WO2016066494A1 - Hole-transport materials for organic solar cells or organic optical sensors - Google Patents

Hole-transport materials for organic solar cells or organic optical sensors Download PDF

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WO2016066494A1
WO2016066494A1 PCT/EP2015/074369 EP2015074369W WO2016066494A1 WO 2016066494 A1 WO2016066494 A1 WO 2016066494A1 EP 2015074369 W EP2015074369 W EP 2015074369W WO 2016066494 A1 WO2016066494 A1 WO 2016066494A1
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organic
group
compound
solar cell
solar cells
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Fabien Nekelson
Hitoshi Yamato
Michaela Agari
Robert SEND
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Basf Se
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D495/00—Heterocyclic compounds containing in the condensed system at least one hetero ring having sulfur atoms as the only ring hetero atoms
    • C07D495/02—Heterocyclic compounds containing in the condensed system at least one hetero ring having sulfur atoms as the only ring hetero atoms in which the condensed system contains two hetero rings
    • C07D495/04—Ortho-condensed systems
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D333/00—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom
    • C07D333/02—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings
    • C07D333/04—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings not substituted on the ring sulphur atom
    • C07D333/06—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings not substituted on the ring sulphur atom with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to the ring carbon atoms
    • C07D333/14—Radicals substituted by singly bound hetero atoms other than halogen
    • C07D333/20—Radicals substituted by singly bound hetero atoms other than halogen by nitrogen atoms
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D409/00—Heterocyclic compounds containing two or more hetero rings, at least one ring having sulfur atoms as the only ring hetero atoms
    • C07D409/14—Heterocyclic compounds containing two or more hetero rings, at least one ring having sulfur atoms as the only ring hetero atoms containing three or more hetero rings
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D495/00—Heterocyclic compounds containing in the condensed system at least one hetero ring having sulfur atoms as the only ring hetero atoms
    • C07D495/12—Heterocyclic compounds containing in the condensed system at least one hetero ring having sulfur atoms as the only ring hetero atoms in which the condensed system contains three hetero rings
    • C07D495/14—Ortho-condensed systems
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D495/00—Heterocyclic compounds containing in the condensed system at least one hetero ring having sulfur atoms as the only ring hetero atoms
    • C07D495/22—Heterocyclic compounds containing in the condensed system at least one hetero ring having sulfur atoms as the only ring hetero atoms in which the condensed system contains four or more hetero rings
    • C—CHEMISTRY; METALLURGY
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    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/50—Organic perovskites; Hybrid organic-inorganic perovskites [HOIP], e.g. CH3NH3PbI3
    • H—ELECTRICITY
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    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/60—Organic compounds having low molecular weight
    • H10K85/631—Amine compounds having at least two aryl rest on at least one amine-nitrogen atom, e.g. triphenylamine
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/60—Organic compounds having low molecular weight
    • H10K85/649—Aromatic compounds comprising a hetero atom
    • H10K85/655—Aromatic compounds comprising a hetero atom comprising only sulfur as heteroatom
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/60—Organic compounds having low molecular weight
    • H10K85/649—Aromatic compounds comprising a hetero atom
    • H10K85/657—Polycyclic condensed heteroaromatic hydrocarbons
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    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/10—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising heterojunctions between organic semiconductors and inorganic semiconductors
    • H10K30/15—Sensitised wide-bandgap semiconductor devices, e.g. dye-sensitised TiO2
    • H10K30/151—Sensitised wide-bandgap semiconductor devices, e.g. dye-sensitised TiO2 the wide bandgap semiconductor comprising titanium oxide, e.g. TiO2
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/50—Photovoltaic [PV] devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/549—Organic PV cells

Definitions

  • the present invention relates to hole-transport materials.
  • the present invention further relates to the use of these materials in organic solar cells or organic optical sensors.
  • the present invention also relates to organic solar cells or organic optical sensors.
  • Organic solar cells and organic optical sensors are promising alternatives to conventional inor- ganic devices mostly based on silicon. It is expected that they can be produced at low cost on large-area flexible substrates by means of printing techniques. However, the solar-to-electrical energy conversion efficiencies and the long-term stability have not yet reached those of the conventional inorganic devices. Therefore, intensive research resources are invested with the goal to improve the efficiency and stability of organic solar cells and organic optical sensors.
  • An organic solar cell containing tris[4-(5-phenylthiophen-2-yl)phenyl]amine as hole-transport material is disclosed by Kageyama et al. (Advanced Functional Materials, Vol. 19 (2009), page 3948-3955). However, their energy conversion efficiency remains relatively low. It was an object of the present invention to provide hole-transport materials for organic solar cells or optical sensors with high energy conversion efficiency. These materials should be easily synthesized with cost-effective precursor materials in a short synthesis route and an easy purification procedure. Also, it was aimed at materials which can easily be processed and yield solar cells with a high degree of reproducibility with regard to the solar cell performance. Another ob- ject of the present invention is to provide hole-transport materials which have little tendency to crystallize even after long periods of time at elevated temperatures.
  • R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group or an aryl group,
  • X 1 , X 2 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group, or an aryl group, wherein X 1 , X 2 can form together a ring and wherein at least one of X 1 , X 2 is not H.
  • the present invention further relates to the use of the compound of general formula (I) according to the present invention in organic solar cells or organic optical sensors.
  • the present invention further relates to an organic solar cell or organic optical sensor comprising a compound of general formula (I) according to the present invention.
  • R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are independent of each other H (which stands for hydrogen), an alkyi group, an alkoxy group, an alkyi thiol group or an aryl group.
  • AlkyI groups include linear alkyi groups like methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, and so on and branched alkyi groups such as iso- propyl, /sobutyl, sec-butyl, fert-butyl, 2-methyl-pentyl, 2-ethyl-hexyl, cyclopropyl, cyclohexyl, indanyl, norbornyl.
  • the alkyi groups are C1-C20 alkyi groups, more preferably C1-C12 alkyi groups, in particular C1-C6 alkyi groups.
  • AlkyI groups in the context of the present invention can also be substituted, for example by halogens like fluoride, chloride, bromide, iodide; by pseudohalogens like cyanide, cyanate, thiocyanate; or by alcohols. It is further possible that one or several methylene units in an alkyi chain are exchanged by oxygen atoms, for example as in a oligoethyleneoxide group.
  • Alkoxy groups include methoxy, ethoxy, 1 -propoxy, 2-propoxy, 1 -butoxy, 2-butoxy or tertbutoxy.
  • alkoxy groups are C1-C12 alkoxy groups, more preferably Ci-Cs alkoxy groups, even more preferably C1-C4 alkoxy groups, in particular methoxy.
  • AlkyI thiol groups include methylthio, ethylthio, 1 -propylthio, 2-propylthio, 1 -butylthio, 2-butylthio or tertbutylthio.
  • alkyi thio groups are C1-C12 alkyi thio groups, more preferably Ci-Cs alkyi thio groups, even more preferably C1-C4 alkyi thio groups, in particular methylthio.
