EP3645766A1 - Homogeneous mixtures - Google Patents

Abstract

The present application relates to a method for preparing a homogeneous composition which comprises at least two vaporizable organic compounds, which method comprises mixing said compounds under heating and rotating in a rotatable vessel.The present invention further relates to the use of such a homogeneous composition for the preparation of an electronic device and an electronic device comprising the homogeneous composition in atleast one functional organic layer.

Description

Homogeneous Mixtures

The present invention relates to a method for preparing a homogeneous composition which comprises at least two vaporizable organic compounds, the use of such a homogeneous composition for the preparation of an electronic device and an electronic device comprising the homogeneous composition in at least one layer.

Electronic devices in the context of this application are understood to mean what are called organic electronic devices, which contain organic semiconductor materials as functional materials. More particularly, these devices are understood to mean organic electroluminescent (EL) devices, especially organic light emitting diodes (OLEDs). The general structure and mode of operation of organic electroluminescent devices is known to the skilled person and is described, for example, in US 4539507, US 5151629, EP 0676461 and WO 98/27136. In general, organic electroluminescent devices contain spaced electrodes separated by one or more layers comprising organic compounds, which form the so-called organic light emitting structure and emit electromagnetic radiation, typically light, in response to the application of an electrical potential difference across the electrodes.

Within the present application, any layer of an organic electronic device which comprises one or more organic compounds as functional materials will also be called "organic layer" or "(multi)functional organic layer", which terms are used interchangeably. The term "multifunctional" indicates that an organic layer comprises one or more organic materials of different functionality.

In recent years, preferred electronic devices have been constructed employing thin-film deposition techniques. For example, using an anode as a device support, the organic light emitting structure has been deposited as a combination of multiple organic thin films, wherein each organic layer has a different functionality within the electronic device, followed by the deposition of a cathode. In order to increase the performance of electronic devices, especially lifetime, efficiency and operating voltage, it is now standard knowledge to use organic layers which are composed of multiple organic compounds, for example, organic layers in which different host (or matrix) materials are mixed (e.g., host + co-host or hole transport material (HTM) + electron transport material (ETM)), or organic layers composed of one or more host materials having a dopant dispersed therein. In principle, there are two possibilities to implement this concept of multifunctional organic layer deposition. According to a first concept, the different organic materials to be deposited are provided in separate, independently controlled evaporation sources (also called "evaporation boat"). Then, each organic material is evaporated from its respective evaporation source and condensed on a substrate, such as an anode or cathode, to form a thin-film deposition, i.e. a multifunctional organic layer, as described for example by Steinbacher et al., "Simplified, yellow, organic light emitting diode by co-evaporation of premixed dye molecules", Organic Electronics (201 1 ), 12, 91 1 -915. However, this so called "co-evaporation" or "co-deposition" process has at least two disadvantages: i) It is difficult and time consuming to precisely control the desired deposition rate of each organic material, and ii) co-evaporation is relatively wasteful in terms of material utilization. According to a second concept, the different organic materials to be deposited are mixed first (so called "premixed" or "premixing"). A single evaporation source is provided that includes the resulting mixture. The single evaporation source is then heated for a sufficient time and

temperature to provide evaporation and deposition of the organic

compounds onto the substrate to form a multifunctional organic layer. This process, which is known as "premix-evaporation", advantageously does not require precise control of multiple independent evaporation sources, is not wasteful in terms of material utilization and enables simple and high-speed evaporative deposition and device fabrication. Moreover, it allows to apply or coat thin organic layers on the substrate, e.g. the anode or cathode, such that the different organic materials are substantially uniformly distributed throughout the layer.

A combination of two or more host materials useful in an organic light emitting device and suitable for premix-evaporation from a single

evaporation source is described in WO 201 1/136755 A1 .

EP 1 274 136 A2, EP 1 337 132 A1 and EP 1 454 736 A2 report mixing or blending powders of organic host and dopant materials to provide a mixture prior to agglomerating the mixture into a solid compacted pellet, and using such pellets in a thermal physical vapour deposition (PVD) source for making an organic layer on a structure which forms part of an OLED.

EP 1 156 536 A2 is related to a method for making an organic

electroluminescent device and describes premixing a host material and an emissive dopant material in a desired ratio followed by melting the mixture. The pre-doped material is then used in evaporation deposition of a doped emitting layer. WO 2004/070787 A2 reports a method for multifunctional thin film

preparation by evaporation from a single evaporation source. The method comprises melting and premixing different organic materials, such as matrix materials and dopants, using a high temperature and high-pressure process, and depositing the organic materials onto the surface of a substrate. Premixing is performed by stirring the material mixture with a stirring bar.

However, using a stirring bar or stirrer for premixing a melt has several disadvantages. First, only localised stirring of the mixture or melt may occur thereby preventing a thorough mixing of the organic materials used. As a result, the mixing performance or mixing quality may be low. Secondly, depending on the viscosity of the melt, a stirring bar or stirrer may require high rotation force. Upon cooling, the viscosity of the mixture will increase and the stirrer will eventually be blocked. The remaining melt may de-mix (i.e. segregation) when solidification starts without stirring based on zone melting principles. Further, due to the insertion of the stirring bar or stirrer into the mixture or melt, there is a high risk for contaminating the premixing materials. In addition, applying a stirring bar or stirrer makes it more difficult to have an inert system for premixing and evaporation. In order to prepare electronic devices that have adequate lifetime and efficiency, it is important for the organic materials to evaporate and deposit uniformly and consistently and to keep the ratio of the materials in the initial mixture in the resulting deposited organic layer. In order to achieve this, an uniform and homogeneously mixed composition has to be used for evaporation deposition.

There is still a need in industry for a method that enables preparing more uniformly mixed homogeneous compositions, in particular compositions capable of being vacuum deposited, especially by premix-evaporation for the production of electronic devices having adequate lifetime and efficiency, which method overcomes the drawbacks of the state of the art.

An object of the present invention is thus to provide a method for preparing a homogeneous composition, in particular a composition which is capable of being vacuum deposited, which overcomes the drawbacks of the state of the art. In particular, it is an object of the present invention to provide a composition which has high purity and improved homogeneity and which is capable of being used for premix-evaporation in the production of electronic devices having improved lifetime and efficiency.

