Transparent organic conducting electrodes for replacing ITO electrodes in indoor-compatible organic photovoltaic modules

Abstract

The present invention relates in particular to a photovoltaic module comprising: a lower electrode having a lower surface and an upper surface in contact with the support, the lower surface being made up of two layers: a first layer covering a support and comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate) having an average thickness of 50 nm to 150 nm and an organic fiber structure; and a second layer based on an organic polymer or molecule covering the first layer; and an upper electrode covering a photovoltaic active layer, the upper electrode comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate), the upper electrode being continuous, having an average thickness of 100 nm to 400 nm and an organic fiber structure.

Description

[Technical Field]

[0001] The present invention relates generally to photovoltaic modules, and more particularly to photovoltaic modules including several organic photovoltaic cells (OPCs).

[0002] For the purposes of this invention, an organic photovoltaic cell is a photovoltaic cell in which at least the active layer is made of an organic material. [Background technology]

[0003] The photovoltaic module that contains organic photovoltaic cells represents a real interest in the field of photovoltaics.In fact, the possibility of replacing commonly used inorganic semiconductors with photovoltaic cells, such as silicon, copper, indium, gallium, selenium or cadmium telluride, increases the number of systems that can be produced and therefore the possibility of use.The development of marketable photovoltaic modules that contain several organic photovoltaic cells is currently a major challenge.

[0004] In recent years, the development of organic photovoltaic cells has evolved through the use of inkjet printing technology for their implementation. [1]、[2] Furthermore, in 2014, the applicant developed a process for manufacturing photovoltaic cells using this technique to print some of the layers of these cells. [3] .

[0005] Initially, much research focused on the fabrication of the interfacial layer by inkjet printing of inks containing a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrene sulfonate), usually referred to by the acronym PEDOT (poly(3,4-ethylenedioxythiophene):PSS (sodium poly(styrene sulfonate)). Research in this area then focused on the inkjet printing of the photovoltaic active layer, usually composed of two organic materials (one electron donor and the other electron acceptor). P3HT:PCBM is a conventional choice for the organic active layer (P3HT is the acronym for poly(3-hexylthiophene), and PCBM is [6,6]-phenyl-C 71 -methylbutanoate).

[0006] As shown in FIG. 1, in a currently used conventional or conventionally structured photovoltaic cell 1, a first interfacial layer 9, for example made of PEDOT:PSS, is applied to a layer of indium tin oxide (ITO) 3, which serves as the anode and is itself applied to a substrate. This ITO layer is made of a metal oxide that, in addition to conducting current, is relatively transparent from 350 nm downward. This is the material most commonly used to collect holes in conventionally structured organic photovoltaic cells. A photovoltaic active layer 5, which may be based on P3HT:PCBM, for example, is applied to the first interfacial layer 9. A second interfacial layer 6 is applied to the photovoltaic active layer 5. An opaque upper electrode 7, typically made of aluminum or silver if applied by inkjet printing, is applied to the second interfacial layer 6. The opaque upper electrode 7 serves as the cathode. The two electrodes used in photovoltaic cells, the bottom electrode and the top electrode, must have certain properties to allow them to be incorporated into organic photovoltaic cells. On the one hand, both electrodes must have a high enough conductivity to allow maximum charge collection. On the other hand, the transparency of the bottom electrode, typically an indium-tin-oxide layer, is also a fundamental property for increasing the number of charges photogenerated in the active layer.

[0007] Nowadays, photovoltaic cells with an inverted structure are also available. The main difference from the conventional structure is that a PEDOT:PSS interfacial layer is located between the active layer and the top electrode, which in this case is the anode. In this configuration, an indium oxide layer integrated into the bottom electrode acts as the cathode and therefore collects electrons. It should be noted that photovoltaic cells with an inverted structure have the advantage of being more stable in air than conventionally structured photovoltaic cells and also generally offer higher conversion efficiencies.

[0008] For the purposes of this invention, the conversion efficiency of a photovoltaic cell is defined as the ratio of the maximum power delivered by the cell to the power of the incident light for a given spectral distribution and intensity.

[0009] Moreover, the above-mentioned higher conversion efficiency is achieved when the current state-of-the-art photovoltaic modules are exposed to external radiation, i.e., ultraviolet (UV), visible light, and infrared light, and at light intensities of more than 5000 lux, in particular about 100,000 lux (about 1,000 W / m 2 equivalent to a light intensity of 100mW / cm 2 It should be noted that the efficiency of the photovoltaic cells is guaranteed when they can reach the standard condition of AM1.5, which corresponds to an exposure light intensity of 1000 W. In particular, the large number of photogenerated charges requires the use of an anode with a very high electrical conductivity to ensure good collection of the photogenerated charges in the active layer, particularly to minimize charge accumulation phenomena. In particular, the large number of photogenerated charges requires the use of an anode with a very high electrical conductivity to ensure good collection of the photogenerated charges in the active layer, particularly to minimize accumulation phenomena in the interfacial layer. This is why, in the case of an inverted structure, the top electrode (or anode) is opaque and made of silver. In this case, the conversion efficiency can reach values ​​exceeding 15% for laboratory-scale organic photovoltaic cells.

