Patent Description:
With climate change, global warming and the fossil fuel depletion, many technologies have been developed over the past few years in order to use alternate resources and in particular renewable energy resources.

A solar cell comprises a P-N junction wherein light is absorbed to create electron-hole pairs and opposite electrodes to collect electrons on one side and holes on the other side.

In order to improve the efficiency of the photovoltaic cells, one way is to stack two photovoltaic cells having different bandgaps to form a tandem photovoltaic cell wherein each photovoltaic cell will convert a different part of the solar spectrum of the incoming light.

The tandem photovoltaic cells usually comprise a back photovoltaic cell based on silicon and having a bandgap around <NUM> eV.

The front photovoltaic cell needs to have a higher bandgap, preferably around <NUM> eV. Perovskite based solar cells enable to achieve such bandgap with a limited cost and are therefore promising candidates for highly efficient tandem solar cells.

However, perovskite absorber materials have also drawbacks, in particular their limited stability with respect to H<NUM>O and O<NUM>. Indeed, perovskite may be degraded by the presence of O<NUM> and H<NUM>O in its environment so that perovskite needs to be protected from such degradation. One way to protect perovskite is to add encapsulation layers over the perovskite. The encapsulation layers refer notably to a layer of indium tin oxide (ITO) arranged on the top of the perovskite layer and providing a transparent carrier transport layer. However, to obtain a good lateral conductivity, the ITO layer requires a high temperature process, for example higher than <NUM> leading to a degradation of the perovskite. Furthermore, the transparent conductive oxides (TCO) such as ITO arranged above the perovskite layer lead to parasitic absorption in the near infra-red spectrum and therefore limit the efficiency and tend to be expensive.

It is therefore necessary to find a solution enabling the production of a perovskite based tandem cell wherein the perovskite is protected by passivation layers without requiring high temperature process, notably process requiring a temperature higher than <NUM> in order to avoid the perovskite degradation during the manufacturing process. Documents <CIT> and <CIT> disclose tandem solar cells of the state of the art.

The present invention aims therefore at providing a solution to obtain a tandem photovoltaic cell based on silicon and perovskite sub-cells with good resistance against oxidation contaminants and high power conversion efficiency.

The present invention refers to a two terminal tandem cell comprising:.

wherein the perovskite top cell comprises alternated back contacts made by a first carrier transport layer arranged on the front contact of the silicon bottom cell to produce a recombination layer or tunnel junction interface and a second carrier transport layer configured to be linked to a second terminal and wherein an insulator layer is arranged on one side between the silicon bottom cell and the second carrier transport layer and on the other side between the first carrier transport layer and the second transport layer.

The first and the second carrier transport layers may have opposite doping type and the combination of the first carrier transport layer, the insulator layer and the second carrier transport layer may produce a P-I-N junction (or a series of P-I-N junctions). Besides, by opposite doping type it is herein meant that one layer has a N-type doping and the other layer has a P-type doping. The second carrier transport layer may be linked to the second terminal via lateral metallic contacts.

The two terminal tandem cell may present one or several of the following aspects taken alone or in combination.

According to another aspect of the present invention, the electrical conductivity, the thickness and the pitch of the second carrier transport layer are configured to ensure lateral carrier transport toward the second terminal.

According to a further aspect of the present invention, the second carrier transport layer comprises at least one sub-layer made of metal or transparent conducting oxide to enhance lateral carrier transport toward the second terminal.

According to another aspect of the present invention, the first carrier transport layer and the second carrier transport layer have opposite doping type. One is n-doped whereas the other one is p-doped.

According to a further aspect of the present invention, the thickness of the first carrier transport layer, the second carrier transport layer and the insulator layer is comprised between <NUM> and <NUM>, preferably between <NUM> and <NUM>.

According to another aspect of the present invention, the thickness of the perovskite layer is comprised between <NUM> to <NUM>.