  • Aryl groups include aromatic hydrocarbons such as five-membered rings like the cyclopentadi- ene anion and six-membered rings like benzene. It is also possible that several aromatic rings are fused such as in naphthalene, anthracene, phenanthrene, the indene anion or the fluorene anion.
  • Aryl groups further include heteroaromatic groups include five-membered rings like furan, pyrrole, thiophene, selenophene, oxazole, isoxazole, imidazole, thiazole, isothiazole, triazole or tetrazole and six-membered rings like pyridine, pyridazine, pyridimine, pyrazine, triazine, or te- trazine.
  • heteroaromatic rings are fused with aromatic rings such as in benzofuran, indole, benzothiophene, benzoselenophene, dibenzofuran, carbazole, dibenzothio- phene, dibenzoselenophene, quinoline, isoquinoline or indazine.
  • aromatic rings such as in benzofuran, indole, benzothiophene, benzoselenophene, dibenzofuran, carbazole, dibenzothio- phene, dibenzoselenophene, quinoline, isoquinoline or indazine.
  • two or more heteroaromatic rings are fused such as in furanofuran, pyrrolopyrrole, thiophenothio- phene, selenophenoselenophene, furanopyrrole, pyrrolothiophene, di pyrrolopyrrole, dithio- phenethiophene.
  • Aryl groups further include more than one aromatic ring which are bond by a single covalent bond. These include several aromatic hydrocarbons bond by a single bond such as biphenyl or terphenyl; several heteraromatic groups such as bipyridyl or bithienyl; or mixed aromatic hydrocarbons and aromatic hydrocarbons such as thienylphenyl.
  • Aryl groups can be substituted, for example with halogens, alkyl groups, alkoxy groups or alkyl thiol groups as described above.
  • R 1 , R 2 , R 3 and R 4 are hydrogen.
  • R 5 , R 6 , R 8 and R 9 are hydrogen.
  • R 7 is an alkoxy group. More preferably, R 1 , R 2 , R 3 R 4 , R 5 , R 6 , R 8 and R 9 are hydrogen and R 7 is an alkoxy group.
  • X 1 , X 2 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group, or an aryl group, wherein X 1 , X 2 can form together a ring and wherein at least one of X 1 , X 2 is not H.
  • alkyl groups, alkoxy groups, alkyl thiol groups, and aryl groups as described for R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 apply for X 1 , X 2 .
  • X 1 and X 2 form together a ring, more preferably X 1 and X 2 form together an aliphatic ring in which methylene groups can be replaced by oxygen groups, even more preferably X 1 and X 2 form together an aliphatic ring which is connected to the thiophene group in ligand L via oxygen atoms.
  • a preferred example for X 1 and X 2 is ethylene dioxy.
  • the compounds of general formula (I) can for example be synthesized by a Buchwald-Hartwig coupling which is for example described in detail by John F. Hartwig (Angew. Chem. Int. Ed. 37 (1998) 2047-2067).
  • the use of palladium catalyst is preferred, in particular a palladium catalyst containing tri-feri-butylphosphine ligands.
  • the compound of general formula (I) is particularly suitable as hole-transport materials in organic solar cells or organic optical sensors. Therefore, the present invention relates to the use of the compound of general formula (I) in organic solar cells or organic optical sensors.
  • the present invention further relates to organic solar cells or organic optical sensors comprising the compound of general formula (I) according to the present invention.
  • Organic solar cells and organic optical sensors are based on the same principle, namely the conversion of incident light to electrical energy. In the case of solar cells the electrical energy is used as power source whereas in the case of optical sensors the electrical energy is used to measure the intensity of the incident light.
  • the following section describes solar cells but equally applies to organic optical sensors which are basically built the same way.
  • An organic solar cell according to the present invention typically comprises
  • the components of the solar cell are generally arranged in a stack of layers.
  • Layer in the context of the present invention refers to a thin structure with an arbitrary surface. It may be flat, but in most cases it is very rough. A layer can even form an interpenetrating network with an adja- cent layer to increase its contact area to the adjacent layers.
  • the order of the layers can be freely chosen with the provision that the two electrodes are not in direct contact with each other and that the substrate is not in between the two electrodes. An example for the order is
  • the substrate can be made of glass such as low-cost soda glass of high strength or non-alkali glass from which no alkaline elution occurs.
  • a transparent polymer film may be used such as tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naph- thalate (PEN), syndiotactic polystyrene (SPS), polyphenylenesulfide (PPS), polycarbonate (PC), polyarylate (PAr), polysulfone (PSF), polyestersulfone (PES), polyimide (PI), polyetherimide (PEI), polycycloolefin such as polynorbornene, or brominated phenoxy resin.
  • Polymer films are preferred, in particular PET, PEN and polynorbornene.
  • the transparent electrode can be made of a transparent conductive oxide (TCO), such as for example indium-tin composite oxides, tin oxides doped with fluorine, antimony or indium and zinc oxide doped with aluminum. Tin oxide doped with fluorine or indium is preferred.
  • TCO transparent conductive oxide
  • the transparent electrode is generally used in form of a thin film, so that it is sufficiently transparent.
  • Transparent in the present context means that the transmittance of light with a wavelength of 550 nm is at least 50 %, preferably at least 70 %, in particular at least 80 %.
  • the transparent electrode has a thickness of 0.02 to 10 ⁇ and more preferably from 0.1 to 1 ⁇ .
  • the electron-transport material can be organic or inorganic. Typical organic electron-transport materials are fullerenes ⁇ , C70, C76, Cso, Cs2, Cs4, Cs6, C90 and C94, preferably C60. It is also possible to use substituted fullerenes, in particular [6,6]-phenyl-C6i-butyric acid methyl ester (PCBM).
  • PCBM substituted fullerenes, in particular [6,6]-phenyl-C6i-butyric acid methyl ester
  • Suitable inorganic electron-transport materials are semi-conductive metal oxides including ox- ides of titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, caesium, niobium or tantalum.
  • composite semiconductors such as M 1 xM 2 yOz may be used, wherein M 1 and M 2 are independent of each other a metal atom, O is an oxygen atom, and x, y and z are numbers including 0 which are chosen such that an non- charged molecule is formed. Examples are T1O2, Sn02, Fe203, WO3, ZnO, Nb20s, SrTiO-3,
  • Ta2C Ta2C"5, CS2O, ZnO, zinc stannate, complex oxides such as barium titanate, and binary and ternary iron oxides.
  • Inorganic electron-transport materials are preferred, more preferred are semiconducting metal oxides. Even more preferred are T1O2, Sn02, Fe203, WO3, ZnO, Nb20s, and SrTi03, in particular
  • the inorganic electron-transport materials are preferably present in amorphous or nanocrystal- line form. More preferably, they are present as nanocrystalline porous layers. Such layers have a large surface area leading to effective charge separation of the exciton formed upon light ab- sorption.
  • the inorganic electron-transport materials may also be present in a structured form, such as nanorods.
  • Preferred methods for producing the semi-conductive metal oxides are sol-gel methods described for example in Materia, Vol. 35, No. 9, Page 1012 to 1018 (1996).
