EP3234212A1

EP3234212A1 - Material with growing gap

Info

Publication number: EP3234212A1
Application number: EP15816162.0A
Authority: EP
Inventors: Virginie Brize
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2014-12-18
Filing date: 2015-12-18
Publication date: 2017-10-25
Also published as: FR3030582A1; WO2016097348A1

Abstract

The present invention relates to a crystalline material that can absorb radiation, made up at least partially of unit cells of a first oxide with perovskite structure and unit cells of a second perovskite oxide other than the first oxide, two adjacent unit cells having a cell mismatch of less than 20%, preferably less than 5%, and said material having a continuously growing gap on either side in at least one direction.

Description

MATERIAL WITH INCREASING GAP

The present invention relates to a material absorbing radiation, intended for photovoltaic applications or applications implementing a measurement of light radiation, including infrared.

In the field of the production of electrical energy from solar radiation, it is actively sought a cell having a yield (that is to say a ratio between the electrical energy produced by the cell on the light energy qu it receives the highest possible. A silicon-based photovoltaic cell has a single n-p junction allowing the acceleration of minority charges and the production of an electric current. Its low efficiency of 20% results notably from the inability of silicon to convert a wide range of wavelengths of the solar spectrum into electrical energy.

Silicon based multi-junction cells were then developed, which absorb a wider range of wavelengths of the solar spectrum. They consist of a stack consisting of alternating layers of p-doped silicon or n, each silicon layer being specifically processed to convert particular wavelengths of the light spectrum, for example in blue or red. In practice, the efficiency of a multi-function cell can reach 40%.

Also known from [Stan] is a triple-junction cell consisting of an arsenic-doped gallium phosphide layer (GalnAs), an indium-doped gallium phosphide layer (GalnP) and a germanium layer (Ge ) stacked successively one on the other. Each of the materials constituting the layers is able to convert a specific wavelength range of the light spectrum. The yield of such a cell, measured in the laboratory is 41%.

However, the manufacture of a multijunction cell is more expensive than a single junction cell. In addition, to obtain the yields mentioned above, it is necessary to have focusing optics to focus the sunlight on the cells, which increases the cost of photovoltaic devices. Finally, arsenic is a toxic element, which imposes compliance with industrial manufacturing constraints.

The article "Photovoltaic effect in micrometer-thick perovskite-type oxide multilayers on Si substrates", H. Lui et al., Applied Physics Letters, vol. 93, page 171911, 2008, discloses a multilayer material consisting of successive alternating oxide layers and perovskite SrNbo.05Tio.95O3 The .9Sr ₀ ₀ .iMnO3.

The article "Growth, crystal structure, and properties of epitaxial BiScOs thin films," S. Trolier-McKinstry et al, Journal of Applied Physics, vol. 104, page 044102, 2008, describes a multilayer material for a piezoelectric device constituted by a stack of BiScC / BiFeCVSrTiC layers.

US 2007/0095653 discloses a multilayer material for a device such as a semiconductor, a piezoelectric element, an ink jet printhead, a surface acoustic wave probe.

The article "Growth and magnetoresistive properties of (LaMnO) _m (SrMnO)) _n superlattices", PA Salvador et al., Applied Physics Letters, Vol. 75, num. 17, 1999, describes a superlattice (LaMnO3) _m (SrMnO3) _n , with n / (M + n) = 0.26 obtained by laser ablation pulsed from targets of LaMnC ^ and SrMnC ^ and is interested in to the magnetoresistive properties of this superlattice.

There is therefore a need for a cell, especially for photovoltaic application or for applications implementing a measurement of light radiation, especially infrared, to overcome the problems described above. The invention aims precisely to meet this expectation.

Thus, it proposes a crystalline and radiation-absorbing material formed at least in part by elementary meshes of a first oxide and elementary meshes of a second oxide different from the first oxide, two contiguous elementary meshes having a mesh size of less than 20%, preferably less than 5%, and said material having an increasing gap continuously from one side to the other in at least one direction X.

The "gap" or "gap energy" corresponds to the energy required to bring an electron to pass it from the valence band to the conduction band of an oxide.

The material according to the invention is advantageous in several ways. First of all, a photovoltaic cell comprising the material according to the invention can absorb a longer wavelength range of light than that absorbed by the monojunction and multijunction cells described above.

In addition, the material according to the invention has a low content of crystalline defects, generating mechanical stresses and known to degrade the photovoltaic properties of the material. Thus, the conversion efficiency of light energy into electrical energy of a photovoltaic cell comprising the material according to the invention is improved.

Finally, the material according to the invention can be manufactured under conditions that are respectable to the environment.

It should be noted that a material according to the invention has, for each oxide which composes it, a continuous concentration gradient. It can not therefore be considered as a multijunction cell, in which the transition at the interface between two layers is characterized by a discontinuity in the concentration of the materials that constitute it. Moreover, the material according to the invention can be free of p / n junction.

GAP GROWING CONTINUOUSLY

A gap-increasing material is such that the gap increases according to the direction of growth of the gap and from one side of the material between a minimum gap value E ™ ⁱⁿ and a maximum gap value E ™ ^ax and different from E ™ ⁱⁿ .

By gap of the continuously increasing material, it is meant that the continuity coefficient C may be less than 1, less than 0.8, less than 0.7, less than 0.5, less than 0.3, or even less than 0, 15.

The coefficient of reliability C is expressed according to the following equation:

where VE _g is the global gap gradient and VE _g is the k-th local gap gradient.

