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  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
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Definitions

• Organic-based charge transport materials generally triarylamine-based hole transporters
• OLEDs or PLEDs organic or polymeric light emitting diodes
• O-SCs organic solar cells
• O-FETs organic field effect transistors
• O-ICs organic circuit elements
• O-lasers organic laser diodes
• organic devices can be produced from solution which entails less technical and cost outlay than vacuum processes, as are generally carried out for low molecular weight compounds.
• colored electroluminescent devices can be produced comparatively simply by processing the materials by surface coating from solution (for example by spin coating, doctor blade technique, etc.).
• the structuring, i.e. driving of individual image points, is usually carried out here in the “leads”, i.e. for example in the electrodes. This may, for example, be done using shadow masks in the manner of a template.
• the structuring of organic circuits and partially organic solar cell panels or laser arrays can be carried out similarly.
• Shadow masks furthermore cannot be readily employed when, for example, full-color displays or organic circuits with different circuit elements are to be produced.
• full-color displays the three primary colors (red, green and, blue) in individual pixels (image points) must be applied next to one another with a high resolution. Similar considerations apply to electronic circuits with different circuit elements. While the individual image points can be produced by evaporating the individual colors using shadow masks in the case of low molecular weight evaporatable molecules (with the associated difficulties already mentioned above), this is not possible for polymeric materials and materials processed from solution, and the structuring can no longer be carried out merely by structuring the electrodes.
• structurable materials are described which are suitable for use in structured devices such as OLEDs, PLEDs, organic lasers, organic circuit elements or organic solar cells. These are organic, in particular electroluminescent materials, which contain at least one oxetane group capable of crosslinking, the crosslinking reaction of which can be deliberately initiated and controlled.
• electroluminescent materials which contain at least one oxetane group capable of crosslinking, the crosslinking reaction of which can be deliberately initiated and controlled.
• Macromol. Rapid Commun. 1999, 20, 225 describes N,N,N′,N′-tetraphenylbenzidines functionalized with oxetane groups, which can be crosslinked in a photoinduced way.
• These compound classes are used as structurable hole conductors directly on the anode of the organic electronic device.
• At least one photoinitiator is added to the materials for crosslinking.
• an acid is generated which initiates a crosslinking reaction by cationic ring-opening polymerization.
• a pattern of regions with crosslinked material and regions with uncrosslinked material can thus be obtained by structured exposure.
• the regions of uncrosslinked material can then be removed by suitable operations (for example washing with suitable solvents). This leads to the desired structuring.
• suitable operations for example washing with suitable solvents.
• Exposure, as employed for the structuring is a standard process in modern electronics and can, for example, be carried out with lasers or by surface exposure using a suitable photomask.
• the mask does not involve the risk of deposition here, since in this case only radiation and no material flux has to be delimited by the mask.
• Chem Phys Chem 2000, 207 such a crosslinked triarylamine layer is introduced as an interlayer between a conductive doped polymer and an organic luminescent semiconductor. A higher efficiency is obtained in this case.
• a photoacid is used for the crosslinking. This appears to be necessary for complete crosslinking of the triarylamine layer.
• the photoacid or its reaction products remain as contamination in the electronic device after the crosslinking. It is generally acknowledged that both organic and inorganic impurities can perturb the operation of organic electronic devices. For this reason, it would be desirable to be able to reduce the use of photoacids as much as possible.
• EP 0637899 proposes electroluminescent arrangements having one or more layers in which at least one layer is obtained by thermal or radiation-induced crosslinking, which furthermore contain at least one emitter layer and at least one charge transport unit per layer.
• the crosslinking may take place radically, ionically, cationically or via a photoinduced ring closure reaction.
• An advantage mentioned is that a plurality of layers can thereby be formed on one another, or that the layers can also be structured in a radiation-induced way.
• no teaching is given as to which of the various crosslinking reactions can be used to produce a suitable device, and how the crosslinking reaction can best be carried out.
• radically crosslinkable units or groups capable of photocycloaddition are preferred, that various types of auxiliaries, for example initiators, may be contained and that the film is preferably crosslinked by means of actinic radiation and not thermally.
• auxiliaries for example initiators
• Suitable device configurations are also not described. It is therefore unclear how many layers the device preferably comprises, and how thick they should be, which material classes are preferably used and which of them should be crosslinked. It is therefore also not apparent to the person skilled in the art how the described invention can be successfully implemented in practice.