This object is solved by a method for preparing a homogeneous

composition, in particular a composition capable of being vacuum

deposited, which comprises at least two vaporizable organic compounds, said method comprising:

a. providing a rotatable vessel containing said at least two vaporizable organic compounds,

b. heating the vessel to form a melt and simultaneously rotating the

vessel in a continuous manner to homogenize the melt. The present inventors have surprisingly found that by means of the method according to the invention compositions having high purity and improved homogeneity can be obtained. Moreover, they have found that the method according to the invention is particularly applicable for preparing

homogeneous compositions which are capable of being vacuum deposited, in particular for producing electronic devices, by using a single evaporation source. The present inventors could further show that electronic devices, in which one or more organic layers were deposited by evaporation deposition using the inventive premixed homogeneous composition, exhibit improved characteristics with regard to efficiency and lifetime compared to using mixtures of the prior art.

Advantageously, the method according to the invention enables thorough mixing of the composition, as localized stirring and mixing of the

composition is prevented, so that a composition with high homogeneity can be obtained. Furthermore, it allows that premixing of the organic

compounds can be performed in an inert system so that unwanted contamination of the composition during premixing is prevented, as the insertion of a stirrer or stirring bar into the melt is not required.

A "composition" as used herein is a material system or mixture made up of two or more different (organic) substances which are mixed but are not combined chemically, i.e. it denotes the physical combination of two or more substances in which their identities are retained. Accordingly, the terms "composition" and "mixture" hereinafter will be used interchangeably.

A "homogeneous composition" as used herein is a type of composition or mixture in which the two or more different (organic) substances are uniformly distributed at the molecular level and make up one phase.

Accordingly, the homogeneous composition or mixture has the same proportions of its components throughout a given sample and every part of the composition or mixture has the same properties.

Within the framework of the present invention, a homogeneous composition is preferably a composition that comprises at least two different vaporizable organic compounds, wherein the standard deviation σ of the ratio of the compounds after premixing is smaller than 1 .0% compared to the initial ratio of these compounds (i.e. compared to the ratio of these compound in the initial mixture). For example, the standard deviation σ is smaller than 0.9%, 0.8%, 0.7%, 0.6% or 0.5%, more preferably smaller than 0.4%, even more preferably smaller than 0.3%, and most preferably smaller than 0.2%. The method according to the present invention is particularly suitable for preparing homogeneous compositions which are capable of being vacuum deposited, in particular for the preparation of electronic devices, preferably organic electroluminescent (EL) devices, which are characterized in that one or more layers are coated by a sublimation process. In this case, the homogeneous composition is applied on a substrate by evaporation deposition from a single evaporation source.

Preferably, the at least two different vaporizable organic compounds are independently from each other selected from the group consisting of host or matrix materials, emissive materials, electron injection materials, electron transport materials, electron blocking materials, wide band gap materials, hole injection materials, hole transport materials, hole blocking materials, exciton blocking materials, n-dopants or p-dopants, and any combination thereof. Within this application, these materials are understood to mean functional organic compounds or materials.

Accordingly, the expression "at least two different vaporizable organic compounds" as used herein is understood to mean that the vaporizable organic compounds or materials which should be part of the homogeneous composition can each be selected from organic compounds having different functionalities, for example from host materials and wide band gap materials, and/or from organic compounds having the same functionality, for example from host materials only, matrix materials only or electron injection materials only.

As used herein, the term "vaporizable organic compound" is understood to mean any functional organic compound or material which can be

evaporated in vacuum and consequently be used in a vacuum deposition process to deposit a thin-film or layer, in particular an organic layer in an electronic device, preferably an organic electroluminescent device. In a preferred embodiment of the present invention, the at least two vaporizable organic compounds for preparing a homogeneous composition are host materials. In that case, the premixed homogeneous composition is preferably used in an emitting layer of an electronic device in combination with one or more emitting compounds, preferably in a phosphorescent emitting layer of a phosphorescent organic electroluminescent device, which is characterised in that it further comprises one or more phosphorescent emitting

compounds. In this case, the homogeneous composition comprising the at least two vaporizable host materials acts as a matrix material for the phosphorescent emitter and does not or not substantially take part in light emission itself. In literature, the term "matrix material" is very often used instead of "host material", in particular when host materials are used in combination with phosphorescent emitting compounds.

Systems comprising a plurality of host or matrix materials ("mixed matrix systems") preferably comprise two or three different host or matrix materials, more preferably two different host or matrix materials. Preferably, in this case, one of the two materials is a (host or matrix) material having hole-transporting properties, that is, a material that significantly contributes to the hole transport, and the other one is a (host or matrix) material having electron-transporting properties, that is, a material that significantly contributes to the electron transport. One source of more detailed

information about mixed matrix systems is the application WO

2010/108579.

Useful host materials, preferably for fluorescent emitting compounds, which can be premixed and used for preparing an emitting layer include materials of various substance classes. Preferred host materials are selected from the classes of the oligoarylenes (e.g. 2,2',7,7'-tetraphenylspirobifluorene according to EP 676461 or dinaphthylanthracene), especially of the oligoarylenes containing fused aromatic groups, the oligoarylenevinylenes (e.g. DPVBi or spiro-DPVBi according to EP 676461 ), the polypodal metal complexes (for example according to WO 2004/081017), the hole- conducting compounds (for example according to WO 2004/05891 1 ), the electron-conducting compounds, especially ketones, phosphine oxides, sulphoxides, etc. (for example according to WO 2005/084081 and WO 2005/084082), the atropisomers (for example according to WO

2006/048268), the boronic acid derivatives (for example according to WO 2006/1 17052) or the benzanthracenes (for example according to WO

2008/145239). Particularly preferred matrix materials are selected from the classes of the oligoarylenes comprising naphthalene, anthracene, benzanthracene and/or pyrene or atropisomers of these compounds, the oligoarylenevinylenes, the ketones, the phosphine oxides and the sulphoxides. Very particularly preferred matrix materials are selected from the classes of the oligoarylenes comprising, anthracene, benzanthracene, benzophenanthrene and/or pyrene or atropisomers of these compounds. An oligoarylene in the context of this invention shall be understood to mean a compound in which at least three aryl or arylene groups are bonded to one another. Preference is further given to the anthracene derivatives disclosed in WO 2006/097208, WO 2006/131 192, WO 2007/065550, WO

2007/1 10129, WO 2007/065678, WO 2008/145239, WO 2009/100925, WO 201 1/054442 and EP 1553154, and the pyrene compounds disclosed in EP 1749809, EP 1905754 and US 2012/0187826.

