DE102010046040B4 - Process for the production of fullerene derivatives - Google Patents

Abstract

Process for the production of fullerene derivatives, wherein a fullerene reacts in a reactor with at least one halogen atom, characterized in that at least one additional chemical element selected from Fe, Co, Ni, Cu, or a mixture of these elements in the form of wire, chips or powder of any size is added to the reactor.

Description

The invention relates to a method for producing fullerene derivatives according to the features of claim 1.

State of the art

The performance and service life of organic semiconducting components such as organic light-emitting diodes (OLED) and organic solar cells (OSC) have been significantly improved in recent years. A decisive criterion is increasing the conductivity of charge-transporting layers made of organic materials [K. Walzer, B. Maennig, M. Pfeiffer, K. Leo, Chem. Rev. 107, 1233 (2007)] . For this purpose, the concept of p- and n-doping of the charge transport layers is used. The molecular doping increases the charge carrier density in the matrix, which compensates for the poor intrinsic charge carrier mobility of the matrix. The concept of molecular doping can increase the conductivity of the transport layers by several orders of magnitude [M. Pfeiffer, K. Leo, X. Zhou, JS Huang, M. Hofmann, A. Werner, J. Blochwitz-Nimoth, Org. Electron. 4, 89 (2003)] . This results in a significant increase in performance, since the operating voltage in the OLED is reduced or the series resistance in the OSZ is lowered. The injection barrier for charge carriers is lowered and a depletion zone is formed, which charge carriers can easily overcome through a tunneling process [J. Blochwitz, T. Fritz, M. Pfeiffer, K. Leo, DM Alloway, PA Lee, NR Amstrong, Org. Electron. 2, 97 (2001)] . The most efficient monochrome ones at the moment [R. Meerheim, R. Nitsche, K. Leo, Appl. Phys. Lett. 93, 043310 (2008)] and white [p. Reineke, F. Lindner, G. Schwartz, N. Seidler, K. Walzer, B. Lüssem, K. Leo, Nature 459, 234 (2009)] OLED, as well as OSZ [press release Heliatek GmbH: http://heliatek.de/, April 2010], use such doped layers. Doping can be achieved by simultaneous evaporation of two materials. The dopant is mixed in a low ratio with the matrix in the gas phase and deposited on a surface. In the case of p-doping (hole transport), such a matrix can contain, for example, N, N, N ', N'-tetrakis- (4-methoxyphenyl) benzidine (MeO-TPD). The prerequisite for dopability is an equal (+/- 0.3 eV) or lower ionization potential of the matrix in relation to the electron affinity of the dopant. The p-dopant (fullerene derivative) should have a reduction potential which, compared to ferrocene (Fc / Fc ⁺ ), is greater than or equal to approximately -0.3 V, preferably greater than or equal to approximately 0.0 V, more preferably greater than or equal to approximately 0, 24 V is. The doping molecules should be able to be introduced uniformly into the matrix and have a low tendency to diffuse. Some p-doping molecules with a high electron affinity (E _A ) are known, e.g. B. the relatively weak electron acceptor tetracyanoquinodimethane (TCNQ) [M. Maitrot, G. Guillaud, B. Boudjema, JJ Andre, J. Simon, J. Appl. Phys. 60, 2396 (1986) ; RC Wheland, JL Gillson, J. Am. Chem. Soc. 98, 3916 (1976)] or the fluorinated modification 3,6-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F ₂ -HCNQ) [ZQ Gao, BX Mi, GZ Xu, YQ Wan, ML Gong, KW Cheah, CH Chen, Chem. Commun., 117 (2008)] and the commonly used 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F ₄ -TCNQ) [J. Blochwitz, M. Pfeiffer, T. Fritz, K. Leo, Appl. Phys. Lett. 73, 729 (1998) ; WY Gao and A. Kahn, Appl. Phys. Lett. 79, 4040 (2001)] . Due to its low molecular mass, this class of material has a high vapor pressure and tends to uncontrolled contamination of the vapor deposition chamber and thus the subsequently vapor-deposited layers. Here, the contamination of the layers in the component can lead to the extinction of excitons, which results in a reduction in the performance of the components [BX Mi, ZQ Gao, KW Cheah, CH Chen, Appl. Phys. Lett. 94, 073507 (2009)] . Furthermore, the layers doped with this class of material have a low thermal stability [P. Wellmann, M. Hofmann, O. Zeika, A. Werner, J. Birnstock, R. Meerheim, G. He, K. Walzer, M. Pfeiffer, K. Leo, J. Soc. Inf. Disp. 13, 393 (2005)] . The consequence is a shortened service life of the component.

