Photovoltaic module

Abstract

The invention relates to photovoltaic modules, and in particular to photovoltaic modules comprising a plurality of organic photovoltaic cells (21, 22) (usually referred to as OPC or Organic Photovoltaic Cells).

Description

Description Title of the invention: Photovoltaic module Technical field of the invention

[0001] The invention relates generally to photovoltaic cells and modules, and in particular to photovoltaic modules comprising several organic photovoltaic cells (usually designated by the English acronym OPC for “Organic Photovoltaic Cells”).

[0002] For the purposes of the present invention, the term organic photovoltaic cell means a photovoltaic cell of which at least the active photovoltaic layer is made of an organic material. Prior art

[0003] Photovoltaic modules comprising organic photovoltaic cells represent a real interest in the field of photovoltaics. Indeed, the possibility of substituting inorganic semiconductors generally used in photovoltaic cells, such as silicon, copper, indium, gallium, selenium, or cadmium telluride, makes it possible to increase the number of feasible systems and therefore the possibilities of use. The development of marketable photovoltaic modules comprising several organic photovoltaic cells currently represents a major challenge.

[0004] In recent years, the development of organic photovoltaic cells has evolved through the use of the inkjet printing technique for their implementation (reference 1, reference 2). Moreover, in 2014 the Applicant developed a process for manufacturing photovoltaic cells using this technique for printing part of the layers of these cells (reference 3).

[0005] Typically, an organic photovoltaic cell uses two electrodes, a top electrode and a bottom electrode, at least one of which is semi-transparent to light and the other is metallic and reflective. These electrodes are adapted to harvest the photocharges generated by the photovoltaic active layer. In order to block the leakage current and improve the extraction of these generated photocharges, the frequently used approach is to insert interfacial layers between the photovoltaic active layer and each of the electrodes so as, among other things, to facilitate the movement of charges in the photovoltaic cell, the photocharges generated being either electrons or holes (positive charges).

[0006] For example, the photovoltaic active layer can be composed of two organic materials, one an electron donor and the other an electron acceptor. For an organic photovoltaic active layer, PsHT:PCBM is typically used (P3HT being the acronym for poly(3-hexylthiophene) and PCBM being the acronym for [6,6]-phenyl-C?i-methyl butanoate).

[0007] As illustrated in Figure 1, in a currently used normal or conventional structure photovoltaic cell 1, a first interfacial layer 9, comprising for example a polymer mixture of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate) (usually designated by the acronym PEDOT:PSS), is arranged on a layer of indium-tin oxide 3 (generally designated by the English acronym ITO for "Indium Tin Oxide") used as a lower electrode, serves here as an anode and is itself applied to a support. This layer of indium-tin oxide consists of a metal oxide which, in addition to conducting current, offers the property of being relatively transparent from 350 nm. It is the most commonly used material for collecting holes in the case of organic photovoltaic cells.Above the first interfacial layer 9 is applied a photovoltaic active layer 5 which may for example be based on PsHTPCBM, and above this photovoltaic active layer 5 is applied a second interfacial layer 6 above which is applied an opaque upper electrode 7 usually made of aluminum, or silver when this layer is applied by inkjet printing, and which serves here as a cathode. The two electrodes, i.e. the lower electrode and the upper electrode, used in the photovoltaic cell must have specific properties to allow their integration into organic photovoltaic cells. On the one hand, the two electrodes must have conductivities high enough to allow the collection of a maximum of charges.On the other hand, the transparency of the lower electrode, i.e. generally the indium-tin oxide layer, is also a fundamental characteristic to increase the number of photo-generated charges in the photovoltaic active layer.

[0008] There are also currently photovoltaic cells with an inverse structure. The major difference compared to the classic structure is that the PEDOTT:PSS interfacial layer is located between the active layer photovoltaic and the upper electrode which is here the anode. In this configuration, the indium oxide layer, which is then the lower electrode, serves as the cathode. It should be noted that photovoltaic cells with an inverse structure have the advantage of having better stability in air than photovoltaic cells with a conventional structure, and in addition of generally having higher conversion efficiencies.

[0009] For the purposes of the present invention, the conversion efficiency of a photovoltaic cell means the ratio of the maximum electrical power delivered by the cell to the incident light power, for a given spectral distribution and intensity.

[0010] It should be noted, moreover, that the high conversion efficiencies mentioned above are ensured when the photovoltaic modules of the current state of the art are exposed to external radiation, that is to say exposed to a light intensity greater than 2000 lux and in particular to radiation under standard AM1.5 conditions which corresponds to an exposure light intensity having a power of 100 mW / cm2 which is equivalent to a light intensity approximately equal to 100000 Lux. In particular, the high number of photo-generated charges requires the use of an anode with very high electrical conductivity to ensure good collection, in the photovoltaic active layer, of photo-generated charges so as, among other things, to minimize the accumulation phenomenon at the level of the interfacial layers. This is why generally, in the case of an inverse structure, the upper electrode (or anode) is opaque and made of silver.In this case, the conversion efficiency can reach, on a laboratory scale, values ​​between 15 and 17% for organic photovoltaic cells.

[0011] In currently used inverse structure photovoltaic cells, the first interfacial layer located between the lower electrode and the photovoltaic active layer is a layer comprising nanoparticles based on metal oxides such as zinc oxide (ZnO), titanium oxides (TiO x ), zinc oxides (AZO) or tin dioxide (SnC>2).

[0012] However, although this first interfacial layer has many advantages and interesting electronic properties, it also has certain disadvantages. Indeed, the availability of the oxides constituting this layer, the cost of the raw materials, the process associated with its implementation The work and its application to create the layer, the quantities of waste, particularly toxic waste, generated during its implementation, and the costly recycling methods to be used to treat this waste are all disadvantages to be noted.

[0013] This is why manufacturers are seeking to replace the first inorganic interfacial layer with an organic interfacial layer (polymers or organic molecules).