The global gradient of the gap VE _g corresponds to the ratio of the difference of the maximum values E ™ ^ax and minimum E ™ ⁱⁿ of the gap on the largest dimension e of the material according to the direction of growth of the gap. This larger dimension is by example the thickness of the material. In other words, the global gap gradient VE _g is expressed as

pmax pmin

v¾ = ½

y e

The k-γm local gradient of the gap VEg is determined by dividing the largest dimension e described above into n regularly spaced intervals, preferably of constant length, n is preferably greater than or equal to 5, or even greater than or equal to 10 , or even greater than or equal to 20. The -th local gap gradient corresponds to the ratio between the gap variation E _g ^} - E _g ^l between the ends i and j of an interval k divided by the length of the gap k, with 1 <k <n. For example, the number of divisions n of the length e can be chosen so that the length l _k is 10 nm.

The k-th, local gradient of the gap VEg can thus be expressed according to the following relation:

pJ

^L k

Preferably, the continuity coefficient C is less than 0.8 and the number of intervals n is greater than or equal to 20.

For example, in one embodiment, a continuously increasing gap material is such that the gap is constant over a distance of less than 10 nm along the direction of growth of the gap and that it expands between two successive zones spaced more than 10 nm along the gap growth direction.

In one variant, a gap material continuously increasing in a direction X may be such that by dividing the material in direction X into slices of constant thickness equal to 10 nm, preferably equal to 5 nm, or even preferably equal to at 2 nm, the gap of the material measured on a first slice consecutive to a second slice is greater than the gap of the material measured on the second slice, whatever the first and second consecutive slices considered along the X direction.

A "direction" has two meanings. Thus, unless otherwise indicated, by increasing evolution of a parameter, for example the gap, it is considered that in the same direction, the parameter increases in one direction and decreases in the opposite direction.

The minimum and maximum bounds between which the gap evolves continuously can be chosen according to the intended application. Preferably, the material has a gap that continuously increases between 0.25 eV and 3.20 eV. It can thus absorb and convert a wavelength range of solar radiation between 380 nm and 5000 nm, both in the visible and in the infrared. For photovoltaic applications, where the range of wavelengths to be converted is generally between 380 nm and 2000 nm, the material preferably has a gap that continuously increases between 0.62 eV and 3.20 eV. For applications for converting infrared radiation, whose wavelength range is generally between 780 nm and 500 μιη, the material preferably has a gap that continuously increases between 0.25 eV and 1.59 eV. Preferably, the material gap increases continuously from 0.25 eV to 1.59 eV and / or from 0.62 eV to 3.20 eV.

In the case where the material is in the form of a layer deposited on a substrate, the growth direction of the gap X may be parallel to the surface of the substrate. Preferably, it is parallel to the thickness of the layer.

In the case where the material is in the form of a layer deposited on a substrate, the gap of the material can grow from the large face of the layer in contact with the substrate to the large face of the layer on the opposite side. Such gap growth is preferred when the material is intended for photovoltaic applications. In particular, two different oxides are such that they have different gaps. The material according to the invention comprising such oxides, the gap of two different areas of the material may vary depending on the concentrations of first and second oxides in each of these areas.

The gap in one area of the material can be measured on the surface of the material by spectroscopic ellipsometry. A first gap measurement is thus obtained. Etching can then be performed on this surface of the material so as to remove material, for example to a depth of 10 nm. A new optical gap measurement is performed on the surface at the bottom of the engraving. By performing a succession of ellipsometry measurement steps and destructive etchings, it is thus possible to measure the evolution of the gap along the gap growth direction. BASIC MESH

The material according to the invention is formed at least partly of elementary meshes of a first oxide and of elementary meshes of a second oxide different from the first oxide with two adjacent elementary meshes having a mismatch of less than 20% mesh.

Two "contiguous" elementary cells share in common some of the atoms or molecules that define each of the two elementary cells.

Preferably, elementary cell meshes of the first oxide and unit cell of the second contiguous oxide have a mismatch of less than 20%, preferably less than 5%.

By way of illustration, an elemental mesh of an oxide of formula ABO3 and of perovskite structure shares with an oxide of formula ΑΒΌ3 and of perovskite structure a crystalline plane of type (100) comprising atoms A and O.

In the plane situated at the interface between two adjacent elementary cells, a direction of the first elementary cell of parameter a and a direction of the second elementary cell of parameter a ₂ are combined in a single direction called the direction of disagreement. Preferably, two contiguous elementary meshes have two different detuning directions. The mesh mismatch between first and second contiguous elementary meshes of mesh parameter ai and a ₂ in a detuning direction is expressed, as a percentage, by the following relation:

a ₌ a _{1 =} a _{1 χ}

a ₂

An elementary cell is defined in particular by its crystallographic structure and by three mesh parameters, each mesh parameter corresponding to the smallest distance in which the atomic or molecular pattern defined by the elementary cell is repeated periodically in a direction of space.

Mesh parameter

This mesh parameter is expressed for an equilibrium configuration of the elementary cell, at a given temperature and at a given pressure. In other words, the mesh mismatch between two elemental meshes is calculated on the basis of elementary cell parameter values, expressed at the same temperature and pressure. The parameter of a unit cell of an oxide can be measured by X-ray diffraction on a sample made of oxide.

Crystallographic structure

By crystallographic structure, we consider the order in which arrange the atoms or molecules constituting the crystal. Thus, two oxide materials may be different while having the same crystallographic structure, for example perovskite type. They can in particular be different by the chemical composition and / or by values of different mesh parameters.

Oxide materials

The first and second oxides may in particular be chosen from oxides of perovskite structure, of K ₂ NiF ₄ structure, and of scheelite structure. Other crystallographic structures can also be envisaged.

Preferably, the elementary cells of one of the first and second oxides are those of a perovskite structure of general formula AB0 ₃ .