In this invention the term "perovskite" refers to a material which may be represented by the formula 'A"B''X'<NUM>, wherein 'A' is at least one cation, 'B' is at least one cation, and 'X' is at least one anion. The cation 'A' can be organic, inorganic, or an organic-inorganic cation. When the cation 'A' is organic, the organic cation can have the formula (R1R2R3R4N)n+ or (R5R6N=CH-NR7R8)n+, where R is hydrogen, unsubstituted or substituted alkyl, or unsubstituted or substituted aryl, and n is equal or superior to one (e.g. 'CH3NH3'+ refers as MA, 'HC(NH2)<NUM>'+ refers as FA, 'C(NH2)<NUM>'+ refers as GA). When the cation 'A' is inorganic, the cation can be selected from the group consisting of Ag+, Li+, Na+, K+, Rb+, Cs+, Be2+, Mg2+, Ca2+, Pb2+, Sr2+, Ba2+, Fe2+, Sc3+, Y3+, and La3+. The cation can be used as a single or multiple ion (e.g. (Mg,Fe)SiO3), YBaCuO3).

When the cation 'A' is organic-inorganic, the cation can be used as a single or multiple ion such as 'A'=(M1n(R21-xR3x) (<NUM>-n)), where R is preferably an organic cation as described above and M is preferably an inorganic cation comprised as described above (e.g. FA1-xGax`B"X'<NUM>, Csx(MAnFA1-n) (<NUM>-x) 'B''X'<NUM>).

The cation 'B' can be a metal cation selected from the group consisting of Pb2+, Sn2+, Ge2+, Bi2+, Cu2+, Au2+, Ag2+, Sb2+, Nb2+, Ti2+, Mg2+, Si2+, Ca2+, Sr2+, Cd2+, Ni2+, Mn2+, Fe2+, Zr4+, Co2+, Pd2+, Yb2+, Eu2+, Ce4+, and Tb4+. The anion 'X' can be selected from the group consisting of halide anions comprising Cl-, Br-, I-, F-, or chalcogenide anions comprising O2-, S2-, Se2-, Te2-, or polyanions comprising BF4-, PF6-, SCN-. The anion can be used as a single or multiple ions such as 'X'=(R1-xRx), where R is an anion as listed above. The invention also includes other type of perovskites that can be elaborated: Cuprate perovskite (La2-xBaxCuO4, YBa2Cu3O7, Ba2MCu3O7, where M is a rare earth ion such as Pr, Y, Nd, Sm, Gd, Dy, Ho). Metal perovskite can be produced based on a RT3M structure, where R is a rare-earth ion, T is a transition metal ion (Pd, Rh, Ru) and M is a light metalloid (e.g. B, C).

The definition above on the range of materials thus includes, but is not limited to, the following compounds: CH3NH3PbX3, Csx(CH3(NH2)<NUM>)<NUM>-xPbX3, Csx((CH3NH3)y(CH3(NH2)<NUM>)<NUM>-y)(<NUM>-x)PbX3, AxCsy((CH3NH3)z(CH3(NH2)<NUM>)<NUM>-z)<NUM>-yPbX3 where A is an alkali metal (Li, Na, K, Rb), BaTiO3, PbTiO3, CaTiO3, SrTiO3, PbZrO3, SrTiO3, KTaO3, KNbO3, NaNbO3, Pb(Mg1/3Nb2/<NUM>)O3, Pb(Zn1/3Nb2/<NUM>)O3, Pb(Mn1/3Sb2/<NUM>)O3, Pb(Co1/3Nb2/<NUM>)O3, Pb(Mn1/3Nb2/<NUM>)O3, Pb(Ni1/3Nb2/<NUM>)O3, Pb(Sb1/2Sn1/<NUM>)O3, Pb(Co1/2W1/<NUM>)O3, Pb(Mg1/2W1/<NUM>)O3, LiNbO3, LiTaO3, BiTiO3, NaTiO3, NaNbO3, KNbO3, La1-xSrxMnO3, La2NiO4, La2CoO4, GdBaCo2O5, PrBaCo2O5, NdBa1-xSrxCoO2O5, Ba1-xSrxCo1-yFeyO3, BiCr1-xGaxO3, NaNbO3, KNbO3, LaFeO3, LaCoxFe1-xO3, La1-xSrxCoO3, LaSrNiO4, LaxSrx-1FeyBiy-1O3, La2NiO4, La2-xSrxCuO4, LaSrNi1-xAlxO4, LaMnO3, LaFeO3, LaCoO3, LaTi1xCuxO3, LiTaO3, NaTaO3, KTaO3, CaTa2O6, SrTa2O6, BaTa2O6, (La1-xSrxCoO3, Pr1-xSrxCoO3, Sm1-xSrxCoO3, Gd1-xSrxCoO3, Tb1-xSrxCoO3, LaCoO3, La1-xSrxMnO3, LaCo1-xNixO3).

