in doping ranging from a value in the range of approximately 5 x 10 ¹⁸ to 1 x 10 ¹⁷ free carriers per cubic centimeter in the zone immediately adjacent to the adjacent layer decreases to a value in the range of 5 x 10 ¹⁵ to 1 x 10 ¹⁸ free carriers per cubic centimeter in the zone adjacent to the pn junction.

The strong lines 612 and 613 shown in 3 illustrate an embodiment of the base doping with an exponential gradation and the emitter doping is linear.

Thus, the doping level through the thickness of the base layer can be exponentially graded from the range of 1 × 10 ¹⁶ free carriers per cubic centimeter to 1 × 10 ¹⁸ free carriers per cubic centimeter as indicated by the curve 613 shown in the figure.

Similarly, the doping level through the thickness of the emitter layer may decrease linearly from 5 × 10 ¹⁸ free carriers per cubic centimeter to 5 × 10 ¹⁷ free carriers per cubic centimeter as indicated by the curve 612 is shown in the figure.

The absolute value of the collecting or collecting field generated by an exponential doping gradient exp [-x / λ] is given by the constant electric field of size E = kT / q (1 / λ)) (exp [-xb / λ], where k is the Boltzman constant, T is the absolute temperature in degrees Kelvin, q is the absolute value of the electron change and A a parameter characteristic of the Dotierabnahme is.

The efficiency of one embodiment of the doping device of the present invention was demonstrated in a test solar cell having an exponential doping profile in the three micron thick base layer of a subcell according to an embodiment.

The exponential doping profile taught by one embodiment of the present disclosure creates a constant field in the doped zone or region. In the particular multi-junction solar cell materials and structure of the present disclosure, the bottom subcell has the smallest circuit short among all the subcells. Since the individual subcells are stacked in a multi-junction solar cell and form a series connection, the total current flow in the entire solar cell is therefore limited by the smallest current produced in any of the subcells. By increasing the short circuit current in the bottom cell, the current approaches closer to that of the higher solar cells and the overall efficiency of the solar cell is also increased. In a multi-junction solar cell with approximate efficiency, implementation of the present doping arrangement would thereby increase efficiency. In addition to increasing efficiency, the collection field created by the exponential doping profile would increase the solar cell's radiation hardness, which is important for space applications.

Although the exponential doping profile is the doping design that has been implemented and verified, other doping profiles may provide an increase to a linearly variable collection field, which offers other advantages as well. For example, another doping profile may create a linear field in the doping zone which would be beneficial for both the minority carrier collection and end-of-life (EOL) life of the solar cell. Such other doping profiles included in one or more base layers are within the scope of the present disclosure.

The doping profiles shown here are for illustration only and other more complex profiles may be used as will be apparent to one skilled in the art without departing from the scope of the present invention.

4A FIG. 12 is a cross-sectional view of a second embodiment of a four-junction or quadruple solar cell. FIG 400 after several stages of manufacture including growth of certain semiconductor layers on the growth substrate to contact layer 322 wherein various subcells are similar to the structure described and shown in FIG 2 , In the interest of brevity, here is the description of the layers 350 . 300 to 304 and 306 to 322 not repeated.

In the embodiment shown in FIG 4A becomes an "intermediate" graded intermediate layer 505 in one embodiment, step-graded sublayers 505a to 505Z over the tunnel diode layer 304 deposited. In particular, the graded interlayer provides a transition in the lattice constant from the lattice constant of the substrate to the larger lattice constant of the second, third, and fourth subcells.

A first "alpha" or threading dislocation barrier 504 or (thread dislocation barrier layer) 504 , preferably composed of p-type InGaP, is placed over the tunnel diode 303 / 304 deposited to a thickness of 0.10 to about 1.0 micron. Such an alpha layer is provided to prevent threaded dislocations from propagating, either opposite to the direction of growth in the subcell D or in the direction of growth in the second subcell C as more fully described in US patent application publication no. 2009/0078309 A1 (Cornfeld and others). More generally, the alpha layer has a composition different from that of the additional layer above and below it. As in 4A shown, the left-hand stepped line, which provides gradual grading of the "in-plane" lattice constants, because of the incremental size of the sublayer or sublayer 505a to the sub or sublayer 505Z is, these sublayers are completely unclaimed.