The elements A and B can be chosen according to their respective valence and that of oxygen so as to form a perovskite of general formula. Preferably, the element A is chosen from the group constituted by hydrogen.

(H), potassium (K), copper (Cu), lithium (Li), silver (Ag) and gold (Au) and element B is selected from the group consisting of bismuth ( Bi), antimony (Sb), niobium (Nb), vanadium (V), or

the element A is chosen from the group formed by calcium (Ca), barium (Ba), strontium (Sr), lead (Pb) and element B is chosen from the group formed by titanium (Ti ), zirconium (Zr), ruthenium (Ru), molybdenum (Mo) and rhodium (Rh), or element A is selected from the group consisting of lanthanum (La), bismuth (Bi), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), praseodymium (Pr), holmium (Ho), erbium (Er), ytterbium (Yb) and lutetium (Lu) and element B is selected from the group consisting of aluminum (Al), chromium (Cr), iron (Fe), gallium (Ga), indium (In), scandium (Se) and manganese (Mn). Alternatively, the elemental cells of one of the first and second oxides may be those of a perovskite structure of general formula A ₂ B ' _X ' B " _X " 06 or of general formula A ₃ B'yB "yO9 as described in US 2006/0148636 A1, where oxygen vacancies are obtained by specific choice of the molar contents in B'and B ".

The first and second oxides may have different crystallographic structures. In this case, especially, when the elemental cells of an oxide are those of a perovskite structure, the elementary cells of the other oxide are preferably those of a K ₂ NiF ₄ or scheelite type structure.

In a preferred variant, the elementary cells of the first and second oxides have an identical crystallographic structure.

A material according to the invention consisting of elementary cells of the same crystallographic structure can thus be easily manufactured.

Preferably, more than 90%, or even more than 95%, or even more than 99% by number, or even all the elemental meshes of the material are elementary cells of perovskite crystallographic structure.

The elemental meshes then form a solid solution. In other words, an elementary cell of a first oxide can be obtained by substitution of an atom or a group of atoms of the second oxide.

For example, a material according to the invention comprising an oxide of perovskite structure of type AB0 ₃ and an oxide of perovskite structure AB'O ₃ form a solid solution obtained for example by substitution of the B atoms of the structure by B 'atoms. Such a solid solution may be designated as A (B, B ') O ₃ or as AB (i _x) B' _x O ₃ where x is the molar concentration of the B 'atom in the solid solution, with 0 <x <1.

Alternatively, the solid solution can be obtained by substitution of A-type atoms by A 'atoms. Such a solid solution can be designated as (A, A ') B0 ₃ or in the form A (i_ _y) A' ₃ _y 0 where y is the molar concentration of the atom A 'in the solid solution, 0 <y <1. In another variant, the solid solution can be obtained by anionic substitution of oxygen, for example with nitrogen. Such a substitution is known from [Mukherj] to modify the gap of a perovskite oxide. Moreover, since the material comprises different first and second meshes of oxides, it may have different intermediate mesh parameter values in different zones.

The intermediate mesh parameter in a direction of disagreement depends in particular on the volume concentrations of the first and second elemental meshes and the mesh parameters in the direction of disagreement. In any case, the intermediate mesh parameter a in a detuning direction is such that a <a <a ₂ , where <¾ and a ₂ are the mesh parameters of the first and second elemental meshes in the detuning direction.

The intermediate mesh parameter can in particular be measured by various methods, in particular by X-ray diffraction and / or by transmission electron microscopy.

Preferably, the intermediate mesh parameter of the crystalline material increases continuously, and preferably linearly, through the material in at least one direction, preferably in the direction of growth of the gap.

By continuously increasing intermediate mesh parameter, it is considered that the intermediate mesh parameter is constant over a distance of less than 10 nm along a direction of growth and that it grows between two successive zones spaced more than 10 nm along of said growth direction.

Preferably, the variation of intermediate mesh parameter, measured along a segment traversing the material from one side to the other is greater than 20%. In particular, the crystalline material according to the invention may comprise elementary meshes of a third oxide having a mismatch of greater than 20% in all directions with the elementary meshes of one of the first or second oxide, but having a mesh discrepancy less than 20% with the elementary meshes of the other of the first or second oxide. The meshes of the third oxide may in particular be contiguous with the first oxide or with the second oxide. More particularly, the material according to the invention may have a zone comprising predominantly one of the first and second oxides on the one hand and the third oxide on the other hand. In addition, it may comprise a zone comprising mainly the other of the first and second oxides on the one hand and the third oxide on the other hand.

For example, in one embodiment, the material according to the invention is such that an elementary mesh of a perovskite structure of formula BilnO ₃ is contiguous to an elementary cell of a perovskite structure of formula BiSc0 ₃ and / or a elemental mesh of a perovskite structure of formula BiSc0 ₃ is contiguous to an elementary cell of a perovskite structure of formula BiGa0 ₃ and / or a unit cell of a perovskite structure of formula BiGa0 ₃ is contiguous to a unit cell of a perovskite structure of formula BiA10 ₃ .

The gap and the elementary mesh parameter can grow in the same direction but in opposite directions. Alternatively, they can grow in the same direction and in the same direction.

In one embodiment, the material may comprise at least one multilayer stack, each layer of the multilayer stack comprising a solid solution formed by the first and second oxides. In particular, the gap growth direction may be parallel to the thickness of the multilayer stack.

Preferably, the layers of the multilayer stack have the same thickness, preferably less than 20 nm, or even preferably less than 10 nm, or even less than 5 nm. In particular, the solid solution can be homogeneous in each layer. In other words, the concentration of first and second oxides in each layer can then be substantially constant along the thickness of the layer. By traversing the multilayer stack from one end to the other depending on its thickness, the concentration of the first oxide can decrease with the passage of two consecutive layers, whatever the two consecutive layers of the multilayer stack. Conversely, the second oxide concentration can increase as the two consecutive layers pass, regardless of the two consecutive layers of the multilayer stack.