According to a further aspect of the present invention, the capping layer of the perovskite top cell is deposited at a temperature lower than <NUM>, preferentially below <NUM>, to avoid damages to the perovskite material.

According to another aspect of the present invention, the capping layer is configured to prevent recombination of free carriers, and is for example made of polymethylmetacrylat "PMMA", Al<NUM>O<NUM>, SiO<NUM> or Phenyl-C61-butyric acid methyl ester "PCBM". The capping layer may be used as a passivation layer for the perovskite layer.

According to a further aspect of the present invention, the front contact of the silicon bottom cell is achieved by one of the following solutions:.

According to another aspect of the present invention, the silicon layer of the silicon bottom cell is made of N-type doped silicon, the front contact of the silicon bottom cell is made of P-type doped silicon and the first carrier transport layer is made of tin oxide "SnOx".

According to a further aspect of the present invention, the second carrier transport layer comprises a layer of silver doped nickel oxide "Ag:NiO".

According to another aspect of the present invention, the silicon layer of the silicon bottom cell is made of P-type doped silicon, the front contact of the silicon bottom cell is made of N-type doped silicon and the first carrier transport layer is made of nickel oxide "NiOx".

According to a further aspect of the present invention, the second carrier transport layer comprises a layer of tin oxide "SnOx".

According to another aspect of the present invention, the second carrier transport layer comprises a high electrical conductivity, for example by a free carrier concentration of at least 1E<NUM> at a carrier mobility of <NUM><NUM>/Vs, and the pitch is lower than <NUM>, for example lower than <NUM>.

According to a further aspect of the present invention, the insulator layer is made of Hafnium dioxide "HfO<NUM>" or aluminum oxide Al<NUM>O<NUM>.

The present invention also refers to a method for manufacturing a two terminal tandem cell comprising a silicon bottom cell and a perovskite top cell wherein the method comprises the following steps:.

The silicon bottom cell may be a manufactured silicon cell of the market.

According to a further aspect of the present invention, the deposition steps are made by sputter deposition or atomic layer deposition "ALD" or plasma-enhanced chemical vapor deposition "PECVD" or similar physical and chemical vapor phase deposition techniques and the etching steps are made by chemical or physical etching. The perovskite deposition may be made by any combination of wet and vacuum based deposition processes.

The following achievements are examples. Although, the specification refers to one or several embodiments, it does not imply that each reference refers to the same embodiment or that the features apply only to a single embodiment. Simple features of different embodiments can also be combined to provide other embodiments.

The present invention refers to a two terminal "2T" tandem photovoltaic cell comprising a silicon based bottom cell and a perovskite based top cell wherein the perovskite top cell comprises alternated back contacts and a capping layer configured as a passivation (and/or encapsulation) layer for the perovskite layer.

<FIG> represents a diagram of the stack of the different layers of such tandem photovoltaic cell <NUM>.

The tandem photovoltaic cell <NUM> comprises a rear contact layer <NUM>, a silicon layer <NUM> and a localized front contact layer <NUM>. By localized front contact layer <NUM>, we herein mean that the front contact layer <NUM> does not cover all the surface of the silicon layer <NUM> but is localized for example in the shape of stripes extending across the silicon layer <NUM>. These layers (<NUM>, <NUM> and <NUM>) correspond to the silicon bottom cell <NUM>. A first carrier transport layer <NUM> is arranged over the front contact layer <NUM> to produce a recombination layer or a tunnel junction interface between the silicon bottom cell <NUM> and the perovskite top cell <NUM>. An insulator layer <NUM> is arranged over the portions of silicon layer <NUM> without front contact <NUM>. A second carrier transport layer <NUM> is arranged over the insulator layer <NUM> and is alternated with the portions of the first carrier transport layer <NUM>. Two adjacent portions of first <NUM> and second <NUM> carrier transport layers are separated by an insulator layer <NUM>. The tandem photovoltaic cell <NUM> comprises for example a first series of stripes corresponding to the first carrier transport layer <NUM> and a second series of stripes corresponding to the second carrier transport layer <NUM>, the first and the second series being alternated and separated by stripes of insulator layer <NUM>. A perovskite layer <NUM> is arranged over the first <NUM> and second <NUM> carrier transport layers and a capping layer <NUM> is arranged over the perovskite layer <NUM>. The first <NUM> and second <NUM> carrier transport layers, the perovskite layer <NUM> and the capping layer <NUM> correspond to the perovskite top cell <NUM>.