  • the method devel- oped by Degussa Company which comprises preparing oxides by subjecting chlorides to a high temperature hydrolysis in an oxyhydrogen salt, is also preferred.
  • sol-gel methods In the case of using titanium oxide as the semi-conductive metal oxides, the above-mentioned sol-gel methods, gel-sol methods, high temperature hydrolysis methods are preferably used.
  • Other preferred sol-gel methods are those described in Barbe et al., Journal of American Ceramic Society, Vol. 80, No. 12, Page 3157 to 3171 (1997) and Burnside et al, Chemistry of Materials, Vol. 10, No. 9, Page 2419 to 2425 (1998).
  • the electron-transport material is sensitized with a light-absorbing material to increase light absorption efficiency such as in a dye-sensitized solar cell (DSC).
  • a light-absorbing material such as in a dye-sensitized solar cell (DSC).
  • DSC dye-sensitized solar cell
  • the electron or hole transport material may itself absorb light such as in a bulk heterojunction (BHJ) solar cell.
  • the light-absorbing material in the solar cell can be chosen from a wide variety of substances. Examples are metal complex dyes including Ru(l l)-dyes (as for example those in WO 98 / 50 393 - page 8 to 1 1 ); indoline dyes (as for example in Adv. Mater.
  • oxazine dyes (as for example those in US 6 359 21 1 ); thiazine dyes (as for example those in US 6 359 21 1 ); acridine dyes (as for example those in US 6 359 21 1 ); porphyrin dyes; methine dyes such as cyanine dyes, merocyanine dyes (as for example those in WO 2009 / 007 340 page 4 to 7), squarylium dyes; rylene dyes including perylene dyes and naphtalenemonoimid dyes (as for example in those WO 2007 / 054 470 page 13 to 18); or a quinolinium dye (for example those in WO 2009 / 109 499 page 42 to 51 ). Ru(l l) dyes, perylene dyes, naphtalenemonoimid dyes, or quinolinium dyes are preferred.
  • Perovskite absorbers are preferred.
  • Perovskite absorbers are typically compounds of the general formula (II): EMX3.
  • E stands for an alkali metal such as Li, Na, K, Rb, Cs; or an ammonium ion in which one or more hydrogen atoms may be exchanged by alkyl chains or acyl groups.
  • Ammonium ions in which one or more hydrogen atoms are exchanged by alkyl chains include monoalkylammonium ions, dialkylammonium ions, trimethylammonium ions, tetrame- thylammonium ions.
  • the alkyl group or groups are independent of each other Ci to C6 alkyl groups, in particular methyl or ethyl.
  • Ammonium ions in which one or more hydrogen atoms are exchanged by alkyl chains include amidinium ions, N-alkylamidinium, and imidinium ions, preferably amidinium ions.
  • the amidinium or imidinium ion is derived from a Ci to C6 carboxamide, in particular from formamide or acetamide.
  • E is Cs or an ion comprising a positively charged nitrogen atom.
  • M stands for a divalent metal atom, preferably for Pb or Sn.
  • X stands for halogens, in particular CI, Br, I.
  • X in compounds of general formula (II) can contain all the same or different halogens.
  • perovskite absorbers include methyl ammonium lead halogenides, such methyl ammonium lead iodide (CHsNHsPb ); methyl ammonium lead mixed halogenides such as CHsNHsPbCl ; formadinium lead halogenides like formadinium lead iodide (HC(NH2)Pbl3), formadinium lead bromide (HC(NH2)PbBr3) or formadinium lead chloride iodide (HC(NH2)PbCl2l); or cesium tin iodide (CsSn ).
  • Solar cells comprising sensitizers of general formula (II) are sometimes referred to as perovskite-sensitized solar cells (PSC).
  • the hole transport layer, the sensitizing dye and the electron transport layer can independent of each other be formed by wet chemical processes and by vapor processes.
  • a solvent preferably an organic solvent.
  • Any solvent which dissolves the dye is suitable, for example ethanol, acetone, iso-propanol, tetrahydrofuran, dimethylforamide, dimethylacetamide, acetonitrile, methoxyace- tonitrile, toluene, N-methylpyrrolidone.
  • the preferred concentration of the sensitizing dye in the solvent is 0.01 to 10 mmol/l, more preferably it is 0.1 to 1 mmol/l.
  • the sensitizing dye dissolved in the solvent is applied to the electron-transport layer by any layer-formation process.
  • layer-formation process include spin-coating, spray-coating, dip-coating, drop-casting, doctor-blading, slot-die coating, 2D ink jet printing, gravure printing, offset printing, flexo printing, screen printing, or microcon- tact (wave) printing.
  • Vapor processes include sublimation, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or direct liquid injection.
  • the material out of which the layer is formed is brought into the gaseous state and deposited onto the other layers.
  • the vapor processes are done under reduced pressure such as from 100 to 10 -8 mbar, more preferably from 10 to 10 "5 mbar, in particular 1 to 10 "2 mbar.
  • the respective layer is preferably heated. Suitable temperatures are 100 to 600 °C, preferably 200 to 500 °C.
  • Suitable time periods are 10 minutes to 2 hours, preferably 20 minutes to 1 hour.
  • the compound of general formula (I) acts as hole-transport material. Its layer usually forms an electrical contact with the optionally sensitized electron-transport layer.
  • the compound of general formula (I) can be the only substance in the hole-transport layer or it can be mixed with other substances.
  • An example are dopants which increase the hole conductivity such as N(PhBr)3SbCl6, silver-bis-(trifluoromethylsulfonyl)imide or V2O5.
  • the layer comprising the hole-transport material containing a dopant is formed by layer- formation process described above wherein the dopant is mixed in the solution for the wet- chemical process or brought into the gas phase together with the hole-transport material.
  • a solar cell according to the present invention may further comprise a blocking layer between the absorber and the electron-transport layer.
  • Materials suitable for blocking lay- ers include metal oxides, for example T1O2, S1O2, AI2O3, Zr02, MgO, Sn02, ZnO, EU2O3, Nb20s or combinations thereof, TiCI 4 ; or polymers, for example poly(phenylene oxide-co-2- allylphenylene oxide) or poly(methylsiloxane). Details of the preparation of such layers are described in, for example, Electrochimica Acta 40, 643, 1995; J. Am. Chem. Soc 125, 475, 2003; Chem. Lett. 35, 252, 2006; J. Phys. Chem. B, 1 10, 1991 , 2006. Preferably, TiCI 4 is used.
  • the blocking layer is usually dense and compact, and is usually thinner than the electron-transport layer.
  • One or both electrodes can independent of each other be coated with very thin layers to adjust the work function of the electrodes.
  • These work function adjustment layers may be generated by self-assembled monolayers of organic molecules, preferably aromatic molecules. Examples are thiol-functionalized thiophenes, pentacene derivatives or cyanobenzene derivatives.
  • the self-assembled monolayers are made by immersing the electrode in a solution containing the organic molecule which assembles on the surface. The electrode is removed from the solution and dried.
  • the solar cell according to the present invention further comprises a counter electrode formed by an electrically conductive material.