Preferably, the multilayer stack comprises more than 10 layers, preferably more than 100 layers, or even more preferably more than 1000 layers.

More particularly, the material may comprise a multilayer stack comprising first and second consecutive layers and the first layer, the second layer, may respectively comprise a solid solution of perovskite oxides. as described above with general formula ΑΒ _χ ΒΊ _χ θ3, ΑΒ _Χ 'ΒΊ _Χ Ό Ό3 respectively, with x <x', 0 <x <1 and 0 <x '<1.

Preferably, in the variant where the multilayer stack comprises more than two layers, two consecutive layers of the multilayer stack may be first and second layers as described in the immediately preceding paragraph, regardless of the two consecutive layers considered.

PROCESS FOR PREPARING A MATERIAL ACCORDING TO THE INVENTION

The invention also relates to a method for manufacturing a material comprising an assembly of first and second solid solutions, consisting in implementing the following successive steps:

a) having a substrate and precursors of first and second oxides, said oxides having different gaps and a mismatch of less than 20%, preferably less than 5%,

b) depositing on the surface of the substrate at least the first oxide by reaction of the precursor (s) of said oxide so as to form the first solid solution,

c) forming in a joining direction in contact with the first solid solution said perovskite oxides by reaction of the precursors of said oxides, so as to assemble the second solid solution with the first solid solution,

steps b) and c) being conducted so that the second oxide concentration of the second solid solution is greater than the second oxide concentration of the first solid solution, and the gaps of the first and second solid solutions are different.

The method according to the invention makes it possible in particular to manufacture a material formed of a single layer capable of absorbing a wide range of solar radiation and of converting this radiation into electrical energy.

Preferably, the method according to the invention is used to manufacture a material according to the invention. Preferably, the assembly direction is parallel to the direction of growth of the gap of the material. The invention also relates to a device comprising a material according to the invention and / or obtained by the method according to the invention. Preferably, the device is chosen from a photovoltaic cell, a light measuring cell, for example in the infra-red, a thermal measurement camera, a fire detector.

According to a variant, the device may comprise a substrate having a first face on which is disposed a first material and a second face, opposite to the first face, on which a second material is disposed, the first and second materials being according to the invention. and / or being obtained by the process according to the invention.

Preferably, the gap of the first material increases continuously in a direction normal to the first face of the substrate, from the first face of the substrate towards the face of the farthest first material and located opposite the first face of the substrate, and the gap of the second material increases continuously in a direction normal to the second face of the substrate, from the second face of the substrate to the face of the second furthest material and located opposite the second face of the substrate. Preferably, the continuous growth of the gap of the first material in the direction normal to the first face of the substrate is identical to the continuous growth of the gap of the second material in the normal direction to the second face of the substrate. In other words, the plot of the evolution of the gap of the first material as a function of the distance to the first face of the substrate in a direction normal to said first face then merges with the plot of the evolution of the gap of the second material according to the distance to said second face of the substrate in a direction normal to the second face. In other words, the first and second materials are preferably identical. Such a device is thus easier to manufacture. For example, after depositing the first material on the first face of the substrate, it is then sufficient to turn the substrate to deposit the second material with process conditions identical to those used to deposit the first material.

The invention will be better understood on reading the detailed description which follows, examples of non-limiting implementation thereof, and on examining the appended drawing, in which: FIG. 1 illustrates a material according to one embodiment of the invention, in the form of a layer and observed in section along a transverse section;

FIG. 2 illustrates the evolution of the concentrations of first and second oxides according to the thickness of the material illustrated in FIG. 1, FIG. 3 illustrates a material according to another embodiment of the invention,

FIG. 4 represents the evolution of the parameters of intermediate mesh and the gap of the material illustrated in FIG. 4 according to its thickness; FIGS. 5 and 6 illustrate alternative embodiments of materials according to the invention;

FIG. 7 illustrates a mode of implementation of the method according to the invention, and

Figure 8 illustrates a device according to one embodiment of the invention. In the appended drawing, the actual proportions of the various constituent elements or their spacings have not always been respected for the sake of clarity.

Figure 1 illustrates a material 5 according to the invention in the form of a layer. The layer is disposed on a substrate 10. It consists of elementary cells of a first oxide 15 and a second oxide 20 different from the first oxide. For the sake of clarity, in FIG. 1, only two meshes have been schematically represented. The first and second oxides are both of perovskite crystallographic structure and form a solid solution. FIG. 2 illustrates the evolution of the elementary cell C concentrations of the first and second oxides between the large faces 22, 23 of the layer along the thickness e. The elementary meshes of the first oxide and the second oxide are arranged within the material such that, along the thickness of the layer, the elementary mesh concentration of the first oxide decreases continuously according to the thickness of the layer between the large face of the layer in contact with the substrate and the large free face located opposite. At the same time, the elemental mesh concentration of the second oxide increases continuously between said large faces. The elemental mesh concentration of an oxide is defined as the ratio of the number of elemental meshes of this oxide to the total number of elemental oxide meshes forming a wafer 35 of the material of thickness e '. By "continuous growth", it is excluded that the concentration is constant between two successive distinct tranches.

Thus, as observed in FIG. 2, the elementary cell concentrations of the first and second oxides increase and decrease respectively monotonically.

The layer may have a thickness e less than 600 μιη, or even less than 100 μιη, or even less than 10 μιη, or even less than 500 nm, or even less than 100 nm, or even less than 15 nm.