[0010] However, on an industrial scale, particularly due to manufacturing constraints, photovoltaic cell modules containing this type of photovoltaic cell have low conversion efficiencies, in particular less than half those obtained on a laboratory scale with cells manufactured in a controlled atmosphere (nitrogen-based inert gas). As a result, these photovoltaic modules have a conversion efficiency of 16.2 W / m under indoor radiation, i.e., when the light intensity is less than 5000 lux. 2 with a power of less than 6.4 W / m, preferably when the light intensity is less than 2000 lux 2 3.3W / m when the power is less than 1000 lux or when the light intensity is less than 1000 lux 2 Even less power cannot be used effectively and sustainably.

[0011] This low conversion efficiency, particularly when the photovoltaic module is exposed to indoor radiation, is due in particular to the fact that photovoltaic modules equipped with current state-of-the-art inverted-structure organic photovoltaic cells have a high series resistance related to the number of layers that form the organic photovoltaic cells and thus the photovoltaic module. As a result, these photovoltaic modules have insufficient (i.e., not high enough) shunt resistance (or parallel resistance), which continues to decrease with increasing light intensity. As a result, these resistors do not optimize the performance and fill factor of this type of organic photovoltaic module. In particular, it is well known that the shunt resistance must be sufficiently high for the photovoltaic module to achieve better output power and fill factor. In fact, with a low shunt resistance, the current collapses rapidly, which means high power losses and a low fill factor.

[0012] Furthermore, the low conversion efficiency of this type of photovoltaic module is also due to the presence of a high dead surface. This dead surface is applied to the substrate in a staggered manner so that each layer of the organic photovoltaic cell partially contacts the support, in order to avoid the deposition of each different constituent layer of an organic photovoltaic cell, particularly one with an inverted structure, from being short-circuited due to, for example, the adverse feedback effect of materials deposited in a liquid state. As a result, photovoltaic cell modules including organic photovoltaic cells with an inverted structure in the current state of the art have a small active area, which means that they cannot generate sufficient photocurrent when the incident light intensity is low.

[0013] In addition, while indium tin oxide layers used as cathodes have many advantages and interesting electronic properties, they also have certain drawbacks. Indeed, the availability of materials constituting the indium tin oxide layer, the cost of raw materials, and the processes involved in its implementation and application to produce the layer are all notable drawbacks. Additionally, the material deposition techniques used to produce indium tin oxide layers involve techniques that are not easily compatible with conventional deposition techniques. Indium tin oxide layers are generally structured to form continuous films on rigid or flexible substrates. These films are usually formed by chemical etching (e.g., using acids) or laser ablation. However, these techniques leave behind effects that can affect the performance of photovoltaic cells and, therefore, the photovoltaic modules containing them, as well as the quality and aesthetics of these photovoltaic modules, for example, due to visible edge effects. Given the cost of indium tin oxide, especially when a film preparation step is performed that requires the removal of a certain amount of indium tin oxide, the entire process is inevitably costly, generates a certain amount of waste, and entails all the resulting drawbacks.

[0014] Therefore, in the current state of the art, there are no organic photovoltaic modules comprising organic photovoltaic cells suitable for indoor irradiation as defined above, which do not comprise an indium-tin oxide layer as the anode.

[0015] Currently, there are also no photovoltaic modules that can be manufactured entirely by inkjet printing.

[0016] SUMMARY OF THE INVENTION It is therefore one object of the present invention to at least partially ameliorate the drawbacks of prior art photovoltaic modules and their manufacturing processes. Summary of the Invention

[0017] According to a first aspect, the present invention provides a photovoltaic module comprising: a transparent support; - at least two photovoltaic cells, a first photovoltaic cell and a second photovoltaic cell, on said support, each of said two photovoltaic cells comprising: i. a lower electrode having a lower surface and an upper surface in contact with the support, the lower electrode comprising two layers: a first layer covering the support and including a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate) having an average thickness of 50 nm to 150 nm and an organic fiber structure; and a second layer based on an organic polymer or molecule covering the first layer; ii. a photovoltaic active layer overlying the top surface of the bottom electrode; iii. a top electrode comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate) covering the photovoltaic active layer, the top electrode being continuous and having an average thickness of 100 nm to 400 nm and an organic fiber structure; The photovoltaic module relates to a photovoltaic module in which the top electrode of a first photovoltaic cell is in contact with a second layer of the bottom electrode of the second photovoltaic cell.

[0018] According to this first aspect, the invention makes it possible to provide a photovoltaic module that can be used under indoor radiation, while avoiding the drawbacks inherent in the use of tin oxide electrodes as described above, in particular those related to the complexities of deposition, etching or cleaning.

[0019] Furthermore, the indium-tin-oxide layer commonly used as the cathode in photovoltaic modules, including prior art inverted structure photovoltaic cells, has a first interfacial layer between it and the active layer. In fact, the presence of a first interfacial layer is currently necessary in cells to facilitate the transfer of charge between the layers, since the work output of the indium-tin-oxide layer is particularly high, in particular equal to about 4.7 eV.