Preferred fluorescent emitting compounds which may be premixed with the host materials are selected from the class of the arylamines. An arylamine or an aromatic amine in the context of this invention is understood to mean a compound containing three substituted or unsubstituted aromatic or heteroaromatic ring systems bonded directly to the nitrogen. Preferably, at least one of these aromatic or heteroaromatic ring systems is a fused ring system, more preferably having at least 14 aromatic ring atoms. Preferred examples of these are aromatic anthraceneamines, aromatic

anthracenediamines, aromatic pyreneamines, aromatic pyrenediamines, aromatic chryseneamines or aromatic chrysenediamines. An aromatic anthraceneamine is understood to mean a compound in which a

diarylamino group is bonded directly to an anthracene group, preferably in the 9 position. An aromatic anthracenediamine is understood to mean a compound in which two diarylamino groups are bonded directly to an anthracene group, preferably in the 9,10 positions. Aromatic pyreneamines, pyrenediamines, chryseneamines and chrysenediamines are defined analogously, where the diarylamino groups in the pyrene are bonded preferably in the 1 position or 1 ,6 positions. Further preferred emitting compounds are indenofluoreneamines or -diamines, for example according to WO 2006/108497 or WO 2006/122630, benzoindenofluoreneamines or - diamines, for example according to WO 2008/006449, and dibenzoindeno- fluoreneamines or -diamines, for example according to WO 2007/140847, and the indenofluorene derivatives having fused aryl groups disclosed in WO 2010/012328. Likewise preferred are the pyrenearylamines disclosed in WO 2012/048780 and in WO 2013/185871 . Likewise preferred are the benzoindenofluoreneamines disclosed in WO 2014/037077, the benzo- fluoreneamines disclosed in WO 2014/106522 and the extended

benzoindenofluorenes disclosed in WO 2014/1 1 1269.

The term "phosphorescent emitting compounds" typically encompasses compounds where the emission of light is effected through a spin-forbidden transition, for example a transition from an excited triplet state or a state having a higher spin quantum number, for example a quintet state.

Suitable phosphorescent emitting compounds (= triplet emitters) are especially compounds which, when suitably excited, emit light, preferably in the visible region, and also contain at least one atom of atomic number greater than 20, preferably greater than 38, and less than 84, more preferably greater than 56 and less than 80. Preference is given to using, as phosphorescent emitting compounds, compounds containing copper, molybdenum, tungsten, rhenium, ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, gold or europium, especially compounds containing iridium, platinum or copper. In the context of the present invention, all luminescent iridium, platinum or copper complexes are considered to be phosphorescent emitting compounds.

Examples of the above-described emitting compounds, which may be premixed with matrix materials, can be found in applications WO 00/70655, WO 01/41512, WO 02/02714, WO 02/15645, EP 1 191613, EP 1 191612, EP 1 191614, WO 05/033244, WO 05/019373 and US 2005/0258742. In general, all phosphorescent complexes as used for phosphorescent OLEDs according to the prior art and as known to those skilled in the art in the field of organic electroluminescent devices are suitable. It is also possible for the person skilled in the art, without exercising inventive skill, to use further phosphorescent complexes in combination with the compounds of formula (I) in organic electroluminescent devices. Further examples are listed in a table which follows.

Preferred host or matrix materials for phosphorescent emitting compounds, which can be premixed and used for preparing an emitting layer of a phosphorescent organic electroluminescent device, are aromatic ketones, aromatic phosphine oxides or aromatic sulphoxides or sulphones, for example according to WO 2004/013080, WO 2004/093207, WO

2006/005627 or WO 2010/006680, triarylamines, carbazole derivatives, e.g. CBP (Ν,Ν-biscarbazolylbiphenyl) or the carbazole derivatives disclosed in WO 2005/039246, US 2005/0069729, JP 2004/288381 , EP 1205527 or WO 2008/086851 , indolocarbazole derivatives, for example according to WO 2007/063754 or WO 2008/056746, indenocarbazole derivatives, for example according to WO 2010/136109, WO 201 1/000455 or WO

2013/041 176, azacarbazole derivatives, for example according to EP 1617710, EP 161771 1 , EP 1731584, JP 2005/347160, bipolar matrix materials, for example according to WO 2007/137725, silanes, for example according to WO 2005/1 1 1 172, azaboroles or boronic esters, for example according to WO 2006/1 17052, triazine derivatives, for example according to WO 2010/015306, WO 2007/063754 or WO 2008/056746, zinc

complexes, for example according to EP 652273 or WO 2009/062578, diazasilole or tetraazasilole derivatives, for example according to WO

2010/054729, diazaphosphole derivatives, for example according to WO 2010/054730, bridged carbazole derivatives, for example according to US 2009/0136779, WO 2010/050778, WO 201 1/042107, WO 201 1/088877 or WO 2012/143080, triphenylene derivatives, for example according to WO 2012/048781 , or lactams, for example according to WO 201 1/1 16865 or WO 201 1/137951 .

In another preferred embodiment, the at least two vaporizable organic compounds used for preparing a homogeneous composition are electron transport materials. In that case, the homogeneous composition is preferably used in an electron transport layer, a hole blocker layer or an electron injection layer of an electronic device, preferably an organic electroluminescent device. An electron transport layer according to the present application is a layer having an electron-transporting function between the cathode and the emitting layer.

Electron transport materials, which can be premixed and used in the electron transport layer of an organic electroluminescent device as defined above, may be any materials as used in the prior art as electron transport materials in the electron transport layer. Especially suitable are aluminium complexes, for example Alq3, zirconium complexes, for example Zrq₄, lithium complexes, for example Liq, benzimidazole derivatives, triazine derivatives, pyrimidine derivatives, pyridine derivatives, pyrazine

derivatives, quinoxaline derivatives, quinoline derivatives, oxadiazole derivatives, aromatic ketones, lactams, boranes, diazaphosphole

derivatives and phosphine oxide derivatives. Further suitable materials are derivatives of the abovementioned compounds as disclosed in JP

2000/053957, WO 2003/060956, WO 2004/028217, WO 2004/080975 and WO 2010/072300.