In a variant, at the level of the large face 22 of the layer disposed on the substrate, only elementary cells of the first oxide are in contact with the substrate, and only elementary cells of the second oxide define the large face 23 opposite the material.

The first and second constituent oxides of the layer have different gaps. The elementary cell concentrations of the first and second evolving differently, it follows that the gap increases continuously from one side to the other of the layer in a direction of growth gap X, parallel to the thickness of the layer. The gap can grow continuously or on the contrary decrease continuously from the large face 22 of the layer in contact with the support towards the large opposite face 23.

On the other hand, the first and second oxides may be such that the mesh parameter of the first oxide is smaller than the mesh parameter of the second oxide. In addition, the gap of the first oxide may be smaller than the gap of the second oxide. Thus, the gap and the intermediate mesh parameter grow continuously in the same direction but in opposite directions. For example, the first oxide may be BilnO ₃ with a perovskite structure, gap Eg ^{1 =} 0.42 eV and a mesh parameter equal to 0.4204 nm depending on the direction (001) and the second oxide may be BiA10 ₃ with a structure perovskite, of gap Eg ² = 1.14 eV and of mesh parameter equal to 0.3871 nm according to the direction (001).

FIG. 3 shows an alternative embodiment of the material according to the invention, in the form of a layer comprising four different oxides and of perovskite structure, forming three different solid solutions within the material and disposed contiguously in pairs.

In the example of Figure 3:

a first solid solution Si consisting of elementary cells 40a of the oxide Biln0 ₃ with a gap Eg ^{1 =} 0.42eV and a mesh parameter equal to a = 0.4204 nm and elementary cells 40b of the BiSc0 ₃ oxide of gap Eg ² = 0.45 eV and of mesh parameter a ₂ = 0.4062 nm is arranged on a substrate and

a second solid solution S ₂ consists of elementary cells 40b of the BiSc0 ₃ oxide and of elementary cells 40c of the BiGaO ₃ oxide with a gap Eg ³ = 0.91 eV and a mesh parameter of ₃ = 0.3895 nm is arranged on the first solid solution and

a third solid solution S ₃ consists of elementary cells 40c of the oxide BiGa0 ₃ and of elementary cells 40d of the oxide BiA10 ₃ with a gap Eg ⁴ = 1.14 eV and a mesh parameter a ₄ = 0.3781 nm is arranged on the third solid solution.

In other words, the material illustrated in FIG. 3 is formed of a series of solid solutions Si, S ₂ and S ₃ successively stacked one on the other.

In the example of FIG. 3, the oxide concentration having the lowest gap is maximum on the large face 22 of the layer in contact with the substrate, and the oxide concentration having the highest gap is greatest on the large face. 23 of the layer located opposite the large face 22 according to the thickness.

Thus, as illustrated in FIG. 4, the gap G can grow continuously along the thickness of the large face of the layer disposed on the substrate towards the large opposite face of the layer. In contrast, the intermediate mesh parameter a may decrease along the thickness of the layer, from the large face of the layer disposed on the substrate to the large opposite face. Alternatively, the gap G may decrease and the intermediate mesh parameter a may grow along the thickness of the layer, from the large face of the layer disposed on the substrate to the large opposite face. As it appears in FIG. 4, the gap increases monotonically along the thickness of the layer between the two large faces of the layer, while the parameter intermediate mesh decreases monotonously. Like the other materials illustrated in the present drawing, the material of FIG. 3 can absorb a continuous range of wavelengths of a spectrum, the minimum wavelengths of the range being determined by the maximum values and minimum of the gap of the material.

In the case of a stack of solid solutions as illustrated in FIG. 3, it is preferred that two contiguous solid solutions comprise at least one oxide in common. By way of illustration, in the embodiment shown in FIG. 3, the first Si and second S ₂ solid solutions comprise the BiSc0 ₃ oxide in common and the second S ₂ and S ₃ solid solutions comprise the BiGaO ₃ oxide in common.

In this way, unlike conventional layers of multijunction cells made of different materials stacked on top of each other, the intermediate mesh parameter evolves continuously as it passes between two contiguous solid solutions, as illustrated in FIG. The invention thus makes it possible to reduce the development of crystalline defects and associated mechanical stresses, conventionally encountered in the multijunction cells of the prior art, particularly related to the discontinuity of the mesh parameter during the passage between two adjacent layers of a stack. In another variant illustrated in FIG. 5, the material according to the invention is in the form of a layer disposed on a substrate and the gap increases continuously in a direction X parallel to the substrate. In particular, the material may have a succession of solid solutions, for example those described in the embodiment illustrated in FIG. 3, except that the solid solutions are in contact and arranged contiguously one after the other. others according to direction X.

The material according to the invention can also be p-type doped or p-type doped.

FIG. 6 illustrates a device 45 comprising a material according to the invention doped with type n 50a and a material according to the invention doped with type p 50b.

The doped n-type material consists of a layer disposed on a substrate 10, formed by the juxtaposition in a direction X parallel to the substrate of solid solutions in a direction parallel to the substrate, preferably formed of elementary meshes of perovskite crystallographic structure oxide. It has the shape of a right prism whose base 55 is a right triangle. The large face of the layer, defined by the hypotenuse 57 of the triangular base and opposite to that 58 disposed on the substrate is inclined relative to the substrate.

The p-type doped material consists of the n-type doped material in a layer formed by the juxtaposition of solid solutions in the X direction. Moreover, it has a shape identical to that of the n-type doped material and is arranged on the n-type doped material such that the hypotenuse-defined faces 57, 59 of the triangular bases of each material are in contact with one another and define an interface 60.

