Method for forming an organic electroluminescence (EL) element with annealing temperatures for different pixels
11081679 · 2021-08-03
Assignee
Inventors
- Hsin-Rong Tseng (Wiesbaden, DE)
- Thorsten Schenk (Glashuetten, DE)
- Peter Levermore (Darmstadt, DE)
- Anja Jatsch (Frankfurt am Main, DE)
Cpc classification
H10K71/00
ELECTRICITY
H10K71/40
ELECTRICITY
International classification
Abstract
The present invention relates to a method for forming an organic EL element having at least one pixel type comprising at least three different layers including a hole injection layer (HIL), a hole transport layer (HTL) and an emission layer (EML), characterized in that the HIL, the HTL and the EML of at least one pixel type are obtained by depositing inks wherein the layers are annealed after said depositing steps in a first, second and third annealing step and the difference of the annealing temperature of the first and of the second annealing step is below 35° C., preferably below 30° C., more preferably below 25° C. and the annealing temperature of the third annealing step is no more than 5° C. above the annealing temperature of the first and/or the second annealing step, preferably the annealing temperature of the third annealing step is equal to or below the annealing temperature of the first and the second annealing step, wherein the first annealing step is performed before the second annealing step and the second annealing step is performed before the third annealing step.
Claims
1. A method for forming an organic electroluminescent (EL) element comprising at least two different pixel types including a first pixel type and a second pixel type, each comprising at least three different layers including a hole injection layer (HIL), a hole transport layer (HTL) and an emission layer (EML), wherein the HIL and the HTL of the first and the second pixel types and the EML of at least one pixel type are obtained by depositing an ink and at least one layer of both pixel types at the same time, annealing the HIL, HTL and EML in a first, second and third annealing step at a first, second or third annealing temperature, wherein the first annealing temperature and the second annealing temperature differ by less than 35° C., and the third annealing temperature is no more than 5° C. above the first and/or the second annealing temperature, wherein the first annealing step is performed before the second annealing step and the second annealing step is performed before the third annealing step.
2. The method according to claim 1, wherein the annealing temperature of the first and of the second annealing step differ by less than 25° C.
3. The method according to claim 2, wherein the ink to form the HIL comprises at least 50% by weight of one or more organic solvent.
4. The method according to claim 2, wherein the EL element has three different pixel types including a first pixel type, a second pixel type and a third pixel type, and wherein the HTL of the second pixel type and the third pixel type are formed by depositing ink, drying and annealing at the same time wherein the annealing step is performed at an annealing temperature T2.
5. The method according to claim 1, wherein the organic EL element has at least three different pixel types wherein the HIL and the HTL of all pixel types and the EML of at least one pixel type are obtained by depositing an ink and at least one layer of all pixel types is deposited by applying an ink at the same time.
6. The method according to claim 1, wherein all pixel types include a HIL, and wherein the HIL of all pixel types is formed by depositing ink, drying and annealing at the same time, and wherein the annealing step is performed at an annealing temperature T1.
7. The method according to claim 1, wherein the HTL of the first pixel type and the EML of the second pixel type are formed by depositing ink, drying and annealing at the same time wherein the annealing step is performed at an annealing temperature T3.
8. The method according to claim 1, wherein the first annealing temperature is at least 180° C.
9. The method according to claim 1, wherein the second annealing temperature is at least 180° C.
10. The method according to claim 1, wherein the third annealing temperature is at least 120° C.
11. The method according to claim 1, wherein the first annealing temperature is at most 250° C.
12. The method according to claim 1, wherein the second annealing temperature is at most 250° C.
13. The method according to claim 1, wherein the third annealing temperature is at most 200° C.
14. The method according to claim 1, wherein at least one layer is crosslinked during the annealing step.
15. The method according to claim 1, wherein in a first step a HIL is formed, in a second step a HTL is formed and in a third step a EML is formed wherein the HIL is formed before the HTL and the HTL is formed before the EML.