In another preferred embodiment, the at least two vaporizable organic compounds used for preparing a homogeneous composition are hole transport materials.

In that case, the homogeneous composition is preferably used in a hole transport layer, an electron blocker layer or a hole injection layer of an electronic device, preferably an organic electroluminescent device.

A hole transport layer according to the present application is a layer having a hole-transporting function between the anode and emitting layer.

Hole injection layers and electron blocker layers are understood in the context of the present application to be specific embodiments of hole transport layers. A hole injection layer, in the case of a plurality of hole transport layers between the anode and emitting layer, is a hole transport layer which directly adjoins the anode or is separated therefrom only by a single coating of the anode. An electron blocker layer, in the case of a plurality of hole transport layers between the anode and emitting layer, is that hole transport layer which directly adjoins the emitting layer on the anode side.

Preferred examples of hole transport materials which can be premixed and used in the hole transport layer, electron blocker layer or hole injection layer of an electroluminescent device as defined above are

indenofluoreneamines and derivatives (for example in accordance with WO 06/122630 or WO 06/100896), the amine derivatives as disclosed in EP 1661888, hexaazatriphenylene derivatives (for example in accordance with WO 01/049806), amine derivatives with condensed aromatics (for example in accordance with U.S. Pat. No. 5,061 ,569), the amine derivatives as disclosed in WO 95/09147, monobenzoindeno-fluoreneamines (for example in accordance with WO 08/006449) or dibenzoindenofluoreneamines (for example in accordance with WO 07/140847). Suitable hole-transport and hole-injection materials are furthermore derivatives of the compounds depicted above, as disclosed in JP 2001/226331 , EP 676461 , EP 650955, WO 01/049806, U.S. Pat. No. 4,780,536, WO 98/30071 , EP 891 121 , EP 1661888, JP 2006/253445, EP 650955, WO 06/073054 and U.S. Pat. No. 5,061 ,569 In another preferred embodiment, one of the at least two vaporizable organic compounds is a host material, preferably a host material having electron-transporting properties or a host material having hole-transporting properties, most preferably a host material having electron-transporting properties, and the other one is a wide band gap material. It is also thinkable within the framework of the present invention to prepare a homogeneous mixture of one or more host materials having electron- transporting properties and one or more host materials having hole- transporting properties. As used herein, wide band gap materials will be understood to mean materials as disclosed in US 7,294,849, which are characterized in having a band gap of at least 3.5 eV. The term "band gap" denotes the distance between the energy level of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a compound. Such systems exhibit especially advantageous performance data in

electroluminescent devices.

In still other preferred embodiments, one of the at least two vaporizable organic compounds used for preparing a homogeneous composition is an electron transport material and the other one is a n-dopant, or one of the at least two vaporizable organic compounds is a hole transport material and the other one is a p-dopant. n-Dopants used according to the present invention are preferably those organic electron donor compounds capable of reducing one or more of the other compounds in the mixture. Preferred examples of n-dopants are W(hpp)₄ und further electron-rich metal complexes according to

WO 2005/086251 A2, P=N-compounds (e.g. WO 2012/175535 A1 ,

WO 2012/175219 A1 ), naphthylencarbodiimides (e.g. WO 2012/168358 A1 ), fluorenes (e.g. WO 2012/031735 A1 ), radicals and biradicals (e.g. EP 1837926 A1 , WO 2007/107306 A1 ), pyridines (e.g. EP 2452946 A1 , EP 2463927 A1 ), N-heterocyclic compounds (e.g. WO 2009/000237 A1 ) and acridines and phenazines (e.g. US 2007/145355 A1 ). p-Dopants used according to the present invention are preferably those organic electron acceptor compounds capable of oxidizing one or more of the other compounds in the mixture. Preferred examples of p-dopants are F₄-TCNQ, Fe-TNAP, NDP-2 (company Novaled), NDP-9 (company

Novaled), quinones (e.g. EP 1538684 A1 , WO 2006/081780 A1 ,

WO 2009/003455 A1 , WO 2010/097433 A1 ), radialenes (e.g. EP 1988587 A1 , US 2010/102709 A1 , EP 2180029 A1 , WO 201 1/131 185 A1 ,

WO 201 1 134458 A1 , US 2012/223296 A1 ), S-containing transition metal complexes (e.g. WO 2007/134873 A1 , WO 2008/061517 A2,

WO 2008/061518 A2, DE 102008051737 A1 , WO 2009/089821 A1 , US 2010/096600 A1 ), bisimidazoles (e.g. WO 2008/138580 A1 ),

phthalocyanines (e.g. WO 2008/058525 A2), bora-tetraazapentalenes (e.g. WO 2007/1 15540 A1 ) fullerenes (e.g. DE 102010046040 A1 ) and main group halogenides (e.g. WO 2008/128519 A2).

In principle, all different kinds of functional vaporizable organic compounds as described above can be premixed using the method according to the present invention in order to form a homogeneous composition.

The proportion of the organic materials to be premixed is not particularly limited. This means, the initial proportion of the organic materials to be premixed using the method of the present invention may range from

99.9:0.1 to 0.1 :99.9, in case two organic materials are premixed.

The vaporizable organic compounds to be premixed are preferably provided in the rotatable vessel in solid form, for example as powder, pellets, particles, granule, sphere, chip, shard or needle, etc., without being limited thereto. This means, a desired quantity of each solid material is first provided in the rotatable vessel, preferably, within a single evaporation source, whereby a solid initial mixture is formed. Then, for premixing the different vaporizable organic compounds according to the method of the present invention, heat is applied to melt said initial mixture, and the vessel containing the melt is continuously rotated in order to uniformly distribute the compounds used and thereby homogenize the melt. It is preferred according to the method of the present invention that the rotating is already performed during the heating-up when the compounds to be premixed are not yet melted, i.e. when the melt is not yet formed.

In order to increase the homogeneity of the composition (i.e. the distribution of the different materials in the melt), the heating and rotating of the vessel containing the melt comprising the at least two vaporizable organic compounds is preferably maintained for at least 1 h after the melt is formed, preferably for 1 h to 5 h, more preferably for 2 h to 3 h.