The device thus formed has a prism shape with a rectangular base. The superposition of the two n-type and p-type doped materials according to the invention thus makes it possible to produce an n-p junction defined by the interface 60.

Preferably, the device is obtained by deposition of the n-type doped material by the method according to the invention followed by the deposition of the p-type doped material on the n-type doped material by the method according to the invention.

Of course, it is also conceivable to form a device in which the p-type doped material is disposed on the substrate and the n-type doped material is disposed on the n-type doped material.

FIG. 7 illustrates a mode of implementation of the process according to the invention for the preparation of a material comprising oxides of perovskite crystallographic structure. It should be noted that prior to step a), a layer of Sn0 ₂ or ZnO or TiO ₂ may be deposited on the substrate.

Furthermore, the substrate may comprise a support covered with a solid solution comprising the first and second oxides.

In step a), oxide precursors are chosen to obtain a material comprising said oxides.

In particular, the precursors may be chosen from oxides and organometallic compounds and mixtures thereof, and are then chosen so as to deposit, in steps b) and c), oxides of perovskite structure. In a particular embodiment, a precursor of the oxide may consist of the oxide itself.

Alternatively, and especially to obtain an oxide of perovskite structure of general formula ABO3, precursor oxides of formula A _x O _y and B _X 'Cy with x, x', y and y 'being integers all greater than or equal to 1 can be chosen, since the valence of the elements A, B and oxygen (O) makes it possible to form an oxide of perovskite structure ABO ₃ . Illustratively, to form a solid solution having a perovskite oxide of the formula SrTi0 _3, may be arranged in step a) of SrO and Ti0 ₂ securities precursor of this oxide. Alternatively, it is possible to have in step a) a precursor formed by SrTiO ₃ itself.

In step b) (Figure 7a), the first solid solution 80 constituted by the first oxide can be obtained by depositing precursors of the first oxide on the substrate 10, which react to form the first oxide. Alternatively, it is possible to form a first solid solution comprising the first and second oxides.

In step c), the second solid solution 85 may be deposited on the first solid solution, so that the first solid solution is sandwiched between the substrate and the second solid solution. A material formed of a stack of solid solutions is thus obtained on a substrate oriented along an assembly direction A normal to the substrate. This stack is illustrated in Figure 7) b).

Alternatively, the second solid solution 85 may be deposited on the substrate in contact with the first solid solution, in a direction of assembly parallel to the substrate.

Steps b) and c) are carried out so that the second oxide concentration of the second solid solution is greater than the second oxide concentration of the first solid solution, and the gaps of the first and second solid solutions are different. Preferably, the first oxide and second oxide concentrations in the first and second solid solutions are non-zero.

In this way, the material formed by the assembly of the first and second solid solutions has a gap continuously increasing or decreasing in the assembly direction. The same goes for the intermediate mesh parameter of the material. By depositing a succession of new solid solutions 90, and by adjusting the concentrations of oxide, preferably perovskite, within each solid solution, it is thus possible to obtain a material according to the invention as described for example in FIGS. 1 and 2 .

The assembly formed in step c) by a stack of solid solutions thus defines a solid solution of the first and second oxides, the first and second solid solutions comprising the same oxides but in different concentrations. The manufacturing method can comprise in particular a step of assembling on the solid solution formed in step c) and in the assembly direction, another solid solution comprising a third oxide and the second oxide. In particular, this other solid solution can be obtained by performing a succession of steps similar to step c), except that the first oxide is replaced by the third oxide.

In this way, it is thus possible to manufacture a material according to the invention, for example such as that illustrated in FIGS. 3 and 4.

According to this variant, to obtain a material whose gap increases continuously in the assembly direction, the third oxide has a larger gap than the second oxide if the gap of the second oxide is greater than the gap of the first oxide. Alternatively, the third oxide has a gap smaller than the gap of the second oxide if the gap of the second oxide is smaller than the gap of the first oxide.

Preferably, the formation of the first, second and optionally third solid solutions can be carried out by a method chosen from pulsed laser ablation (Pulsed Laser Deposition or PLD in English), especially in combinatorial mode (dual-PLD in English). ), the deposition of atomic layers (Atomic Layer Deposition or PLD in English), chemical vapor deposition (CVD), physical vapor deposition (PVD), and co-evaporation. Atomic layer deposition and pulsed laser ablation are the preferred methods.

In particular, the atomic layer deposition method can be of the thermal or plasma-assisted type (Plasma Enhanced ALD). It can also be of the liquid injection type (Liquid Injection ALD in English) so as to promote the crystallization of solid solutions. In the variant where the pulsed laser ablation method is implemented, the precursors in step a) are preferably in oxide form. In the variant in which the atomic layer deposition method is implemented, the precursors in step a) are preferably in the form of organometallic compounds.

In a particular embodiment, pulsed laser ablation can be implemented by performing the steps of:

i) having at least three targets comprising oxide precursors of the general formula A _x O _y , B ⁽¹⁾ _X 'Cy and B ⁽²⁾ _x O _y ", x, x', x", y, y ' and y "being integers all greater than or equal to 1, said precursors being capable of forming, by chemical reaction with each other, preferably by vapor phase deposition, crystalline oxides of perovskite structure of general formula AB ⁽¹⁾ O ₃ and AB ⁽²⁾ 0 ₃ ;

ii) subjecting at least two of the targets to laser pulses, the number of laser pulses per target being defined so as to form on the substrate a first solid crystalline oxide solution of general formula of the type with u between 0 and 1;

iii) subjecting at least two of the targets to laser pulses, the number of laser pulses per target being defined to form a second crystalline oxide solution of formula with v between 0 and 1, v being greater than u, the second solid solution being contiguous with the first solid solution deposited in step ii).