[0020] The present invention then has the advantage of overcoming this problem by providing a bottom electrode consisting of two layers. The second layer, based on an organic polymer or molecule, reduces the energy barrier between the active layer and the first layer of the bottom electrode by lowering the work output of the first layer of the bottom electrode. The end result is an ohmic contact, rather than a Schottky contact, which is advantageous for charge collection, especially electron collection. In particular, according to the present invention, the adsorption of the polymer or organic molecule is due to the transfer of charges, especially protons, from the hydroxyl groups to the amino groups, resulting in a charge transfer.

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[0021] Additionally, the second layer of the bottom electrode also acts as a barrier to prevent positive charges from passing through, resulting in reduced leakage current and further improving photovoltaic module performance.

[0022] The present invention according to this first aspect also makes it possible to have a photovoltaic module that does not include an indium tin oxide layer used as the bottom electrode, which is commonly used in prior art photovoltaic modules. In particular, the bottom electrode here can be called a double-layer bottom electrode because it consists of two layers. Each of the layers that make up the bottom electrode is organic.

[0023] Other transparent substrates include polyethylene terephthalate (commonly known by the acronym PET), polyethylene naphthalate (commonly known by the acronym PEN), and glass.

[0024] Having a bilayer allows the photovoltaic module to function in a manner that requires the work output of the bottom electrode to be different from the work output of the top electrode. In particular, the use of a second layer based on an organic polymer or molecule allows the bottom electrode to be structurally distinct from the top electrode. The presence of this second layer based on an organic polymer or molecule also allows the bilayer bottom electrode to serve both as a first interfacial layer (or electron transport layer) and as a work output modifier for the polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate).

[0025] Preferably, the material constituting the first layer of the lower electrode can be the same as the material constituting the upper electrode. In this way, it is possible to avoid the need to develop an inkjet-printable formulation specifically for forming this first layer of the lower electrode. This also avoids the disadvantages, particularly ecological and economical, associated with the use of additional formulations. Furthermore, the material used to manufacture the upper electrode, and therefore potentially the first layer of the lower electrode, is abundant and made from organic materials.

[0026] Preferably, the bottom electrode is photon-supporting so as to collect as much photo-generated charge as possible. It may be sufficiently transparent to allow passage from the body to the active layer.

[0027] In certain embodiments, the second layer of the bottom electrode may be 2-5 nm thick and may include amine groups on its bottom surface in contact with the top surface of the first layer of the bottom electrode.

[0028] In certain embodiments, the bottom electrode second layer can be continuous, transparent, and free of metal oxides, thus providing a non-toxic bottom electrode second layer.

[0029] In certain embodiments, the top electrode can have a sheet surface resistance of 50 Ω / □ to 300 Ω / □, which can be achieved by fabricating the layer using inkjet printing.

[0030] In certain embodiments, the top electrode may have a root mean square (RMS) roughness of 5 nm or less.

[0031] In certain embodiments, the second layer of the bottom electrode can have an RMS roughness of 5 nm or less.

[0032] In certain embodiments, the second layer of the bottom electrode can include nitrogen.

[0033] In certain embodiments, all of the layers that make up the module (except the support) are organic, so as to obtain an environmentally friendly module. As a result, the photovoltaic module can be organic in the sense that the module only includes organic printed layers.

[0034] In certain embodiments, the organic polymer or molecule is 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), ethoxylated polyethyleneimine, amine (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-dimethylpropane-1-amineoxide)perylene-3,4,9,10-tetracarboxylic acid diimide (PDI-NO), or N,N'-bis{3-[3-(dimethylamino)propylamino]propyl}perylene-3,4,9,10-tetracarboxylic acid diimide (PDINN).

[0035] According to a second aspect, the present invention relates to a process for manufacturing a photovoltaic module as defined above, comprising: a) providing a transparent support; b) providing on said support two layers of a first layer of a bottom electrode comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate); c) realizing, on each of the two layers of the first layer of the bottom electrode, a second layer of the bottom electrode based on organic polymers or molecules; d) realizing a photovoltaic active layer on each of the two layers of the second layer of the bottom electrode; e) providing a top electrode on said photovoltaic active layer, The process relates to a process characterized in that steps b), c), d), and e) are each carried out by depositing an ink composition by digital inkjet printing, followed by a thermal treatment.

[0036] According to this second aspect, the present invention makes it possible to manufacture a photovoltaic module comprising a double-layer bottom electrode made from two different ink compositions by digital inkjet printing. Both of these compositions are preferably based on non-toxic solvents known to those skilled in the art and organic materials, so that they can be deposited in ambient air by digital inkjet printing. As a result, steps b) and c) for manufacturing the first and second layers of the bottom electrode, respectively, are easy to implement, since they omit the structuring step for the indium-tin oxide layer currently used in the state of the art.

[0037] Additionally, the fact that all process steps are performed by depositing ink compositions using digital inkjet printing reduces the manufacturing costs of the photovoltaic module.