A first terminal is linked to the rear contact layer <NUM> and a second terminal is linked to the portions of the second carrier transport layer <NUM>.

The front contact <NUM> may be made by diffusion doped layers or by heterojunction such as amorphous silicon "SiA" or by passivating contacts such as polysilicon.

As indicated previously, the front contact <NUM> and the first carrier transport layer <NUM> may form a recombination layer wherein for example the electrons from the perovskite layer <NUM> are recombined with holes of the silicon layer <NUM> to produce pairs of electron-hole. Alternatively, the front contact <NUM> and the first carrier transport layer <NUM> may form a tunnel junction enabling for example electrons from the perovskite layer <NUM> to be transmitted toward the silicon layer <NUM> to be collected at the first terminal.

Depending on the doping of the different layers, the electrons may come from the silicon bottom cell <NUM> and be recombined in the recombination layer (<NUM> and <NUM>) or be transmitted toward the perovskite layer <NUM> to be collected at the second terminal.

The first <NUM> and the second <NUM> carrier transport layers are configured to have opposite doping type. One has a N-type doping while the other has a P-type doping. Different material may be used for the first <NUM> and second <NUM> carrier transport layers such as TiO2, NiO, ZnO, MnO, CuSCN, SnO<NUM>, CuO, CrO, SrO or VO. The first <NUM> and the second <NUM> carrier transport layers together with the insulator layer <NUM> form a horizontal P-I-N configuration of the perovskite top cell <NUM> as represented in <FIG>.

The silicon based bottom cell <NUM> comprising the rear contact <NUM>, the silicon layer <NUM> and the front contact <NUM> may be a silicon photovoltaic cell of the market (without anti-reflection layer) and the other layers may then be deposited (and possibly etched) over the provided silicon cell. Furthermore, concerning the capping layer <NUM>, its deposition should be achieved at a temperature lower than <NUM>, preferentially below <NUM>, to avoid damaging the perovskite layer <NUM>. Such low temperature may be achieved due to the fact that no collection of free carriers is achieved at the capping layer <NUM>. The capping layer <NUM> may be configured to avoid recombination of electron-hole pairs in the capping layer <NUM>.

The capping layer <NUM> may also be made from typical charge transport materials, such as Phenyl-C61-Butyric acid Methyl ester "PCBM".

Such structure enables therefore the deposition of the carrier transport layers <NUM> and <NUM> requiring a high temperature process, for example <NUM> or more to be achieved before the deposition of the perovskite layer <NUM>.

It has to be noted that <FIG> represents a basic pattern which may be replicated laterally to produce an alternation of portions of first carrier transport layer <NUM> and portions of second carrier transport layer <NUM> which are interdigitated as represented in <FIG>. Thus, lateral dimensions may be extended to large scale manufacturing. <FIG> represents a sectional view according to the cut line A-A which extends laterally across a central portion of the tandem photovoltaic cell <NUM> as represented in <FIG>. However, it has to be noted that <FIG> represents only a portion of the section A-A comprising two stripes of second carrier transport layer <NUM> and one stripe of first carrier transport layer <NUM> but as indicated the pattern of <FIG> is replicated multiple times across the A-A section. It has also to be noted that <FIG> corresponds to <FIG>. <FIG> represents a sectional view according to the cut line B-B which also extends laterally but across a portion of the tandem photovoltaic cell <NUM> without the perovskite layer <NUM> and without the capping layer <NUM>.