  • the electrically conductive material used for the counter electrically conductive layer include metals such as platinum, gold, silver, copper, aluminum, magnesium, indium or mixtures or alloys thereof, preferably of aluminum and silver; carbon; electrically conductive metal oxides such as indium-tin composite oxides and fluorine- doped tin oxides; mixed inorganic/organic electrodes; polylayer electrodes such as LiF/AI elec- trades.
  • Preferred electrically conductive materials are platinum, gold, silver, copper, aluminum or magnesium, more preferred silver or gold.
  • the thickness of the counter electrode is not particularly limited, preferably it is 3 nm to 10 ⁇ .
  • the counter electrode can be made by applying metal-plating or vapor-depositing such as phys- ical vapor deposition or chemical vapor to deposit the electrically conductive material directly onto the layer it shall contact. It can also be deposited via a printing or coating process from a metal containing ink or paste or a conductive carbon-based formulation.
  • the solar cells according to the present invention show high light to electrical power
  • Perovskite Solar Cells were prepared according to the following procedure.
  • a ⁇ 2 blocking layer was prepared on a fluorine-doped tin oxide (FTO)-covered glass substrate using spray pyrol- ysis (cf. B. Peng, G. Jungmann, C. Jager, D. Haarer, H. W. Schmidt, M. Thelakkat, Coord. Chem. Rev. 2004, 248, 1479).
  • a ⁇ 2 scaffold was deposited by spin-coating a ⁇ 2 paste (Dyesol) diluted with ethanol. The two layers were sintered at 450 °C for 30 min.
  • a perovskite layer was prepared by spin-coating a 40 wt.-% solution of CH 3 NH 3 l:PbCl2 (molecular ration 3:1 ) in DMF ( ⁇ , ⁇ -Dimethylformamide) and annealing the resulting layer for 30 min in an oven at 1 10°C.
  • the hole-transport material according to the present invention was deposited by spin-coating a solution in chlorobenzene containing also lithium bis(trifluoromethylsulfonyl)imide (LiTFSi) and tert-butylpyridine (tBP).
  • the counter electrodes consisted of 50 nm gold layers evaporated through a mask, defining the active area of the solar cell by the size of these contacts (0.13 cm 2 ). For measurements, the cells were masked by an aperture of the same area.
  • Table 1 Current-voltage characteristics of the perovskite-sensitzed solar cells with the hole- transport materials according to the present invention, Isc stands for short-circuit current, Voc for open-circuit voltage, FF for fill factor and ⁇ for the solar-to-electric power conversion efficiency.
  • Example 7 Preparation of optical sensors
  • Optical sensors were prepared according to the following procedure.
  • a T1O2 blocking layer was prepared on a fluorine-doped tin oxide (FTO)-covered glass substrate using spray pyrolysis (cf. B. Peng, G. Jungmann, C. Jager, D. Haarer, H. W. Schmidt, M. Thelakkat, Coord. Chem. Rev. 2004, 248, 1479).
  • a Ti0 2 scaffold was deposited by spin-coating a Ti0 2 paste (Dyesol) diluted with ethanol. The two layers were sintered at 450 °C for 30 min. After sintering the sample was cooled to 60 to 80°C. The sample was then treated with an additive as disclosed in
  • WO 2012 / 001 628 A1 5 mM of the additive in ethanol was prepared and the intermediate was immersed for 17 hours, washed in a bath of pure ethanol, briefly dried in a nitrogen stream and subsequently immersed in a 0.5 mM solution of dye ID504, a perylenedicarboximide derivative as disclosed e.g. in WO 2012 / 1 10 924 A1 , in a mixture solvent of acetonitrile + t-butyl alcohol (1 :1 ) for 2 hours so as to adsorb the dye. After removal from the solution, the specimen was subsequently washed in acetonitrile and dried in a nitrogen flow.
  • the hole-transport material according the present invention was applied by using a chlorobenzene solution with 0.165 M of the hole-transport material and 20mM LiN(S02CFs)2 (Wako Pure Chemical Industries, Ltd.). 20 ⁇ /cm 2 of this solution was applied onto the specimen and allowed to act for 60 s. The supernatant solution was then spun off for 30 s at 2000 revolu- tions per minute. The substrate was stored overnight under ambient conditions.
  • Ag was evaporated by thermal metal evaporation in a vacuum at a rate of 0.5 nm/s in a pressure of 10 "5 mbar, so that an approximately 100 nm thick Ag layer was obtained.
  • Table 2 In focus-current of the sensors.

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Abstract

The present invention relates to hole-transport materials in organic solar cells. In particular the present invention relates to a compound of general formula (I), wherein R1, R2, R3, R4, R5, R6, R7, R8, R9 are independent of each other H, an alkyi group, an alkoxy group, an alkyi thiol group or an aryl group, X1, X2 are independent of each other H, an alkyi group, an alkoxy group, an alkyi thiol group, or an aryl group, wherein X1, X2 can form together a ring and wherein at least one of X1, X2 is not H.

Description

Hole-transport Materials for Organic Solar Cells or Organic Optical Sensors Description The present invention relates to hole-transport materials. The present invention further relates to the use of these materials in organic solar cells or organic optical sensors. The present invention also relates to organic solar cells or organic optical sensors.
Organic solar cells and organic optical sensors are promising alternatives to conventional inor- ganic devices mostly based on silicon. It is expected that they can be produced at low cost on large-area flexible substrates by means of printing techniques. However, the solar-to-electrical energy conversion efficiencies and the long-term stability have not yet reached those of the conventional inorganic devices. Therefore, intensive research resources are invested with the goal to improve the efficiency and stability of organic solar cells and organic optical sensors.
An organic solar cell containing tris[4-(5-phenylthiophen-2-yl)phenyl]amine as hole-transport material is disclosed by Kageyama et al. (Advanced Functional Materials, Vol. 19 (2009), page 3948-3955). However, their energy conversion efficiency remains relatively low. It was an object of the present invention to provide hole-transport materials for organic solar cells or optical sensors with high energy conversion efficiency. These materials should be easily synthesized with cost-effective precursor materials in a short synthesis route and an easy purification procedure. Also, it was aimed at materials which can easily be processed and yield solar cells with a high degree of reproducibility with regard to the solar cell performance. Another ob- ject of the present invention is to provide hole-transport materials which have little tendency to crystallize even after long periods of time at elevated temperatures.
The above objects were achieved by a compound of general formula (I)
Figure imgf000002_0001
wherein
R1, R2, R3, R4, R5, R6, R7, R8, R9 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group or an aryl group,
X1, X2 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group, or an aryl group, wherein X1, X2 can form together a ring and wherein at least one of X1, X2 is not H.
The present invention further relates to the use of the compound of general formula (I) according to the present invention in organic solar cells or organic optical sensors. The present invention further relates to an organic solar cell or organic optical sensor comprising a compound of general formula (I) according to the present invention.
Preferred embodiments of the present invention can be found in the description and the claims. Combinations of different embodiments fall within the scope of the present invention.