[0014] It should be noted, however, that the mobility of photocharges generated in organic layers is generally very low (charge mobilities in semiconducting polymers are much lower than those observed in silicon (1000 cm 2 V' 1 if 1 ) and are generally weaker than those measured in molecular semiconductors (about 1-15 cm 2 V' 1 if 1)), which has the effect of limiting their thickness to only around ten nanometers, without which the transfer of photo-generated charges would not be possible. However, the deposition techniques used do not allow for the controlled deposition of organic interfacial layers with such thicknesses and which are continuous and uniform.

[0015] As things stand, the production of photovoltaic cells comprising a first organic interfacial layer is therefore not only expensive, but does not yet guarantee the production of photovoltaic cells with optimal performance, or at least sufficient to ensure long-term use. Statement of the invention

[0016] The present invention aims to remedy the aforementioned drawbacks.

[0017] More specifically, the present invention aims to propose a solution that allows the long-term use of a photovoltaic cell whose manufacturing process is less expensive than those of the prior art and comprising a first organic interfacial layer depositable by inkjet printing on the first lower electrode. This first interfacial layer is uniform and has a very low thickness (generally < 5 nm). The low thickness of this first organic interfacial layer allows for significant transparency to light and therefore efficient passage of photons to reach the photovoltaic active layer and also a significant reduction in the cost of raw material.

[0018] To this end, the invention provides a photovoltaic cell, comprising at least one transparent support, a lower electrode covering said support, said lower electrode comprising an upper surface and a lower surface, a first interfacial layer, said first interfacial layer comprising an upper surface and a lower surface, a photovoltaic active layer; a second interfacial layer covering said photovoltaic active layer, the photovoltaic cell being characterized in that the first interfacial layer is an organic layer having a thickness of between 2 and 5 nm and comprising amine groups on its lower surface in contact with the upper surface of the lower electrode, and in that the first interfacial layer is continuous, transparent, and free of metal oxide.

[0019] By lower surface amine groups in contact with the upper surface of the lower electrode, within the meaning of the present invention, is meant a polar organic chemical compound derived from ammonia, resulting from the replacement of one or more hydrogens of the ammonia molecule by other substituents or radicals (alkyl or aryl). When one, two or three hydrogen atoms are substituted, the amines are respectively primary, secondary and tertiary. Quaternary ammonium compounds can also be found which are ammonia derivatives consisting of a nitrogen atom substituted by 4 alkyl groups.

[0020] The photovoltaic cell according to the invention makes it possible in particular to overcome the problem linked to the effect of prolonged exposure to light radiation in an indoor environment manifested by the variation in the output power of the solar cells which can be measured after illumination (commonly referred to in English as the "light soaking effect") insofar as the first interfacial layer is free of metal oxide which is mainly the cause of this effect. Thus, in the absence of this effect, the photovoltaic cells can be exposed in an indoor environment and operate both under solar radiation and also under artificial radiation.

[0021] Indeed, this effect generally appears in the inverse structure photovoltaic cells of the prior art which integrate a first interfacial layer comprising oxides, in particular zinc oxides. This effect is reflected in particular, in the context of an outdoor environment, by the improvement of the performances of the photovoltaic cells under solar radiation over time. In particular, it has been noted that the photovoltaic cells currently used and subjected to an outdoor environment see their performances increase gradually over a certain period, before tending towards limit values. As a result, the prolonged absence of exposure to UV light will generate a degradation of the performances and exposure to light will again be necessary to improve the performances.However, in the context of an indoor environment where UV radiation is absent (LED type lighting with emission in the visible range), the "light soaking effect" only generates a successive degradation of the performance of the photovoltaic cell over time.

[0022] By solar radiation, within the meaning of the present invention, is meant all the electromagnetic waves emitted by the sun which cover a wide wavelength band which goes from ultraviolet (approximately 200 to approximately 380 nm) to infrared (approximately 780 to approximately 10,000 nm) passing through the visible range (approximately 380 to approximately 780 nm).

[0023] Artificial radiation, for the purposes of the present invention, means exposure under illumination defined by a light spectrum that does not cover, or only very little, ultraviolet radiation. Generally, artificial radiation comes from an LED-type lighting source with emission in the visible range (wavelength between approximately 380 nm and approximately 780 nm).

[0024] By transparent support or transparent layer, within the meaning of the present invention, is meant a support defined or a layer defined by a transparency coefficient greater than or equal to 80%, preferably greater than or equal to 85%, when exposed to radiation covering a light spectrum extending between 380 nm and 780 nm.

[0025] For example, the transparent support may be made of glass or a polymeric material, preferably a support selected from polyethylene supports. teraphthalate (commonly referred to by the acronym PET), polyethylene naphthalate (commonly referred to by the acronym PEN) or glass.

[0026] For example, the lower electrode can be a layer of indium-tin oxide, a layer based on silver nanowires, a composite layer consisting of a silver grid and high-conductivity PEDOT:PSS, a layer of reduced graphene oxide or a layer of carbon nanotubes.

[0027] It is noted that the first interfacial layer is an electron transport layer and is located between the lower electrode and the photovoltaic active layer.

[0028] The photovoltaic active layer may be based on a so-called "donor" material composed of a p-type semiconducting polymer and a so-called "acceptor" material which may be a fullerene derivative or a non-fullerene n-type derivative.For example, the photovoltaic active layer may comprise a polymer blend comprising methyl [6,6]-phenyl-C71-butanoate combined with poly(thienol[3,4-b]-thiophene or PBDB-T-2F (donor): IO4CI (acceptor), PffBT4T-2OD (donor): EH-IDTBR (acceptor), D18 (donor): Y6 (acceptor), PBDB-T-2F: Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'- c:4',5'-c']dithiophene-4,8-dione)], IO4CI: 3,9-bis[5,6-dichloro-1 H-indene- 1,3(2H)dione]-5,5,11,11 -tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s- indaceno[1 ,2-b:5,6-b']dithiophene, PffBT4T-2OD: Poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'”-di(2-octyldodecyl)-2,2',5',2”,5”,2'”-quaterthiophene-5,5'”-diyl)], EH-IDTBR: C72H88N6O2S8.

[0029] It should be noted that the second interfacial layer is a hole transport layer and, in a first case, may be located between the photovoltaic active layer and an upper electrode. In a second case, the second interfacial layer may be the upper electrode and in this case plays the role of interface between the photovoltaic active layer and the environment outside the photovoltaic cell.