<FIG> represents a sectional view according to the cut line C-C which extends laterally across a lateral portion of the tandem photovoltaic cell <NUM> comprising the metallic contacts <NUM> as represented in <FIG>. In this C-C section, the insulator layer <NUM> covers the first carrier transport layer <NUM> and the second carrier transport layer <NUM> is disposed all over the insulator layer <NUM>. The metallic contact <NUM> also called finger is then disposed over the second carrier transport layer <NUM>.

Actually, the portions of first carrier transport layer <NUM> and the portions of second carrier transport layer <NUM> are not exactly interdigitated. Indeed, the portions of the second carrier transport layer <NUM> (in the shape of parallel stripes as represented in <FIG> for example) are linked to metallic contacts <NUM> (also called fingers) at both of their extremities whereas there is no connection between the portions (also parallel stripes for example) of the first carrier transport layer <NUM> at their extremities.

<FIG> represents a sectional view according to the cutline D-D which extends across a longitudinal portion of the tandem photovoltaic cell <NUM> along a stripe of first carrier transport layer <NUM>. The stripe of the first carrier transport layer <NUM> does not extend over the whole length of the tandem photovoltaic cell <NUM> but only remains in the central part without metallic contact. An insulator layer <NUM> is disposed at both ends of the stripe of the first carrier transport layer <NUM>. The insulator layer <NUM> is then covered by a second carrier transport layer <NUM> and a metallic contact <NUM> at the longitudinal ends of the tandem photovoltaic cell <NUM> whereas in the central part, the first carrier transport layer is covered by the perovskite layer <NUM> and the capping layer <NUM>. A gap is arranged between the perovskite layer <NUM> and capping layer <NUM> of the central part a Thus, there is no contact between the stripes of first carrier transport layer <NUM> and the metallic contacts <NUM>. There is also no contact between the different stripes of first carrier transport layer <NUM>.

<FIG> represents a sectional view according to the cutline E-E which extends across a longitudinal portion of the tandem photovoltaic cell <NUM> along a stripe of the second carrier transport layer <NUM>. The stripe of the second carrier transport layer <NUM> extends over the whole length of the tandem photovoltaic cell <NUM>. The central part of the stripe is covered by a perovskite layer <NUM> and a capping layer <NUM> whereas the end parts are covered by the metallic contacts <NUM>. A gap is arranged between the perovskite layer <NUM> and capping layer <NUM> of the central part and the metallic contacts <NUM> of the end parts o the tandem photovoltaic cell <NUM>. The different stripes of second transport carrier layer <NUM> are therefore connected to each other.

Besides, concerning the second carrier transport layer <NUM>, its free carrier concentration, its thickness and its pitch P are configured to ensure the lateral transport of the free carrier toward the second terminal (which is linked to the metallic contact s <NUM>). The pitch P corresponds to the distance between the ends of a portion of the second carrier transport layer <NUM> as represented in <FIG> or more precisely to the distance between the two metallic contacts <NUM> arranged at both ends of the second carrier transport layer <NUM> The metallic contacts <NUM> may be made of Au, Ag, Al, Cu or other metal or alloys.

Thus, the concentration of free carrier in the second carrier transport layer <NUM> may be increased in order to allow the use of a larger pitch P and a higher thickness of the second carrier transport layer <NUM>. Furthermore, the second carrier layer <NUM> may comprise one or several sub-layers made of metal or transparent conducting oxide to enhance the lateral conductivity. These sub-layers may sandwich the main layer of the second carrier transport layer <NUM>.

The thickness of the first <NUM> and second <NUM> carrier layers as well as the insulator layer <NUM> are comprised between <NUM> and <NUM>. The thickness of the perovskite layer <NUM> is comprised between <NUM> and <NUM>.

The capping layer <NUM> may partly embed into the grain boundaries of the perovskite layer <NUM>. The capping layer <NUM> may be made of any suitable material which may be deposited at a temperature below <NUM> and which is stable with respect to the ultra-violet rays. Examples of such materials are, PMMA, Al<NUM>O<NUM>,.

The thickness of the capping layer <NUM> may be comprised between <NUM> and <NUM>.