[0038] Indeed, in prior art photovoltaic modules, the chemical etching step typically performed to structure the bottom electrode, for example comprising indium-tin oxide, requires several costly substeps, in particular due to the etching time, the costs inherent in the use of cross-linkable resins, and the use of deposition equipment. In particular, this chemical etching step generally consists of at least several substeps: a mask application step, an actual etching step (for example using one or more acid baths), and a cleaning step to remove the remaining parts of the mask.

[0039] In certain embodiments, it is advantageous not to change the substrate during the annealing treatment in step b), so that the heat treatment in step b) can be an annealing treatment carried out at a temperature between 100°C and 160°C for a duration between 1 and 5 minutes.

[0040] In certain embodiments, it is advantageous not to modify the previously fabricated substrate and layers in step c), so that the heat treatment of step c) can be an annealing treatment carried out at a temperature between 100°C and 160°C for a duration between 1 and 5 minutes.

[0041] In certain embodiments, the wettability of the composition from which the first layer of the bottom electrode is derived may preferably be compatible with a flexible substrate, e.g., polyethylene terephthalate, to facilitate the formation of a continuous film with well-defined edges by digital inkjet printing.

[0042] Preferably, during step b) of producing the two layers of the second layer of the lower electrode, the following composition can be applied to the support by digital inkjet printing, said composition having a viscosity of 2 to 50 mPa.s at 20 ° C.: - 0.1% to 0.5% by weight, relative to the total weight of the ink composition, of at least one polymer or organic molecule, the polymer or organic molecule containing amine groups and soluble in a polar solvent; 2% by weight to 10% by weight of an additive based on the total weight of the ink composition; - 80% to 90% by weight of one or more polar solvents, based on the total weight of the ink composition; - 1 wt % to 5 wt % of water based on the total weight of the ink composition.

[0043] Polymers or organic molecules have the advantage of being insensitive to UV radiation, due to their inherent properties that differ from those of metal oxide nanoparticles that are typically used in the layers of the lower electrodes of photovoltaic modules in the prior art. In particular, metal oxides classically used in the prior art in interfacial layers, such as TiO2 or ZnO, are not very effective under solar irradiation due to their high gap energy, which is due to the fact that they are not easily affected by UV radiation. This means that the photovoltaic module can be activated only when exposed to UV light. This activation allows charges (electrons) to flow through the interfacial layer and reach the electrode without being trapped. However, the requirement for UV exposure can pose a major problem if the photovoltaic module is intended for indoor applications where artificial light sources are used, typically LEDs that do not emit in the UV range.

[0044] Additives are used to solubilize polymers or organic molecules to obtain compositions which, on the one hand, are defined by a high evaporation temperature, preventing clogging of the nozzles of digital inkjet printing application devices, and, on the other hand, improve the viscosity of the ink composition.

[0045] The polar solvent is preferably non-toxic to ensure deposition of the ink composition in ambient air using the nozzles of industrial digital inkjet printing application equipment.

[0046] Preferably, the polymer or organic molecule may be selected from poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) dibromide (PFN-Br), polyethyleneimine (PEI), ethoxylated polyethyleneimine (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-dimethylpropane-1-amineoxide)perylene-3,4,9,10-tetracarboxylic acid diimide (PDI-NO) or N,N′-bis{3-[3-(dimethylamino)propylamino]propyl}perylene-3,4,9,10-tetracarboxylic acid diimide (PDINN).

[0047] Preferably, the one or more solvents may be selected from ethanol, isopropanol, hexanol, terpiniole, ethylene glycol, deionized water, phosphate saline buffer solution, butanol, diethylene glycol, glycerol.

[0048] In certain embodiments, the polymer or organic molecule can include nitrogen.

[0049] Further advantages and features of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings and the following examples. [Brief explanation of the drawings]

[0050] [Figure 1] 1 shows a schematic cross section of a photovoltaic cell having a conventional structure. [Figure 2] 1 shows a schematic cross-sectional view of a photovoltaic module comprising a photovoltaic cell according to a particular mode of the present invention. [Figure 3] 1 shows the characteristic spectrum of a Philips 60×60 cm 2 LED panel used in the examples. [Figure 4]The transmission spectra of the ITO electrodes used to manufacture modules M2A and M2B according to the prior art and of the bilayers used to manufacture modules M1A and M1B according to the invention are shown with wavelength (λ) on the x-axis and transmittance (T) on the y-axis. DETAILED DESCRIPTION OF THE INVENTION

[0051] FIG. 1 is described in the above summary of the prior art, while FIG. 2 is described in more detail in the following examples, which illustrate the present invention without limiting its scope. [Example]

[0052] product

[0053] PET or glass support 20

[0054] Washing solvent:

[0055] For rigid glass supports, deionized water, acetone, ethanol, isopropanol, and

[0056] For flexible substrates, cleaning is not required as with rigid substrates, as the flexible substrate is protected by a plastic film.

[0057] A first ink composition E11 for producing a discontinuous first layer 210A comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate), wherein the substrate is partially covered with the first layer 210A of the bilayer bottom electrode 210 of the photovoltaic cells 21 and 22 of the photovoltaic module of FIG. 2. Ink E11, PEDOT:PSS sold under the trade name IJ1005 by Agfa®, as detergent / surfactant, Triton X-100 (formula Oct-C6H4-(OCH2CH2) sold by Merck® xInk E11 comprising (4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol) wherein OH, x=9-10.