According to the present invention R1, R2, R3, R4, R5, R6, R7, R8, R9 are independent of each other H (which stands for hydrogen), an alkyi group, an alkoxy group, an alkyi thiol group or an aryl group. AlkyI groups include linear alkyi groups like methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, and so on and branched alkyi groups such as iso- propyl, /sobutyl, sec-butyl, fert-butyl, 2-methyl-pentyl, 2-ethyl-hexyl, cyclopropyl, cyclohexyl, indanyl, norbornyl. Preferably, the alkyi groups are C1-C20 alkyi groups, more preferably C1-C12 alkyi groups, in particular C1-C6 alkyi groups. AlkyI groups in the context of the present invention can also be substituted, for example by halogens like fluoride, chloride, bromide, iodide; by pseudohalogens like cyanide, cyanate, thiocyanate; or by alcohols. It is further possible that one or several methylene units in an alkyi chain are exchanged by oxygen atoms, for example as in a oligoethyleneoxide group.
Alkoxy groups include methoxy, ethoxy, 1 -propoxy, 2-propoxy, 1 -butoxy, 2-butoxy or tertbutoxy. Preferably, alkoxy groups are C1-C12 alkoxy groups, more preferably Ci-Cs alkoxy groups, even more preferably C1-C4 alkoxy groups, in particular methoxy.
AlkyI thiol groups include methylthio, ethylthio, 1 -propylthio, 2-propylthio, 1 -butylthio, 2-butylthio or tertbutylthio. Preferably, alkyi thio groups are C1-C12 alkyi thio groups, more preferably Ci-Cs alkyi thio groups, even more preferably C1-C4 alkyi thio groups, in particular methylthio.
Aryl groups include aromatic hydrocarbons such as five-membered rings like the cyclopentadi- ene anion and six-membered rings like benzene. It is also possible that several aromatic rings are fused such as in naphthalene, anthracene, phenanthrene, the indene anion or the fluorene anion.
Aryl groups further include heteroaromatic groups include five-membered rings like furan, pyrrole, thiophene, selenophene, oxazole, isoxazole, imidazole, thiazole, isothiazole, triazole or tetrazole and six-membered rings like pyridine, pyridazine, pyridimine, pyrazine, triazine, or te- trazine. It is also possible that heteroaromatic rings are fused with aromatic rings such as in benzofuran, indole, benzothiophene, benzoselenophene, dibenzofuran, carbazole, dibenzothio- phene, dibenzoselenophene, quinoline, isoquinoline or indazine. Another possibility is that two or more heteroaromatic rings are fused such as in furanofuran, pyrrolopyrrole, thiophenothio- phene, selenophenoselenophene, furanopyrrole, pyrrolothiophene, di pyrrolopyrrole, dithio- phenethiophene. Aryl groups further include more than one aromatic ring which are bond by a single covalent bond. These include several aromatic hydrocarbons bond by a single bond such as biphenyl or terphenyl; several heteraromatic groups such as bipyridyl or bithienyl; or mixed aromatic hydrocarbons and aromatic hydrocarbons such as thienylphenyl. Aryl groups can be substituted, for example with halogens, alkyl groups, alkoxy groups or alkyl thiol groups as described above.
Preferably, R1, R2, R3 and R4 are hydrogen. Preferably, R5, R6, R8 and R9 are hydrogen. Preferably R7 is an alkoxy group. More preferably, R1, R2, R3 R4, R5, R6, R8 and R9 are hydrogen and R7 is an alkoxy group.
According to the present invention X1, X2 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group, or an aryl group, wherein X1, X2 can form together a ring and wherein at least one of X1, X2 is not H. The same definitions and preferred embodiments with regard to alkyl groups, alkoxy groups, alkyl thiol groups, and aryl groups as described for R1, R2, R3, R4, R5, R6, R7, R8, R9 apply for X1, X2. Preferably X1 and X2 form together a ring, more preferably X1 and X2 form together an aliphatic ring in which methylene groups can be replaced by oxygen groups, even more preferably X1 and X2 form together an aliphatic ring which is connected to the thiophene group in ligand L via oxygen atoms. A preferred example for X1 and X2 is ethylene dioxy.
The compounds of general formula (I) can for example be synthesized by a Buchwald-Hartwig coupling which is for example described in detail by John F. Hartwig (Angew. Chem. Int. Ed. 37 (1998) 2047-2067). The use of palladium catalyst is preferred, in particular a palladium catalyst containing tri-feri-butylphosphine ligands.
Some preferred examples are:
Figure imgf000005_0001
Figure imgf000005_0002
The compound of general formula (I) is particularly suitable as hole-transport materials in organic solar cells or organic optical sensors. Therefore, the present invention relates to the use of the compound of general formula (I) in organic solar cells or organic optical sensors. The present invention further relates to organic solar cells or organic optical sensors comprising the compound of general formula (I) according to the present invention. Organic solar cells and organic optical sensors are based on the same principle, namely the conversion of incident light to electrical energy. In the case of solar cells the electrical energy is used as power source whereas in the case of optical sensors the electrical energy is used to measure the intensity of the incident light. The following section describes solar cells but equally applies to organic optical sensors which are basically built the same way.
An organic solar cell according to the present invention typically comprises
· a substrate,
• a transparent electrode,
• an electron-transport material,
• a light-absorbing material,
• the compound of general formula (I) as hole-transport material, and
· a counter electrode.
The components of the solar cell are generally arranged in a stack of layers. Layer in the context of the present invention refers to a thin structure with an arbitrary surface. It may be flat, but in most cases it is very rough. A layer can even form an interpenetrating network with an adja- cent layer to increase its contact area to the adjacent layers. The order of the layers can be freely chosen with the provision that the two electrodes are not in direct contact with each other and that the substrate is not in between the two electrodes. An example for the order is
1 . the substrate,
2. the transparent electrode,
3. the electron-transport material,
4. a light-absorbing material,
5. the compound of general formula (I) as hole-transport material, and
6. the counter electrode. The substrate can be made of glass such as low-cost soda glass of high strength or non-alkali glass from which no alkaline elution occurs. Alternatively, a transparent polymer film may be used such as tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naph- thalate (PEN), syndiotactic polystyrene (SPS), polyphenylenesulfide (PPS), polycarbonate (PC), polyarylate (PAr), polysulfone (PSF), polyestersulfone (PES), polyimide (PI), polyetherimide (PEI), polycycloolefin such as polynorbornene, or brominated phenoxy resin. Polymer films are preferred, in particular PET, PEN and polynorbornene.
The transparent electrode can be made of a transparent conductive oxide (TCO), such as for example indium-tin composite oxides, tin oxides doped with fluorine, antimony or indium and zinc oxide doped with aluminum. Tin oxide doped with fluorine or indium is preferred. The transparent electrode is generally used in form of a thin film, so that it is sufficiently transparent. Transparent in the present context means that the transmittance of light with a wavelength of 550 nm is at least 50 %, preferably at least 70 %, in particular at least 80 %. Preferably the transparent electrode has a thickness of 0.02 to 10 μηι and more preferably from 0.1 to 1 μηη.
