Electronic device

Abstract

Electronic device comprising: a substrate, a first electrode, at least one organic functional layer, and a second electrode, wherein the at least one organic functional layer is arranged between the first electrode and the second electrode, and wherein the at least one organic functional layer comprises at least a first matrix material, a second matrix material, and a third matrix material, and the third matrix material having a lowest unoccupied molecular orbital (LUMO) that is energetically lower than the LUMO of the second matrix material and the LUMO of the first matrix material, and wherein the second matrix material has a highest occupied molecular orbital (HOMO) that is energetically higher than the HOMO of the first matrix material and the HOMO of the third matrix material, and wherein the first matrix material has a LUMO that is energetically higher than the LUMO of the second matrix material and the LUMO of the third matrix material, and an HOMO,which is energetically lower than the HOMO of the second matrix material and the HOMO of the third matrix material.

Description

The invention relates to an electronic device and a method for manufacturing an electronic device.Electronic devices are shown in the document WO 07 / 1 27 063 A2.Electronic devices, such as organic light emitting diodes (OLEDs), consist of a sequence of a plurality of functional organic layers. Emission layers have a matrix material which is doped with emitter molecules. In the emission layer, excitons are formed by recombination of electrons and "holes" that lead to light emission. In order to obtain high efficiency of the electronic device, the ratio between electrons and "holes" transported in the emission layer is critical. An unbalanced relationship between hole and electron transport results in low radiation efficiency of the device.It is an object of the invention to provide an electronic device which has improved charge carrier transport and improved charge carrier balance in the organic layers and thus increased efficiency. Another object of the invention is to provide a method for manufacturing an electronic device. These objects are achieved by an electronic device according to claim 1 and a method of manufacturing the electronic device according to claim 12. Further embodiments of the apparatus and of the method are the subject matter of further claims.According to an embodiment, an electronic device is provided, comprising a substrate, a first electrode, at least one organic functional layer and a second electrode, wherein the at least one organic functional layer is arranged between the first electrode and the second electrode. For example, the first electrode can be arranged on the substrate, the at least one organic functional layer on the first electrode and the second electrode on the at least one organic functional layer. The at least one organic, functional layer comprises at least a first matrix material, a second matrix material and a third matrix material, wherein the third matrix material is a lowest unoccupated molecular orbital (LUMO) that is lower in energy than the LUMO of the second matrix material and the LUMO of the first matrix material, and wherein the second matrix material is a highest occluded molecular orbital (HOMO) that is higher in energy than the HOMO of the first matrix material and the HOMO of the third matrix material. Thus, an electronic device is provided comprising more than two different matrix materials in an organic functional layer. In this case, three different matrix materials can be present, and more than three can also be present, as required.According to molecular orbital theory, there are different molecular orbitals in one molecule with different energy levels which can be occupied by the electrons present. These molecular orbitals become populated as the energy level increases. The LUMO is the lowest molecular orbital in energy, which is no longer occupied by an electron. The HOMO is the most energetic molecular orbital still occupied by an electron.This electronic device has improved charge carrier transport and charge carrier balance in the organic functional layer, and an adjustable ratio between hole and electron transport. The first matrix material is selected in such a way that it has a large band gap, i.e. the difference between HOMO and LUMO, for example such that its HOMO is lower in terms of energy than the HOMO of the other two matrix materials and its LUMO is higher in terms of energy than the LUMO of the other two matrix materials.Furthermore, the first matrix material may comprise a LUMO that is higher in energy than the LUMO of the second matrix material and the LUMO of the third matrix material, and a HOMO that is lower in energy than the HOMO of the second matrix material and the HOMO of the third matrix material.Furthermore, in the electronic device, the second matrix material may include a LUMO that is higher in energy than the LUMO of the third matrix material and a HOMO that is higher in energy than the HOMO of the third matrix material. Thus, the first matrix material can have the largest band gap between HOMO and LUMO compared to the second and third matrix materials and the second matrix material has a band gap which