16. The method to claim 1, comprising drying the ink before the annealing, and wherein drying is performed under reduced pressure.
17. The method according to claim 1, wherein depositing comprises inkjet printing at least one layer.
18. The method according to claim 1, further comprising depositing a common layer by vacuum deposition technique.
19. An electronic device, obtained by the method according to claim 1.
20. The method according to claim 1, wherein the annealing temperature of the third annealing step is equal to or below the annealing temperature of the first and the second annealing step.
Description
(1) The present invention also relates to an electronic device obtainable by a method according to the present invention.
(2) In
(3) The present invention furthermore relates to an electronic device having at least one functional layer comprising at least one organic functional material which is obtainable by the above-mentioned process for the production of an electronic device.
(4) An electronic device is taken to mean a device comprising two electrodes and at least one functional layer in between, where this functional layer comprises at least one organic or organometallic compound.
(5) The organic electronic device is preferably an organic electroluminescent device (OLED), a polymeric electroluminescent device (PLED), an organic light-emitting transistor (O-LET), a light-emitting electrochemical cell (LEC) or an organic laser diode (O-laser).
(6) Active components are generally the organic or inorganic materials which are introduced between the anode and the cathode, where these active components effect, maintain and/or improve the properties of the electronic device, for example its performance and/or its lifetime, for example charge-injection, charge-transport or charge-blocking materials, but in particular emission materials and matrix materials. The organic functional material which can be employed for the production of functional layers of electronic devices accordingly preferably comprises an active component of the electronic device.
(7) Organic electroluminescent devices (OLEDs) are a preferred embodiment of the present invention. The OLED comprises a cathode, an anode and at least one emitting layer.
(8) It is furthermore preferred to employ a mixture of two or more triplet emitters together with a matrix. The triplet emitter having the shorter-wave emission spectrum serves as co-matrix here for the triplet emitter having the longer-wave emission spectrum.
(9) The proportion of the matrix material in the emitting layer in this case is preferably between 50 and 99.9% by volume, more preferably between 80 and 99.5% by volume and most preferably between 92 and 99.5% by volume for fluorescent emitting layers and between 70 and 97% by volume for phosphorescent emitting layers.
(10) Correspondingly, the proportion of the dopant is preferably between 0.1 and 50% by volume, more preferably between 0.5 and 20% by volume and most preferably between 0.5 and 8% by volume for fluorescent emitting layers and between 3 and 15% by volume for phosphorescent emitting layers.
(11) An emitting layer of an organic electroluminescent device may also encom-pass systems which comprise a plurality of matrix materials (mixed-matrix systems) and/or a plurality of dopants. In this case too, the dopants are generally the materials whose proportion in the system is the smaller and the matrix materials are the materials whose proportion in the system is the greater. In individual cases, however, the proportion of an individual matrix material in the system may be smaller than the proportion of an individual dopant.
(12) The mixed-matrix systems preferably comprise two or three different matrix materials, particularly preferably two different matrix materials. One of the two materials here is preferably a material having hole-transporting properties or a wide-band-gap material and the other material is a material having electron-transporting properties. However, the desired electron-transporting and hole-transporting properties of the mixed-matrix components may also be combined principally or completely in a single mixed-matrix component, where the further mixed-matrix component(s) fulfil(s) other functions. The two different matrix materials may be present here in a ratio of 1:50 to 1:1, preferably 1:20 to 1:1, more preferably 1:10 to 1:1 and most preferably 1:4 to 1:1. Mixed-matrix systems are preferably employed in phosphorescent organic electroluminescent devices. Further details on mixed-matrix systems can be found, for example, in WO 2010/108579.
(13) Apart from these layers, an organic electroluminescent device may also comprise further layers, for example in each case one or more hole-injection layers, hole-transport layers, hole-blocking layers, electron-transport layers, electron-injection layers, exciton-blocking layers, electron-blocking layers, 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. It is possible here for one or more hole-transport layers to be p-doped, for example with metal oxides, such as MoO.sub.3 or WO.sub.3, or with (per)fluorinated electron-deficient aromatic compounds, and/or for one or more electron-transport layers to be n-doped. It is likewise possible for interlayers, which have, for example, an exciton-blocking function and/or control the charge balance in the electroluminescent device, to be introduced between two emitting layers. However, it should be pointed out that each of these layers does not necessarily has to be present.