• an interlayer of a conductive doped polymer is often introduced as a charge injection layer between the electrode (in particular the anode) and the function material ( Appl. Phys. Lett. 1997, 70, 2067-2069).
• a conductive doped polymer may also be used directly as the anode (or even as the cathode, depending on the application).
• the most common of these polymers are polythiophene derivatives (for example poly(ethylenedioxythiophene), PEDOT) and polyaniline (PANI), which are generally doped with polystyrene sulfonic acid or other polymer-bound Brönstedt acids and thus brought into a conductive state.
• Protons or other cationic impurities have a negative effect in particular when the functional semiconductor layer applied onto this layer is cationically crosslinkable and, as described above, is intended to be structured.
• the functional layer is already partially or fully crosslinked by the presence of protons or other cationic impurities, without providing the opportunity to control the crosslinking, for example by actinic radiation.
• the advantage of the controlled structurability is therefore lost.
• Cationically crosslinkable materials thus in principle do provide the possibility of structuring and therefore an alternative to printing techniques. However, technical implementation of these materials is not to date possible since the problem of uncontrolled crosslinking on a doped charge injection layer is not yet resolved.
• the electronic properties of the devices can be significantly improved when at least one buffer layer, which is cationically crosslinkable, is introduced between the doped interlayer and the functional organic semiconductor layer.
• Particularly good properties are obtained with a buffer layer whose cationic crosslinking is induced thermally, i.e. by a temperature rise to from 50 to 250° C., preferably from 80 to 200° C., and to which no photoacid is added.
• Another advantage of this buffer layer is that the uncontrollable crosslinking of a cationically crosslinkable semiconductor can be avoided by using the buffer layer, which for the first time permits controlled structuring of the semiconductor.
• Yet another advantage of crosslinking the buffer layer is that the glass transition temperature of the material and therefore the stability of the layer are increased by the crosslinking.
• the invention therefore relates to electronic devices containing at least one layer of a conductive doped polymer and at least one layer of an organic semiconductor, characterized in that at least one conducting or semiconducting organic buffer layer which is cationically polymerizable, and to which less than 0.5% of a photoacid is added, is introduced between these layers.
• a photoacid is a compound which releases a protic acid by a photochemical reaction when exposed to actinic radiation.
• photoacids are 4-(thio-phenoxyphenyl)-diphenylsulfonium hexafluoroantimonate or ⁇ 4-[(2-hydroxytetradecyl)-oxyl]-phenyl ⁇ -phenyliodonium hexafluoroantimonate and the like, as described for example in EP 1308781.
• the photoacid may be added for the crosslinking reaction, in which case a proportion of from approximately 0.5 to approximately 3% by weight is preferably selected according to the prior art.
• Electronic devices in the context of this invention are organic or polymeric light emitting diodes (OLEDs, PLEDs, for example EP 0676461, WO 98/27136), organic solar cells (O-SCs, for example WO 98/48433, WO 94/05045), organic field effect transistors (O-FETs, for example U.S. Pat. No. 5,705,826, U.S. Pat. No. 5,596,208, WO 00/42668), field quench elements (FQDs, for example US 2004/017148), organic circuit elements (O-ICs, for example WO 95/31833, WO 99/10939), organic optical amplifiers or organic laser diodes (O-lasers, WO 98/03566).
• OLEDs organic or polymeric light emitting diodes
• PLEDs for example EP 0676461, WO 98/27136
• O-SCs organic solar cells
• O-SCs for example WO 98/48433, WO 94/0504
• Organic in the context of this invention means that at least one layer of an organic conductive doped polymer, at least one conducting or semiconducting organic buffer layer and at least one layer containing at least one organic semiconductor are present; further organic layers (for example electrodes) may also be present in addition to these. Moreover, layers which are not based on organic materials may also be present, for example inorganic interlayers or electrodes.
• the electronic device is constructed from a substrate (conventionally glass or a plastic sheet), an electrode, an intermediate layer of a conductive doped polymer, a crosslinkable buffer layer according to the invention, an organic semiconductor and a back electrode.
• This device is accordingly (depending on the application) structured, contacted and hermetically sealed, since the lifetime of such devices is drastically shortened in the presence of water and/or air. It may also be preferred to use a conductive doped polymer as the electrode material for one or both electrodes and not to introduce an interlayer of conductive doped polymer.