A metamorphic layer (or graded interlayer) 505 is over the alpha layer 504 deposited, using a Sufaktants. The layer 505 is preferably a compositionally graded series of p-type InGaAs or InGaAlAs layers, preferably with monotonically varying lattice constants, to provide a graded transition in lattice constant in the semiconductor structure of the fourth subcell D to the third subcell C while these thread dislocations are minimized. In another embodiment, the band gap of the layer 505 constant throughout the thickness of the layer, preferably approximately equal to 1.22 to 1.34 eV, or otherwise consistent with a value slightly greater than the bandgap of the third subcell C , In a further embodiment, the band gap of the sub-layer of the layer varies 505 in the range of 1.22 to 1.34 eV, with the first layer having a relatively high band gap and subsequent layers having incrementally lower band gaps. An embodiment of the graded interlayer may also be expressed as constructed of In _x Ga _1-x As, where x between 0 and 1, y between 0 and 1 and x and y are selected such that the bandgap of the intermediate layer remains constant at approximately 1.22 to 1.34 eV or other suitable bandgap.

In one embodiment, aluminum is added to a sub-layer to make one particular sub-layer harder than another, thereby forcing dislocations into the softer material.

In the surfactant-supported growth of the metamorphic intermediate graded layer 505 a suitable chemical element is introduced into the reactant during the growth of the layer 505 to improve the surface characteristics of the layer. In the preferred embodiment, such element may be a dopant or donor atom such as selenium (Se) or tellurium (Te). Small amounts of Se or Te are therefore in the metamorphic layer 406 incorporated and remain in the finished solar cell. Although Se or Te are the preferred n-type dopant atoms, other non-isoelectric surfactants may also be used.

Surfactant-assisted growth gives a much smoother or richer surface. Since the surface topography affects the overall properties of the semiconductor material as it grows and the layer thickens, the use of the surfactants minimizes threaded dislocations in the active zone, and therefore overall solar cell efficiency improves.

As an alternative to using a non-isoelectronic (surfactant) one may use an iso-electronic surfactant. The isoelectric "iso-electronic" refers to surfactants such as antimony (Sb) or bismuth (Bi) because such elements have the same number of valence electrons as the P atom of InGaP or the As atom in InGaAlAs in the metamorphic buffer layer. Such Sb or Bi surfactants are not typically in the metamorphic layer 505 incorporated.

In one embodiment of the present disclosure, the metamorphic layer exists 505 of a plurality of layers of InGaAs with monolithically changing lattice constants, each layer having a band gap in the range of 1.22 to 1.34 eV. In some embodiments, the band gap is constant in the range of 1.27 to 1.31 eV, through the thickness of the layer 505 therethrough. In some embodiments, the constant band gap is in the range of 1.28 to 1.29 eV.

The advantage of using a constant band gap material, such as InGaAs, is that arsenic based semiconductor material is much easier to process in the commercial standard of MOCVD reactors.

Although the described embodiment of the present disclosure includes a plurality of layers of InGaAs for the metamorphic layer 505 For reasons of manufacturability and radiation transparency, other embodiments of the present disclosure could use different systems to detect a change in lattice constants from the second subcell C to the first subcell D to reach. Other embodiments of the present disclosure, in contrast to step-graded materials, may use continuously graded materials. More generally, the graded interlayer may be constructed of any of the As, P, N, Sb based III-V compound semiconductors, taking into account the limitations of having planar lattice parameters less than or equal to the third subcell C and greater than or equal to the fourth subcell D , In some embodiments, the layer has 50 a band gap energy greater than that of the third subcell C and in other embodiments, it has a band gap energy level less than that of the third subcell C ,

In some embodiments, a second "alpha" or thread dislocation inhibiting layer is disclosed 507 , preferably composed of p-type GalnP, over the metamorphic buffer layer 50 deposited to a thickness of 0.10 to about 1.0 micron. Such an alpha layer is intended to prevent the propagation of threading dislocations, either opposite to the direction of growth into the first subcell D or in the direction of growth into the second subcell C as disclosed in US patent application publication no. 2009/0078309 A1 (Cornfeld and others).