[0030] For example, the second interfacial layer can be a PEDOT:PSS layer.

[0031] It should be noted that the first interfacial layer is an organic layer having a thickness of between 2 and 5 nm so as, on the one hand, not to hinder the absorption of photons from the active photovoltaic layer in origin of external light radiation, and on the other hand, to avoid having a significant resistance (polymers as well as small organic molecules have low charge mobility and therefore thick layers have high resistivities). Indeed, the photo-generated charges in the photovoltaic active layer must cross the first interfacial layer longitudinally before reaching the electrode and therefore the thicker the first interfacial layer, the longer the distance to be covered by the charges and consequently the chances of losing these charges by recombination phenomena are high.

[0032] By lower surface of the first interfacial layer, within the meaning of the present invention, is meant the surface in contact with the upper surface of the lower electrode.

[0033] By first interfacial layer free of metal oxide, within the meaning of the present invention, is meant a layer which does not contain metal oxide such as, for example, zinc oxide (ZnO), titanium oxides (TiO x ), zinc oxides (AZO) or even tin dioxide (SnC ).

[0034] Furthermore, by way of example only, as a first interfacial layer, mention may be made of a layer comprising, as a substitute for the metal oxides currently used, a material chosen from Poly(9,9-bis(3'-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN-Br), polyethyleneimine (PEI), PEIE, Poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), N,N'-Bis(N,N-dimethylpropan-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide (PDI-NO) or N,N'-Bis{3-[3-(Dimethylamino)propylamino]propyl}perylene- 3,4,9, 10-tetracarboxylic diimide (PDINN).

[0035] Advantageously, it is preferable to optimize the interfaces between the first interfacial layer and the adjacent layers to ensure efficient transfer of the generated photocharges. Therefore, the first interfacial layer may have an Rms roughness of less than 5 nm, preferably between 2 nm and 5 nm.

[0036] Advantageously, the first interfacial layer may comprise nitrogen.

[0037] Advantageously, the second interfacial layer may comprise a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrene-sulfonate).

[0038] In a first variant of a particular embodiment, the photovoltaic cell may further comprise an upper electrode covering the second interfacial layer.

[0039] For example, this upper electrode may be a reflective metal electrode, for example silver.

[0040] In a second variant of a particular embodiment, the second interfacial layer comprising the polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrene-sulfonate) may be an upper electrode.

[0041] According to this second variant of a particular embodiment, the second interfacial layer may preferably be continuous, and may have a fibrous structure and an average thickness of between 100 nm and 400 nm. Under these conditions, the second interfacial layer can have an electrical resistivity between 50 and 150 ohm / sq.

[0042] By continuous, for the purposes of the present invention, is meant a layer which does not contain holes (the entire surface of the layer is covered by the material of the interfacial layer).

[0043] By fibrous structure, in the sense of the present invention, is meant a particular structuring of the layer at a nanometric scale by forming PEDOT: PSS fibers. The conductive PEDOT: PSS fibers are well percolated between them and ensure the continuity of the material and consequently the transport of charges in the layer is facilitated: there will be less resistance to the transport of charges in the layer and therefore the conductivity of the layer is improved.

[0044] According to this second variant, a significant lifetime of the photovoltaic cell is ensured under artificial radiation. This second variant also has the advantage of guaranteeing the operation of organic photovoltaic cells under artificial radiation by freeing itself from the need to be exposed to solar radiation, in particular the need to be exposed to ultraviolet irradiation.

[0045] According to one or other of the two variants of an embodiment described above, the photovoltaic cell can be entirely organic.

[0046] For the purposes of the present invention, a fully organic photovoltaic cell means a photovoltaic cell in which each of the layers constituting it is of an organic nature, except for the substrate. In addition to the carbon which is the essential component of an organic material, the latter can also contain the elements hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), sulfur (S), iron (Fe).

[0047] Advantageously, the photovoltaic cell comprises a first interfacial layer obtained by digital inkjet printing on the lower electrode of a composition of an organic ink having a viscosity of between 2 and 50 mPa.s at 20°C and comprising: - between 0.1% and 0.5% by mass of at least one organic polymer or organic molecule relative to the total mass of said ink composition, the organic polymer or organic molecule comprising amine groups and being soluble in polar solvents, - between 2% and 10% by mass of additives relative to the total mass of said ink composition, - between 80% and 90% by mass of one or more polar solvents relative to the total mass of said ink composition, and - between 1% and 5% by mass of water relative to the total mass of said ink composition.

[0048] The invention also proposes a photovoltaic module comprising at least two photovoltaic cells according to one or other of the two variants of an embodiment described above, a first photovoltaic cell and a second photovoltaic cell, the upper electrode of the first photovoltaic cell being in contact with the lower electrode of the second photovoltaic cell.

[0049] The photovoltaic module according to the invention has the advantage of being efficient when exposed to brightness between 5000 and 10000 lux. This therefore allows it to operate in mixed lighting conditions, namely under solar radiation or under artificial radiation.

[0050] The photovoltaic module according to the invention exhibits high stability under accelerated aging in artificial light.

[0051] The photovoltaic module according to the invention has high stability under accelerated aging in artificial light emitted by LEDs, due to the fact that the first interfacial layer used according to the invention is organic and therefore has no sensitivity to UV radiation (no "light soaking" effect). The absence of UV does not hinder the operation of such a first interfacial layer, unlike interfacial layers based on metal oxides (commonly used in OPV) which require activation under UV to make the layers functional. Indeed, the absence of UV generally causes significant drops in performance over time for interfacial layers based on metal oxides.

[0052] The invention also provides a composition of an organic ink, capable of being applied by digital inkjet printing to a lower electrode of a photovoltaic cell described above, to produce a first interfacial layer, the organic ink having a viscosity of between 2 and 50 mPa.s at 20°C and comprising: - between 0.1% and 0.5% by mass of at least one organic polymer or organic molecule relative to the total mass of the ink composition, the organic polymer or organic molecule comprising amine groups and being soluble in polar solvents, - between 2% and 10% by mass of additives relative to the total mass of the ink composition, - between 80% and 90% by mass of one or more polar solvents relative to the total mass of the ink composition, and - between 1% and 5% by mass of water relative to the total mass of the ink composition.