<FIG> represents an embodiment of the present invention. In this embodiment, the front contact <NUM> of the silicon bottom cell <NUM> is made of a P-type doped amorphous silicon "p+aSi" and the first carrier transport layer <NUM> is made of tin oxide "SnO<NUM>". The first carrier transport layer <NUM> is a N-type doped layer. As indicated previously, the combination of the front contact <NUM> made of p-type doped amorphous silicon and the tin oxide layer <NUM> produces a tunnel junction between the silicon bottom cell <NUM> and the perovskite top cell <NUM>.

The insulator <NUM> may be made of an insulating oxide, such as hafnium oxide HfO<NUM> or aluminum oxide Al<NUM>O<NUM>.

The second carrier transport layer comprises silver doped nickel oxide "AgNiO" and is a P-type doped layer. As indicated previously, the layer of AgNiO may be sandwiched with sub-layers of a metal such as Ni or a transparent conductive oxide "TCO" such as indium tin oxide "ITO" to enhance its lateral conductivity. However, the thickness of a TCO sub-layer needs to remain weak, for example smaller than <NUM> in order to limit parasitic absorption in the near infra-red spectrum. The pitch P of the second carrier transport layer <NUM> is chosen smaller than <NUM>, for example smaller than <NUM>.

<FIG> show different simulations achieved on different configurations of the second carrier transport layer <NUM> and may be used to determine the different parameters and notably the free carrier concentration according to the desired pitch P. In this simulation a <NUM> thick ITO layer with a carrier mobility of <NUM><NUM>/Vs is studied as the second carrier transport layer <NUM> with various free carrier concentration from <NUM>,7E<NUM> and <NUM>,1E<NUM> cm-<NUM>. Indeed, <FIG> represents the simulated efficiency and open circuit voltage of the perovskite top cell in a tandem architecture as a function of the free carrier concentration for different values of pitch P, respectively <NUM>, <NUM> and <NUM>. <FIG> shows the simulated fill factor and short circuit current density of the perovskite top cell <NUM> in a tandem architecture as a function of the free carrier concentration for different values of pitch P, respectively <NUM>, <NUM> and <NUM>.

<FIG> shows the simulated absorber photocurrent density in the silicon bottom cell <NUM> and the residual photocurrent density in the second carrier transport layer <NUM> as a function of the free carrier concentration.

One can observe that a concentration of 1E<NUM> cm-<NUM> is necessary for pitches P higher than <NUM> to obtain an efficiency higher than <NUM>% or a fill factor higher than <NUM>%. The low fill factor arises from the increase of non-radiative recombination in the perovskite layer <NUM> and the increase of serial resistance in the second carrier transport layer <NUM>.

It also appears that no significant variation is found on the open circuit voltage and the short circuit current density. Significant loss of photocurrent density in the silicon bottom cell is observed when the free carrier concentration in the second carrier transport layer is larger than 1E<NUM> cm-<NUM>.

<FIG> represents the simulated external quantum efficiency "EQE" of the perovskite top cell <NUM> and the silicon bottom cell <NUM> and the sum of both of them as well as the residual absorption spectrum of the second carrier transport layer <NUM>. <FIG> shows that the second carrier transport layer <NUM> of high free carrier concentration mostly introduces photocurrent losses in the infra-red region of the spectrum which results in less photocurrent generated in the silicon bottom cell and therefore to a lower efficiency. Thus, to obtain high efficiency of a perovskite/silicon tandem photovoltaic cell, the free carrier concentration in the second carrier transport layer <NUM> has to be adjusted to balance the lateral conductivity and the infra-red transparency and therefore to obtain a tandem photovoltaic cell with an improved yield.

The perovskite layer <NUM> may be an intrinsic layer or a N-doped perovskite layer. The capping layer <NUM> may be made of Phenyl-C61-Butyric acid Methyl ester "PCBM".

The present invention is not limited to the embodiment represented in <FIG> which is only a particular example. Two terminal tandem cell comprising other types of material notably for the front contact layer, the first and second carrier transport layers, the insulator layer or the capping layer are also covered by the present invention.

The present invention also refers to an exemplary method for manufacturing a two-terminal "2T" tandem photovoltaic cell comprising a silicon based bottom cell <NUM> and a perovskite based top cell <NUM>. Other manufacturing methods may be envisaged.