In the in 4B embodiment shown is an intermediate intermediate layer intermediate 506 which in one embodiment step-graded sublayers 505a to 505zz disposed above the tunnel diode layer 304 , In particular, the following applies: The graded interlayer provides for a transition in the lattice constant, from the lattice constants of the substrate and the first solar subcell to the larger lattice constants of the second, third and fourth subcells C . B and A and it differs from that of the second embodiment of 4A only insofar as the upper or uppermost sublayer 505zz the graded intermediate layer 506 is claimed or only partially relieved (unlike the fully relaxed layer below it) because it has a lattice constant greater than that of the layer above it, that is, the alpha layer 507 (should a second alpha layer be present) or the BSF layer 306 , In short, in this embodiment, there is a "overshoot" of the graded layers as shown on the left side of FIG 4B which shows the step degradation of the lattice constants, which becomes larger from the layer 505a to 505zz ,

5 is a cross-sectional view of a fourth embodiment of a quadruple solar cell 500 after several stages of manufacture, including the growth of certain semiconductor layers on the growth substrate to the contact layer 322 , with different subcells similar to the structure described and shown in 2 . 4A and 4B ,

In this embodiment, both a graded intermediate layer and a DBR layer between the third subcell C and the fourth subcell D arranged. The layers 450 . 400 to 404 . 504 to 507 and 305 to 322 are essentially similar to those in the 2 and 4A or 4B and the description need not be repeated here.

In this embodiment, distributed Bragg reflector (DBR) layers are 305 adjacent to and above the alpha layer 507 (or the metamorphic buffer layer 506 when the layer 507 not present) grew up. The DBR layers 305 are arranged such that light enters and through the third solar subcell C and at least a portion thereof back to the third subcell C can be reflected, through the DBR layer 305 , In the in 5 The embodiment shown is the distributed Bragg reflector (DBR) layers 305 especially between the third subcell C and the metamorphic layer 506 arranged.

For some embodiments, the distributed Bragg reflector (DBR) layers 305 from a variety of alternating layers 305a to 305z lattice-matched materials, with discontinuities in their respective indices of refraction. For certain embodiments, the difference in refractive indices between alternating layers is maximized to reduce the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines the stop band and its limiting wavelength ,

In some embodiments, the distributed Bragg reflector (DBR) layers are 305a to 305z a first DBR layer composed of a plurality of p-type In _z Al _x Ga _{1 -xz} As layers and a second DBR layer disposed over the first DBR layer and constructed of a plurality of p-type In _w Al _y Ga _1-yw As layers, where w is between 0 and 1, x between 0 and 1, y between 0 and 1, z between 0 and 1, and y greater than x.

6 FIG. 12 is a cross-sectional view of a portion of the solar cell assembly according to the present disclosure mounted on a plate or panels or support substrate, the figure depicting two adjacent solar cells. FIG 601 and 701 shows and corresponding CIC's 600 or. 700 ,

As mentioned before, the solar cell knows for applications in space 601 . 701 a cover glass 603 or. 703 over the semiconductor device to provide radiation resistant shielding from particles that could damage the semiconductor material in the vicinity of the space. The cover glass 602 . 702 is typically a cerium-doped borosilicate glass which is typically from three to six mils Has thickness and is attached by a transparent adhesive 602 or. 702 at the corresponding solar cell 601 . 701 ,

Connection contacts and connection pads of a first and second polarity type are provided on each solar cell. In one embodiment, a back metal forms 604 or. 704 Contacts of a first polarity type. On the upper surface of each solar cell is a metal contact 705 provided and an edge of the solar cell forms a contact of the second polarity.

A variety of electrical interconnections 607 is provided, each constructed of a strip of silver-plated nickel-cobalt-iron-ferrite alloy material, each interconnect with a corresponding connection pad 612 and 705 is welded to each solar cell array and that for electrically connecting the adjacent solar cell assemblies of the arrangement in a series electrical connection.

An aluminum honeycomb panel ( 606 ) with a carbon composite face plate 605 is provided with a thermal expansion coefficient (CTE) which is substantially arranged on the germanium of the four solar subcells in each solar cell, each CIC 600 . 700 or the solar cell array are arranged thereon.