• the structure also contains a further electrode (gate) which is separated from the organic semiconductor by an insulator layer generally having a high dielectric constant. It may furthermore be expedient to introduce yet other layers into the device.
• the electrodes are selected so that their potential coincides as well as possible with the potential of the adjacent organic layer, in order to ensure maximally efficient electron or hole injection. If the cathode is to inject electrons, as is the case for example in OLEDs/PLEDs or n-type conducting O-FETs, or receive holes, as is the case for example in O-SCs, then metals with a low work function, metal alloys or multilayered structures comprising different metals, for example alkaline-earth metals, alkali metals, main group metals or lanthanides (for example Ca, Ba, Mg, Al, In, Mg, Yb, Sm, etc.) are preferred for the cathode.
• metals with a low work function metal alloys or multilayered structures comprising different metals, for example alkaline-earth metals, alkali metals, main group metals or lanthanides (for example Ca, Ba, Mg, Al, In, Mg, Yb, Sm, etc.) are preferred for
• the cathodes are conventionally between 10 and 10,000 nm, preferably between 20 and 1000 nm, thick. It may also be preferred to introduce a thin interlayer of a material having a high dielectric constant between a metal cathode and the organic semiconductor (or other functional organic layers which may optionally be present).
• Alkali metal or alkaline-earth metal fluorides may for example be suitable for this (for example LiF, Li 2 O, BaF 2 , MgO, NaF, etc.).
• the layer thickness of this dielectric layer is preferably between 1 and 10 nm.
• the anode preferably has a potential of more than 4.5 eV vs. vacuum.
• metals with a high redox potential are suitable for this, for example Ag, Pt or Au.
• Metal/metal oxide electrodes for example Al/Ni/NiO x , Al/Pt/PtO x
• the anode may also consist of a conductive organic material (for example a conductive doped polymer).
• At least one of the electrodes must be transparent in order to allow either irradiation of the organic material (O-SCs) or output of light (OLEDs/PLEDs, O-lasers, organic optical amplifiers).
• O-SCs organic material
• O-lasers organic optical amplifiers
• a preferred construction uses a transparent anode.
• Preferred anode materials here are conductive mixed metal oxides. Indium-tin oxide (ITO) or indium-zinc oxide (IZO) are particularly preferred.
• Conductive doped organic materials, in particular conductive doped polymers, are furthermore preferred.
• a similar construction also applies to inverted structures, in which the light is output from the cathode or incident on the cathode.
• the cathode then preferably consists of the materials described above, with the difference that the metal is very thin and therefore transparent.
• the layer thickness of the cathode is preferably less than 50 nm, particularly preferably less than 30 nm, and in particular less than 10 nm.
• a further transparent conductive material is applied thereon, for example indium-tin oxide (ITO), indium-zinc oxide (IZO) etc.
• Various organic doped conductive polymers may be suitable for the conductive doped polymer (either as an electrode or as an additional charge injection layer or “Planarization Layer”, in order to compensate for unevennesses of the electrode and thus minimize short circuits).
• the conductive doped polymer is applied onto the anode or functions directly as the anode.
• the potential of the layer is preferably from 4 to 6 eV vs. vacuum.
• the thickness of the layer is preferably between 10 and 500 nm, particularly preferably between 20 and 250 nm.
• the layers are generally thicker in order to ensure a good outward electrical connection and a low capacitive impedance.
• Derivatives of polythiophene are particularly preferably used (particularly preferably poly(ethylenedioxythiophene), PEDOT) and polyaniline (PANI).
• the doping is generally carried out using acids or oxidizing agents.
• the doping is preferably carried out using polymer-bound Brönsted acids.
• polymer-bound sulfonic acids in particular poly(styrene sulfonic acid), poly(vinyl sulfonic acid) and PAMPSA (poly(2-acrylamido-2-methyl-propane sulfonic acid)) are particularly preferred for this.
• the conductive polymer is generally applied from an aqueous solution or dispersion and is insoluble in organic solvents. The subsequent layer can thereby be readily applied from organic solvents.
• Low molecular weight oligomeric, dendritic or polymeric semiconducting materials are in principle suitable for the organic semiconductor.
• An organic material in the context of this invention is intended to mean not only purely organic materials, but also metallorganic materials and metal coordination compounds with organic ligands.
• the oligomeric, dendritic or polymeric materials may be conjugated, non-conjugated or partially conjugated.