(14) The thickness of the layers, for example the hole-transport and/or hole-injection layer, can preferably be in the range from 1 to 500 nm, more preferably in the range from 2 to 200 nm.
(15) In a further embodiment of the present invention, the device comprises a plurality of layers. The ink according to the present invention can preferably be employed here for the production of a hole-transport, hole-injection, electron-transport, electron-injection and/or emission layer.
(16) The present invention accordingly also relates to an electronic device which comprises at least three layers, but in a preferred embodiment all said layers, from hole-injection, hole-transport, emission, electron-transport, electron-injection, charge-blocking and/or charge-generation layer and in which at least one layer has been obtained by means of an ink to be employed in accordance with the invention.
(17) The device may furthermore comprise layers built up from further low-molecular-weight compounds or polymers which have not been applied by the use of inks. These can also be produced by evaporation of low-molecular-weight compounds in a high vacuum.
(18) It may additionally be preferred to use the compounds to be employed not as the pure substance, but instead as a mixture (blend) together with further polymeric, oligomeric, dendritic or low-molecular-weight substances of any desired type. These may, for example, improve the electronic or emission properties of the layer.
(19) In a preferred embodiment of the present invention, the organic electroluminescent device here may comprise one or more emitting layers. If a plurality of emission layers are present, these preferably have a plurality of emission maxima between 380 nm and 750 nm, resulting overall in white emission, i.e. various emitting compounds which are able to fluoresce or phosphoresce are used in the emitting layers. Very particular preference is given to three-layer systems, where the three layers exhibit blue, green and orange or red emission (for the basic structure see, for example, WO 2005/011013). White-emitting devices are suitable, for example, as backlighting of LCD displays or for general lighting applications.
(20) It is also possible for a plurality of OLEDs to be arranged one above the other, enabling a further increase in efficiency with respect to the light yield to be achieved.
(21) In order to improve the out-coupling of light, the final organic layer on the light-exit side in OLEDs can, for example, also be in the form of a nano-foam, resulting in a reduction in the proportion of total reflection.
(22) In a specific embodiment of the present invention, a common layer is deposited by vacuum deposition technique. Common layer means a layer which is applied for all the different pixel types. Preferably, the common layer being deposited by vacuum deposition technique comprises a light emitting material.
(23) Preference is furthermore given to an OLED in which one or more layers are applied by means of a sublimation process, in which the materials are applied by vapour deposition in vacuum sublimation units at a pressure below 10.sup.−5 mbar, preferably below 10.sup.−6 mbar, more preferably below 10.sup.−7 mbar.
(24) It may furthermore be provided that one or more layers of an electronic device according to the present invention are applied by means of the OVPD (organic vapour phase deposition) process or with the aid of carrier-gas sublimation, in which the materials are applied at a pressure between 10.sup.−5 mbar and 1 bar.
(25) It may furthermore be provided that one or more layers of an electronic device according to the present invention are produced from solution, such as, for example, by spin coating, or by means of any desired printing process, such as, for example, screen printing, flexographic printing or offset printing, but particularly preferably LITI (light induced thermal imaging, thermal transfer printing) or inkjet printing.
(26) An orthogonal solvent can preferably be used here, which, although dissolving the functional material of a layer to be applied, does not dissolve the layer to which the functional material is applied.
(27) The device usually comprises a cathode and an anode (electrodes). The electrodes (cathode, anode) are selected for the purposes of the present invention in such a way that their band energies correspond as closely as possible to those of the adjacent, organic layers in order to ensure highly efficient electron or hole injection.