In a further preferred embodiment of the method according to the invention, the heating and rotating are performed under a reduced pressure, which is preferably in the range of 10 ³ to 10 ⁸ bar, more preferably in the range of 10^"5 to 10^"7 bar.

Applying vacuum during heating and melting of the at least two vaporizable organic compounds bears the advantage that the temperature gap between the melting points of the different organic compounds to be premixed is getting lower, so that organic compounds having dissimilar physical properties, in particular diverging melting points, can also be used for preparing a homogeneous composition. Accordingly, the method according to the invention is not limited to mixing organic compounds having similar physical properties, in particular regarding their melting points. Moreover, the application of vacuum accelerates the melting, so that the whole premixing process is speeded up. The temperature applied during the heating and rotating depends on several factors, i.e., the melting points of the organic compounds to be premixed, the vacuum level applied and the mixing proportion of the components. A person skilled in the art however knows which temperature level has to be set during the heating step in order to melt the vaporizable organic compounds to be premixed. Preferably, the temperature is set to 100-500°C under a vacuum level of 10^"5-10^"7 bar.

The rotation speed of the vessel during the heating and mixing is not particularly limited. To ensure proper mixing and homogenization of the melt, however, the rotation speed of the vessel is preferably set from 2 to 10 rpm, more preferably from to 4 to 8 rpm. If the rotation speed of the vessel during heating and mixing is within this range, the best mixing performance and mixing quality with respect to homogeneity is achieved within a reasonable timeframe.

In a still further preferred embodiment of the method according to the invention, the vessel containing the mixture of the at least two vaporizable organic compounds rotates about a rotational axis that is substantially horizontally disposed. In case of a vertical axis rotation, the gravity might hinder the uniformity of the mixture, as materials having a higher density will go down in the melt and materials having a lower density will go up. This gravity effect is much less pronounced in case of horizontal rotation and thus will not affect so much the mixture uniformity, so that a more thorough mixing is achieved.

"Substantially horizontally disposed" as used herein will be understood to mean that the rotational axis of the rotating vessel does not have to be strictly horizontally disposed, i.e. the deviating angle a of the rotational axis deviating from horizontal alignment where a = 0° may be other than zero. Preferably, a = < ±45°, more preferably < ±30°, even more preferably < ±20°. Particularly preferably, a = < 10°, and most preferably, a = 0°. The deviations from a = 0° do not disturb the performance of the mixing device. Upon cooling, the viscosity of the mixture will increase and the remaining melt may de-mix when solidification starts without rotating or stirring based on zone melting principles. As mentioned above, a conventional stirrer will eventually be blocked due to the increase of viscosity. In contrast, by using the rotatable vessel according to method of the invention, rotating and mixing can be performed even upon cooling of the mixture. Thus, it is preferred according to the method of the invention that the rotating is still performed during the cooling down period in order to prevent any de-mixing processes. Accordingly, in a preferred embodiment of the method according to the invention, said method further comprises the step of c. cooling the homogenized melt under rotation. Preferably, the premixed homogenized melt is cooled to room temperature, so that the homogeneous composition can be collected from the mixing chamber. The cooling rate and the cooling time is not particular limited. The cooling time may vary depending on the operation temperature. In the following, an exemplary rotatable mixing device capable for preparing a homogeneous composition according to the method of the invention is described with reference to Fig. 1 , which is however not to be considered as limiting for the scope of the invention. Similar devices have been reported in WO2015/022043 and details of the following description including

advantages of different embodiments can be reviewed form this source.

Fig. 1 is a schematic illustration of the rotatable mixing device used for premixing at least two vaporizable organic compounds according to the method of the invention. The mixing device comprises a heated oven (1 ), a mixing unit (2), a rotational coupling (3), and a high vacuum pump (4).

The oven (1 ) can be heated with any state of the art heating mechanism. Preferably indirect heating mechanisms are used, e.g. hot gas or air. The temperature may be controlled by any appropriate type, for example it may be a thermocouple, and may be controlled by a controller (not shown). The hot air in the oven is evenly distributed to avoid any hotspots with regards to the materials to be melted and premixed. For example, a stainless pan in front of the heater may be used to evenly distribute heat within the oven (1 ), which is even ensured under rotation. The oven may comprise a window for monitoring the melting behavior and controlling the heating temperature (not shown).

The connections between the units (2), (3), and (4) are typically sealed air- tight. The entire set-up is preferably horizontal (in Fig. 1 , a = 0°), though deviations from this angle do not disturb the performance of the mixing device, as described above. The mixing unit (2) is charged with the desired quantity of at least two different vaporizable organic materials. After the melting process, the generated premix can be isolated from the mixing unit (2). The material of the mixing unit (2) is not particularly limited. However, as transparent chambers are preferred to monitor melting behavior and control heating temperature, glassware is the most adapted material.

The rotational coupling (3) is a high vacuum driving source that drives the rotation of the mixing unit (2) while maintaining a high vacuum seal between the rotating part of the mixing unit (2) and the static part of the high vacuum pump (4). The direction of rotation, clockwise or counterclockwise, is of no influence to the efficiency of the mixing process. The drive source may be of any appropriate size, shape, configuration and/or type. For example, the drive source may be a commercially available rotation motor combined with a ferrofluidic seal.

A vacuum pump (4) of any appropriate type may be used to apply vacuum to the mixing unit (2). A cold trap (not shown) may be located near the vacuum pump (4) under high vacuum connections.

Other suitable rotatable mixing devices are also disclosed in

WO2015/022043.

It is also envisioned by the present invention that the rotatable mixing device is or is part of a vacuum deposition device or an evaporation system. In this case, the mixing unit (2) represents the evaporation source or boat and the homogenized melt is not cooled after premixing.

As mentioned above, the method according to the present invention allows for preparing compositions comprising at least two vaporizable organic compounds having high purity and homogeneity, wherein the homogeneity is defined by the standard deviation of the ratio of the compounds

comprised in the composition after premixing compared to the ratio of the compounds in the initial mixture.