For example, to form the material according to FIG. 1, the pulsed laser ablation method can be implemented in the following manner.

Within the chamber of a pulsed laser ablation device, a target Bi ₂ 0 ₃ , a target of ln ₂ 0 ₃ and a crystalline substrate having a parameter less than 20%, preferably less than 5 % with perovskite oxide BilnO ₃ .

In order to form a first solid solution on the substrate, each of the targets of Bi ₂ 0 ₃ and In ₂ 0 ₃ is irradiated successively for identical periods so as to remove from these targets the constituent elements of the plasma, such as free radicals and ions. Since the substrate is placed opposite the plasma, the plasma elements reorganize on the surface of the substrate so as to form a deposit on the oxide substrate. Biln0 ₃ of perovskite structure. A first solid solution of BilnO _{3 is} thus obtained at the surface of the substrate.

Then, the targets of Bi ₂ 0 ₃ , In ₂ 0 ₃ and Sc ₂ 0 ₃ are irradiated successively with the aid of the laser beam, the irradiation time of the Bi ₂ 0 ₃ target being greater than the irradiation duration. target ln ₂ 0 ₃ , which itself is greater than the irradiation time of the Sc ₂ 0 ₃ target. In this way, the plasma generated by the ablation of the targets has a concentration Bi ₂ 0 ₃ greater than the concentration in ln ₂ 0 ₃ , itself higher than the concentration Sc ₂ 0 ₃ . This plasma is then deposited on the first crystalline solid solution consisting of BilnO ₃ . The oxides of the plasma form a solid solution of elemental cells of BilnO ₃ and BiSc0 ₃ which grow on the elemental cells of BilnO ₃ of the first solid solution. The first and second solid solutions thus define a solid solution of BilnO ₃ and BiSc0 ₃ in which the concentrations of BilnO ₃ and BiSc0 ₃ , measured according to the assembly direction, move in opposite directions from each other.

Thus, in the direction of normal deposition to the substrate, starting from the substrate to the free surface of the second solid solution, the elemental mesh concentration of BilnO ₃ decreases and the elemental mesh concentration of BiSc0 ₃ increases.

The solid solution deposition process is reiterated by modifying the exposure times of the laser beam on the targets ln ₂ 0 ₃ and Bi ₂ 0 ₃ so as to obtain a concentration of elemental cells of ln ₂ 0 ₃ and Sc ₂ 0 ₃ decreasing and increasing respectively with each deposit of a new solid solution.

To obtain the last solid solution of the stack, consisting of cells of BiSc0 ₃ , only the targets of Bi ₂ 0 ₃ and Sc ₂ 0 ₃ are irradiated.

A material according to the invention is thus manufactured as illustrated in FIG. 1, consisting of a solid solution of perovskite structure oxides BilnO ₃ and BiSc0 ₃ .

To manufacture a material as described in FIG. 3 comprising a succession of solid solutions of different oxides, it is possible, for example, to have, within the chamber of the pulsed laser ablation device, a Ga ₂ 0 ₃ target and a target of A1 ₂ 0 ₃ in addition to the targets described above. On the solid solution Si of BilnO ₃ and BiScO ₃ oxides described above, solid solutions comprising BiSc0 ₃ and BiGa0 ₃ can then be formed by pulsed laser ablation by successively irradiating the Bi ₂ O ₃ targets. Sc2O3 and Ga ₂ 03 as described above. It is thus possible to form a solid solution S ₂ of oxides BiSc0 ₃ and BiGa0 ₃ .

Thus, the solid solutions Si (of Biln0 ₃ and BiSc0 ₃ ) on the one hand and S ₂ (of BiSc0 ₃ and BiGa0 ₃ ) on the other hand, arranged on one another, both comprise the BiSc0 ₃ oxide. in common.

Finally, on the solid solution S ₂ of BiSc0 ₃ and BiGa0 ₃ , solid solutions containing BiGa0 ₃ and B1AIO ₃ can be formed by pulsed laser ablation by successively irradiating the targets of Bi ₂ O ₃ , Ga ₂ O ₃ and A1 ₂ 0 ₃ . Thus, a solid solution S ₃ of oxides BiGa0 ₃ and B1AIO3 can be formed.

Thus, the solid solutions S ₂ (of BiSc0 ₃ and BiGa0 ₃ ) on the one hand and S ₃ (of

BiGa0 ₃ and B1AIO ₃ ), on the other hand, arranged on one another both contain the oxide BiGa0 ₃ in common.

FIG. 8 illustrates a device 95 according to the invention comprising a substrate 100 and first 105 and second 110 materials, each material being in accordance with the invention. In the example of FIG. 8, the first and second materials are identical to the material described previously in the example of FIG.

The first and second materials are arranged on the substrate so that the gap of the first material increases continuously, in a direction Di normal to the first face 115 of the substrate, from the first face of the substrate to the face 116 of the farthest first material and located opposite the first face of the substrate, and the gap of the second material increases continuously, in a direction D ₂ normal to the second face 120 of the substrate, from the second face of the substrate to the face 121 of the second material further away and located opposite the second face of the substrate.

The device of FIG. 8 may further comprise at least one antireflection layer 125i, 125 ₂ , preferably made of silicon nitride S1 ₃ N ₄ , disposed on the face of the first material and / or the second material situated opposite the substrate.

The substrate may further comprise a support 130, whose first face and / or the second face are covered with an electrode layer 135i, 135 ₂ , for example made of a material chosen from Sn0 ₂ , TiO ₂ , ZnO and their mixtures, sandwiched between the support and the first material and / or the second material respectively. The support can be in a glass and can be covered with an accommodation layer. Those skilled in the art know how to choose the constituent materials of the substrate so that the first material and / or the second material adhere to it.