[0058] Second ink compositions (E12A and E12B) for producing a second layer 210B based on organic polymers or molecules, in which the first layer 210A of the bilayer bottom electrode 210 is partially covered by the second layer 210B of the bilayer bottom electrode 210 to form the cathodes of the various organic photovoltaic cells 21 and 22 of the photovoltaic module of FIG. 2 described below: E12A ink, First solvent 1: butanol in a mass concentration approximately equal to 91.094% relative to the total weight of the E12A ink; Second Solvent 2: deionized water at a concentration equal to about 3.124% by weight relative to the total weight of the E12A ink; Additive: ethylene glycol at a concentration of approximately 5.563% by weight based on the total weight of the E12A ink; - An E12A ink comprising PEI at a concentration of about 0.219 wt. % based on the total weight of the E12A ink. Solvents, additives, and PEI are commercially available from Merck®. E12B ink, -9 mL of butanol, 500 μL of ethylene glycol, - 100 μL of commercially available aqueous PEIE solution (at a mass concentration approximately equal to 37% in water) and E12B ink. Solvents, additives, and PEIE are commercially available from Merck®.

[0059] Third ink composition E20 for producing the photovoltaic active layer 211 of the photovoltaic cells 21 and 22 of the photovoltaic module of FIG. 2: A polymer blend of an acceptor fullerene derivative, -PC60BM:

[60] PCBM, 3'H-cyclopropa[1,9][5,6]fullerene-C60, commercially available from Special Carbon Products -Ih-3'-butanoic acid 3'-phenylmethyl ester, and - a polymer blend comprising a semiconducting donor sold by Raynergy Tek® under the trade name PV2000, O-xylene (ortho-xylene of formula C6H4(CH3)2) as solvent, and - Tetralin (1,2,3,4-tetrahydronaphthalene) as an additive. The PV2000 polymer is present at 15 mg / ml in these third ink compositions. The weight ratio of PV2000 polymer to PC60BM is 1:1.5. The volume ratio between the o-xylene solvent and the tetralin additive is 50:50 in these second compositions. The third E20 ink composition is kept on a hot plate at 80° C. with stirring at a speed of 700 RPM for 24 hours.

[0060] A fourth ink composition E30 for producing the upper electrodes 212 (or anodes) of the photovoltaic cells 21 and 22 of the photovoltaic module shown in FIG. 2: PEDOT:PSS sold under the trade name IJ1005 by Agfa®, As a detergent / surfactant, Triton X-100 (formula Oct-C6H4-(OCH2CH2) sold by Merck®) x OH, x=9-10, (4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol),

[0061] test

[0062] RMS roughness measurement

[0063] These measurements were carried out using an atomic force microscope (Nanoscope III Multimode SPM from Brucker®, used in intermittent contact mode (or "tapping mode") and sold by MiKromasch®, with a hq:nsc15 tip with a radius of curvature of 8 nm), measurements were carried out on various samples of photovoltaic cells according to the invention and according to the prior art.

[0064] Measuring layer thickness

[0065] The thickness of the printed layer is measured using a DektakXT tip profilometer sold by BRUKER, based on scratches made with a cutter blade (thus creating channels with the thickness of the deposit). This is a contact profilometer that measures changes in relief by applying a constant contact force and moving a pointed stylus vertically across the surface, revealing any irregularities. The sample is placed on a plate that allows the sample to move over a selected distance at a given speed. The thickness values ​​presented in this patent application correspond to the average of five measurements made at six different points on the same step of the sample. Before the measurement is performed, the length of the scanned zone, its duration, the force of the stylus press, and the measurement range must be defined.

[0066] Electrical Resistivity Measurement

[0067] The measurements are performed using the four-chip method as follows. - Aligning the 4-chip distal to the edge of the layer to be characterized, -These 4 chips are equidistant from each other, A current is generated between the outer tips by a current generator, while a 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.

[0068] Viscosity measurement:

[0069] The viscosity of a fluid is reflected in the resistance of the fluid to deformation or relative sliding of its layers. For example, during the flow of a viscous fluid in a capillary tube, the velocity (v) of the molecules is highest at the axis of the tube and decreases until it reaches zero at the wall, while relative sliding occurs between the layers, resulting in tangential friction forces. In a fluid, the tangential forces depend on the properties of the fluid and its flow regime.

[0070] The Ubbelohde viscometer is placed in a thermostat maintained at a constant temperature (in our case 25° C.) We measure the flow time of a fixed volume V defined by two reference marks (M1 and M2) located on either side of a small reservoir above the capillary tube.

[0071] Indoor photovoltaic performance measurements:

[0072] A characterization bench is used indoors to study the aging of manufactured modules under permanent illumination. The characterization bench includes an opaque enclosure (to avoid any light coming from outside) equipped with an LED light source (specifically, a Keithley 2450 light source meter) and a computer with a LabVIEW program for automated measurement of module performance (determination of photovoltaic parameters) at a defined frequency (e.g., 10 times per day). The photovoltaic modules are irradiated with light according to the standard NF In accordance with Class C of C 42-710, the room is permanently illuminated by a light source having a light intensity of approximately 1000 lux as measured by a lux meter (in particular, the Chauvin Arnoux Ca 1110 lux meter) that is compatible with a wide variety of light sources, including LEDs and fluorescent lamps up to 200,000 lux.