Accordingly, the subject of the present invention is also a homogeneous composition comprising at least two vaporizable organic compounds obtainable or obtained by the method according to the invention. In particular, the resulting homogeneous composition is characterized in that the standard deviation σ of the ratio of the compounds after the premixing is smaller than 1 .0% compared to the initial ratio of the compounds (i.e.

compared to the ratio of these compounds in the initial mixture). For example, the standard deviation σ is smaller than 0.9%, 0.8%, 0.7%, 0.6% or 0.5%, more preferably smaller than 0.4%, even more preferably smaller than or 0.3%, and most preferably smaller than 0.2%. As described above, it is desirable that a composition for use in vacuum deposition methods is homogeneous in order to ensure uniform and consistent evaporation and deposition of the composition and to keep the ratio of the organic materials in the initial mixture in the resulting organic layer deposition, in particular in cases in which the composition is

evaporated from a single evaporation source to deposit a (multi)functional organic layer in an electronic device. As could be shown by the present inventors (see experimental part below), using the homogeneous

composition according to the present invention in the production process of an electronic device, preferably an organic electroluminescent (EL) device such as an organic light emitting diode (OLED), resulted in an improvement of the device performance in terms of lifetime and efficiency.

Accordingly, the object of the present invention is further achieved by the use of a homogeneous composition according to the present invention, or a homogeneous composition prepared according to the method of the present invention, for the preparation of an electronic device, preferably an organic electroluminescent (EL) device, by evaporating the composition from a single evaporation source.

In particular, depending on the vaporizable organic compounds selected for premixing, i.e. their functionality, the homogeneous composition of the present invention can be used to prepare (multi)functional organic layers of an electronic device, in particular an organic electroluminescent device, by evaporation deposition of said homogeneous composition using a single evaporation source.

Apart from cathode, anode and emitting layer, organic electroluminescent devices may also comprise further functional layers. These are selected, for example, from in each case one or more hole injection layers (HIL), hole transport layers (HTL), hole blocker layers (HBL), electron transport layers (ETL), electron injection layers (EIL), electron blocker layers, exciton blocker layers (EBL), interlayers, charge generation layers (IDMC 2003, Taiwan; Session 21 OLED (5), T. Matsumoto, T. Nakada, J. Endo, K. Mori, N. Kawamura, A. Yokoi, J. Kido, Multiphoton Organic EL Device Having Charge Generation Layer) and/or organic or inorganic p/n junctions. The present invention thus further relates to a layer obtainable by

evaporating a homogeneous composition according to the present invention, or a homogeneous composition prepared according to the method of the present invention, from a single evaporation source.

Preferably, the layer thus obtained is a functional organic layer within the organic light emitting structure of an organic electroluminescent device.

The sequence of the layers of an organic electroluminescent device, one or more of which layers may be applied by evaporation deposition using the inventive homogeneous composition, is preferably as follows: anode/hole injection layer/hole transport layer/optionally further hole transport layer/optionally electron blocker layer/emitting layer/optionally hole blocker layer/electron transport layer/electron injection layer/cathode. It is

additionally possible for further layers to be present in the organic

electroluminescent device.

Accordingly, the present invention also relates to an electronic device, preferably an organic electroluminescent (EL) device, comprising at least one layer obtainable by evaporation deposition of the inventive

homogeneous composition, or the homogeneous composition prepared according to the method of the present invention, using a single evaporation source, wherein the layer is preferably selected from the group consisting of electron transport layer (ETL), hole blocker layer (HBL), hole transport layer (HTL), electron blocker layer (EBL), hole injection layer (HIL) electron injection layer (EIL) and emissive layer (EML).

More preferably, the at least one layer is selected from an EML, an EIL or an ETL, most preferably it is an EML.

The electronic devices comprising the at least one layer obtainable by evaporation deposition of the inventive homogeneous composition, or the homogeneous composition prepared according to the method of the present invention, using a single evaporation source is preferably selected from organic light emitting diodes (OLEDs), polymer light emitting diodes

(PLEDs), organic light emitting transistors (OLETs), organic light emitting electrochemical cells (OLECs), organic field-quench devices (OFQDs), organic light emitting electrochemical transistors (OLEETs), organic field effect transistors (OFETs), thin film transistors (TFTs), organic solar cells (OSCs), organic laser diodes (O-lasers), organic integrated circuits (OICs), radio frequency identification (RFID) tags, photodetectors, sensors, logic circuits, memory elements, capacitors, charge injection layers, Schottky diodes, planarising layers, antistatic films, conducting substrates or patterns, photoconductors, electrophotographic elements, organic solar concentrators, organic spintronic devices, and an organic plasmon emitting devices (OPEDs), more preferably from OLETs, OLEDs, OLECs, OFQDs and O-lasers, and most preferably from OLEDs.

As mentioned before, the electronic device according to the present invention is characterized in that one or more layers are coated by a vacuum deposition process using a sublimation and condensation process. In this case, the premixed material composition is applied by vapour deposition in vacuum sublimation systems at an initial pressure of less than 10^"5 mbar, preferably less than 10^"6 mbar, using a single evaporation source. In this case, however, it is also possible that the initial pressure is even lower, for example less than 10^"7 mbar.

Preference is likewise given to an electronic device, characterized in that one or more layers are coated by the OVPD (organic vapour phase deposition) method or with the aid of a carrier gas sublimation. In this case, the premixed material composition is provided to a single evaporation source and applied at a pressure between 10^"5 mbar and 1 bar.

Therefore, the present invention also relates to a method for preparing an electronic device, preferably an OLET, OLED, OLEC, OFQD or O-laser, and most preferably an OLED, the method comprising:

a. providing a substrate,

b. preparing a homogeneous composition according to the method of the present invention, which comprises at least two vaporizable organic compounds; and

c. evaporating the homogeneous composition from a single evaporation source to form a layer on said substrate. The substrate is preferably an anode or cathode, the materials of which are known to the skilled person. In case more than one layers are to be applied by this method, steps b. and c. may optionally be repeated for each further layer. Accordingly, in this case the substrate can also be an already deposited layer.

For the evaporation of the homogeneous composition in step c, any vacuum deposition process known to those skilled in the art and described in literature may be used. The single evaporation source is heated for a sufficient time and at a sufficient temperature under vacuum to provide evaporation deposition of the organic compounds onto the surface of the substrate to form a (multi)functional layer. The person skilled in the art will be able, within the scope of his common knowledge in the art, to determine and set the conditions and parameter appropriate for evaporation.

The invention is described in more detail below with the help of examples which are not to be considered as limiting the scope of the invention.