Perfluorinated fullerenes also have a comparable electron affinity of about 5 eV [N. Liu, Y. Morio, F. Okino, H. Touhara, OV Boltalina, VK Pavlovich, Synth. Metals 86, 2289 (1997)]. In polymer layers that were applied by solution-based processes, the perfluorinated fullerene C ₆₀ F _{36 has} already been investigated as a p-dopant [O. Solomeshch, YJ Yu, AA Goryunkov, LN Sidorov, RF Tuktarov, DH Choi, J.-Il Jin, N. Tessler, Adv. Mater. 21, 4456 (2009)].

There are few published reports in the literature on the preparation of fluorinated fullerenes. Boltalina et al. synthesized fluorinated fullerenes with the help of various fluoroplumbates [Troshin PA, Boltalina OV, Polykova NV, Klinkina ZE, J. Fluor. Chem. 110, 157, (2001)] , Fluorides of the lanthanoid series [AA Goryunkov, Z. Mazej, B. Žemva, SH Strauss, OV Boltalina, Mendeleev Commun. 16, 159 (2006)] or transition metal fluorides in conjunction with fluorine gas [NS Chilingarov, AV Nikitin, JV Rau, IV Golyshevsky, AV Kepman, FM Spiridonov, LN Sidorov, J. Fluor. Chem. 113, 219 (2002)] . All of the aforementioned methods are based on the use of molecular fluorine gas during fluorination or in the synthesis of reagents suitable for fluorination. Fluorine is classified as highly toxic and has a corrosive effect on many materials commonly used in apparatus engineering. the The necessary occupational health and safety measures make these production examples very impractical and costly. The methods showed only moderately good selectivity with regard to C ₆₀ F ₃₆ with very low to moderate yields of less than 30%. Boltalina et al. published a fluorine gas-free variant for the synthesis of C ₆₀ F ₃₆ , in which a trituration of manganese (III) fluoride and C _{60 was placed} in a nickel tube that was closed at one end [O. Boltalina, A. Borschevskii, L. Sidrov, J. Street, R. Taylor, Chem. Comm., 529 (1996)] . The filled nickel tube was placed in a glass sublimation tube. At a pressure of 10 ^-2 mbar, the glass tube was heated in a tube furnace to 330 ° C. in the course of 30 minutes and held at this temperature for 24 hours. During this time, a mixture of different fluorinated fullerenes deposited on the cold glass wall. According to mass spectrometric analysis, this mixture consisted of 51% C ₆₀ F ₃₆ , 33 C ₆₀ % (unconverted fullerene), 8% C ₆₀ F ₃₄ and 15% C ₆₀ F ₃₂ . All of the cited methods have the disadvantage of not being scalable to a millimolar scale.

RU 2 160 226 C2 relates to a process for producing chlorine derivatives of fullerene.

The present invention is therefore based on the object of providing an improved method for producing a fullerene derivative. The object is achieved by the method for production according to claim 1 and corresponding dependent claims.

In the process for producing fullerene derivatives, fullerene is reacted with at least one halogen in a reactor, with at least one additional chemical element being added to the reactor.

The advantages of this process are the fluorine-free production, the higher yield and the greater purity of the materials produced.

The fullerene is preferably selected from the formula C _m , where m is selected from 36, 60, 70, 76, 78, 80, 82, 84, 86, 90,, 94 or any other natural number that is suitable such to form spherical molecule. Preferably m = 60, 70, 76, 80, 82, 84, 86, 90, or 94.

