Method for producing a semiconducting organic film

Abstract

A method for producing a semiconducting organic film comprising the steps: preparing a first mixture comprising a first organic semiconducting material of type p having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1 and a first organic semiconducting material of type n having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1, adding a second organic semiconducting material to the first mixture to form a second mixture, wherein the second organic semiconducting material is one or more polymers having a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1, and forming the organic film from the second mixture.

Claims

1. A production method for producing a semiconducting organic film comprising the steps: preparing a first mixture comprising a first organic semiconducting material of type p having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1 and a first organic semiconducting material of type n having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1, adding a second organic semiconducting material to the first mixture to form a second mixture, wherein the second organic semiconducting material is one or more conjugated polymers having a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1, and forming the organic film from the second mixture.

2. The method according to claim 1, wherein the second organic semiconducting material is an organic semiconducting polymer of type n or an organic semiconducting polymer of type p.

3. The method according to claim 2, wherein in the second mixture has a mass ratio of the second organic semiconducting material to the first organic semiconducting material of the same type that of second organic semiconducting material that is between 0.8 and 1.2.

4. The method according to claim 2, wherein in the second mixture has a mass ratio of the second organic semiconducting material to the first organic semiconducting material of the same type that of second organic semiconducting material that is between 0.9 and 1.1.

5. The method according to claim 2, wherein in the second mixture has a mass ratio of the second organic semiconducting material to the first organic semiconducting material of the same type that of second organic semiconducting material that is 1.0.

6. The method according to claim 1, wherein the second mixture has a mass ratio of the sum of the second organic semiconducting material, which is of type n, and the first organic semiconducting material of type n to the first organic semiconducting material of type p that is between 0.8 and 1.2.

7. The method according to claim 1, wherein the first mixture further comprises a solvent or a mixture of solvents.

8. The method according to claim 7, wherein the second mixture is more soluble than the first mixture in the solvent or mixture of solvents.

9. The method according to claim 1, wherein the second mixture has a viscosity of more than 2 mPa.Math.s.

10. The method according to claim 1, wherein the organic film is formed using a coating technique or a printing technique, wherein the coating technique is selected from the group consisting of slot-die coating, slide coating, dip coating, curtain coating, knife coating, doctor blading, and spin coating, and the printing technique is selected from the group consisting of flexography, heliography, heliogravure, offset printing, ink jet printing, screen printing, and roll-to-roll printing.

11. An organic film produced by a method comprising: preparing a first mixture comprising a first organic semiconducting material of type p having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1 and a first organic semiconducting material of type n having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1, adding a second organic semiconducting material to the first mixture to form a second mixture, wherein the second organic semiconducting material is one or more conjugated polymers having a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1, and forming the organic film from the second mixture.

12. An organic photovoltaic cell comprising an active layer, wherein the active layer is an organic film produced by a method comprising: preparing a first mixture comprising a first organic semiconducting material of type p having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1 and a first organic semiconducting material of type n having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1, adding a second organic semiconducting material to the first mixture to form a second mixture, wherein the second organic semiconducting material is one or more conjugated polymers having a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1, and forming the organic film from the second mixture.

13. An organic photovoltaic module comprising at least two organic photovoltaic cells connected in series or parallel, wherein each such organic photovoltaic cell comprises an active layer, wherein the active layer is an organic film produced by a method comprising: preparing a first mixture comprising a first organic semiconducting material of type p having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1 and a first organic semiconducting material of type n having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1, adding a second organic semiconducting material to the first mixture to form a second mixture, wherein the second organic semiconducting material is one or more conjugated polymers having a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1, and forming the organic film from the second mixture.

14. A method for manufacturing an active layer of an organic photovoltaic cell of a photovoltaic module, the method comprising coating a substrate with strips of an organic film produced by a method comprising: preparing a first mixture comprising a first organic semiconducting material of type p having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1 and a first organic semiconducting material of type n having a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1, adding a second organic semiconducting material to the first mixture to form a second mixture, wherein the second organic semiconducting material is one or more conjugated polymers having a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1, and forming the organic film from the second mixture.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) A method for producing a semiconducting organic film is proposed.