[0073] The light source used for indoor and performance measurements is a Philips LED panel 60x60cm2-4385K with an emission spectrum in the visible range (see spectrum shown in Figure 3).

[0074] Morphological characterization:

[0075] AFM (atomic force microscope) measurements to reproduce the surface topography and TEM (transmission electron microscopy) to verify the crystallinity of the material and the size of the nanoparticles present in the layer.

[0076] Measuring double layer transmittance:

[0077] To determine the transmission spectrum of the bilayer printed according to the invention (see spectrum shown in Figure 3), a Cary 5000 UV-Vis-NIR UV-visible spectrometer was used. The method is based on the use of the instrument to determine the transmittance of a thin layer for a given wavelength or a judiciously selected range of wavelengths. The sample is placed on a sample holder and irradiated with monochromatic radiation. A computer compares the intensity (I) of the test sample (PET substrate and deposited layer) with the intensity (I0) of a reference sample (PET substrate only). By scanning several wavelengths in the range 300-800 nm (in the present case), it displays the transmission spectrum of the bilayer. On the ordinate, this spectrum represents the transmittance T( %) is indicated.

[0078] Example 1: An example of a first ink composition E10 for producing a first layer 210A of a double-layer bottom electrode is obtained.

[0079] This first E10 ink composition for producing the first layer of the bottom electrode is obtained as follows: - First, filter the PEDOT:PSS solution (IJ1005) stored in the refrigerator through a 0.45 μm filter. - Mix 30 μl of Triton X-100 with 10 ml of filtered PEDOT:PSS solution The resulting mixture is stirred on a magnetic stirrer at room temperature for 16 hours. - The final E10 solution is degassed in an ultrasonic bath for 3-5 minutes before printing.

[0080] Example 2: An example of second ink compositions E12A and E12B for manufacturing the second layer 210B of the bottom electrode 210 is obtained.

[0081] Depending on whether PEI or PEIE is used, E12A and E12B ink compositions are obtained, respectively, the compositions of which are detailed below.

[0082] The E12A ink formulation is prepared in two steps.

[0083] Step 1: Preparation of stock solutions: -Weigh out 0.35 g of PEI (Intercalated Polymer) - 5 ml of ionized water is added to these 0.35 g of PEI Stir at -60°C for at least 4 hours to obtain a stock solution.

[0084] Step 2: Preparation of E12A ink formulation: -Take 250 μL of stock solution -Add 9 ml of butanol -Add 400 μL of ethylene glycol. The mixture is stirred at room temperature for 24 hours to give the E12A formulation. - Filter the E12A formulation before printing using an AC filter with a cutoff of approximately 0.2 μm.

[0085] The E12B ink formulation is prepared in a single step.

[0086] Preparation of E12B ink formulation: - Take a 100 μL volume of commercially available PEIE aqueous solution. - Add 9 ml of butanol (solvent). -Add 500 μL of ethylene glycol (additive) The mixture is stirred at room temperature for 24 hours to give the E12B ink formulation. An AC filter with a cutoff of approximately 0.2 μm is used to filter the E12B formulation before printing.

[0087] Example 3: An example of a third ink composition E20 for producing a photovoltaic active layer 211 is obtained.

[0088] PC60BM is used as the acceptor in combination with PV2000 as the donor to obtain the E20 ink composition detailed in Table 1 below. [Table 1]

[0089] The E20 ink composition is obtained as follows. 15 mg of PV2000 are mixed with 22.5 mg of PC60BM in 0.5 ml of o-xylene and 0.5 ml of tetralin (corresponding to a weight ratio of 1:1.5). The mixture is placed on a hot plate at 80° C. under magnetic stirring for 24 hours. -Before printing, the ink is filtered using an AC filter with a cutoff of about 0.45 micrometers.

[0090] Example 4: An example of a fourth ink composition E30 for producing the upper electrode layer 212 is obtained.

[0091] An example of a fourth E30 ink composition is provided for the top electrode layer 212.

[0092] This fourth ink composition E30 for producing the upper electrode layer 212 is obtained as follows. - The PEDOT:PSS solution (IJ1005), initially stored in the refrigerator, is filtered through a filter with a cutoff of approximately 0.45 μm. - Mix 30 μl of Triton X-100 with 10 ml of filtered PEDOT:PSS solution The resulting mixture is stirred on a magnetic stirrer at room temperature for 16 hours. - The final E30 solution is degassed in an ultrasonic bath for 3-5 minutes before printing.