The halogen is selected from F, Cl, Br, with F being preferred. It is preferred that the halogen is used in the form of a halogen-metal ion salt compound (here called halogen compound). The metal ion can be selected from: chromium (Cr), manganese (Mn), ruthenium (Ru), molybdenum (Mo), iron (Fe), tungsten (W), cobalt (Co), rhodium (Rh), iridium (Ir ), Nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), thallium (Tl), tin (Sn), antimony (Sb), tellurium (Te ), Lead (Pb), bismuth (Bi), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb ), Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu). The preferred compound is MnF ₃ .

The additional chemical element is used in the form of wire, chips or powder of any size. It can be used in pure form, as an alloy or as a mixture.

The additionally added chemical element is selected from iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu).

The fullerene-halogen derivative preferably has the formula C _m F _n , where n = 1 to m. _{C 60} F ₃₆ (m = 60 with n = 36) and C ₆₀ F ₃₄ to 48 (m = 60 with n = 34) are particularly preferred.

In one embodiment of the invention, the fullerene is mixed with at least one additional chemical element before the reaction. The fullerene, at least one additional chemical element and the halogen compound are preferably mixed before the reaction.

The reactor is a chemical reactor that is separated from the environment (e.g. air) during the reaction. The chemical reactor can be, for example, a boiler, pipe, or other vessel. Several linked vessels can also be used.

In an advantageous embodiment of the invention, the reactor is an elongated vessel, such as, for. B. a sublimation tube, the production taking place with simultaneous isolation by sublimation.

It is envisaged that the fullerene derivative will be used in an organic semiconductor layer. The fullerene derivative can form an organic semiconductor layer.

It is also within the meaning of the invention that the organic semiconductor layer is a doped layer which comprises an organic hole-transporting semiconductor material, as matrix, and the fullerene derivative, as p-dopant. A doped organic semiconductor material with increased charge carrier density and effective charge carrier mobility can be produced by a method according to the invention.

The fullerene derivative is expediently part of an organic diode, an organic photoactive component, in particular a solar cell, photodetector or light-emitting diode.

Organic components are components that contain at least one organic semiconductor layer. Fullerenes and their derivatives are also to be understood here under the term organic. The organic semiconductor layers contain, among other things, organic molecules, so-called “small molecules”, or organic polymers, the organic molecules and the organic polymers as a single layer or as a mixture with other organic (e.g. in US 2005/0 110 009 A1 described) or inorganic materials have semiconductor or metal-like properties. Organic light-emitting diodes usually consist of different layers of organic materials, at least one layer (emission layer) containing an electroluminescent substance that can be made to emit light by applying a voltage (Tang, U.S. 4,769,292 A ). Highly efficient OLEDs are, for example, in US 7 074 500 B2 described. The structure of organic solar cells is known to the person skilled in the art, see EP 1 861 886 A1 and EP 1 859 494 A1 . Particularly preferred components are doped components according to Walzer et al. [Chem. Rev. 107, 1233 (2007)] .

The fullerene derivative is expediently part of a battery, preferably as a cathode [N. Liu, H. Touhara, F. Okino, S. Kawasaki, Y. Nakacho, J. Electrochem. Soc. 143, 2267 (1996)]