[0053] Advantageously, the organic ink has a viscosity of between 2 and 50 mPa.s at 20°C, and preferably between 2 and 20 mPa.s, and even more preferably between 7 and 12 mPa.s.

[0054] It should be noted that such a composition exhibits significant stability compared to inks based on metal oxide nanoparticles used in the prior art to produce the interfacial layers of the photovoltaic cells generally used.

[0055] In particular, the ink according to the invention also has the advantage of not generating any aggregation or phase separation for a few hours, or even a few days (at least two hours), which makes it possible to ensure a stable printing phase without loss of nozzles. Furthermore, this ink composition makes it possible to have a nozzle opening time of more than 5 minutes, or even 10 minutes, which makes it possible to avoid rapid clogging of the nozzles during the inkjet printing phase.

[0056] In addition, this composition has the advantage of having a low cost because organic polymers and organic molecules are less expensive than metal oxides, and their use concentration is lower than the latter.

[0057] Furthermore, this composition makes it possible to print by digital inkjet printing complete and uniform layers having roughnesses < 2 nm and having well-defined edges with thicknesses between 2 nm and 5 nm and to overcome the problems linked to the use of metal oxides, in particular the problems which can arise from the effect of prolonged exposure to light radiation. This stable composition is formulated to be applied by digital inkjet printing from usual non-toxic solvents allowing this composition to be deposited in ambient air.

[0058] In particular, organic polymers and organic molecules have the advantage of not being sensitive to ultraviolet radiation, this being linked to their intrinsic characteristics which are different from those of metal oxide nanoparticles.

[0059] Indeed, a conventional organic photovoltaic cell containing a metal oxide electron transport layer (e.g., zinc oxide or titanium oxide) generally needs to be exposed to UV light to form an ohmic contact between the metal oxide and the other layers (photovoltaic active layer and electrode). The nature of the bond between the organic interlayer and the bottom electrode (ITO) facilitates the formation of an ohmic contact without exposure to UV light, thus reducing damage to the organic photovoltaic cell resulting from such exposure.

[0060] Additives can be used here that solubilize the organic polymer or molecule and have high evaporation temperatures to prevent nozzle clogging and improve ink viscosity. Materials typically used for inorganic interfacial layers (such as metal oxides) are soluble in specific solvents, which are usually highly volatile alcohols that are not desired in inkjet printing. Organic materials such as polymers or molecules can be soluble in a wide variety of solvents, and therefore there are more choices for preventing nozzle clogging and improving ink viscosity. ink. For example, additives include ethylene glycol, diethylene glycol, glycerol.

[0061] Advantageously, the organic polymer or the organic molecule may comprise a nitrogen-containing compound, preferably an amine compound and more preferably a primary amine group, a secondary amine group, or a tertiary amine group. The amine compound may further comprise an acyclic group (the nitrogen atom is linked to one or more alkyl groups), an alicyclic group (the nitrogen atom is linked to a non-aromatic ring), an aromatic group (the nitrogen atom is linked to an aromatic ring) and / or a heterocyclic group (the nitrogen atom is engaged in a ring which may or may not be aromatic).

[0062] Advantageously, non-toxic solvents such as alcohols or water are good solvents for the polymer or organic molecule. Therefore, said one or more solvents may be chosen from ethanol, isopropanol, hexanole, terpiniole, ethylene glycol, deionized water, saline phosphate buffer solution, butanol, di-ethylene glycol, glycerol

[0063] Advantageously, the intermediate layer comprises an electron donor compound, preferably a nitrogen-containing compound, a phosphorus-containing compound and / or a sulfur-containing compound.

[0064] Advantageously, the organic polymer or the organic molecule may be chosen from Poly(9,9-bis(3'-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN-Br), polyethyleneimine (PEI), PEIE, Poly [(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), N,N'-Bis(N,N-dimethylpropan-1-amine oxide)perylene- 3,4,9, 10-tetracarboxylic diimide (PDI-NO) or N,N'-Bis{3-[3- (Dimethylamino)propylamino]propyl}perylene-3,4,9,10-tetracarboxylic diimide (PDINN).

[0065] The invention has the advantage of overcoming a problem related to the use of the lower electrode (preferably based on ITO, which is a material having an output work equal to 4.7 eV) which constitutes a barrier for the circulation of charges from the photovoltaic active layer to the lower electrode layer. The first organic layer free of metal oxide makes it possible to reduce the energy barrier between the photovoltaic active layer and the lower electrode layer by reducing the output work of the latter. Rather than being in the presence of a Schottky contact, we ultimately have an ohmic contact which is favorable to the collection of charges, in particular to the collection of electrons. In particular, according to the invention, the adsorption of the first organic layer free of metal oxide, due to the transfer of charges, in particular protons, from the hydroxyl groups to the amine groups, generates a dipole opposite to A0 (A0 being a surface dipole) resulting in a reduction of A0, which allows the reduction of the output work of the lower electrode.

[0066] Advantageously, the thickness of the second layer of the lower electrode may be between 2 and 5 nm and may comprise amine groups on its lower surface in contact with the upper surface of the first layer of the lower electrode.

[0067] Advantageously, the organic polymer or organic molecule may comprise nitrogen.

[0068] The invention further provides a method for manufacturing a photovoltaic cell, comprising the following steps: a) providing a support; b) producing a lower electrode on said support; c) producing a first organic interfacial layer on said lower electrode comprising a lower surface comprising amine groups in contact with the lower electrode, the first interfacial layer having a thickness of between 2 and 5 nm, being continuous, transparent, free of metal oxide and capable of being obtained after digital inkjet printing of the aforementioned ink composition; d) producing a photovoltaic active layer on said first interfacial layer; e) producing a second interfacial layer on said photovoltaic active layer;said method being characterized in that steps b), c), d) and e) are each carried out by depositing ink compositions by digital inkjet printing, followed by heat treatment, said ink composition used in step c) comprising a mixture based on organic molecules soluble in polar solvents.;

[0069] Advantageously, the invention makes it possible to manufacture a photovoltaic cell comprising a first interfacial layer from a ink composition by digital inkjet printing. This composition is preferably made from non-toxic solvents known to those skilled in the art and from organic materials free of metal oxide so as to allow their deposition in ambient air by digital inkjet printing. As a result, step c) of producing the first organic interfacial layer is simple to implement insofar as this step makes it possible to dispense with the use of interfacial layers based on metal oxides requiring special precautions when using them in a standard environment (ambient air).