(2) The production method includes a step for preparing a first mixture.

(3) The first mixture includes an organic semiconducting material of type p and a first organic semiconducting material of type n.

(4) The first organic semiconducting material of type n has a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1.

(5) Advantageously, the semiconducting material of type n is selected from the list consisting of: fullerene, methyl[6,6]-phenyl-C61-butyrate (also noted as PC60BM), [6,6]-phenyl C61-butyric acid methyl ester (C60-PCBM), [6,6]-phenyl C71-butyric acid methyl ester (C70-PCBM), bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)[6.6]C62 (Bis-C60-PCBM), 3-Phenyl-3H-cyclopropa[8,25][5,6]fullerene-C70-bis-D5h(6)-3-butanoic acid methyl ester (Bis-C70-PCBM), indene-C60-bisadduct (ICBA) and mono indene nil C60 (ICMA).

(6) Preferably, the semiconducting material of type n is PC60BM.

(7) The first organic semiconducting material of type p has a molar mass of less than or equal to 2,000 g.Math.mol.sup.?1.

(8) Advantageously, the first organic semiconducting material of type p is selected from the list consisting of DTS-(FBTTH2)2, IBTP, IDF, DTS-(PTTH2), boro-dipyromethene, diketopyrrolopyrrole, oligothiophene, indigo, quinacridone, merocyanin, squarain and so-called push-pull compounds. A so-called push-pull compound is an assembly of a so-called push group with a so-called pull group via a ? bond. A carbazole group or a triphenylamine group are so-called push group examples. A dicyanovinylene or benzothiadiazole group are so-called pull group examples. The ? bond is for example applied by means of a thiophene, of a phenyl or of a vinyl. The dithienosilol is a so-called push-pull compound example.

(9) According to a preferred embodiment, the first organic semiconducting material of type p is DTS-(FBTTH2)2.

(10) Preferably, the first mixture is prepared in the presence of a solvent.

(11) Advantageously, the solvent is non-halogenated.

(12) Advantageously, the solvent is non-chlorinated.

(13) Preferentially, the solvent is non-toxic.

(14) Preferably, the solvent is compatible with the use of a thermal drier, i.e. the self-inflammation point is above 200? C. This gives the possibility of contemplating the use of the solvent in an industrial context, while observing the health of the co-workers and the environment.

(15) As an example, the solvent is selected from a list consisting of dimethyl sulfoxide (also noted as DMSO), acetone, tetrahydrofurane (also noted as THF), methyl ethyl ketone (also noted as MEK), toluene, propylene glycol, cyclohexane, 2-butanol, cyclohexanone, 2-propanol, methylisobutylketone (also noted as MIBK), acetophenone, methyl isopropyl ketone, dimethyl ethanolamine, methyl n-propyl ketone, ethylene glycol, o-xylene, 1-methyl-naphthalene, 3-methylthiophene, nonane, anisole, ethylcyclohexane, 2-ethyl-hexanol, indane, dodecane, 1,2-hexanediol, 1-butanol, thiodiethylene glycol, dimethyl glutarate, dimethyl succinate, ethylene glycol diacetate, dipropylene glycol monomethyl ether, diethylene glycol, methyl cyclohexane, mesitylene, aniline, benzaldehyde, acetonitrile, p-xylene or m-xylene.

(16) At the end of the application of the preparation step, a first mixture is obtained including the organic semiconducting material of type n and the organic semiconducting material of type p.

(17) The production method also includes a step for adding to the first mixture a polymer in order to form a second mixture.

(18) A polymer is a chain consisting of a number of monomeric units which are repeated.

(19) According to an embodiment, the polymer is an organic semiconducting polymer of type p.