The electron-transport material can be organic or inorganic. Typical organic electron-transport materials are fullerenes Οβο, C70, C76, Cso, Cs2, Cs4, Cs6, C90 and C94, preferably C60. It is also possible to use substituted fullerenes, in particular [6,6]-phenyl-C6i-butyric acid methyl ester (PCBM).
Suitable inorganic electron-transport materials are semi-conductive metal oxides including ox- ides of titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, caesium, niobium or tantalum. Further, composite semiconductors such as M1xM2yOz may be used, wherein M1 and M2 are independent of each other a metal atom, O is an oxygen atom, and x, y and z are numbers including 0 which are chosen such that an non- charged molecule is formed. Examples are T1O2, Sn02, Fe203, WO3, ZnO, Nb20s, SrTiO-3,
Ta2C"5, CS2O, ZnO, zinc stannate, complex oxides such as barium titanate, and binary and ternary iron oxides.
Inorganic electron-transport materials are preferred, more preferred are semiconducting metal oxides. Even more preferred are T1O2, Sn02, Fe203, WO3, ZnO, Nb20s, and SrTi03, in particular
The inorganic electron-transport materials are preferably present in amorphous or nanocrystal- line form. More preferably, they are present as nanocrystalline porous layers. Such layers have a large surface area leading to effective charge separation of the exciton formed upon light ab- sorption. The inorganic electron-transport materials may also be present in a structured form, such as nanorods.
Preferred methods for producing the semi-conductive metal oxides are sol-gel methods described for example in Materia, Vol. 35, No. 9, Page 1012 to 1018 (1996). The method devel- oped by Degussa Company, which comprises preparing oxides by subjecting chlorides to a high temperature hydrolysis in an oxyhydrogen salt, is also preferred.
In the case of using titanium oxide as the semi-conductive metal oxides, the above-mentioned sol-gel methods, gel-sol methods, high temperature hydrolysis methods are preferably used. Other preferred sol-gel methods are those described in Barbe et al., Journal of American Ceramic Society, Vol. 80, No. 12, Page 3157 to 3171 (1997) and Burnside et al, Chemistry of Materials, Vol. 10, No. 9, Page 2419 to 2425 (1998).
Preferably, the electron-transport material is sensitized with a light-absorbing material to increase light absorption efficiency such as in a dye-sensitized solar cell (DSC). Generally 0.01 to 1 mmol of light-absorbing material is used per 1 g of electron-transport material. Furthermore, the electron or hole transport material may itself absorb light such as in a bulk heterojunction (BHJ) solar cell. The light-absorbing material in the solar cell can be chosen from a wide variety of substances. Examples are metal complex dyes including Ru(l l)-dyes (as for example those in WO 98 / 50 393 - page 8 to 1 1 ); indoline dyes (as for example in Adv. Mater. 2005, 17, 813); oxazine dyes (as for example those in US 6 359 21 1 ); thiazine dyes (as for example those in US 6 359 21 1 ); acridine dyes (as for example those in US 6 359 21 1 ); porphyrin dyes; methine dyes such as cyanine dyes, merocyanine dyes (as for example those in WO 2009 / 007 340 page 4 to 7), squarylium dyes; rylene dyes including perylene dyes and naphtalenemonoimid dyes (as for example in those WO 2007 / 054 470 page 13 to 18); or a quinolinium dye (for example those in WO 2009 / 109 499 page 42 to 51 ). Ru(l l) dyes, perylene dyes, naphtalenemonoimid dyes, or quinolinium dyes are preferred.
Other light-absorbing materials include quantum dots like CdSe quantum dots and perovskite absorbers. Perovskite absorbers are preferred. Perovskite absorbers are typically compounds of the general formula (II): EMX3. E stands for an alkali metal such as Li, Na, K, Rb, Cs; or an ammonium ion in which one or more hydrogen atoms may be exchanged by alkyl chains or acyl groups. Ammonium ions in which one or more hydrogen atoms are exchanged by alkyl chains include monoalkylammonium ions, dialkylammonium ions, trimethylammonium ions, tetrame- thylammonium ions. Preferably, the alkyl group or groups are independent of each other Ci to C6 alkyl groups, in particular methyl or ethyl. Ammonium ions in which one or more hydrogen atoms are exchanged by alkyl chains include amidinium ions, N-alkylamidinium, and imidinium ions, preferably amidinium ions. Preferably, the amidinium or imidinium ion is derived from a Ci to C6 carboxamide, in particular from formamide or acetamide. Preferably E is Cs or an ion comprising a positively charged nitrogen atom.
In general formula (II) M stands for a divalent metal atom, preferably for Pb or Sn. X stands for halogens, in particular CI, Br, I. X in compounds of general formula (II) can contain all the same or different halogens. Specific examples for perovskite absorbers include methyl ammonium lead halogenides, such methyl ammonium lead iodide (CHsNHsPb ); methyl ammonium lead mixed halogenides such as CHsNHsPbCl ; formadinium lead halogenides like formadinium lead iodide (HC(NH2)Pbl3), formadinium lead bromide (HC(NH2)PbBr3) or formadinium lead chloride iodide (HC(NH2)PbCl2l); or cesium tin iodide (CsSn ). Solar cells comprising sensitizers of general formula (II) are sometimes referred to as perovskite-sensitized solar cells (PSC).
The hole transport layer, the sensitizing dye and the electron transport layer can independent of each other be formed by wet chemical processes and by vapor processes. For wet chemical processes the material out of which the layer is formed is dissolved in a solvent, preferably an organic solvent. Any solvent which dissolves the dye is suitable, for example ethanol, acetone, iso-propanol, tetrahydrofuran, dimethylforamide, dimethylacetamide, acetonitrile, methoxyace- tonitrile, toluene, N-methylpyrrolidone. The preferred concentration of the sensitizing dye in the solvent is 0.01 to 10 mmol/l, more preferably it is 0.1 to 1 mmol/l. The sensitizing dye dissolved in the solvent is applied to the electron-transport layer by any layer-formation process. These include spin-coating, spray-coating, dip-coating, drop-casting, doctor-blading, slot-die coating, 2D ink jet printing, gravure printing, offset printing, flexo printing, screen printing, or microcon- tact (wave) printing.
Vapor processes include sublimation, physical vapor deposition, chemical vapor deposition, atomic layer deposition, or direct liquid injection. The material out of which the layer is formed is brought into the gaseous state and deposited onto the other layers. Preferably, the vapor processes are done under reduced pressure such as from 100 to 10-8 mbar, more preferably from 10 to 10"5 mbar, in particular 1 to 10"2 mbar. After deposition the respective layer is preferably heated. Suitable temperatures are 100 to 600 °C, preferably 200 to 500 °C. Suitable time periods are 10 minutes to 2 hours, preferably 20 minutes to 1 hour.
In the solar cell according to the present invention the compound of general formula (I) acts as hole-transport material. Its layer usually forms an electrical contact with the optionally sensitized electron-transport layer. The compound of general formula (I) can be the only substance in the hole-transport layer or it can be mixed with other substances. An example are dopants which increase the hole conductivity such as N(PhBr)3SbCl6, silver-bis-(trifluoromethylsulfonyl)imide or V2O5. The layer comprising the hole-transport material containing a dopant is formed by layer- formation process described above wherein the dopant is mixed in the solution for the wet- chemical process or brought into the gas phase together with the hole-transport material.