• Conjugated polymers in the context of this invention are polymers which contain primarily sp 2 -hybridized carbon atoms in the main chain, which may also be replaced by corresponding heteroatoms. In the simplest case, this means the alternate presence of double and single bonds in the main chain.
• conjugated polymer Primarily means that naturally occurring defects, which lead to conjugation interruptions, do not invalidate the term “conjugated polymer”.
• conjugated likewise applies in this application text when the main chain contains for example arylamine units and/or particular heterocycles (i.e. conjugation via N, O or S atoms) and/or metallorganic complexes (i.e. conjugation via the metal atom).
• Units such as, for example, simple alkene chains, (thio)ether bridges, ester, amide or imide linkages would however be unequivocally defined as non-conjugated segments.
• conjugated organic material is also intended to include ⁇ -conjugated polysilanes, -germylenes and analogues which carry organic side groups, and can therefore be applied from organic solvents, for example poly(phenylmethylsilane).
• Non-conjugated materials are materials in which no lengthy conjugated units occur in the main chain or in the dendrimer backbone.
• partially conjugated materials is intended to mean those materials which have lengthy conjugated sections in the main chain or in the dendrimer backbone, which are bridged by non-conjugated units, or which contain lengthy conjugated units in the side chain.
• conjugated polymers are poly-para-phenylenevinylene (PPV), polyfluorenes, polyspirobifluorenes or systems which are based in the broadest sense on poly-p-phenylene (PPP), and derivatives of the structures.
• PPP poly-para-phenylenevinylene
• PPP polyfluorenes
• PPP polyspirobifluorenes or systems which are based in the broadest sense on poly-p-phenylene (PPP), and derivatives of the structures.
• Materials with a high charge carrier mobility are primarily of interest for use in O-FETs. These are for example oligo- or poly(triarylamines), oligo- or poly(thiophenes) and copolymers which contain a large proportion of these units.
• the layer thickness of the organic semiconductor is preferably 10-500 nm, particularly preferably 20-250 nm, depending on the application.
• dendrimer is intended to mean a highly branched compound which is constructed from a multifunctional core to which branched monomers are bound in a regular structure, so that a tree-like structure is obtained. Both the core and the monomers may assume any branched structures which consist both of purely organic units and of organometallic compounds or coordination compounds.
• dendrimers are to be understood as described for example in M. Fischer, F. Vögtle, Angew. Chem., Int. Ed. 1999, 38, 885-905.
• crosslinkable organic layers have been developed (WO 02/10129). After the crosslinking reaction, these are insoluble and therefore can no longer be attacked by solvents during the application of further layers.
• Crosslinkable organic semiconductors also have advantages for the structuring of multicolored PLEDs. The use of crosslinkable organic semiconductors is thus furthermore preferred.
• Preferred crosslinking reactions are cationic polymerizations, based on electron-rich olefin derivatives, heteronuclear multiple bonds with heteroatoms or heterogroups or rings with heteroatoms (for example O, S, N, P, Si, etc.). Particularly preferred crosslinking reactions are cationic polymerizations based on rings with heteroatoms. Such crosslinking reactions are described in detail below for the buffer layer according to the invention.
• Semiconducting luminescent polymers which can be chemically crosslinked are generally disclosed in WO 96/20253.
• Oxetane-containing semiconducting polymers, as described in WO 02/10129, have proved particularly suitable. They can be crosslinked deliberately and in a controlled way by adding a photoacid and irradiation.
• Crosslinkable low molecular weight compounds may furthermore be suitable, for example cationically crosslinkable triarylamines (M. S. Bayer et al., Macromol. Rapid Commun. 1999, 20, 224-228; D. C. Müller et al., Chem Phys Chem 2000, 207-211). These descriptions are incorporated into the present invention by reference.
• the introduction of a buffer layer which is introduced between the conductive doped polymer and the organic semiconductor, and which carries the cationically crosslinkable units, is such that it can absorb low molecular weight cationic species and intrinsic cationic charge carriers which may diffuse out of the conductive doped polymer.
• the buffer layer may be both low molecular weight and oligomeric, dendritic or polymeric.
• the layer thickness is preferably in the range of 5-300 nm, particularly preferably in the range of 10-200 nm.
• the potential of the layer preferably lies between the potential of the conductive doped polymer and that of the organic semiconductor. This can be achieved by a suitable choice of the materials for the buffer layer and suitable substitution of the materials.