(20) According to another embodiment, the polymer is an organic semiconducting polymer of type n.

(21) In the following, the second organic semiconducting material is simply designated under the name of polymer.

(22) The second semiconducting material is a photoactive material.

(23) The polymer has a molar mass greater than or equal to 10,000 g.Math.mol.sup.?1

(24) Advantageously, the organic semiconducting polymer of type p is selected from the list consisting of polythiophene, poly(alkyl-3-thiophene) in which the alkyl group has 6 to 16 carbon atoms, poly(3-hexylthiophene) (also noted as P3HT), poly[N-9-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole] (also noted as PCDTBT), poly(p-phenylene-vinylene) (also noted as PPV), and alkoxy derivatives of poly(p-phenylene-vinylene), poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene-vinylene] (also noted as MDMO-PPV), poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene] (also noted as MEH-PPV), poly(2,5-dimethoxy-p-phenylene-vinylene) (also noted as PDMPV), poly(3,4-ethylenedioxythiophene) (also noted as PEDOT) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (also noted as PEDOT:PSS), polyacetylene, polyphenylene, poly[2,6-(4,4-bis-(2-ethylhexyle)-4H-cyclopenta[2,1-b;3,4-b]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (also noted as PCPDTBT), polyphenylacetylene, polydiphenylacetylene, polyaniline, polythiophene, poly(thienylenevinylene), poly(2,5-thienylenevinylene), polyfluorene, porphyrin macrocycles, thiol-derivatised polyporphyrins, polymetallocene, polyferrocene, polyphthalocyanin, polyvinylene, polyphenylvinylene, polysilane, polyisothianaphthalene, polythienylvinylene, derivatives of any of the materials of the list or a combination of the materials of the list. As an example of derivatives, the materials of the list comprise pendant groups, such as a cyclic ether, epoxy, oxetane, furane or cyclohexene oxide.

(25) Optionally, the aforementioned polymers are conjugate polymers.

(26) Alternatively, the derivatives of the aforementioned materials alternatively or additionally include other substituents. For example, the thiophene groups comprised in the aforementioned materials may comprise a phenyl group or an alkyl group, for example in position 3 of the thiophene ring. Examples of such thiophenes are thiophenes such that R3 is a C.sub.1-C.sub.8 alkyl group or a C.sub.1-C.sub.6 alkyl alkyl-C(?O)OC.sub.1-C.sub.6 alkyl group. The poly[3-(ethyl-4-butanoate)thiophene-2,5-diyl] is an example of such a thiophene. As another example, an alkyl, alkoxy, cyano, amino group, and/or hydroxy substituent groups may be present in any one of polyphenylacetylene, polydiphenylacetylene, polythiophene and poly(p-phenylene-vinylene).

(27) According to another embodiment, the polymer is carbazole.

(28) Preferably, the polymer is P3HT, PCDTBT or PTB7.

(29) According to another embodiment, the organic semiconducting polymer of type n is selected as described in the article Facchetti, Antonio. Polymer donor-polymer acceptor (all-polymer) solar cells Materials Today 16, no. 4 (2013): 123-132.

(30) At the end of the application of the addition step, a second mixture is obtained including the first organic semiconducting material of type n, the first organic semiconducting material of type p and an organic semiconducting polymer.

(31) The second mixture has better solubility than the first mixture.

(32) The solubility is a physical quantity designating the maximum molar concentration of the solute in the solvent, at a given temperature. The thereby obtained solution is then saturated. The solubility is measured by saturating the formulation, centrifuging and taking up the supernatant and measuring the absorbance of the formulation with a spectrophotometer, from which the concentration is inferred.

(33) The materials are introduced with saturation in the solvent(s) and stirred at 50? C. at 900 rpm for 24 h. The test volumes will be set to 2 ml.

(34) The mixtures are then centrifuged in order to recover the supernatant containing the material(s) which has(have) been solubilized. The supernatant is then analyzed after dilution by UV-Visible spectroscopy in order to determine the concentration of the material solubilized in the solvent.