Another feature of the solar cell array of in 6 illustrated embodiment is that the cover glasses 603 . 703 one wrapped metal clip each 608 shown in CIC 600 the contact makes with the surface of the cover glass 603 and extending down the gap of the room, along the side of the solar cell array 600 between the CICs 600 and 700 so as to make electrical contact with the metal connection pad or contact 612 on the back surface of the CIC 600 who in turn makes contact with electrical ground. This is how the clip grounds 608 the electrical charge build-up on the surface of the cover glass 603 , to the earth of the panels (plate) or the spaceship. Other configurations of grounding methods for the surface (s) of the cover glass 603 . 703 are possible within the scope of this disclosure.

7 is a graphical representation of the bandgap of certain several materials and their lattice constants. The bandgap (bandgap) and lattice constants of ternary materials are placed on the leads drawn between typical associated binary materials (such as the AIGaAs ternary material) placed between the GaAs and AlAs dots on the graph, with the bandgap of the ternary material between 1.4 eV for GaAs and 2.16 eV for AlAs, depending on the relative size of the individual components. Thus, depending on the desired bandgap, the material components of the ternary materials can be suitably selected for growth.

8th is an enlargement of part of the graph of the 7 and different compounds of GalnAs and GalnP representing different properties of gallium and indium and the location of the specific compounds on the graph.

The present disclosure provides a multi-junction solar cell following a design rule of incorporating as many high-pitch subcells as possible to achieve the goal of increasing high-temperature EOL efficiency. For example, high bandgap subcells may retain a greater percentage of cell voltage as the temperature rises, thereby offering lower power loss as the temperature rises. As a result, both HT-BOL and HT-EOL performance of exemplary multiple solar cells according to the present disclosure can be expected to be greater than traditional cells.

The exemplary solar cell described herein may require use of aluminum in the semiconductor composition of each of the top two subcells. The incorporation of aluminum is known in the III-V compound semiconductor industry to reduce BOL subcell performance due to the low level of donor defects, higher doping compensation, shorter minor carrier lifetime and lower cell voltage, and an increase in BOL E _g / qV _oc metric. In short, the increased BOL E _g / qV _oc may be the most problematic disadvantage of the aluminum-containing subcell; the other limitations can be reduced by modifying the doping scheme or thinning the base thicknesses.

In view of the different satellite and spacecraft requirements with respect to operating ambient temperature, exposure to radiation, and operating life, a range of Subclass constructions employing the design principles of the present disclosure provide satisfactorily defined customer and mission requirements, and further, several illustrative embodiments are discussed herein for comparison purposes along with the calculation of end-of-life efficiency. As described in detail below, the solar cell performance after exposure to radiation is experimentally measured using 1 MeV electron fluence per square centimeter (abbreviated to e / cm ^{2 for brevity} ) so that a comparison can be made between current commercial devices and the embodiment disclosed in the present disclosure.

As an example of different mission requirements, a low earth orbit (LEO) satellite typically experiencing radiation equivalent to 5 x 10 ¹⁴ electron fluence per square centimeter (hereinafter referred to as "5E14 e / cm ² ") is discussed a five-year life. A geosynchronous Earth orbit (GEO) satellite will typically receive radiation in the range of 5 x 10 ¹⁴ e / cm ² to 1 x 10 ¹⁵ e / cm ² over a fifteen-year lifetime.

The following table shows, for example, the cell efficiency (%) measured at room temperature (RT) 28 ° C and a high temperature (HT) 70 ° C at the beginning of life (BOL = end of life) and end of life (EOL = end of life). for a commercial triple solar cell (ZTJ): Table 1 State efficiency BOL 28 ° C 29.1% BOL 70 ° C 26.4% EOL 70 ° C 23.4% after 5E14 e / cm ² radiation EOL 70 ° C 22.0% after 1E14 e / cm ² radiation

For those in the reservation U.S. Patent Application Serial Number 14 / 828,206 of 17 August 2015 (according to the published European patent application EP 2 133 65 A1 ) are the corresponding data in Table 2 called. Table 2 State efficiency BOL 28 ° C 29.1% BOL 70 ° C 26.5% EOL 70 ° C 24.5% after 5E14 e / cm ² radiation EOL 70 ° C 23.5% after 1E14 e / cm ² radiation

The solar cell described in earlier applications has a slightly higher cell efficiency than the commercial standard solar cell (ZTJ) at BOL 70 ° C. However, the solar cell described in one embodiment of the disclosure exhibits a significantly improved cell efficiency (%) over the commercial standard solar cell (ZTJ) at 1 MeV electron equivalent flux of 4 x 10 ¹⁴ e / cm ² , and dramatically improved cell efficiency (%) over the commercial standard solar cell (FIG. ZTJ) at 1 MeV electron equivalent fluence of 1 × 10 ¹⁵ e / cm ² .