is shifted in terms of energy to the band gap of the third matrix material. Electrons can thus be transported on the LUMO of the third matrix material and holes can be transported on the HOMO of the second matrix material, since these energy levels are in each case most favourable in terms of energy for the respective charge transport.The first matrix material may have a charge carrier mobility in the electronic device that is lower than the charge carrier mobility of the second and third matrix materials. The first matrix material may be an ultra wide band gap (UGH) material, which has a large band gap compared to the other matrix materials. As a result, it cannot have any proportion in the charge carrier transport.The second matrix material may further comprise a hole transport material and the third matrix material may comprise an electron transport material.The charge carrier transport, i.e. the hole transport and the electron transport, depends in particular on the mobility of the holes or of the electrons in a material and on the position of the energy levels HOMO and LUMO of the matrix materials. The HOMO and LUMO of a material is responsible for charge carrier injection.In order to produce a hole in the matrix, which is composed of the three matrix materials, an electron, for example, must be removed from the HOMO, which is more difficult in the case of an HOMO with an energy depth than in the case of an HOMO with an energy height. Thus, the second matrix material, which has a higher HOMO than the third matrix material, is better suited as hole transport material than the third matrix material. The same applies analogously to the generation of electrons in LUMOs, which is favourable in terms of energy in the case of LUMOs located lower in terms of energy. Thus, the third matrix material, which has a lower LUMO than the second matrix material, is suitable as electron transport material.If holes and electrons are generated, the mobility of these charge carriers in the material is also important. Depending on how these two factors cooperate in a material, a matrix material may serve as an electron transport material or a hole transport material. In this case, the charge carrier transport of the other charge also takes place in each case, but the transport of a charge carrier predominates. If no charge carrier transport takes place in a matrix material, as in one embodiment of the invention in the first matrix material, this can either be due to the fact that no charge carriers are generated or that no mobility of the charge carriers is present. In addition to the first matrix material, further matrix materials may be present in the organic, functional layer, which do not contribute to charge carrier transport.The energy levels HOMO and LUMO of a material may be measured to select suitable materials for first, second and third matrix materials. Thus, the HOMO of a material can be determined by means of cyclovoltametry. The band gap, i.e. the energy difference between HOMO and LUMO, can furthermore be determined by means of spectroscopy, in which the wavelength of the emitted light is measured and the excitons produced and the band gap are calculated therefrom. The energy level of the LUMO is then calculated from the determined HOMO and the band gap. Alternatively, the HOMO can also be determined by photoelectron spectroscopy.The mobility of electrons and holes may depend on the molecular distance, i.e. the mean distance of charge carrier transporting molecules in the respective matrix material. Thus, the concentration of a matrix material in the mixture of several matrix materials plays a role. The first matrix material, which has the largest band gap and the smallest charge carrier mobility compared to the second and third matrix materials, can serve to adjust the concentration of the second and third matrix materials separately from one another. Depending on the selected concentration of the second and third matrix materials, the distances between the respective molecules change. The microscopic charge carrier transport depends on the molecular distance of the charge carrier transporting molecules in the respective matrix material, so that the mobility of electrons and holes in the matrix, which has at least three matrix materials, can be adjusted absolutely separately from one another by adjusting the concentration.According to Miller and Abraham, the mobility can be determined as follows: in this model, a solid is constructed, viewed schematically, from the sites i and j in which the charge carriers can be located. Each location represents a localized state. The transport of a charge carrier between the locations i and j is represented by a resistor R ij. The size of the temperature-dependent resistance reflects the spatial distance between the locations and the required activation energy for the transition. The parameter γ stands for the drop in the electronic wave function of the charge carriers, a is the parameter for the average lattice spacing. The phonon frequency v 0 indicates the number of attempts of a charge carrier to pass from one localized state to another localized state, is in the range of about 10 13 s -1 and takes into account the strength of the electron-phonon coupling.The electronic