• Preferred materials for the buffer layer are derived from hole-conductive materials, such as those used as hole conductors in other applications.
• Cationically crosslinkable triarylamine-based, thiophene-based or triarylphosphine-based materials or combinations of these systems are particularly preferably preferred for this.
• Copolymers with other monomer units, for example fluorene, spirobifluorene, etc., with a high proportion of these hole-conductive units are also suitable. The potentials of these compounds can be adjusted by suitable substitution.
• electron-withdrawing substituents for example F, Cl, CN, etc.
• electron-repelling substituents for example alkoxy groups, amino groups, etc.
• the buffer layer according to the invention may comprise low molecular weight compounds which are crosslinked in the layer and thus rendered insoluble. Oligomeric, dendritic or polymeric soluble solutions, which are rendered insoluble by subsequent cationic crosslinking, may also be suitable. Mixtures of low molecular weight compounds and oligomeric, dendritic and/or polymeric compounds may furthermore be used.
• cationic species that can diffuse out of the conductive doped polymer are firstly protons which may originally come from the dopant being used (often polymer-bound sulfonic acids) but also ubiquitous water. Cationic species, for example metal ions, may also be present as (undesired) impurities in the conductive polymer.
• cationic species is the electrode on which the conductive polymer is applied.
• indium ions may emerge from an ITO electrode and diffuse into the active layers of the devices.
• Other low molecular weight cationic species that may possibly be present are monomeric and oligomeric constituents of the conductive polymer, which are converted into a cationic state by protonation or by other doping. It is furthermore possible for charge carriers introduced by oxidative doping to diffuse into the semiconductor layer.
• the cationically crosslinkable buffer layer can trap diffusing cationic species so that the crosslinking reaction is subsequently initiated; on the other hand, the buffer layer is simultaneously rendered insoluble by the crosslinking, so that the subsequent application of an organic semiconductor from conventional organic solvents presents no problems.
• the crosslinked buffer layer represents a further barrier against diffusion.
• Preferred cationically polymerizable groups of the buffer layer are the following functional groups:
• Non-aromatic cyclic systems in which one or more ring atoms are identically or differently O, S, N, P, Si, etc., are generally suitable for this.
• Cyclic systems having from 3 to 7 ring atoms, in which from 1 to 3 ring atoms are identically or differently O, S or N, are preferred.
• Examples of such systems are unsubstituted or substituted cyclic amines (for example aziridine, azeticine, tetrahydropyrrole, piperidine), cyclic ethers (for example oxiran, oxetane, tetrahydrofuran, pyran, dioxane), as well as the corresponding sulfur derivatives, cyclic acetals (for example 1,3-dioxolane, 1,3-dioxepane, trioxane), lactones, cyclic carbonates, but also cyclic structures which contain different heteroatoms in the cycle, for example oxazolines, dihydrooxazines or oxazolones. Cyclic siloxanes having from 4 to 8 ring atoms are furthermore preferred.
• low molecular weight, oligomeric or polymeric organic materials in which at least one H atom is replaced by a group of the formula (I), (II) or (III),
• the crosslinking of these units is preferably carried out by thermal treatment of the device at this stage. It is not necessary, and not even desirable, to add a photoacid for the crosslinking since this would introduce impurities into the device. Without wishing to be bound by a special theory, we suspect that the crosslinking of the buffer layer is initiated by the protons emerging from the conductive doped polymer.
• This crosslinking preferably takes place at a temperature of from 80 to 200° C. and for a duration of from 0.1 to 120 minutes, preferably from 1 to 60 minutes, particularly preferably from 1 to 10 minutes, in an inert atmosphere.
• This crosslinking particularly preferably takes place at a temperature of from 100 to 180° C. and for a duration of from 20 to 40 minutes in an inert atmosphere.
• auxiliaries which are not photoacids, but which can promote the crosslinking, to be added to the buffer layer.
• Salts in particular inorganic salts, for example tetrabutylammonium hexafluoroantimonate, which are added as a supporting electrolyte in order to improve the crosslinking, acids, in particular organic acids, for example acetic acid, or further addition of polystyrene sulfonic acid to the conductive polymer, or oxidizing substances, for example nitrylium or nitrosylium salts (NO + , NO 2 + ), may for example be suitable for this.
• auxiliaries can easily be washed out and therefore do not remain as contamination in the film.