[0093] Example 5: Example of a photovoltaic module according to the invention is obtained:

[0094] Two photovoltaic modules M1A and M1B according to the present invention are fabricated by the following process. -Supply of transparent PET or glass substrates. - Production on said support of two layers of the first layer 210A of the bottom electrode 210 from the composition E10 of Example 1. In particular, these layers are produced by digital inkjet printing of the E10 ink composition followed by thermal annealing at 145°C for 3 minutes in a convection oven. The thickness of the first printed layer 210A of the bottom electrode 210 is approximately 100 nm and the RMS roughness is less than 5 nm. On each of the two layers, a first layer 210A of the bottom electrode 210 and a second layer 210B of the bottom electrode 210 are produced using either the ink composition E12A of Example 2 (photovoltaic module M1A) or the ink composition E12B of Example 2 (photovoltaic module M1B). In particular, these layers are produced by digital inkjet printing with either the ink composition E12A or E12B, followed by thermal annealing at 145° C. for 3 minutes in a convection oven. The printed second layer 210B of the bottom electrode 210 has a thickness of 2-5 nm and an RMS roughness of less than 2 nm. The photovoltaic active layer 211 is applied to each of the two layers of the second layer 210B of the bottom electrode 210 by digital inkjet printing using the ink composition E20 from Example 3, followed by thermal annealing in a convection oven at 145° C. for 3 minutes. The thickness of the photovoltaic active layer is approximately 350 nm, and the RMS roughness is less than 5 nm. A top electrode 212 is applied to each of the photovoltaic active layers 211 by digital inkjet printing using ink composition E30 from Example 4, followed by thermal annealing in a convection oven at 145° C. for 3 minutes. The thickness of the printed top electrode layer 212 is about 500 nm and the RMS roughness is less than 10 nm. - Production of an electrical contact layer 213 consisting of adhesive-backed copper tape 3 mm wide and 58 mm long. This tape is marketed by 3M and is cut into strips (3 x 58 mm²) using a mechanical cutter (Kongsberg XE). This electrical contact layer 213 is then deposited to ensure contact between the top electrode layer 212 of the first photovoltaic cell of the photovoltaic module (M1A or M1B) and the second layer of the bottom electrode 210B of the second photovoltaic cell of the photovoltaic module (M1A or M1B).

[0095] At the end of the manufacturing process, a photovoltaic module (either M1A or M1B) is obtained comprising organic photovoltaic cells 21 and 22, which further comprise, inter alia, a double-layer bottom electrode according to an embodiment of the present invention and a top electrode characterized by a micrometric organic fiber structure.

[0096] Results and Comparison: Characterization of the photovoltaic modules obtained in previous Examples M1A and M1B and comparison with prior art photovoltaic module examples.

[0097] Various photovoltaic modules according to the present invention and the prior art have been characterized according to the tests described above and the results of these characterizations in Table 2 below.

[0098] Two prior art photovoltaic modules (M2A and M2B) were fabricated under the same conditions used to fabricate the photovoltaic modules M1A and M1B according to embodiments of the present invention.

[0099] The first prior art photovoltaic module M2A differs from the photovoltaic modules M1A and M1B according to the invention by the presence of a lower electrode comprising an indium-tin oxide layer and an interfacial layer based on a metal oxide, in particular AZO (aluminum-doped zinc oxide). The second prior art photovoltaic module M2B differs from the photovoltaic modules M1A and M1B according to the invention by the presence of a lower electrode comprising an indium-tin oxide layer and an interfacial layer based on a metal oxide, in particular SnO2 (tin dioxide). AZO is commercially available from Genesink, and SnO2 is commercially available from Avantama.

[0100] Prior art photovoltaic modules M2A and M2B were manufactured with an inverted structure having an active layer PV2000:PC60BM and a top electrode PEDOT:PSS, i.e. the same active layer and top electrode as the examples according to the invention.

[0101] The photovoltaic modules M1A, M1B according to the invention and the prior art photovoltaic modules M2A, M2B were characterized under the same conditions using the same characterization bench described above under the same light intensity.

[0102] Repeated production of a photovoltaic module corresponding to the M1A module gave the results shown in Table 2 below under the reference M1A'. [Table 2]

[0103] The above table shows the photovoltaic parameters (voltage, current, maximum power, and fill factor) measured under LED-based indoor lighting (1000 Lux) and clearly shows that the photovoltaic modules M2A and M2B according to the invention achieve photovoltaic performances very close to, and sometimes even better than, those of modules manufactured according to the state of the art under the same conditions (same active layer and same top electrode). The current generated by the modules according to the invention is of the same order of magnitude as the current generated by modules made according to the prior art.

[0104] The photovoltaic performance measured with the M1A and M1B photovoltaic modules according to the invention is very encouraging and confirms the good functionality of the double layer bottom electrode according to the invention in the case of indoor applications (low light intensity LED type lighting). References

[0105] [1] Sharaf Sumaiya, Kamran Kardel, and Adel El-Shahat. “Organic Solar Cell by Inkjet Printing-An Overview.” 53, Georgia, USA: Technologies, 2017, Vol. 5.

[0106] [2] Peng, X., Yuan, J., Shen, S., Gao, M., Chesman, ASR, & Yin, H. (2017). Organic Solar Cells Fabricated by Inkjet Printing: Progress and Prospects”,Adv.Funct.Mater.2017,1703704

[0107] [3] European patent application EP2960957 by DRACULA TECHNOLOGIES, filed June 25, 2015, published December 30, 2015.