device may further include an organic functional layer selected from a group comprising emission layers, electron transport layers, hole transport layers, electron blocking layers, hole blocking layers, hole injection layers, electron injection layers, and intermediate layers. Intermediate layers are layers which are arranged between two emission layers. Depending on what is selected for an organic, functional layer, these layers can also contain additional dopants. The organic, functional layer can be an emission layer and can be doped with at least one emitter material. Emitter materials may comprise small molecules or polymers. The concentration of the emitter material in an emission layer can be up to 10% by weight. Furthermore, the emitter material can have only a low charge carrier mobility on account of the low concentration in the emission layer and therefore contribute only slightly to the charge carrier transport.Two or three emitter materials may also be present in the emission layer. The emitter materials can be selected, for example, from green-emitting Ir(ppy) 3( tris(2-phenylpyridine)iridium(III)), red-emitting Ir(piq) 3( tris(1-phenylisoquinoline)iridium(III)) or blue-emitting Firpic (bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III)).The concentrations of the emitting material and the matrix materials in the organic functional layer may have a gradient within the organic functional layer. Thus, for example, the concentration of the emitter material can be higher in a first partial region of the layer than in a second partial region of the layer.By omitting the doping with emitter materials, transport, intermediate and blocking layers can be produced.A plurality of organic, functional layers can also be present in an electronic device, it being possible for the layers to have different functions or identical functions. For example, an electronic device may include a sequence of a plurality of functional organic layers, which is composed, for example, of a hole injection layer, a hole transport layer, a first emission layer, an intermediate layer, a second emission layer, an electron transport layer and an electron injection layer. Each of these layers may comprise a matrix comprising at least a first, a second and a third matrix material. The matrix materials in the various organic functional layers can be chosen to be the same or different in all layers.Depending on where the emission layer is located in the layer stack of the electronic device, the mobility of electrons and holes within this layer can be optimized separately from one another if the emission layer comprises a first, a second and a third matrix material. Mobility can also be optimized across multiple layers.Also, when the emission layer comprising the three matrix materials is close to an anode or a cathode, the mobility of electrons and holes can be adjusted so that the ratio of holes and electrons in the emission layer is equalized. Depending on which charge carrier type is to have a higher mobility, the matrix may contain a higher concentration of the respective matrix material. Thus, a large number of excitons can be formed in the emission layer regardless of the position of the emission layer of the electronic device.If the organic functional layer is an emission layer comprising an emitter material, the LUMO of the emitter material may be higher in energy than the LUMO of the first, second and third matrix materials and the HOMO of the emitter material may be higher in energy than the HOMO of the first, second and third matrix materials. Thus, the band gap between HOMO and LUMO of the emitter material is smaller than the band gaps of the three matrix materials and is also present in terms of energy between all band gaps of all matrix materials. Ambipolar charge transport in an emission layer is thus possible.The molecules of the second and third matrix materials preferably transport only one charge carrier species, holes or electrons in each case, so that no excitons form on them. The lifetime of the materials is thus increased, since no degradation by excitation energy can take place. Excited states (excimers) are formed between the various molecules of the matrix materials, which states can transfer their excitation energy to the emitter molecules by energy transfer. Thus, the efficiency of the electronic device is further increased.An electronic device may also have multiple emission layers, for example to combine phosphorescent and fluorescent emitter materials in one device. The insertion of an intermediate layer between the emission layers may then be necessary, which may have ambipolar charge transport properties, for example. This is possible by the combination of three matrix materials.By adjusting the charge carrier mobility with the aid of the three matrix materials, it is possible to influence the position of the recombination zone in an emission layer in a targeted manner. The recombination zone can be located within one layer or distributed over a plurality of layers. By introducing the first matrix, which has no charge transport, within an emission layer, the absolute value of the charge carrier mobility decreases. This results in a recombination zone, the zone in which excitons are formed, which