Working examples

Materials

TMM-001 (WO 04/093207, WO 05/054403)

1 )

Both TMM-293 and TMM-310 can be purchased from Merck KGaA.

Preparation of premixed OLED material compositions

Homogeneous mixtures according to the present invention are prepared using the rotatable mixing device as describe above with reference to Fig. 1 .

For preparing the premixed compositions, each material which should be part of the homogeneous composition according to the present invention is weighted using a precision balance and put directly into the mixing chamber. Total weight of each mixture is 100 g. The mixing chamber is fitted to the rotatable mixing device. The mixing chamber is rotated at a rotation speed of 4 rpm and heated until 250 °C under a vacuum level 10^~5 bar. After melting, the rotating and mixing under these conditions is maintained for 2 h. When the mixing is finished, the mixture is allowed to cool down to room temperature under rotation. The obtained solidified homogeneous mixtures are collected by scratching out. Example 1 :

Preparation of Mixtures A1 , A2 and A3

Mixtures A1 , A2 and A3 are prepared according to the procedure of the present invention as described above by initially mixing vaporizable organic compounds TMM-001 (melting point 384 °C) and TMM-002 (melting point 305 °C) respectively in 1/3, 1/1 and 3/1 ratios. Total weight of each mixture is 100 g.

Example 2

Preparation of Mixtures B1 , B2 and B3

Mixtures B1 , B2 and B3 are prepared according to the procedure of the present invention as described above by initially mixing vaporizable organic compounds TMM-293 (melting point 343 °C) and TMM-310 (melting point 292 °C) respectively in 1/3, 1 /1 and 3/1 ratios. Total weight of each mixture is 100 g.

Comparative example 1

Preparation of Comparative Mixtures C1 , C2 and C3 Comparative mixtures C1 , C2 and C3 are prepared according to the procedure described in WO 2004/070787 by initially mixing vaporizable organic compounds TMM-001 and TMM-002 respectively in 1/3, 1/1 and 3/1 ratios. Total weight of each mixture is 100 g. Comparative example 2

Preparation of Comparative Mixtures D1 , D2 and D3

Comparative mixtures D1 , D2 and D3 are prepared according to the procedure described in WO 2004/070787 by initially mixing vaporizable organic compounds TMM-293 and TMM-310 respectively in 1/3, 1/1 and 3/1 ratios. Total weight of each mixture is 100 g. Example 3

Characterization of the Mixtures

Ten samples are collected from each of the above mixtures after premixing and analysed by high-performance liquid chromatography (HPLC). The weight of each sample analysed is 10 mg. The ratio of the compounds determined by HPLC for each sample is compared to the ratio of the compounds in the initial mixture. The homogeneity of each mixture is determined by the standard deviation (SD) σ.

The standard deviation (SD) σ is calculated using the following formula: _σ _ | (xi-m)² + (x₂-m)² + ---+(x_n-m)²

n-1 wherein m =—— -, x = data value, n is the number of samples.

The analytic results and σ are as shown in Tables 1 to 6.

Table 1. Analytic data for Mixture-A1 and Comparative Mixture-C1

Mixture- Sample Ratio determined by Mixtu re- Sample Ratio determined by A1 No. HPLC CI No. HPLC

TMM-001 TMM-002 TMM-001 TMM-002

A1 1 24.7 75.3 C1 1 24.5 75.5

A1 2 25.1 74.9 C1 2 24.2 75.8

A1 3 25.1 74.9 C1 3 23.8 76.2

A1 4 24.9 75.1 C1 4 26.0 74.0

Mixture-A1 , which is prepared according to the procedure of the present invention using a rotatable mixing device related to the present invention, is more homogeneous (SD = 0.18) than the comparative mixture-C1 (SD = 1 .22).

Table 2. Analytic data for Mixture-A2 and Comparative Mixture-C2

Mixture- Sample Ratio determined by Mixture- Sample Ratio determined by A2 No. HPLC C2 No. HPLC

TMM-001 TMM-002 TMM-001 TMM-002

A2 1 50.0 50.0 C2 1 51.1 48.9

A2 2 49.8 50.2 C2 2 52.0 48.0

A2 3 50.2 49.8 C2 3 47.7 52.3

A2 4 50.0 50.0 C2 4 50.4 49.6

A2 5 50.2 49.8 C2 5 48.0 52.0

A2 6 50.0 50.0 C2 6 53.2 46.8

A2 7 49.7 50.3 C2 7 50.0 50.0

A2 8 50.3 49.7 C2 8 52.9 47.1

A2 9 50.0 50.0 C2 9 48.3 51.7

A2 10 50.0 50.0 C2 10 51.9 48.1

Standard deviation 0.18 Standard deviation 2.02

(SD) (SD) Mixture-A2, which is prepared according to the procedure of the present invention using a rotatable mixing device related to the present invention, is more homogeneous (SD = 0.18) than the comparative mixture-C2 (SD = 2.02).

Table 3. Analytic data for Mixture-A3 and Comparative Mixture-C3

Mixture-A3, which is prepared according to the procedure of the present invention using a rotatable mixing device related to the present invention, is more homogeneous (SD= 0.10) than the comparative mixture-C3 (SD = 1 .60).

Table 4. Analytic data for Mixture-B1 and Comparative Mixture-D1

Mixture- Sample Ratio determined by Mixture- Sample Ratio determined by

B1 No. HPLC D1 No. HPLC

TMM-293 TMM-310 TMM-293 TMM-310

B1 1 24.9 75.1 D1 1 25.0 75.0

Mixture-B1 , which is prepared according to the procedure of the present invention using a rotatable mixing device related to the present invention, is more homogeneous (SD = 0.07) than the comparative mixture-D1 (SD = 1 .21 ).

Table 5. Analytic data for Mixture-B2 and Comparative Mixture-D2

Mixture- Sample Ratio determined by Mixture- Sample Ratio determined by

B2 No. HPLC D2 No. HPLC

TMM-293 TMM-310 TMM-293 TMM-310

B2 1 50.0 50.0 D2 1 47.8 52.2

B2 2 50.0 50.0 D2 2 49.0 51.0

B2 3 51.3 48.7 D2 3 53.1 46.9

B2 4 50.2 49.8 D2 4 52.9 47.1

B2 5 50.0 50.0 D2 5 51.1 48.9

B2 6 49.8 50.2 D2 6 46.9 53.1

B2 7 50.0 50.0 D2 7 50.5 49.5

B2 8 48.7 51.3 D2 8 48.9 51.1

B2 9 50.0 50.0 D2 9 47.1 52.9

B2 10 50.0 50.0 D2 10 49.5 50.5

Mixture-B2, which is prepared according to the procedure of the present invention using a rotatable mixing device related to the present invention, is more homogeneous (SD = 0.62) than the comparative mixture-D2 (SD = 2.21 ).