• eine schematische Darstellung der Apparatur zur Herstellung von C₆₀F₃₆ im millimolarem Maßstab
• eine massenspektrometrische Untersuchung des Reaktionsproduktes
• eine Molekülstruktur der p-Dotanden F₄-TCNQ und C₆₀F₃₆, sowie Struktur von MeO-TPD
• Messungen zum Kontaminationsverhalten der p-Dotanden F₄-TCNQ und C₆₀F₃₆ mittels UPS und XPS.
• eine Struktur von BF-DPB.
• eine Darstellung der thermische Stabilität der F₄-TCNQ bzw. C₆₀F₃₆ enthaltenden Lochtransportschichten
• Schichtaufbau und Zusammensetzung der OLED, sowie Strukturen von Bphen, Spiro-TAD, α-NPD und Ir(MDQ)₂acac
• einen Vergleich der Elektro-Lumineszenz-Spektren der OLED.
• einen Vergleich der charakteristischen I(V)-Kennlinen und der Lumineszenz beider OLED.
• einen Vergleich der Energieausbeute und der externen Quanteneffizienz der OLED
• Schicht-Aufbau und Zusammensetzung der OSZ, sowie Struktur von ZnPc.
• einen Vergleich der charakteristischen I(V)-Kennlinen beider OSZ unter Beleuchtung mit einem Sonnensimulator (AMI.5) und im Dunkeln, sowie aller charakteristischen Leistungsparameter.
• einen Vergleich der charakteristischen Parameter im zeitlichen Verlauf der Alterung.

The invention is explained in more detail below on the basis of exemplary embodiments. Show it:

• a schematic representation of the apparatus for the production of C ₆₀ F ₃₆ on a millimolar scale
• a mass spectrometric analysis of the reaction product
• a molecular structure of the p-dopants F ₄ -TCNQ and C ₆₀ F ₃₆ , as well as the structure of MeO-TPD
• Measurements of the contamination behavior of the p-dopants F ₄ -TCNQ and C ₆₀ F ₃₆ using UPS and XPS.
• a structure of BF-DPB.
• a representation of the thermal stability of the F ₄ -TCNQ or C ₆₀ F ₃₆ containing hole transport layers
• Layer structure and composition of the OLED, as well as structures of Bphen, Spiro-TAD, α-NPD and Ir (MDQ) ₂ acac
• a comparison of the electro-luminescence spectra of the OLED.
• a comparison of the characteristic I (V) curves and the luminescence of both OLEDs.
• a comparison of the energy yield and the external quantum efficiency of the OLED
• Layer structure and composition of the OSZ, as well as the structure of ZnPc.
• a comparison of the characteristic I (V) curves of both OSCs under illumination with a sun simulator (AMI.5) and in the dark, as well as all characteristic performance parameters.
• a comparison of the characteristic parameters in the course of aging over time.

Synthesis example C ₆₀ F ₃₆

Traces of water and oxygen were removed from the _{MnF 3} (ABCR, 98%) used for the synthesis within 24 hours at a pressure of 10 ^{-3 mbar and at a temperature of 200 ° C.} Fullerene C ₆₀ was obtained from a chemical supplier (e.g. American Dye Source) and purified by sublimation three times. The fullerene C ₆₀ (1.00 g; 1.388 mmol) and MnF ₃ (5.59 g; 60.15 mmol) were well ground in a mortar in a nitrogen atmosphere. Nickel powder was added to the mixture in a nickel crucible (6.6 g) and the filled nickel crucible was accordingly used in the sublimation apparatus. The sublimation tube was heated to a temperature of 330 ° C. at a pressure of 4.10 ^-4 mbar for 24 hours, the fluorinated reaction products condensing on the colder parts of the sublimation tube in the form of a white-yellowish solid (0.76 g). The rings covered with the condensate were subjected to a further sublimation, at the end of which 0.75 g (0.534 mmol, 38% of the theoretical yield) of the product could be isolated. To analyze the additionally sublimed product, a sample was completely dissolved in toluene and completely evaporated in a mass spectrometer. The total ion current was measured and is in shown. The ratios of the intensities of all compounds contained in the sample correspond to the composition 84% C ₆₀ F ₃₆ , 14% C ₆₀ F ₃₄ and 2% C ₆₀ .

Embodiment 1

Documentation of the contamination behavior of the dopant C ₆₀ F ₃₆ in comparison to F ₄ -TCNQ. The aim here is to investigate the volatility of the dopants F ₄ -TCNQ and C ₆₀ F ₃₆ and to prove that C ₆₀ F _36, in contrast to F ₄ -TCNQ, does not show any chamber contamination.