The simplest way of describing the different embodiments of the present disclosure and their efficiency compared to the above-mentioned standard solar cell is to specify the embodiments with the specification of the composition of each of the successive subcells and their corresponding bandgap and then the calculated efficiency.

Thus, for a quadruple solar cell as configured and described in the present disclosure, four embodiments and their corresponding end-of-life (EOL) efficiency data are as follows: Embodiment 1 bandgap composition Subcell A 2.1 AlInGaP Subcell B 1.73 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Subcell C 1.41 (In) GaAs Subcell D 0.67 Ge Efficiency at 70 ° C after 5E14e / cm ² Radiation: 24.5%
Efficiency at 70 ° C after 1E14e / cm ² Radiation: 23.5% Embodiment 2 bandgap composition Subcell A 2.1 AlInGaP Subcell B 1.67 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Subcell C 1.34 (In) GaAs Subcell D 0.67 Ge Efficiency at 70 ° C after 1E14e / cm ² Radiation: 24.9% Embodiment 3 bandgap composition Subcell A 2.1 AlInGaP Subcell B 1.65 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Subcell C 1.30 (In) GaAs Subcell D 0.67 Ge Efficiency at 70 ° C after 1E15e / cm ² Radiation: 25.3% Embodiment 4 bandgap composition Subcell A 2.03 AlInGaP Subcell B 1.55 InGaP / AIInGaAs or AlInGaAs / AlInGaAs Subcell C 1.2 (In) GaAs Subcell D 0.67 Ge Efficiency at 70 ° C after 1E15e / cm ² Radiation: 25.7%

Although the differences in bandgap among the various embodiments described above, that is, on the order of 0.1 to 0.2 eV, might appear relatively small, these settings have a surprising result and an unexpected increase in EOL solar cell performance. Efficiency of 24.4% reported in the parent application US Patent Application Serial No. 14 / 828.206 of 17 August 2015 (and in the corresponding European Patent Application Publication EP 3 133 650 A1 ) to 25.7% for the solar cell embodiment 4 as described above. Such a surprising and unexpected improvement resulting from the relatively small change in bandgap implies a recognizable inventive step over related configurations described in the patent application and the European patent application publication, even in the field of solar cell devices for room applications Improvements in efficiency are typically considered important.

Although the described embodiments of the present disclosure utilize a vertical stack of four subcells, various aspects and features of the present disclosure are applicable to stacks having fewer or greater numbers of subcells, that is, dual cells, triple cells, quintuple cells, six compartment cells, etc.

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 patent literature

• US 8962993 [0012, 0014]
• US 4667059 [0013]
• US 14828206 [0123]
• EP 213365 A1 [0123]
• US Pat. No. 14/828206 [0127]
• EP 3133650 A1 [0127]

Claims (10)