Furthermore, a solar cell according to the present invention may further comprise a blocking layer between the absorber and the electron-transport layer. Materials suitable for blocking lay- ers include metal oxides, for example T1O2, S1O2, AI2O3, Zr02, MgO, Sn02, ZnO, EU2O3, Nb20s or combinations thereof, TiCI4; or polymers, for example poly(phenylene oxide-co-2- allylphenylene oxide) or poly(methylsiloxane). Details of the preparation of such layers are described in, for example, Electrochimica Acta 40, 643, 1995; J. Am. Chem. Soc 125, 475, 2003; Chem. Lett. 35, 252, 2006; J. Phys. Chem. B, 1 10, 1991 , 2006. Preferably, TiCI4 is used. The blocking layer is usually dense and compact, and is usually thinner than the electron-transport layer.
One or both electrodes can independent of each other be coated with very thin layers to adjust the work function of the electrodes. These work function adjustment layers may be generated by self-assembled monolayers of organic molecules, preferably aromatic molecules. Examples are thiol-functionalized thiophenes, pentacene derivatives or cyanobenzene derivatives. The self-assembled monolayers are made by immersing the electrode in a solution containing the organic molecule which assembles on the surface. The electrode is removed from the solution and dried.
The solar cell according to the present invention further comprises a counter electrode formed by an electrically conductive material. Examples of the electrically conductive material used for the counter electrically conductive layer include metals such as platinum, gold, silver, copper, aluminum, magnesium, indium or mixtures or alloys thereof, preferably of aluminum and silver; carbon; electrically conductive metal oxides such as indium-tin composite oxides and fluorine- doped tin oxides; mixed inorganic/organic electrodes; polylayer electrodes such as LiF/AI elec- trades. Preferred electrically conductive materials are platinum, gold, silver, copper, aluminum or magnesium, more preferred silver or gold.
The thickness of the counter electrode is not particularly limited, preferably it is 3 nm to 10 μηη. The counter electrode can be made by applying metal-plating or vapor-depositing such as phys- ical vapor deposition or chemical vapor to deposit the electrically conductive material directly onto the layer it shall contact. It can also be deposited via a printing or coating process from a metal containing ink or paste or a conductive carbon-based formulation.
The solar cells according to the present invention show high light to electrical power
efficiency, are easily produced with high reproducibility and show high stability.
Examples
Example 1 : Synthesis of tris[4-(5-(4-methoxyphenyl)-3,4-ethylenedioxythiophen-2- yl)phenyl]amine (C-1 )
Figure imgf000010_0001
To a solution of palladium(ll) acetate (5 mg, 0.02 mmol), P(mTol)3 (14 mg, 0.04 mmol), and cesium carbonate (0.48 g, 1.4 mmol) in toluene (20 ml_), was added 3,4-ethylenedioxy-2-(4- methoxyphenyl)thiophene (0.34 g, 1.3 mmol) and tris(4-iodophenyl)amine (0.28 g, 0.44 mmol) under nitrogen atmosphere. The reaction mixture was then heated at 1 10 °C under nitrogen overnight. After the reaction mixture had cooled to room temperature, water was added and extracted with CH2CI2. The organic phase is washed with water, dried over MgSC , and concentrated. The residue is purified by flash chromatography on silica gel with hexane and ethyl ace- tate (2:1 ) as eluent, yielding 0.16 g (0.16 mmol; 37 %) of compound C-1 as a yellow solid. The structure is confirmed by the 1H-NMR spectrum (CDCI3) δ in ppm: 3.83 (s, 9H), 4.43 (s, 12H), 6.98 (d, 6H), 7.15 (d, 6H), 7.69 (d, 6H), 7.72 (d, 6H). Synthesis of 3,4-ethylenedioxy-2-pinacoltoboratothioph
Figure imgf000011_0001
Under Ar, a stirred solution of 3,4-ethylenedioxythiophene (4.3 g, 30 mmol) in distilled THF (100 mL) was cooled to -78 °C. A 2.5 M solution of butyllithium (12 mL, 1 eq.) was added dropwise and the solution was stirred at this temperature during 1 h. Triisopropylborate (21 mL, 3 eq.) was added and the reaction mixture was allowed to warm to room temperature. After 2.5 h, a solution of pinacol (10.6 g, 3 eq.) in THF (30 mL) was added. The reaction was stirred during 30 min and then the solvent was removed in vacuo. The residue dissolved in diethyl ether was washed twice with water and dried over magnesium sulfate. The solvent was removed in vacuo. The product (6.8 g) was used in the next step without further purification.
Example 1 .2: Synthesis of 3,4-ethylenedioxy-2-(4-methoxyphenyl)thiophene
Figure imgf000011_0002
A mixture of 4-iodoanisole (2.54 g, 10.4 mmol), 3,4-ethylenedioxy-2-pinacoltoboratothiophene (2.87 g, 10.3 mmol), tetrakis(triphenylphosphine) palladium (1.2 g, 1 .0 mmol), potassium carbonate (1 .72 g, 12.4 mmol), dimethylformamide (15 mL) was stirred at 100 °C nitrogen atmosphere for 5 h. The mixture was added to water and extracted with CH2CI2. The organic phase was washed with water, dried over MgSC , and concentrated. The residue was purified by flash chromatography on silica gel with hexane and ethyl acetate (9:1 ) as eluent, yielding 0.8 g
(3.2 mmol; 31 %) of 3,4-ethylenedioxy-2-(4-methoxyphenyl)thiophene as a light yellow liquid. H-NMR spectrum (CDCI3) δ in ppm: 3.82 (s, 3H), 4.22-4.30 (m, 4H), 6.91 (d, 2H), 7.63 (d, 2H) Example 2: Synthesis of tris[4-(5-(4-ethoxyphenyl)-3,4-ethylenedioxythiophen-2-yl)phenyl]amine (C-2)
Figure imgf000012_0001
Compound C-2 was obtained in analogy to compound C-1 using corresponding reagents. The product was obtained as yellow solid.
H-NMR spectrum (CDCI3) δ in ppm: 1 .42 (t, 9H), 4.03 (q, 6H), 4.33 (s, 12H), 6.87 (d, 6H), 7.09 (d, 6H), 7.60 (d, 6H), 7.64 (d, 6H).
Example 3: Synthesis of tris[4-(5-(4-n-butyloxyphenyl)-3,4-ethylenedioxythiophen-2- yl)phenyl]amine (C-3)
Figure imgf000012_0002
Compound C-3 was obtained in analogy to compound C-1 using corresponding reagents. The product was obtained as brown solid.
H-NMR spectrum (CDCI3) δ in ppm: 0.98 (t, 9H), 1 .47-1 .55 (m, 6H), 1 .73-1 .81 (m, 6H), 4.03 (t, 6H), 4.42 (s, 12H), 6.97 (d, 6H), 7.14 (d, 6H), 7.67 (d, 6H), 7.70 (d, 6H).