<FIG> represents the different steps of the manufacturing method.

The first step <NUM> refers to providing a silicon bottom cell <NUM> corresponding to a first intermediate structure. Such silicon bottom cell <NUM> may be provided by a manufacturer of the market. Preferably, the silicon bottom cell <NUM> is provided without anti-reflection layer. As represented in <FIG>, the silicon bottom cell <NUM> comprises a rear contact <NUM> configured to be linked to a first terminal of the tandem photovoltaic cell, a silicon layer <NUM> arranged over the rear contact <NUM> and a front contact <NUM> arranged over the silicon layer <NUM>.

The second step <NUM> refers to depositing a first carrier transport layer <NUM> over the front contact layer <NUM> as represented in <FIG> which represents a second intermediate structure. This deposition may be sputter deposition or atomic layer deposition "ALD" or plasma-enhanced chemical vapor deposition "PECVD" or similar physical and chemical vapor phase deposition techniques.

The third step <NUM> refers to etching selectively the first carrier transport layer <NUM> and the front contact layer <NUM> to produce a third intermediate structure represented in <FIG>. In <FIG>, only one stripe of contact layer <NUM> and first carrier transport layer <NUM> is represented but in practice several parallel stripes may be achieved. The etching may be a chemical or a physical etching according to a process known from the state of the art.

The fourth step <NUM> refers to depositing an insulator layer <NUM> and a second carrier transport layer <NUM> over the third intermediate structure to produce a fourth intermediate structure as represented in <FIG>.

The second carrier transport layer <NUM> is configured to be linked to a second terminal of the tandem photovoltaic cell <NUM>, for example via metallic contacts <NUM> arranged at the ends of the stripes of the second carrier transport layer <NUM>. These depositions may be sputter deposition or atomic layer deposition "ALD" or plasma-enhanced chemical vapor deposition "PECVD" or similar physical and chemical vapor phase deposition techniques.

The fifth step <NUM> refers to etching the fourth intermediate structure to remove the layers covering the first carrier transport layer <NUM> to produce a fifth intermediate structure as represented in <FIG>. Such etching enables obtaining a smooth structure with an alternation of stripes of the first <NUM> and of the second <NUM> carrier transport layers, two adjacent stripes being separated by an insulator layer <NUM> to provide a plurality of P-I-N junctions along the lateral axis of the tandem photovoltaic cell. The etching may be a chemical or a physical etching according to a process known from the state of the art.

The sixth step <NUM> refers to depositing a perovskite layer <NUM> over the fifth intermediate structure to produce a sixth intermediate structure as represented in <FIG>. This deposition may be performed via single-step or multi-step state-of-the-art wet solution processing, such as spin-casting, slot-die coating etc, vacuum based processes such as thermal evaporation or hybrid deposition processes combining wet- and vacuum-based procedures.

The seventh step <NUM> refers to depositing a capping layer <NUM> over the sixth intermediate structure at a temperature lower than <NUM>, in particular lower than <NUM> to obtain the stack of layers of the embodiment of the invention presented in <FIG>.

Claim 1:
Two terminal tandem cell (<NUM>) comprising:
- a silicon bottom cell (<NUM>) comprising a silicon layer (<NUM>), a rear contact (<NUM>) configured to be linked to a first terminal and a front contact (<NUM>),
- a perovskite top cell (<NUM>) comprising a layer of perovskite (<NUM>) and a capping layer (<NUM>),
wherein the perovskite top cell comprises alternated back contacts made by a first carrier transport layer (<NUM>) arranged on the front contact (<NUM>) of the silicon bottom cell (<NUM>) to produce a recombination layer or a tunnel junction interface and a second carrier transport layer (<NUM>) configured to be linked to a second terminal and wherein an insulator layer (<NUM>) is arranged on one side between the silicon bottom cell (<NUM>) and the second carrier transport layer (<NUM>) and on the other side between the first carrier transport layer (<NUM>) and the second transport layer (<NUM>) and wherein the first carrier transport layer (<NUM>) and the second carrier transport layer (<NUM>) have opposite doping type.