A quadruple solar cell (200, 400, 450, 500) comprising: a growth substrate (300); a fourth solar subcell (D) disposed over or in the growth substrate (300); a graded interlayer (505) disposed over the fourth solar subcell (D), and the growth substrate (300) followed by a sequence of layers of semiconductor material having a plurality of solar subcells, including a third solar subcell (C) over and lattice mismatched with respect to the growth substrate (300) and having a band gap in the range of 0.9 to 1.6 eV, at least a second solarsub cell (B) disposed over the third solarsub cell (C) and having a band gap in the range of approximately 1.5 to 1.8 eV, and an upper first solar subcell (A) disposed over the second solar subcell (B) and having an aluminum content above 30% of the mole fraction, a band gap in the range of 2.0 to 2.20 eV; wherein the graded interlayer (505) is compositionally graded for lattice matching of the growth substrate (300) on one side and the third solar subcell (C) on the other side and further constructed of any of the As, P, N, Sb based III-V compound semiconductors , subject to the limitations of the "in-plane" grid parameter d. H. parallel to the surface, over its entire thickness, greater than or equal to that of the growth substrate (300). The solar cell after Claim 1 , wherein the following is provided: the second solar subcell (b) has a band gap of approximately 1.73 eV and is lattice-matched with the third solar subcell (C) and the upper first solar subcell (A) has a band gap of 2 , 05 eV and is lattice-matched with the second solar subcell (B), and the average bandgap of all four solar subcells is equal to or greater than 1.35 eV. The solar cell according to any one of the preceding claims, wherein the upper first Solarsubzelle is constructed (A) composed of a base layer of (In _x Ga ₁ - _{x) 1-y} Al _y P wherein x is 0.505 and y 0.142 is corresponding to a band gap of 2 , 10 eV and an emitter layer of (In _{x G} a _1-x ) _1-y Al _y P, where x is 0.505 and y is 0.107, corresponding to a band gap of 2.05 eV. The solar cell of any one of the preceding claims, further comprising: a tunnel diode (303, 304) disposed over the fourth solar subcell (D) and below the graded interlayer (505), the graded interlayer (505) being compositionally graded to be lattice matched to the third solar subcell (C) on one side and the tunnel diode (303, 304) on the other side and further constructed of any of the As, P, N, Sb based III-V compound semiconductors, subject to the limitations the in-plane lattice parameter is greater than or equal to that of the third solar subcell (C) and different from that of the tunnel diode (303, 304), and further having a bandgap energy greater than that of the fourth solar subcells (D). The solar cell of any one of the preceding claims, wherein the graded interlayer is compositionally graded with between one and four lattice matching of the third solar subcells on one side and constructed of InGaAs or (In _x Ga _1-x ) _y Al _1-y As, where x between 0 and 1, y between 0 and 1, and x and y are selected such that the bandgap is also graded in the range of 1.15 to 1.41 eV across its entire thickness. The solar cell of any one of the preceding claims, wherein the graded interlayer (505) has a band gap in the range of 1.15 to 1.41 eV or 1.2 to 1.35 eV or 1.25 to 1.30 eV. The solar cell of any one of the preceding claims, wherein either (i) the emitter layer (320); or (ii) the base layer (319) and emitter layer (320) of the upper first solar subcell (A) have different lattice constants to the lattice constants of the directly adjacent second solar subcell (B). The solar cell of any one of the preceding claims, further comprising: a distributed Bragg reflector (DBR) layer (305) adjacent to and below the third solar subcell (C) and arranged so that light enters and passes through the third solar subcells (C ), at least a portion of which may be reflected back into the third solar cell (C) through the DBR layer (305), wherein the distributed Bragg reflector layer (305) is composed of a plurality of alternating ones Layers of lattice-matched materials having discontinuities in their respective refractive indices, maximizing the difference in refractive indices between alternating layers to minimize the number of periods required to achieve a given reflectivity, and wherein the thickness and refractive index of each period determines the stop band and its limiting wavelength, and wherein the DBR layer (305) comprises a first DBR layer composed of a plurality of p-type In _z Al _x Ga _1-xz As layers and a second DBR layer arranged over the first DBR layer and composed of a plurality of p-type In _w Al _y Ga _1-yw As layers, where w is between 0 and 1, x is between 0 and 1 , y is between 0 and 1 and z is between 0 and 1 and y is greater than x; and wherein the graded interlayer (505) is compositionally step-graded to lattice match the DBR layer (305) on one side and the fourth solar subcell (D) on the other side, and further composed of any As, P, N, Sb-based III -V compound semiconductor, which is subject to the limitations of having an in-plane lattice parameter greater than or equal to the DBR layer 305 and less than or equal to that of the fourth solar subcell (D) and having a bandgap energy greater than that of the fourth Solar subcell (D). The solar cell of any one of the preceding claims, further comprising: a first threading dislocation layer having a thickness in the range of 0.10 to 1.0 microns and disposed over the growth substrate and having a different composition from the graded interlayer; and a second threading dislocation layer having a thickness in the range of 0.10 to 1.0 micron and constructed of InGa (Al) P, the second threading dislocation barrier layer disposed over and immediately adjacent to said added interlayer to reduce Reproduction of threading dislocations, wherein the second threading dislocation barrier layer has a composition different from the composition of the first threading dislocation and the graded interlayer. The solar cell of any one of the preceding claims, wherein at least one of the upper sub-layers of the graded interlayer (505) has a larger lattice constant than the adjacent layers (506, 306) to the upper sub-layer disposed over the graded interlayer.

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