(35) The limiting concentration of materials in the first mixture is therefore less than the concentration of materials in the second mixture. The addition of the material for forming the second mixture gives the possibility of increasing the solubility of the second mixture and of having, for a same volume, more active materials while having better performances in terms of coating (wettability, roughness and homogeneity of the films) as shown in the table Observation of the coating quality.

(36) The second mixture has a higher viscosity than the mixtures of the state of the art.

(37) The production method also includes a step for forming the organic film from the second mixture.

(38) Preferably, the formation step is applied by using a roll-to-roll coating or printing technique.

(39) Alternatively, the formation step is applied by using a slot-die coating technique.

(40) According to another alternative, the formation step is applied by a screen printing method, a flexographic method or an inkjet method.

(41) At the end of the formation step, a film is obtained.

(42) The film obtained at the end of the formation step has better properties in terms of homogeneity, roughness and definition of the edges.

(43) The obtained film also has improved homogeneity, resulting in a better internal structure, better morphology and better interface quality with the optional other layers with which the film will have to interact.

(44) Further, the film has a wider absorption spectrum of incident light.

(45) Further, obtaining the film does not involve the use of toxic or noxious solvents.

(46) The film is therefore particularly suitable for obtaining an active layer of a photovoltaic cell having improved properties. The film may also be used for producing organic light-emitting diodes (also called OLEDs) or photodiodes.

(47) Preferably, the second mixture consists in an organic semiconducting material of type n, an organic semiconducting material of type p and the polymer.

(48) Advantageously, the polymer is a semiconducting polymer of type p or of type n.

(49) Advantageously, in the second mixture, the mass ratio between the polymer and the organic semiconducting material of the same type is comprised between 0.8 and 1.2. In all the continuation of the description, by the expression of comprised between X and Y is meant that the relevant amount is greater than or equal to X on the one hand and less than or equal to Y on the other hand.

(50) Preferably, in the second mixture, the mass ratio between the polymer and the first organic semiconducting material of the same type is comprised between 0.9 and 1.1.

(51) Preferably, in the second mixture, the mass ratio between the polymer and the first organic semiconducting material of the same type is equal to 1.0.

(52) Advantageously, in the second mixture, the mass ratio between the whole of the polymer and of the first organic semiconducting material of type p on the one hand and the organic semiconducting material of type n on the other hand is comprised between 0.8 and 1.2.

(53) Preferably, in the second mixture, the mass ratio between the whole of the polymer and of the first organic semiconducting material of type p on the one hand and the organic semiconducting material of type n on the other hand is comprised between 0.9 and 1.5.

(54) Preferably, in the second mixture, the mass ratio between the whole of the polymer and of the first organic semiconducting material of type p on the one hand and the organic semiconducting material of type n on the other hand is equal to 1.0.

(55) According to an alternative, the second mixture includes a solvent or a solvent mixture, the solvent being a mixture of two compounds.

(56) Advantageously, the absorption of at least one from among the organic semiconducting polymer and the first organic semiconducting material of same type is greater by 10% for an incident light wave having a wavelength comprised between 300 nm and 800 nm.

(57) This gives the possibility of improving the absorption of the mixture on a wavelength comprised between 250 nm and 600 nm. The result of this is that the mixture has a wider absorption spectrum than the absorption spectrum of the organic semiconducting polymer alone or of the first organic semiconducting material of the same type alone.

(58) Preferably, the absorption of at least one from among the organic semiconducting polymer and the first organic semiconducting material of same type is greater by 10% for an incident light wave having a wavelength comprised between 300 nm and 600 nm.

(59) This gives the possibility of improving the absorption of the second mixture on a wavelength comprised between 100 nm and 600 nm. The result of this is that the second mixture has a wider absorption spectrum than the absorption spectrum of the organic semiconducting polymer alone or of the first organic semiconducting material of the same type, alone.