Of course, the invention is not limited to the embodiments provided as examples.

References

[Stan] M. Stan et al, Journal of Crystal Growth, vol. 310, num. 23, pages 5204-

5208, 2008

[Mukherj] A. Mukherji, The Journal of Physical Chemistry, vol. 115, pp. 15674-15678, 2011.

Claims

1. Crystalline and radiation-absorbing material (5) formed at least in part of elementary meshes of a first oxide (15) and of elementary meshes of a second oxide (20) different from the first oxide two contiguous elementary meshes having a mesh mismatch of less than 20%, preferably less than 5%, and said material having a growing gap continuously through at least one direction X, the continuously increasing gap of the material being such that the continuity coefficient C is less than 1.

2. Material according to the preceding claim, wherein the elemental meshes of one of the oxides are those of a perovskite structure of general formula

AB0 ₃ .

3. Material according to the preceding claim, wherein

element A is selected from the group consisting of hydrogen (H), potassium (K), copper (Cu), lithium (Li), silver (Ag) and gold (Au) and element B is chosen from the group formed by bismuth (Bi), antimony (Sb), niobium (Nb), vanadium (V),

or

the element A is chosen from the group formed by calcium (Ca), barium (Ba), strontium (Sr), lead (Pb) and element B is chosen from the group formed by titanium (Ti ), zirconium (Zr), ruthenium (Ru), molybdenum (Mo) and rhodium (Rh),

or

the element A is chosen from the group formed by lanthanum (La), bismuth (Bi), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), praseodymium (Pr), Pholmium (Ho), erbium (Er), Pytterbium (Yb) and lutetium (Lu) and element B is selected from the group consisting of aluminum (Al), chromium (Cr), iron (Fe), gallium (Ga), indium (In), scandium (Se) and manganese (Mn).

4. The material according to claim 1, wherein all the elementary meshes are elementary meshes of perovskite structures.

5. Material according to the preceding claim, wherein the elementary meshes form a solid solution.

A material according to any one of the preceding claims, wherein an intermediate mesh parameter of the crystalline material continuously increases across the material in at least one direction.

7. Material according to the preceding claim, wherein the variation of intermediate mesh parameter, measured along a segment traversing the material from side to side is greater than 20%.

8. Material according to the preceding claim, wherein the growth direction of the intermediate mesh parameter is parallel to the X direction of gap growth.

9. Material according to any one of the preceding claims, being in the form of a layer.

10. The material according to claim 1, wherein the gap increases continuously between 0.25 eV and 3.20 eV.

11. Material according to any one of the preceding claims, wherein

an elemental mesh of a perovskite structure of formula BilnOs is contiguous with an elementary cell of a perovskite structure of formula BiSc0 ₃

and or

an elemental mesh of a perovskite structure of formula BiSc0 ₃ is contiguous with an elementary cell of a perovskite structure of formula BiGa0 ₃

and or

an elemental mesh of a perovskite structure of formula BiGa0 ₃ is contiguous with an elementary cell of a perovskite structure of formula BiA10 ₃ .

12. A method of manufacturing a material comprising an assembly of first and second solid solutions, consisting in implementing the following successive steps: a) having a substrate and precursors of first and second oxides, said oxides having different gaps and a mismatch of less than 20%, preferably less than 5%,

b) depositing on the surface of the substrate at least the first oxide by reaction of the precursor (s) of said oxide, so as to form the first solid solution (80),

c) forming, in an assembly direction X, preferably normal or parallel to the substrate, and in contact with the first solid solution, said oxides by reaction of the precursors of said oxides, so as to assemble the second solid solution (85) with the first solid solution, steps b) and c) being conducted so that the second oxide concentration of the second solid solution is greater than the second oxide concentration of the first solid solution, and the gaps of the first and second solid solutions are different, the material obtained in step c) being according to any one of claims 1 to 11.

13. The method of claim 12, wherein in step a), the precursors of the first and second oxide are selected so as to form in steps b) and c) oxides of perovskite structure.

14. The manufacturing method according to one of claims 12 to 13, comprising a step of forming on the assembly formed at the end of step c) and in the assembly direction, a solid solution comprising a third oxide and the second oxide.

15. The method of claim 14, wherein the third oxide is determined so as to have a gap greater than the second oxide if the gap of the second oxide is greater than the gap of the first oxide, or is determined so as to have a gap less than gap of the second oxide if the gap of the second oxide is smaller than the gap of the first oxide.

16. A method according to any one of claims 12 to 15, wherein the assembly of the first, second and optionally third solid solutions is carried out with a method chosen from pulsed laser ablation, the deposition of atomic layers, chemical vapor deposition, physical vapor deposition and co-evaporation.

17. Method according to the preceding claim, wherein the pulsed laser ablation method is implemented by performing the steps of:

ii) subjecting at least two of the targets to laser pulses, the number of laser pulses per target being defined so as to form on the substrate a first crystal oxide layer of general formula of the type with u between 0 and 1;

iii) subjecting at least two of the targets to laser pulses, the number of laser pulses per target being defined to form a second crystal oxide layer of formula with y between 0 and 1, v being greater than u, the second layer being contiguous with the first layer deposited in step ii).

18. Device comprising a material according to any one of claims 1 to 11 and / or obtained by the method according to any one of claims 12 to 17, preferably selected from a photovoltaic cell, a light measuring cell, for example in Γ infra-red, a thermal measuring camera, a fire detector.

19. Device (95) according to the preceding claim, comprising a substrate (100) having a first face (115) on which is disposed a first material (105) and a second face (120), opposite to the first face, on which a second material (110) is arranged, the first and second materials being according to the invention and / or being obtained by the method according to the invention.