Example 4: Synthesis of tris[4-(5-(4-n-hexyloxyphenyl)-3,4-ethylenedioxythiophen-2- yl)phenyl]amine (C-4)
Figure imgf000013_0001
Compound C-4 was obtained in analogy to compound C-1 using corresponding reagents. The product was obtained as yellow solid.
1H-NMR spectrum (CDCIa) δ in ppm: 0.91 (t, 9H), 1.23-1.41 (m, 18H), 1.74-1.83 (m, 6H), 4.03 (t, 6H), 4.42 (s, 12H), 6.98 (d, 6H), 7.15 (d, 6H), 7.68 (d, 6H), 7.72 (d, 6H).
Example 5: Synthesis of tris[4-(5-(4-methoxyphenyl)-3,4-diethylthiophen-2-yl)phenyl]amine (C- 5)
Figure imgf000013_0002
Compound C-5 was obtained in analogy to compound C-1 using corresponding reagents. The product was obtained as yellow solid.
1H-NMR spectrum (CDCI3) δ in ppm: 1 .14 (t, 9H), 1.18 (t, 9H), 2.61 -2.78 (m, 12H), 3.84 (s, 9H), 6.95 (d, 6H), 7.21 (d, 6H), 7.40 (d, 6H), 7.42 (d, 6H). Example 6: Perovskite Solar Cells
Perovskite Solar Cells were prepared according to the following procedure. A ΤΊΟ2 blocking layer was prepared on a fluorine-doped tin oxide (FTO)-covered glass substrate using spray pyrol- ysis (cf. B. Peng, G. Jungmann, C. Jager, D. Haarer, H. W. Schmidt, M. Thelakkat, Coord. Chem. Rev. 2004, 248, 1479). A ΤΊΟ2 scaffold was deposited by spin-coating a ΤΊΟ2 paste (Dyesol) diluted with ethanol. The two layers were sintered at 450 °C for 30 min. After cooling the substrates down to room temperature, a perovskite layer was prepared by spin-coating a 40 wt.-% solution of CH3NH3l:PbCl2 (molecular ration 3:1 ) in DMF (Ν,Ν-Dimethylformamide) and annealing the resulting layer for 30 min in an oven at 1 10°C. The hole-transport material according to the present invention was deposited by spin-coating a solution in chlorobenzene containing also lithium bis(trifluoromethylsulfonyl)imide (LiTFSi) and tert-butylpyridine (tBP). The counter electrodes consisted of 50 nm gold layers evaporated through a mask, defining the active area of the solar cell by the size of these contacts (0.13 cm2). For measurements, the cells were masked by an aperture of the same area.
The current-voltage characteristics for all cells were measured with a Keithley 2400 under 1000 W/m2, AM 1.5G conditions (LOT ORIEL 450 W). The results are given in table 1.
Figure imgf000014_0001
Table 1 : Current-voltage characteristics of the perovskite-sensitzed solar cells with the hole- transport materials according to the present invention, Isc stands for short-circuit current, Voc for open-circuit voltage, FF for fill factor and η for the solar-to-electric power conversion efficiency. Example 7: Preparation of optical sensors
Optical sensors were prepared according to the following procedure. A T1O2 blocking layer was prepared on a fluorine-doped tin oxide (FTO)-covered glass substrate using spray pyrolysis (cf. B. Peng, G. Jungmann, C. Jager, D. Haarer, H. W. Schmidt, M. Thelakkat, Coord. Chem. Rev. 2004, 248, 1479). A Ti02 scaffold was deposited by spin-coating a Ti02 paste (Dyesol) diluted with ethanol. The two layers were sintered at 450 °C for 30 min. After sintering the sample was cooled to 60 to 80°C. The sample was then treated with an additive as disclosed in
WO 2012 / 001 628 A1. 5 mM of the additive in ethanol was prepared and the intermediate was immersed for 17 hours, washed in a bath of pure ethanol, briefly dried in a nitrogen stream and subsequently immersed in a 0.5 mM solution of dye ID504, a perylenedicarboximide derivative as disclosed e.g. in WO 2012 / 1 10 924 A1 , in a mixture solvent of acetonitrile + t-butyl alcohol (1 :1 ) for 2 hours so as to adsorb the dye. After removal from the solution, the specimen was subsequently washed in acetonitrile and dried in a nitrogen flow. Subsequently, the hole-transport material according the present invention was applied by using a chlorobenzene solution with 0.165 M of the hole-transport material and 20mM LiN(S02CFs)2 (Wako Pure Chemical Industries, Ltd.). 20 μΙ/cm2 of this solution was applied onto the specimen and allowed to act for 60 s. The supernatant solution was then spun off for 30 s at 2000 revolu- tions per minute. The substrate was stored overnight under ambient conditions.
As the metal back electrode, Ag was evaporated by thermal metal evaporation in a vacuum at a rate of 0.5 nm/s in a pressure of 10"5 mbar, so that an approximately 100 nm thick Ag layer was obtained.
To determine the applicability as a distance sensor according to WO/2014/097181 , a green light spot (520 nm) was focused on the sensor and the in focus-current was measured. The results are shown in table 2. In all examples, the out of focus-current dropped to less than 10% of the in-focus current, ensuring the applicability as a distance sensor according to
WO 2014 / 097 181 .
Figure imgf000015_0001
Table 2: In focus-current of the sensors.

Claims

Claims
1 . A compound of general formula (I)
Figure imgf000016_0001
wherein
R1, R2, R3, R4, R5, R6, R7, R8, R9 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group or an aryl group,
X1, X2 are independent of each other H, an alkyl group, an alkoxy group, an alkyl thiol group, or an aryl group, wherein X1, X2 can form together a ring and wherein at least one of X1, X2 is not H.
2. The compound according to claim 1 or 2 wherein R7 is an alkoxy group.
3. The compound according to claim 1 or 2 wherein X1 and X2 form together an aliphatic ring which is connected to the thiophene group in ligand L via oxygen atoms.
4. The compound according to any of the claims 1 to 3 wherein X1 and X2 form together an ethylene dioxy ring.
5. The compound according to any of the claims 1 to 4 wherein R1, R2, R3 and R4 are hydrogen.
6. The compound according to any of the claims 1 to 5 wherein R5, R6, R8 and R9 are hydrogen.
7. Use of the compound of general formula (I) according to any of the claims 1 to 6 in organ- ic solar cells or organic optical sensors.
8. An organic solar cell or organic optical sensor comprising a compound of general formula (I) according to any of the claims 1 to 6.
9. The organic solar cell or organic optical sensor according to claim 8, wherein the organic solar cell or organic optical sensor further comprises a semiconducting metal oxide as electron transport material and a light-absorbing material.
10. The organic solar cell or organic optical sensor according to claim 9, wherein the metal oxide is T1O2.
1 1 . The organic solar cell or organic optical sensor according to claim 9 or 10, wherein the light-absorbing material is a Ru(ll) dye, a perylene dye, a naphtalenemonoimid dye, or a quinolinium dye.
12. The organic solar cell or organic optical sensor according to claim 9 or 10, wherein the light-absorbing material is a perovskite absorber.
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