is shifted from the edges of an emitting layer toward the center. This increases the efficiency of the device since, inter alia, the nonradiative deregation of excitons (quenching) is reduced and more excitons are formed in the actual emission layer than in the adjacent layers.The electronic device may be a radiation-emitting device, for example an organic light-emitting device. This light emitting device may be an organic light emitting diode (OLED). Furthermore, the electronic device may comprise a solar cell or a transistor.For example, the at least one organic, functional layer in a transistor is arranged between the first and second electrodes. Furthermore, a third electrode is present. The electrodes may be selected from gate, source and drain electrodes. A transistor may be used for switching or amplifying electrical signals.In a solar cell, light can be converted into electrical energy. Here, the organic, functional layer is arranged between the first and the second electrode, wherein at least one of the electrodes is formed transparently.The device can have in an organic functional layer as first matrix material, for example mCP (m-bis(N-carbazolylbenzene)), as second matrix material, which can be a hole transport material, TCTA (9H-carbazole, 9, 9', 9"-(1,3,5-benzenetriyl)tris-(9Cl)), and as third matrix material, which can be an electron transport material, for example TPBi (1,3,5-tris(N-phenylbenzylimidazol-2-yl). If a matrix for an emission layer is to be provided, the emitter material used may be, for example, the yellow emitter rubrene (5,6,11,12-tetraphenylnaphthalene).A method of manufacturing an electronic device having the characteristics described above is further provided. The method comprises method steps A) providing a substrate, B) providing a first electrode and a second electrode, C) arranging at least one organic layer between the first electrode and the second electrode. In process step C), at least one first matrix material, one second matrix material and one third matrix material are applied simultaneously. The application in method step C) can be effected, for example, by vapor deposition (coevaporation). By means of the simultaneous application, the concentration of the respective matrix material can be determined independently of the other matrix materials, such that the matrix materials can be applied in different concentrations.The invention will be explained in more detail with reference to the figures and exemplary embodiments: FIG. 1 shows the schematic side view of an electronic device, FIG. 2 shows a schematic view of the energetic states of the various matrix materials, FIG. 3 shows a schematic side view of an electronic device, FIG. 4 shows the simulation of the mobility of the charge carriers in an emission layer, FIG. 5 shows the schematic structure for producing a layer having a plurality of matrix materials.FIG. 1 shows the schematic side view of an electronic device comprising a substrate 10, a first electrode 20, an emission layer 30, and a second electrode 40. The first electrode may be an anode and the second electrode a cathode, for example. Depending on whether the substrate and the first electrode or the second electrode are transparent, the electronic device can be a bottom-emitting or a top-emitting device, for example an OLED. The emission layer 30 may include a first, a second and a third matrix material and may be doped with an emitter material.FIG. 2 shows the schematic illustration of the energy levels of the respective materials in the emission layer in an exemplary embodiment. The HOMO and LUMO of the first matrix material 30N, the second matrix material 30B, and the third matrix material 30A is shown. The first matrix material has a HOMO that is lower in energy than the HOMO of the second matrix material and the third matrix material. Furthermore, the first matrix material has a LUMO which is higher in energy terms than the LUMO of the second matrix material and of the third matrix material. The second matrix material has a LUMO that is higher in energy than the LUMO of the third matrix material and a HOMO that is higher in energy than the HOMO of the third matrix material. The first matrix material thus has lower charge carrier mobilities than the two other matrix materials, the second matrix material can comprise a hole transport material and the third matrix material an electron transport material.The emitter material 30E includes a HOMO and LUMO having the smallest band gap compared to the matrix materials, and is interposed between the LUMOs and the HOMOs of the three matrix materials.To the right of the scheme, the sum of the different energy levels is shown. A represents the energy level at which electron transport takes place, B represents the energy level at which hole transport takes place. d1and d2represent the energetic distances between the LUMOs of the first and second matrix material (d1) and the HOMOs of the first and third matrix material (d2). d3represents the band gap of the emitter material. If no emitter material is used, the layer can also be a charge carrier transport, charge carrier injection or charge carrier blocking layer. Furthermore, it is also possible to use a plurality of emitter materials. The emitter material