[0070] Advantageously, it is preferable not to alter the support and the layers previously produced in step c). Consequently, the heat treatment of step c) may be an annealing treatment carried out at a temperature between 70°C and 130°C, for a duration between 1 and 5 minutes.

[0071] Advantageously, the wettability of the composition from which the first organic interfacial layer is derived may preferably be compatible with flexible substrates made of polyethylene terephthalate for example, to facilitate the formation of a continuous film with well-defined edges by digital inkjet printing.

[0072] Other advantages and particularities of the present invention will result from the description which follows, made with reference to the appended figures and the following examples: Brief description of the figures

[0073] [Fig 1] represents a schematic sectional view of a photovoltaic cell of conventional structure; and

[0074] [Fig 2] represents a schematic sectional view of a photovoltaic module 10 comprising photovoltaic cells 21 and 22 according to a particular embodiment according to the invention.

[0075] Figure 1 is described in the preceding presentation of the prior art, while Figure 2 is described in more detail in the following examples, which illustrate the invention without limiting its scope. EXAMPLES

[0076] Products

[0077] support 20 in PET or glass;

[0078] cleaning solvents:

[0079] o in the case of rigid glass supports: deionized water, Acetone, Ethanol, Isopropanol, and

[0080] o in the case of flexible substrates, the latter being protected by plastic films, they do not require cleaning as in the case of rigid substrates;

[0081] A first lower electrode 210 based on ITO already deposited on the support 20 of the photovoltaic cell 21 and a first lower electrode 220 based on ITO already deposited on the support 20 of the photovoltaic cell 22 marketed by Addev Materials Micel (France).

[0082] A first ink composition E11 for producing a first organic interfacial layer 211 comprising a lower surface comprising amine groups in contact with the discontinuous lower electrode (ITO) so that the lower electrode is partly covered with the first interfacial layer 221 of the photovoltaic cells 21 and 22 of the photovoltaic module of FIG. 2 o The ink E11 comprises: - a first solvent 1: Butanol at a mass concentration approximately equal to 91.094% relative to the total weight of the ink E11, - a second solvent 2: deionized water at a mass concentration approximately equal to 3.124% relative to the total weight of the E11 ink, - an additive: ethylene glycol at a mass concentration approximately equal to 5.563% relative to the total weight of the E11 ink, - a PEI at a mass concentration approximately equal to 0.219% relative to the total weight of the E11 ink, Solvents, additives and PEI are marketed by Merck®

[0083] A second ink composition E20 for producing the photovoltaic active layers 212 and 222 of the photovoltaic cells 21 and 22 of the photovoltaic module of figure 2. o The ink E20 for producing the photovoltaic active layers 212 of the photovoltaic cell 21 comprises: - polymer blend E21 of methyl [6,6]-phenyl-C?i-butanoate (marketed by Nano-C® under the trade name PC70BM) and poly(thienol[3,4-b]-thiophene (marketed by Raynergy Tek® under the trade name PV2000); - O-xylene as solvent (ortho-xylene of formula CeH^CHs^); and - Tetraline (1,2,3,4-tetrahydronaphthaline) as an additive. o The E20 ink for producing the photovoltaic active layers 222 of the photovoltaic cell 22 comprises: - polymer mixture E22 of [6,6]-phenyl-C?i-methyl butanoate (marketed by Nano-C® under the trade name PC70BM) and poly(thienol[3,4-b]-thiophene (marketed by 1 -Materials under the trade name PTB7-Th); - O-xylene as solvent (ortho-xylene of formula CeH^CHs^); and - Tetralin (1,2,3,4-tetrahydronaphthaline) as an additive. The PV2000 polymer of the E21 mixture or the PTB7-Th polymer of the E22 mixture are present in these second ink compositions at a rate of 10 mg / ml. The mass ratio between the PV2000 polymer of the E21 blend or the PTB7-Th polymer of the E22 blend and the PC70BM is 1:1.5. The volume ratio between the O-xylene solvent and the Tetraline additive is 97:3 in these second compositions. A second E20 ink composition is produced by adding the solvent and additive to the E21 or E22 polymer mixture and maintaining this mixture for 24 hours under agitation on a hot plate at 80°C at a speed of 700 RPM.

[0084] A second alternative E20 ink composition (E20-alt) for producing the photovoltaic active layers 212 and 222 of the photovoltaic cells 21 and 22 of the photovoltaic module of Figure 2. o The E20-alt ink comprises: - PC60BM:

[0060] PCBM, 3'H-cyclopropa[1,9][5,6]fullerene-C60-lh-3'-butanoic acid 3'-phenyl methyl ester marketed by Special Carbon Products; - poly(thienol[3,4-b]-thiophene marketed by Raynergy Tek® under the trade name PV2000); - O-xylene as solvent (ortho-xylene of formula CeH^CHs^); and - Tetralin (1,2,3,4-tetrahydronaphthaline) as an additive. The PV2000 polymer is present in this second ink composition at a rate of 15 mg / ml. The mass ratio between the PV2000 polymer and the PC60BM polymer is 1:1.5. The volume ratio between the O-xylene solvent and the Tetraline additive is 50:50 in these two second compositions. The second E20-alt ink composition is kept stirring for 24 hours on a hot plate at 80°C at a speed of 700 RPM.