(60) Thus, the method described earlier gives the possibility of resolving a technical contradiction which is to attain industrially viable processability parameters: reproducibility of the formulations (properties of the small molecules unlike the polymer which has much variabilitychain lengthcausing unstable properties). Indeed, length of the chains and the variability of molar mass of the polymers actually causes unstable properties from batch to batch. film homogeneity of the formulations intended to be coated by roll-to-roll industrial methods. This property is intrinsic to the nature of the polymers. This property may be adjusted during steps for formulating the polymers. The viscosity gives the possibility of obtaining sharp contours required for manufacturing modules.

(61) Both of these constraints are fulfilled while retaining optimum photoactive properties for producing electrically performing and therefore economically viable photovoltaic devices.

(62) Adding the semiconducting photoactive polymer gave the possibility of solving this contradictory problem by improving the film homogeneity of a formulation based on small molecules while retaining and even improving the photoactive properties of the film.

(63) Indeed, adding an insulating polymer such as polystyrene allows modification of the mechanical properties of a formulation, however this addition also has an impact on the electric properties of the mixture. Indeed, adding a material for forming a second mixture causes reorganization of the donor/acceptor lattice at the origin of the extraction of the charges.

(64) The charge transport properties of semiconducting polymers are greater than the transport properties of an insulating polymer like polystyrene, but the modification of the equilibrium of the first mixture may lead to a variety of morphological modifications and to the reorganization of the donor/acceptor lattices and their electric properties are very difficult to predict.

(65) In fact, an improvement in the solubility of the second mixture was observed: it was not expected that the addition of a semiconducting photoactive polymer would cause an improvement in the solubility and will allow addition of a material having as a consequence a potential increase in the extraction of the charges.

(66) On the other hand, semiconducting photoactive polymers have complex molecular structures, notably with more or less long side chains, which also affect their solubility and their film homogeneity (the Hansen parameters explain the difficulty of solubilizing photoactive polymers). For more details relative to the Hansen parameters, please report to Solubility parameters, Charles M. Hansen, Alan Beerbower, Kirk Othmer, supplement volume, pp. 889 ? 8902? edition 1971; C. M. Hansen, Hansen Solubility Parameters: A User's Handbook, CRC Press, Boca Raton, Fla. 2000; and A. F. M. Barton, CRC handbook of solubility parameters and other cohesion parameters 2nd ed., CRC Press, Boca Raton, Fla. 1991.

(67) The molecular interactions between the polymer chains, and therefore the intermolecular cohesion explain the degree of film homogeneity of the polymers.

(68) Therefore, it is not surprising that by adding a photoactive semiconductor it is possible to adjust the viscosity and to adapt it to the specifications of the roll-to-roll coating methods.

(69) The development of an industrializable coating method is actually the goal reached with the present method. This involves the use of non-chlorinated solvents and roll-to-roll methods as listed in the description which are fundamentally different from the spin coating methods used in the documents known from the state of the art.

(70) Experiments

(71) The experiments are conducted for a second mixture in which: the first material is DTS(FBTTH2)2, the polymer is P3HT, and the organic semiconducting material of type p is PCBM.

(72) In the applied experiments, certain parameters are invariant: the ratio between donor and acceptor is a mass ratio of 1 for 1; the solvent ratio is 50% by mass of o-xylene for 50% by mass of 1-methyl naphthalene (Mna); the total donor concentration is 20 g.Math.L.sup.?1, and the formulation amount is 10 ml.

(73) On the contrary, other parameters are variable in the following experiments, i.e.: the relative polymer mass proportion, the relative polymer mass proportion being defined as a ratio for which the numerator is the mass of the polymer in the second mixture and the denominator is the sum of the masses of the polymer and of the first material of the same type in the second mixture, and the relative first material mass proportion, the relative first material mass proportion being defined as a ratio for which the numerator is the mass of the first material in the second mixture and the denominator is the sum of the masses of the polymer and of the first material of the same type in the second mixture.