• the auxiliaries have the advantage that the crosslinking can thereby be fully carried out more easily and that thicker buffer layers can thereby also be produced.
• this crosslinkable buffer layer which is introduced between the conductive doped polymer and the organic semiconductor, offers the following advantages:
• the phases were separated and the process was repeated once more with 40 ml of the dithiocarbamate solution.
• the phases were separated, the organic phase was washed with 3 ⁇ 150 ml of water and precipitated by adding it in two times the volume of methanol.
• the raw polymer was dissolved in chlorobenzene, filtered using celite and precipitated by adding two times the volume of methanol. 1.84 g (64% Th.) of the polymer P2 were obtained, which is soluble in chlorobenzene but insoluble in toluene, THF or chloroform.
• the LEDs were produced according to a general method which was adapted to the respective conditions (for example solution viscosity and optimal layer thickness of the functional layers in the device) in the particular case.
• the LEDs described below were respectively three-layer systems (three organic layers), i.e. substrate//ITO//PEDOT//buffer layer//polymer//cathode.
• PEDOT is a polythiophene derivative (Baytron P4083 from H. C. Stark, Goslar). Ba from Aldrich and Ag from Aldrich were used for the cathode in all cases.
• the way in which PLEDs can generally be produced is described in detail in WO 04/037887 and the literature cited therein.
• a cationically crosslinkable semiconductor was applied as a buffer layer on the PEDOT layer.
• the crosslinkable polymers P1 and P2 or the crosslinkable low molecular weight compound V1 were used as materials for the buffer layer.
• a solution (with a concentration of 4-25 mg/ml in for example toluene, chlorobenzene, xylene etc.) of the crosslinkable material was taken and dissolved by stirring at room temperature. Depending on the material, it may also be advantageous to stir for some time at 50-70° C. After the complete dissolving of the compound, it was filtered through a 5 ⁇ m filter.
• the buffer layer was then spin coated at variable speeds (400-6000 rpm) with a spin coater in an inert atmosphere.
• the layer thicknesses could thus be varied in a range of from approximately 20 to 300 nm.
• the crosslinking was subsequently carried out by heating the device to 180° C. for 30 minutes on a hotplate in an inert atmosphere.
• the organic semiconductor and the cathode were then applied onto the buffer layer, as described in WO 04/037887 and the literature cited therein.
• the structured LEDs were produced similarly as Example 4 up to and including the step of crosslinking the buffer layer.
• cationically crosslinkable semiconductors were used for the organic semiconductors. These were red, green and blue emitting conjugated polymers based on poly-spirobifluorene, which were functionalized with oxetane groups. These materials and their synthesis are already described in the literature ( Nature 2003, 421, 829).
• a solution (generally with a concentration of 4-25 mg/ml in for example toluene, chlorobenzene, xylene:cyclohexanone (4:1)) was taken and dissolved by stirring at room temperature. Depending on the compound, it may also be advantageous to stir for some time at 50-70° C.
• the film was then heat-treated in an inert atmosphere for 3 minutes at 130° C., subsequently treated with a 10 ⁇ 4 molar LiAlH 4 solution in THF and washed with THF.
• the non-crosslinked positions in the film were thereby washed off.
• This process was repeated with the other solutions of the crosslinkable organic semiconductors, and the three primary colors were thereby successively applied in a structured way.
• the evaporation coating of the electrodes and the contacting were then carried out as described above.
• the polymer exhibits a lifetime of approximately 500 h.
• An LED was also produced whose buffer layer was photochemically crosslinked by adding 0.5% by weight of ⁇ 4-[(2-hydroxytetradecyl)-oxyl]-phenyl ⁇ -phenyliodonium hexafluoroantimonate with exposure to UV radiation (3 s, 302 nm) and subsequent heating to 90° C. for 30 seconds. The buffer layer was then washed with THF and heated to 180° C. for 5 minutes. Under otherwise equal conditions, this LED had a lifetime of approximately 630 h.
• the measurement was repeated with polymer P2 as the buffer layer, as described in Example 6 under otherwise identical conditions.
• the polymer exhibits a lifetime of approximately 1500 h without addition of photoacid to the buffer layer, and approximately 600 h with addition of photoacid.
• the measurement was repeated with compound V1 as the buffer layer, as described in Example 6 under otherwise identical conditions.
• the polymer exhibits a lifetime of approximately 1350 h without addition of photoacid to the buffer layer, and approximately 550 h with addition of photoacid.

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