[0085] Third ink composition E30 for the production of the upper electrodes 213 and 223 (or anode) of the photovoltaic cells 21 and 22 of the photovoltaic module of figure 2. o The ink E30 comprises: - PEDOT: PSS marketed by Agfa® under the trade name IJ1005 or PEDOT: PSS marketed by Agfa® under the trade name ORGACON S315; - Triton X-100 (4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol of formula- Oct-C6H4-(OCH2CH2) X OH, x= 9-10) marketed by Merck® as a detergent / surfactant; - Ethanediol (or ethylene glycol, with the formula HOCH2CH2OH) marketed by Merck®; - glycerol (1,2,3-Propanetriol or glycerin, of formula HOCH2CH(OH)CH2OH) marketed by Merck®; - Deionized water, produced in the laboratory or marketed by the company PURELAB® classic under the brand ELGA® for water.

[0086] A third alternative E30 ink composition (E30-alt) for producing the upper electrodes 213 and 223 (or anode) of the photovoltaic cells 21 and 22 of the photovoltaic module of Figure 2. o The E30-alt ink comprises: - PEDOT:PSS marketed by Agfa® under the trade name IJ1005, - Triton X-100 (4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol of formula Oct- C6H4-(OCH2CH2)XOH, X= 9-10) marketed by Merck® as a detergent / surfactant.

[0087] Tests

[0088] Rms roughness measurement

[0089] These measurements are carried out using an atomic force microscope (Nanoscope III Multimode SPM from Brucker®, used in intermittent contact mode (or “tapping mode”), with hq:nsc15 tips marketed by MiKromasch® and having a radius of curvature of 8 nm), the measurements were carried out on different samples of photovoltaic cells according to the invention and according to the prior art.

[0090] Measuring the thickness of the layers

[0091] The thickness of the printed layers is measured using a DektakXT brand tip profilometer marketed by BRUKER using a scratch made with a cutter blade (a channel with the same thickness as the deposit is thus created). This is a contact profilometer that measures variations in relief by moving a tip stylus vertically across the surface, applying a constant contact force and revealing all the unevenness. The sample is placed on a plate that allows it to move at a given speed and over a chosen distance. The thickness values ​​presented in this patent application correspond to the average of five measurements taken at six different points during the same step of a sample. Before carrying out the measurements, the length of the scanned area, its duration, the pressure force of the stylus and the measuring range must be defined.

[0092] Measurement of electrical resistivity

[0093] This measurement is carried out using the 4-point technique, as follows: - we place the 4 aligned points far from the edges of the layer to be characterized; - these 4 points are equidistant from each other; and - current is generated by a current generator between the outer tips, while voltage is measured between the inner tips. The ratio of the measured voltage to the current flowing through the sample gives the resistance of the section between the inner tips.

[0094] Viscosity measurement:

[0095] The viscosity of a fluid is manifested by its resistance to deformation or to the relative sliding of its layers. During the flow of a viscous fluid in a capillary tube, for example, the speed of the molecules (v) is maximum in the axis of the tube and decreases until it is zero at the wall, while between the layers a relative sliding develops; hence the appearance of tangential friction forces. Tangential forces in fluids depend on the nature of the fluid considered and its flow regime.

[0096] The viscometer used is of the Ubbelhode type, it is placed in a thermostat maintained at a constant temperature (25 °C in our case study). We measure the flow time of a constant volume V defined by two reference lines (M1 and M2) located on either side of a small reservoir above the capillary.

[0097] Measurement of photovoltaic performance indoors:

[0098] The study of the aging of the modules produced under permanent lighting is carried out through an indoor characterization bench. This characterization bench includes an opaque closed enclosure (to avoid any light coming from outside) equipped with an LED type lighting source (in particular a Keithley 2450 Source-meter) and a computer with a LabVIEW program allowing to automatically measure the performance of the modules (determination of the photovoltaic parameters) with a well-defined frequency (for example 10 times per day). The photovoltaic modules are permanently illuminated by a lighting source under a light intensity approximately equal to 1000 lux measured by a luxmeter (in particular by the Chauvin Arnoux Ca 1110 luxmeter) compatible with a wide variety of light sources, including LED and fluorescent light up to 200,000 lux in compliance with class C of the NF C 42-710 standard.