Claims

1. 1. A photovoltaic module comprising: a transparent support, - at least two photovoltaic cells, a first photovoltaic cell and a second photovoltaic cell, on said support, each of said two photovoltaic cells comprising: i. a lower electrode having a lower surface and an upper surface in contact with the support, the lower electrode consisting of two layers: a first layer covering the support and comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate) having an average thickness of 50 nm to 150 nm and an organic fibrous structure; and a second layer based on an organic polymer or molecule covering the first layer; ii. a photovoltaic active layer covering the top surface of the bottom electrode; iii. a top electrode covering the photovoltaic active layer, the top electrode comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate), the top electrode being continuous and having an average thickness of 100 nm to 400 nm and an organic fiber structure; A photovoltaic module, wherein the top electrode of the first photovoltaic cell is in contact with the second layer of the bottom electrode of the second photovoltaic cell.

2. 2. The photovoltaic module (10) of claim 1, wherein the second layer of the bottom electrode has a thickness of 2 to 5 nm and includes amine groups on a bottom surface in contact with the top surface of the first layer of the bottom electrode.

3. 3. The photovoltaic module (10) of claim 1 or 2, wherein the second layer of the bottom electrode is continuous, transparent, and metal oxide-free.

4. The photovoltaic module (10) of any one of claims 1 to 3, wherein the top electrode has a sheet resistance of between 50 ohms / square and 300 ohms / square.

5. The photovoltaic module of any one of claims 1 to 4, wherein the top electrode has an RMS roughness of 5 nm or less.

6. The photovoltaic module of any one of claims 1 to 5, wherein the second layer of the bottom electrode has an RMS roughness of 5 nm or less.

7. The photovoltaic module of any one of claims 1 to 6, wherein the second layer of the bottom electrode comprises nitrogen.

8. Photovoltaic module according to any one of claims 1 to 7, characterized in that it is organic.

9. The polymer or organic molecule is selected from poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) dibromide (PFN-Br), polyethyleneimine (PEI), ethoxylated polyethyleneimine (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-dimethylpropane-1-amineoxide)perylene-3,4,9,10-tetracarboxylic acid diimide (PDI-NO), or N,N′-bis{3-[3-(dimethylamino)propylamino]propyl}perylene-3,4,9,10-tetracarboxylic acid diimide (PDINN). A photovoltaic module according to any one of claims 1 to 8.

10. A method for manufacturing a photovoltaic module according to any one of claims 1 to 9, comprising the steps of: a) providing a transparent support; b) realizing on said support two layers of the first layer of said bottom electrode comprising a polymer blend of poly(3,4-ethylenedioxythiophene) and sodium poly(styrenesulfonate); c) realizing, on each of the two layers of the first layer of the bottom electrode, a second layer of the bottom electrode based on polymers or organic molecules; d) realizing a photovoltaic active layer on each of the two layers of the second layer of the bottom electrode; e) providing a top electrode on said photovoltaic active layer, The process is characterized in that steps b), c), d), and e) are each carried out by depositing the ink composition by digital inkjet printing, followed by thermal treatment.

11. 11. The manufacturing process of claim 10, wherein said heat treatment of step b) is an annealing treatment carried out at a temperature between 100°C and 160°C for a duration between 1 and 5 minutes.

12. 12. The manufacturing process according to claim 10 or 11, wherein said heat treatment of step c) is an annealing treatment carried out at a temperature between 100°C and 160°C for a duration between 1 and 5 minutes.

13. 13. The manufacturing process according to any one of claims 10 to 12, wherein during step b) of producing the two layers of the second layer of the bottom electrode, the following composition is applied onto the support by digital inkjet printing, said composition having a viscosity of 2 to 50 mPa s at 20°C: - 0.1% to 0.5% by weight, relative to the total weight of the ink composition, of at least one polymer or organic molecule, the polymer or organic molecule comprising amine groups and being soluble in a polar solvent; - 2% to 10% by weight of additives relative to the total weight of the ink composition; - 80% to 90% by weight of one or more polar solvents, based on the total weight of the ink composition; and 1% to 5% by weight of water based on the total weight of the ink composition.

14. 14. The process of claim 13, wherein the polymer or organic molecule is selected from poly(9,9-bis(3'-(N,N-dimethyl)-N-ethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) dibromide (PFN-Br), polyethyleneimine (PEI), ethoxylated polyethyleneimine (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-dimethylpropane-1-amineoxide)perylene-3,4,9,10-tetracarboxylic acid diimide (PDI-NO), or N,N'-bis{3-[3-(dimethylamino)propylamino]propyl}perylene-3,4,9,10-tetracarboxylic acid diimide (PDINN).

15. 15. The process of claim 13 or 14, wherein the one or more solvents are selected from ethanol, isopropanol, hexanol, terpineol, ethylene glycol, deionized water, phosphate buffer solution, butanol, diethylene glycol, glycerol.

16. The process of any one of claims 13 to 15, wherein the polymer or organic molecule comprises nitrogen.

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