The volatility of the dopants F ₄ -TCNQ and C ₆₀ F ₃₆ was investigated on the basis of their fluorine signals in undoped MeO-TPD layers using X-ray photoelectron spectroscopy (XPS). shows the comparison of the 1s fluorine nuclear signals of the XPS Measurement on 10 nm thick intrinsic MeO-TPD layers. These were made in chambers that either contained neither of the dopants, or one of the two in an unheated source. A significant fluorine signal at a binding energy of 689.5 eV can only be observed in the layer which was evaporated in the chamber in the _{presence of F 4 -TCNQ.} Furthermore, this layer shows a doping effect in the form of a clear shift of 0.53 eV of the highest occupied molecular orbital (HOMO) of the MeO-TPD in the direction of the Fermi energy (E _B = 0 eV) in ultraviolet photoelectron spectroscopy (UPS) . This contamination proves contamination _{potential of F 4} -TCNQ molecules, in contrast to a sample that was vaporized in the presence of C ₆₀ F ₃₆ . In the case of samples from the chamber with C ₆₀ F ₃₆ , no fluorine signal in the XPS or a HOMO shift in the UPS, ie no contamination of the MeO-TPD layers, is observed. The very low volatility of C ₆₀ F ₃₆ in comparison with F ₄ -TCNQ means a strong advantage when it comes to processing hole transport layers.

Embodiment 2

Documentation of the temperature stability with C ₆₀ F ₃₆ doped hole transport layers compared to F ₄ -TCNQ. The temperature stability of hole transport layers doped with C ₆₀ F ₃₆ should be demonstrated.

In order to investigate the temperature stability, the matrix material N, N '- ((Diphenyl-N, N'-bis) 9,9, -dimethyl-fluoren-2-yl) -benzidine (BF-DPB) due to the high glass transition temperature ( T _G = 160 ° C) selected ( US 2002/0 171 358 A1 ). The behavior of the conductivity as a function of the temperature up to the T _G is therefore due to the dopants. At ratios of 26 mol% for F ₄ -TCNQ and 21 mol% for C ₆₀ F ₃₆ , both layers show a comparable conductivity of 3 · 10 ⁶ S cm ^-1 at room temperature ( ). The lower doping with C ₆₀ F _{36 shows} the higher doping efficiency of the dopant. Since the LUMO of F ₄ -TCNQ is energetically about the same as the HOMO level of BF-DPB (-5.23 eV) determined by UPS, an inefficient charge transfer results in this system. Therefore, it can be assumed that C ₆₀ F _{36 has} a higher electron affinity compared to F ₄ -TCNQ. As the temperature rises, the conductivity of both layers rises _{to the maximum with activation energies of 265 meV and 692 meV for F 4} -TCNQ and C ₆₀ F ₃₆ , with a further rise in temperature the conductivity collapses. With the BF-DPB / F ₄ -TCNQ layer, a lower stability is observed with the decrease in conductivity at 145 ° C. The BF-DPB / C ₆₀ F ₃₆ layer does not collapse until 180 ° C and is therefore higher than the T _{G of} the matrix material. The drop in conductivity cannot therefore be directly assigned to the dopant C ₆₀ F ₃₆ .

Embodiment 3

Documentation of the use of C ₆₀ F ₃₆ doped hole transport layers in OLED in comparison to F ₄ -TCNQ. Phosphorescent pin OLEDs with orange-red emission are used to compare the dopants in components.