[0099] The lighting source used to perform the interior measurements as well as the performance measurements is a Philips 60x60 cm LED panel. 2 - 4385K with an emission spectrum in the visible. [000100] Characterization of the morphology: [000101] AFM (Atomic Force Microscope) measurements to reproduce surface topography and TEM (Transmission Electron Microscopy) to validate the crystalline nature of the materials as well as the sizes of nanoparticles present at the layer level. [000102] Fill factor [000103] The fill factor corresponds to the ratio of the maximum electrical power to the product of the short-circuit current and the open-circuit voltage. It is generally expressed as a percentage. [000104] EXAMPLE 1: obtaining an example of ink composition E11 for producing the first organic interfacial layer 211 on the lower electrode layer 210. [000105] PEI is used to obtain the ink composition E11, the composition of which is detailed below: [000106] The preparation of the E11 ink formulation is carried out in two stages: [000107] Step 1: Preparation of the mother solution: - Weigh 0.35 g of PEI (intermediate layer polymer) - Add 5 ml of ionized water to these 0.35 g of PEI - Stir at a temperature of 60°C for at least 4 hours to obtain the mother solution. [000108] Step 2: Preparation of the E11 ink formulation: - Take a volume of 250 pL of the mother solution, - Add 9 ml of Butanol, - Add 400 pL of ethylene glycol, Stir the mixture at room temperature for 24 hours to obtain formulation E11. - The E11 formulation is filtered before any printing using an AC filter with a cut-off threshold of approximately 0.2 pm. [000109] EXAMPLE 2: obtaining an example of a second ink composition E20 for producing the photovoltaic active layer 212. [000110] Depending on whether PC70BM combined with PV2000 or PC70BM combined with PTB7-Th is used, the ink compositions E201 and E202 are obtained respectively, the compositions of which are detailed in Table 1 below: [000111] [Table 1] [000112] The ink composition E201 is obtained as follows: - 10 mg PTB7-th mixed with 15 mg of PC70BM (corresponding to a mass ratio of 1:1.5) in 1 milliliter of o-xylene and 60 microliters of tetralin. - The mixture is stirred magnetically on a hot plate at 80°C for 24 hours. - Before printing, the ink is pre-filtered with a 0.45 micrometer AC filter. - The printed layers then undergo thermal annealing on a hot plate at 85°C for 2 minutes. [000113] The ink composition E202 is obtained as follows: - 10 mg PV2000 mixed with 15 mg PC70BM (corresponding to a mass ratio of 1:1.5) in 1 milliliter of o-xylene and 60 microliters of tetralin. - The mixture is stirred magnetically on a hot plate at 80°C for 24 hours. - Before inkjet printing, the E142 ink is filtered with a 0.45 micrometer AC filter. - After inkjet printing of E201 or E202, photovoltaic active layers are obtained which, once printed, are subjected to thermal annealing on a hot plate at 85°C for 2 minutes. [000114] EXAMPLE 3: obtaining an example of a second ink composition E20 for producing the photovoltaic active layer 212. [000115] PC60BM is used as an acceptor combined with PV2000 as a donor to obtain the ink composition E203, the composition of which is detailed in Table 1 below: [Table 1] [000116] The ink composition E203 is obtained as follows: - 15 mg PV2000 mixed with 22.5 mg PC60BM (corresponding to a mass ratio of 1:1.5) in 0.5 milliliter o-xylene and 0.5 milliliter tetralin. - The mixture is stirred magnetically on a hot plate at 80°C for 24 hours. - Before printing, the ink is pre-filtered with an AC filter with a cut-off threshold of approximately 0.45 micrometers. - After inkjet printing of E203, a photovoltaic active layer is obtained which, once printed, is subjected to thermal annealing on a hot plate at 85°C for 2 minutes. [000117] EXAMPLE 4: obtaining examples of third ink composition E30 for producing the upper electrode layer 213 when the latter is also the second interfacial layer. [000118] This third ink composition E30 for producing the upper electrode layer 213 is obtained as follows: - the PEDOT:PSS is filtered with a 0.45 pm filter; - 500 μl of Triton X-100 (a) are mixed with 200 μl Ethylene Glycol (b), 200 μl Glycerol (c) and 100 μl Ethanolamine (d) in 9 ml of deionized water (e); - the mixture thus obtained is placed under magnetic stirring at 50°C on a hot plate for 30 minutes, then under magnetic stirring at room temperature for 20 minutes; - the initially filtered PEDOT:PSS is mixed with the mixture thus obtained after stirring, in the following proportions: 30 μl of mixture of the 3 additives in deionized water for 1 ml of PEDOT:PSS; the resulting mixture (with PEDOT:PSS) is placed under magnetic stirring on a hot plate at room temperature for at least 1 hour; and - the final solution thus obtained E30 is degassed for 3 to 5 minutes in an ultrasonic bath before printing. [000119] Depending on whether PEDOT:PSS IJ 1005 or PEDOT:PSS ORGACON S315 is used, the ink compositions E301 and E302 are obtained respectively, the compositions of which are detailed in the two tables 2 and 3 below: [Table 2] [Table 3: [000120] EXAMPLE 5: obtaining an example of a third ink composition E30 for producing the upper electrode layer 213. [000121] This third ink composition E303 for producing the upper electrode layer 213 is obtained as follows: - the PEDOT:PSS solution (IJ1005) initially stored in a refrigerator is filtered with a filter having a cut-off threshold approximately equal to 0.45 pm; - 30 μl of Triton X-100 are mixed with 10 ml of the filtered PEDOT:PSS solution, - the mixture thus obtained is placed under magnetic stirring at room temperature on a magnetic stirrer for 16 hours, and - the final solution thus obtained E30 is degassed for 3 to 5 minutes in an ultrasonic bath before printing. [000122] EXAMPLE 6: obtaining examples of photovoltaic modules according to the invention: [000123] A photovoltaic cell C1 in accordance with the invention is produced according to the following method: - Provision of a transparent PET or glass support containing the first lower electrode. - Production on said first lower electrode of a first organic interfacial layer from the composition E11 of example 1. In particular, production of this layer by digital inkjet printing of the ink composition E11, then subsequent thermal annealing in a convection oven at 145°C for 3 minutes. The thickness of a first organic interfacial layer 211 printed on the layers of the lower electrode 210 is approximately 2-5 nm with roughnesses Rms less than 2 nm. - Production on said first organic interfacial layer 211 of a photovoltaic active layer 212 following the application by digital inkjet printing of the ink composition E203 of example 3 before carrying out thermal annealing in a convection oven at 145°C for 3 minutes. The thickness of the printed photovoltaic active layers 212 is approximately equal to 350 nm with roughnesses Rms less than 5 nm. - Production on said photovoltaic active layer 212 of an upper electrode 213 following the application by digital inkjet printing of the ink composition E303 of Example 5 before carrying out a thermal annealing in a convection oven at 145°C for 3 minutes. The thickness of the printed upper electrode layers 213 is approximately equal to 500 nm with roughnesses Rms less than 10 nm. [000124] At the end of the manufacturing process, a photovoltaic cell C1A is obtained which comprises, among other things, a first continuous, transparent interfacial layer free of metal oxide according to exemplary embodiments of the invention. [000125] RESULTS AND COMPARISONS: characterization of the photovoltaic cell C1 obtained in example 5 and comparison with examples of photovoltaic cells according to the prior art. [000126] The different photovoltaic cells, according to the invention and prior art, were characterized according to the tests indicated previously and the results of these characterizations in table 4 below. [000127] Two photovoltaic cells (C2A and C2B) according to the prior art were produced under the same conditions as those used for producing the photovoltaic cell C1 according to exemplary embodiments according to the invention. [000128] The first photovoltaic cell C2A according to the prior art differs from the photovoltaic cell C1 according to the invention by the presence of a lower electrode comprising a layer of indium-tin oxide and an interfacial layer based on metal oxides, in particular AZO (Aluminum Doped ZnO) and the second photovoltaic cell C2B according to the prior art differs from the photovoltaic cell C1 according to the invention by the presence of a lower electrode comprising a layer of indium-tin oxide and an interfacial layer based on metal oxides, in particular SnO2 (Tin dioxide). AZO is marketed by the company Genesink and SnO2 is marketed by the company Avantama. [000129] The photovoltaic cells C2A and C2B according to the prior art were produced in inverse structure with the photovoltaic active layer PV2000: PC60BM and the PEDOT: PSS as upper electrode, that is to say with the same active layers and upper electrodes as example 5 according to the invention. [000130] The photovoltaic cell C1 according to the invention and the photovoltaic cells C2A, C2B according to the prior art were characterized in the same conditions with the same characterization bench described previously under the same light intensity. [Table 4] 000131] Using the table above which represents the photovoltaic parameters (voltage, current, maximum power and fill factor) measured under LED type interior lighting (1000 LUX), it can be seen that the photovoltaic cell according to the invention C1 makes it possible to find photovoltaic performances very close to and sometimes better than those of cells produced according to the state of the art under the same conditions (same photovoltaic active layer and same electrodes (lower and upper)). The current generated by the cell according to the invention is of the same order of magnitude as that generated by the cells produced according to the prior art. [000132] The filling factor obtained with the cell produced according to the invention is higher than that obtained with the cells produced according to the state of the art under the same conditions, which indicates a better quality of interface between this interfacial layer and the other layers (lower electrode and active layer). [000133] The photovoltaic performances measured with the photovoltaic cell C1 according to the invention are very encouraging and confirm the good functionality of the first interfacial layer according to the invention in the case of an interior application (low-brightness LED-type lighting). Bibliographic references [000134] Reference 1: Sharaf Sumaiya, Kamran Kardel, and Adel El-Shahat. “Organic Solar Cell by Inkjet Printing — An Overview.” 53, Georgia, USA: Technologies, 2017, Vol. 5. [000135] Reference 2: Peng, X., Yuan, J., Shen, S., Gao, M., Chesman, ASR, & Yin, H. (2017). “Perovskite and Organic Solar Cells Fabricated by Inkjet Printing: Progress and Prospects”, Adv. Funct. Mater. 2017, 1703704 [000136] Reference 3: European patent application EP2960957 from DRACULA TECHNOLOGIES, filed on June 25, 2015 and published on December 30, 2015.