Table 6. Analytic data for Mixture-B3 and Comparative Mixture-D3

Mixture-B3, which is prepared according to the procedure of the present invention using a rotatable mixing device related to the present invention, more homogeneous (SD = 0.12) than the comparative mixture-D3 (SD = 1 .47).

Accordingly, all mixtures prepared according to the procedure of the present invention using a rotatable mixing device as described before are more homogeneous compared with mixtures prepared according to the prior art, irrespective of the mixing ratio and whether the vaporizable organic compounds premixed have dissimilar melting points. Example 4

Device examples

OLED devices are prepared according to the following process:

The substrates used are glass plates coated with structured ITO (indium tin oxide) in a thickness of 50 nm. The OLEDs basically have the following layer structure: substrate / hole-injection layer (HIL) / hole-transport layer (HTL) / emission layer (EML) / electron-transport layer (ETL) / electron-injection layer (EIL) and finally a cathode. The cathode is formed by an aluminium layer with a thickness of 10Onm.

All materials are evaporated by thermal vapour deposition in a vacuum chamber. The emission layer always consists of premixed host material according to the invention and an emitting dopant (emitter). Analogously, other layers may also consist of a mixture of two or more materials.

The OLEDs are characterized by standard methods.

The data for the various OLEDs containing inventive and comparative materials are summarized in Table 13.

Table 7. Device data for OLEDs

C1 48.5 48

C2 45.0 49

C3 46.2 45

D1 53.3 58

D2 54.0 59

D3 59.7 57

OLEDs comprising the homogeneous mixtures obtained from the method according to the invention (A1 , A2, A3, B1 , B2, B3) in the emission layer exhibit both higher efficiencies [Cd/A] and also improved lifetimes [h] compared with OLEDs comprising mixtures premixed according to the prior art (C1 , C2, C3, D1 , D2, D3).

Claims

Claims

Method for preparing a homogeneous composition, in particular a composition capable of being vacuum deposited, which comprises at least two vaporizable organic compounds, said method comprising: a. providing a rotatable vessel containing said at least two

vaporizable organic compounds,

b. heating the vessel to form a melt and simultaneously rotating the vessel in a continuous manner to homogenize the melt.

Method according to claim 1 , wherein the at least two vaporizable organic compounds are independently from each other selected from the group consisting of host or matrix materials, emissive materials, electron injection materials, electron transport materials, electron blocking materials, wide band gap materials, hole injection materials, hole transport materials, hole blocking materials, exciton blocking materials, n-dopants or p-dopants, and any combination thereof.

Method according to claim 1 or 2, wherein the at least two vaporizable organic compounds are host materials.

Method according to claim 1 or 2, wherein the at least two vaporizable organic compounds are electron transport materials.

Method according to claim 1 or 2, wherein the at least two vaporizable organic compounds are hole transport materials.

Method according to claim 1 or 2, wherein one of the at least two vaporizable organic compounds is a host material, preferably a host material having electron-transporting properties or a host material having hole-transporting properties, most preferably a host material having electron-transporting properties, and the other one is a wide band gap material. Method according to claim 1 or 2, wherein one of the at least two vaporizable organic compounds is an electron transport material and the other one is a n-dopant.

Method according to claim 1 or 2, wherein one of the at least two vaporizable organic compounds is a hole transport material and the other one is a p-dopant.

Method according to one or more of claims 1 to 8, wherein the heating and rotating are performed under a reduced pressure of 10^~3 to 10^~8 bar.

Method according to one or more of claims 1 to 9, wherein the heating and rotating of the vessel is maintained for at least 1 h after the melt is formed.

1 1 . Method according to one or more of claims 1 to 10, wherein a rotation speed of the vessel is from 2 to 10 rpm. 2. Method according to one or more of claims 1 to 1 1 , wherein the vessel rotates about a rotational axis that is substantially horizontally disposed.

13. Method according to one or more of claims 1 to 12, said method

further comprising c. cooling the homogenized melt obtained in step b under rotation.

14. Homogeneous composition comprising at least two vaporizable

organic compounds obtainable or obtained by the method according to one or more of claims 1 to 13.

Use of a homogeneous composition according to claim 14 or prepared according to a method according to one or more of claims 1 to 13 for the preparation of an electronic device by evaporating the composition from a single evaporation source. Layer obtainable by evaporating a homogeneous composition according to claim 14 or prepared according to a method according to one or more of claims 1 to 13 from a single evaporation source.

Electronic device comprising at least one layer according to claim 16, wherein the layer is preferably selected from the group consisting of electron-transport layer (ETL), hole-blocking layer (HBL), hole- transport layer (HTL), electron-blocking layer (EBL), hole injection layer (HIL) electron injection layer (EIL) and emissive layer (EML).

Electronic device according to claim 17, wherein the device is selected from organic light emitting diodes (OLEDs), polymer light emitting diodes (PLEDs), organic light emitting transistors (OLETs), organic light emitting electrochemical cells (OLECs), organic field-quench devices (OFQDs), organic light emitting electrochemical transistors (OLEETs), organic field effect transistors (OFETs), thin film transistors (TFTs), organic solar cells (OSCs), organic laser diodes (O-lasers), organic integrated circuits (OICs), radio frequency identification (RFIDs) tags, photodetectors, sensors, logic circuits, memory elements, capacitors, charge injection layers, Schottky diodes, planarising layers, antistatic films, conducting substrates or patterns, photoconductors, electrophotographic elements, organic solar concentrators, organic spintronic devices, and an organic plasmon emitting devices (OPEDs).

Method for preparing an electronic device according to claim 17 or 18, the method comprising:

a. providing a substrate,

b. preparing a homogeneous composition according to a method according to one or more of claims 1 to 13, which comprises at least two vaporizable organic compounds; and

c. evaporating the homogeneous composition from a single

evaporation source to form a layer on said substrate.