has a concentration of ≤10% by weight in the emission layer.FIG. 3 shows the schematic side view of a further embodiment of the electronic device, which has an emission layer 30, which is adjoined in each case on one side by an electron transport layer 32 and a hole transport layer 31. Here, the first electrode 20 is an anode. Each of the emission layer 30, the electron transport layer 32, and the hole transport layer 31 may have matrices composed of three or more matrix materials.FIG. 4 shows the simulation of charge carrier transport in an OLED in which an emission layer, a hole transport layer 31 and an electron transport layer 32 are present. The x-axis shows the distance of the respective layer from the anode D [nm], the y-axis shows the normalized recombination rate R n. It can be seen that as the absolute value of the charge carrier mobility in the emission layer 30 is reduced compared to the hole transport layer 31 and the electron transport layer 32, the recombination zone is shifted from the edges of the emission layer towards the center. That is, as mobility of carriers in the emission layer 30 decreases, recombination in the adjacent layers 32 and 31 decreases and shifts to the center of the emission layer 30.In the simulation, electron and hole mobility in the emission layer were equalized, i.e. a charge transport with ambipolar charge was assumed. Ohmic injection was assumed, all energy barriers between HOMO and LUMO of the two layers were 400 meV for the respective charge carrier species. For the various line forms, the respective mobilities of the charge carriers are indicated in m 2 / Vs in the diagram; they range between 10 -8 and 10 -12.FIG. 5 is a schematic side view of a structure for manufacturing the electronic device. Four evaporation sources 50 are applied by way of example on a holder 51, from which matrix materials and / or dopants can be respectively vapor-deposited onto the deposition substrate 60. In order to be able to determine the respective concentration of the matrix material and / or of the dopant exactly, the evaporation rate is measured and adjusted via layer thickness monitors 55. The layer thickness monitors can be, for example, quartz crystal.For example, with a structure according to FIG. 5, an emission layer can be produced which contains a first matrix material which comprises mCP (m-bis(N-carbazolylbenzene)) and is applied at a vapor deposition rate of 3.8 Å / s. The second matrix material, the hole transport material, may be TCTA (9H-carbazole, 9,9',9"-(1,3,5-benzenetriyl)tris-(9C1)) and deposited at a deposition rate of 8 Å / S. The third matrix material, the electron transport material, can be, for example, TPBi (1,3,5-tris(N-phenylbenzylimidazol-2-yl) and deposited at a deposition rate of 8 Å / S. As emitter material, for example, the yellow emitter rubrene (5,6,11,12-tetraphenylnaphthalene) can be introduced and applied at a vapor deposition rate of 0.2 Å / S. This results in a layer having a volume concentration of 40% for the charge carrier transport materials and 1% for the emitter. Table 1 lists the HOMOs and LUMOs of these materials. The values of the HOMOs of TCTA, TPBi, mCP were determined by UV photoemission spectroscopy, the corresponding LUMO values were estimated by adding the energy required for absorption to the HOMO value. Rubrene HOMO and LUMO were determined by cyclic voltammetry and photoelectron spectrometry. Table 1 Table 1mCP-5,9-2,4TCTA-5,7-2, 3TPBi-6, 3-2, 8Rubrene-5,5-3, 0The third matrix material TPBi has the lowest value for the LUMO compared to the other matrix materials and is thus electron transport material. The second matrix material TCTA has the greatest value for the HOMO compared to the other matrix materials and is thus hole-transport material. The first matrix material mCP is not involved in charge carrier transport, since its LUMO is not lower than the LUMO of the third matrix material and its HOMO is not higher than the HOMO of the second matrix material.Further possible hole transport materials are:TCTA4,4',4"-Tris(carbazol-9-yl)triphenylamineCPB4,4'-Bis(carbazol-9-yl)biphenyl1T-NATA4,4',4"-Tris(N-(1-naphthyl)-N-phenyl-amino)-triphenylamineSpiro-TAD2,2',7,7'-tetrakis(N,N-diphenylamino)-9,9'-spirobifluoreneElectron transport materials which can furthermore be used are:TAZ3-(4-Biphenylyl)-4-phenyl-5- tert-butylphenyl-1,2,4-triazoleAlq 3Tris(8-hydroxyquinolinato)aluminumBCP2,9-Dimethyl-4,7-diphenyl-1,10-phenanthrolineNTAZ4-(Naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazoleBalqBis-(2-methyl-8-quinolinolat)-4-(phenylphenolato)aluminumAs the first matrix material, which has the lowest charge carrier mobility compared to the other matrix materials, it is possible to use:UGH-21,4-Bis(triphenylsilyl)benzeneUGH-31,3-Bis(triphenylsilyl)benzenemCP1,3-Bis(carbazol-9-yl)benzeneThe HOMOs of UGH-2 and UGH-3 have values of -7.2 ± 0.1 eV, the LUMOs are 2.8 eV. These HOMO values can be determined by photoelectron spectroscopy, the LUMO values can be estimated from the distance of HOMO values and LUMO values at the intersection of the absorption and the fluorescence spectrum.Possible emitter materials are:Ir (ppy) 3Tris(2-phenylpyridine) iride (III)Ir (ppy) 2 (acac)Bis(2-phenylpyridazine) (acetylacetonat)iridium(II )BczHCi4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenylFirBis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxy-pyridyl)iridium(III)RubreneTetraphenylnaphthacenIr (piq) 3Tris(1-phenylisoquinoline)iridium(III)These emitter materials are small, non-polymeric molecules. The use of polymeric emitter materials is likewise possible.Further possible materials which, depending on the position of their HOMOs and LUMOs with respect to one another, can be used as first, second or third matrix are:DPAVBi4,4'-Bis(2-(4-(N,N-diphenylamino)phenyl)vinyl)biphenylCuPCPhthalocyanine Copper ComplexS-DPVBi2,2',7,7'-tetrakis(2,2-diphenylvinyl)spiro-9,9'-bifluoreneCPFTAPC1,1-Bis-(4-bis(4-methylphenyl)aminophenyl)cyclohexaneTBANN9,10-Bis(2-naphthyl)-2-t-butylanthraceneTPDN,N,N',N'-tetraphenylbenzidineSome of the electron- and hole-transport materials may also serve as the first matrix material. Important in the composition of the first, second and third matrix materials for the matrix are the relative ratio of the LUMOs and HOMOs of the three combined materials and their position with respect to one another.The matrix cannot be chosen arbitrarily for phosphorescent emitters on account of the chemical compatibility. The red emitter iridium (III) bis(2-methyldibenzo[f,h]quinoxaline) acetylacetonate) is only efficient in one NBP matrix. However, NPB is a hole transport material. If there is now a further emitter layer on the anode side, this is not supplied sufficiently with electrons. By doping in an electron transport material, for example BCP, the relative transport properties can be adjusted. Fine tuning of the transport properties is effected with UGH4.The embodiments shown in the figures and exemplary embodiments can be varied as desired.

Claims

Electronic device comprising - a substrate, - a first electrode, - at least one organic functional layer, and - a second electrode, wherein the at least one organic functional layer is arranged between the first electrode and the second electrode and wherein the at least one organic functional layer comprises at least a first matrix material, a second matrix material and a third matrix material and the third matrix material comprises a lowest unoccupated molecular orbital (LUMO) that is lower in energy than the LUMO of the second matrix material and the LUMO of the first matrix material, and wherein the second matrix material comprises a highest occluded molecular orbital (HOMO) that is higher in energy than the HOMO of the first matrix material and the HOMO of the third matrix material, wherein the first matrix material comprises a LUMO, the LUMO is higher in energy than the LUMO of the second matrix material and the LUMO of the third matrix material, and has a HOMO which is lower in energy than the HOMO of the second matrix material and the HOMO of the third matrix material.The electronic device of any preceding claim, wherein the first matrix material has a charge carrier mobility that is less than the charge carrier mobilities of the second and third matrix materials.The electronic device of any preceding claim, wherein the second matrix material comprises a hole transport material.The electronic device of any preceding claim, wherein the third matrix material comprises an electron transport material.The electronic device according to any one of the preceding claims, wherein the organic functional layer is selected from a group comprising emission layers, electron transport layers, hole transport layers, electron blocking layers, hole blocking layers, hole injection layers, electron injection layers and intermediate layers.Electronic device according to one of the preceding claims, wherein the organic, functional layer is an emission layer and is doped with at least one emitter material.Electronic device according to the preceding claim, wherein the emitter material in the emission layer has a concentration of ≤ 10 wt%.The electronic device of the preceding claim, wherein the concentration of the emitter material in the emission layer has a gradient.The electronic device of any of claims 6 to 8, wherein the LUMO of the emitter material is energetically lower than the LUMO of the first, second and third matrix materials and the HOMO of the emitter material is energetically higher than the HOMO of the first, second and third matrix materials.Electronic device according to one of the preceding claims, which is designed as a radiation-emitting device.The electronic device according to any one of claims 1 to 9, wherein the device is selected from a group comprising an organic light emitting device, a solar cell, and a transistor.Method for producing an electronic device according to Claims 1 to 11, having the method steps A) providing a substrate, B) providing a first electrode and a second electrode, C) arranging at least one organic, functional layer between the first electrode and the second electrode, wherein in method step C) at least the first matrix material, the second matrix material and the third matrix material are applied simultaneously.The method according to the preceding claim, wherein in method step C) the first matrix material, the second matrix material and the third matrix material are applied by vapor deposition.

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