Claims

CLAIMS

1. Photovoltaic cell, comprising at least - a transparent support, - a lower electrode covering said support, said lower electrode comprising an upper surface and a lower surface, - a first interfacial layer, said first interfacial layer comprising an upper surface and a lower surface, - a photovoltaic active layer; - a second interfacial layer covering said photovoltaic active layer, said photovoltaic cell being characterized in that said first interfacial layer is an organic layer having a thickness of between 2 and 5 nm and comprising amine groups on its lower surface in contact with the upper surface of the lower electrode, and in that said first interfacial layer is continuous, transparent, and free of metal oxide.

2. Photovoltaic cell according to claim 1, according to which said first interfacial layer has a roughness Rms of less than 5 nm.

3. Photovoltaic cell according to one of claims 1 to 2, according to which said first interfacial layer comprises nitrogen.

4. A photovoltaic cell according to one of claims 1 to 3, wherein said second interfacial layer comprises a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrene-sulfonate).

5. Photovoltaic cell according to one of claims 1 to 4, further comprising an upper electrode covering said second interfacial layer.

6. Photovoltaic cell according to one of claims 1 to 5, according to which said second interfacial layer comprising said mixture Poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate) polymer is an upper electrode.

7. Photovoltaic cell according to one of claims 6, according to which said second interfacial layer is continuous and has a fibrous structure and an average thickness of between 100 nm and 400 nm.

8. Photovoltaic cell according to one of claims 6 or 7, characterized in that it is entirely organic.

9. Photovoltaic cell according to one of claims 1 to 8, in which the first interfacial layer is obtained by digital inkjet printing on the lower electrode of a composition of an organic ink having a viscosity of between 2 and 50 mPa.s at 20°C and comprising: - between 0.1% and 0.5% by mass of at least one organic polymer or organic molecule relative to the total mass of said ink composition, the organic polymer or organic molecule comprising amine groups and being soluble in polar solvents, - between 2% and 10% by mass of additives relative to the total mass of said ink composition, - between 80% and 90% by mass of one or more polar solvents relative to the total mass of said ink composition, and - between 1% and 5% by mass of water relative to the total mass of said ink composition.

10. The photovoltaic cell of claim 9, wherein the organic polymer or molecule is selected from Poly(9,9-bis(3'-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN-Br), polyethyleneimine (PEI), PEIE, Poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), N,N'-Bis(N,N-dimethylpropan-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide (PDI-NO) or N,N'-Bis{3-[3-(Dimethylamino)propylamino]propyl}perylene- 3,4,9, 10-tetracarboxylic diimide (PDINN).

11. Photovoltaic cell according to one of claims 9 or 10, according to which said one or more solvents are chosen from ethanol, isopropanol, hexanole, terpiniole, ethylene glycol, deionized water, a saline phosphate buffer solution, butanol, di-ethylene glycol, glycerol.

12. Photovoltaic cell according to one of claims 9 to 11, according to which the organic polymer or the organic molecule comprises nitrogen.

13. Photovoltaic module comprising at least two photovoltaic cells according to any one of claims 5 to 8, a first photovoltaic cell and a second photovoltaic cell, the upper electrode of the first photovoltaic cell being in contact with the lower electrode of the second photovoltaic cell.

14. A method of manufacturing a photovoltaic cell, comprising the following steps: a) providing a support; b) producing a lower electrode on said support; c) producing a first organic interfacial layer on said lower electrode comprising a lower surface comprising amine groups in contact with the lower electrode, the first interfacial layer having a thickness of between 2 and 5 nm, being continuous, transparent, and free of metal oxide; d) producing a photovoltaic active layer on said first interfacial layer; e) producing a second interfacial layer on said photovoltaic active layer.

15. A manufacturing method according to claim 14, wherein steps b), c), d) and e) are each carried out by deposition of ink compositions by digital inkjet printing, followed by heat treatment, said ink composition used in step c) comprising a mixture based on organic molecules soluble in polar solvents.

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