(74) Five experiments are then applied for various relative polymer mass proportions (of the first material respectively):

(75) TABLE-US-00001 Polymer (relative mass First material (relative Experiments proportion in %) mass proportion in %) 1 0 100 2 25 75 3 50 50 4 75 25 5 100 0

(76) For each of the experiments, the mass composition of the second mixture is therefore the following:

(77) TABLE-US-00002 First organic First organic Organic semiconducting semiconducting semiconducting 1-methyl- Experiments material of type p material of type n polymer of type p o-xylene naphthalene 1 0.20 0.21 0.00 4.80 4.80 2 0.15 0.21 0.05 4.80 4.80 3 0.10 0.21 0.10 4.80 4.80 4 0.05 0.21 0.15 4.80 4.80 5 0.00 0.21 0.21 4.80 4.80

(78) For each of the experiments, the operating procedure comprises the following operations: 1) weighing the organic semiconducting material of type n (PCBM) and the solvents in 20 ml glass vials, 2) mixing the organic semiconducting material of type n and the solvents, 3) starting stirring of the obtained mixture at the end of step 2) at 900 rpm for 3 hours at 60? C., 4) weighing and adding the first material of type p (DTS(FBTTH2)2), 5) preparing the first mixture, 6) weighing and adding the semiconducting polymer of type p (P3HT), 7) obtaining the second mixture, 8) starting stirring of the second mixture at 900 rpm for 18 hours at 60? C., 9) observing the solubility of the second mixture with the naked eye, 10) rheological measurements applied while keeping the second mixture in an oven at 30? C., the measurements being carried out with a RheoStress Rheometer, the viscosity being analyzed with the C35/0.5? cone. The viscosity is measured for several speeds of rotation of the apparatus, i.e. 500 s.sup.?1, 1,000 s.sup.?1 or 10,000 s.sup.?1, 11) coating the second mixture on ITO and PET at a temperature of 40? C. and at a speed of 40 mm/s by using an automatic film applicator or a doctor-blade provided with a 12.5 ?m slot, 12) drying applied at the temperature of 80? C., 13) observing the quality of the coating with the naked eye, and 14) measuring the absorbance of the layer on a UV-Visible spectrophotometer.

(79) The following table summarizes the results obtained for the characteristics relating to the viscosity of the second mixture:

(80) TABLE-US-00003 Viscosity of the second mixture in mPa .Math. s for a speed of rotation of the Solubility observed RheoStress Rheometer of Experiments visually during step 9) 500 s.sup.?1 1,000 s.sup.?1 10,000 s.sup.?1 1 Good 1.1 1.1 1.2 2 Good 1.6 1.6 1.7 3 Good 2.2 2.2 2.3 4 Good 2.8 2.8 3.0 5 Good 3.5 3.6 3.7

(81) It appears that the second mixtures using a solvent based on o-xylene/1-methylnaphthalene have very good solubility.

(82) It is also observable that addition of the polymer increases the viscosity.

(83) The following table summarizes the results obtained for the properties relating to the coating of the second mixture:

(84) TABLE-US-00004 Observations of the quality of the coating Experiments on PET on ITO 1 Homogenous coating Homogenous coating Presence of agglomerates Presence of agglomerates 2 Homogenous coating Homogenous coating A few agglomerates A few agglomerates 3 Homogenous coating Homogenous coating A few agglomerates A few agglomerates 4 Homogenous coating Homogenous coating A few agglomerates A few agglomerates 5 Homogenous coating Homogenous coating Absence of agglomerates Absence of agglomerates

(85) It appears that the films obtained from the first mixture have the most agglomerates due to the low solubility of the materials of the first mixture.

(86) It is also observable that the iso-mass formulation of the first material and of the polymer corresponds to the best performances in terms of coating: wettability of the mixtures, roughness and homogeneity of the films.