The layer structure of the components produced is in shown. The organic layers are located between a 90 nm thick indium tin oxide (ITO) anode on a glass substrate and a 100 nm thick silver cover contact. 60 nm thick MeO-TPD layers, doped with 1 wt% F ₄ -TCNQ or 8 wt% C ₆₀ F _36, which result in conductivities of approx. 2 · 10 ^-5 S cm ^-1 , are used as the hole transport layer (HTL). The electron transport layer (ETL) is 65 nm cesium-doped 4,7-diphenyl-1,10-phenanthroline (BPhen) with a comparable conductivity. In order to concentrate the injected charges in the emission layer (EML), 10 nm thick electron and hole blocker layers (EBL, HBL) made of 2,2 ', 7,7'-tetrakis- (N, N-diphenylamino) -9,9 '-spirobifluoren (Spiro-TAD) and BPhen inserted around the EML. The 20 nm thick EML consists of N, N'-di (naphthalen-2-yl) -N, N'diphenylbenzidine (α-NPD), doped with 10 wt% of the triplet emitter iridium (III) bis (2-methyldibenzo - [f, h] quinoxaline) acetylacetonate (Ir (MDQ) ₂ (acac)). Both OLEDs show accordingly , identical electroluminescence spectra, which excludes _{parasitic absorption of C 60} F _36. The current-voltage curves of both comparison components are similar ( ), whereby the I (V) characteristic curves with the C ₆₀ F ₃₆ dopant are steeper, which indicates better hole injection with the same layer conductivity. The higher hole injection increases the charge carrier density or shifts the charge carrier balance in the EML, which results in _{increased efficiencies of the C 60} F _{36 -OLED (} ).

Embodiment 4

Documentation of the use of C ₆₀ F ₃₆ doped hole transport layers in OSZ compared to F ₄ -TCNQ. The lifetime measurements of the components obtained show the stability of the component using mixed layers of zinc phthalocyanine (ZnPc) and C ₆₀ as a donor-acceptor-absorber pair.

The layer structure of the component created is in shown. A 60 nm thick MeO-TPD layer doped with 2 wt% F ₄ -TCNQ or 8 wt% C ₆₀ F ₃₆ serves as the hole transport layer (HTL). A 30 nm mixed layer of C ₆₀ and ZnPc (1: 1) acts as an absorber layer, which is followed by a 30 nm thick layer of intrinsic C ₆₀ . Electron transport is made possible by a 15 nm thick layer of C ₆₀ doped with 3 wt% 3,6-bis (dimethylamino) acridine (AOB). The reflective cathode is formed by a 100 nm thick layer of aluminum. Both solar cells are in accordance Comparable with regard to all parameters and show only minimal differences that lie in the area of measurement uncertainty. The open terminal voltage (Voc) is not influenced by the dopants. Doping with C ₆₀ F ₃₆ leads to a slightly lower series resistance.

The solar cells were aged at 50 ° C. and illuminated with white LEDs at a power of 500 mW cm ^-2. illustrates the different lifetimes of the OSZ. Due to the low glass transition temperature of F ₄ -TCNQ, the solar cells with this dopant have a service life of less than one hundred hours, which makes commercial use of this material impossible. In contrast, the _{cells containing C 60} F ₃₆ show constant cell parameters over a period of 500 hours. The stability of these cells is accordingly significantly greater than cells containing _{F 4 -TCNQ.}

With regard to the application as p-dopant in pin OLED and OSZ, it can be concluded that the exchange of F ₄ -TCNQ leads to improved performance of the components and also leads to a higher stability of the components. Furthermore, the low vapor pressure of the C ₆₀ F ₃₆ dopant does not lead to any chamber contamination during the manufacturing process.

Claims (6)

Process for the production of fullerene derivatives, wherein a fullerene reacts with at least one halogen atom in a reactor, characterized in that at least one additional chemical element selected from Fe, Co, Ni, Cu, or a mixture of these elements in the form of wire, chips or powder of any size is added to the reactor. Process for the production of fullerene derivatives according to Claim 1 , characterized in that at least one halogen atom is selected from F and Cl. Process for the preparation of fullerene derivatives according to one of the preceding claims, characterized in that the fullerenes are spherical carbon clusters with the formula C _m , where m is selected from 60 and 70. Process for the preparation of fullerene derivatives according to one of the preceding claims, characterized in that the halogen atom is used as at least one salt or salt mixture, the salt containing a metal ion and the metal ion being selected from Mn, Fe, Co, Ni, Cu , Ag, Tl, Pb, Bi, Ce. Process for the production of fullerene derivatives according to one of the preceding claims, wherein the additional chemical element is nickel. Process for the production of fullerene derivatives according to one of the preceding claims, wherein the production takes place with simultaneous isolation by sublimation.

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