(28) The cathode preferably comprises metal complexes, metals having a low work function, metal alloys or multilayered structures comprising various metals, such as, for example, alkaline-earth metals, alkali metals, main-group metals or lanthanoids (for example Ca, Ba, Mg, Al, In, Mg, Yb, Sm, etc.). In the case of multilayered structures, further metals which have a relatively high work function, such as, for example, Ag, can also be used in addition to the said metals, in which case combinations of the metals, such as, for example, Ca/Ag or Ba/Ag, are generally used. It may also be preferred to introduce a thin interlayer of a material having a high dielectric constant between a metallic cathode and the organic semiconductor. Suitable for this purpose are, for example, alkali-metal or alkaline-earth metal fluorides, but also the corresponding oxides (for example LiF, Li.sub.2O, BaF.sub.2, MgO, NaF, etc.). The layer thickness of this layer is preferably between 0.1 and 10 nm, more preferably between 0.2 and 8 nm, and most preferably between 0.5 and 5 nm.
(29) The anode preferably comprises materials having a high work function. The anode preferably has a potential greater than 4.5 eV vs. vacuum. Suitable for this purpose are on the one hand metals having a high redox potential, such as, for example, Ag, Pt or Au. On the other hand, metal/metal oxide electrodes (for example Al/Ni/NiO.sub.x, Al/PtO.sub.x) may also be preferred. For some applications, at least one of the electrodes must be transparent in order to facilitate either irradiation of the organic material (O—SCs) or the coupling-out of light (OLEDs/PLEDs, 0-lasers). A preferred structure uses a transparent anode. Preferred anode materials here are conductive, mixed metal oxides. Particular preference is given to indium tin oxide (ITO) or indium zinc oxide (IZO). Preference is furthermore given to conductive, doped organic materials, in particular conductive, doped polymers, such as, for example, poly(ethylenedioxythiophene) (PEDOT) and polyaniline (PANI) or derivatives of these polymers. It is furthermore preferred for a p-doped hole-transport material to be applied as hole-injection layer to the anode, where suitable p-dopants are metal oxides, for example MoO.sub.3 or WO.sub.3, or (per)fluorinated electron-deficient aromatic compounds. Further suitable p-dopants are HAT-CN (hexacyanohexaazatriphenylene) or the compound NPD9 from Novaled. A layer of this type simplifies hole injection in materials having a low HOMO energy, i.e. an HOMO energy with a large negative value.
(30) In general, all materials which are used for the layers in accordance with the prior art can be used in the further layers of the electronic device.
(31) The electronic device is correspondingly structured in a manner known per se, depending on the application, provided with contacts and finally hermetically sealed, since the lifetime of such devices is drastically shortened in the presence of water and/or air.
(32) The inks useful for the present invention and the electronic devices, in particular organic electroluminescent devices, obtainable therefrom are distinguished over the prior art by one or more of the following surprising advantages: 1. The electronic devices obtainable using the methods according to the present invention exhibit very high stability and a very long lifetime compared with electronic devices obtained using conventional methods. 2. The electronic devices obtainable using the methods according to the present invention exhibit a high efficiency, especially a high luminance efficiency and a high external quantum efficiency. 3. The inks useful for the present invention can be processed using conventional methods, so that cost advantages can also be achieved thereby. 4. The organic functional materials employed in the methods according to the present invention are not subject to any particular restrictions, enabling the process of the present invention to be employed compre-hensively. 5. The layers obtainable using the methods of the present invention exhibit excellent quality, in particular with respect to the uniformity of the layer. 6. The inks useful for the present invention can be produced in a very rapid and easy manner using conventional methods, so that cost advantages can also be achieved thereby.
(33) These above-mentioned advantages are not accompanied by an impair-ment of the other electronic properties.
(34) It should be pointed out that variations of the embodiments described in the present invention fall within the scope of this invention. Each feature disclosed in the present invention can, unless this is explicitly excluded, be replaced by alternative features which serve the same, an equivalent or a similar purpose. Thus, each feature disclosed in the present invention is, unless stated otherwise, to be regarded as an example of a generic series or as an equivalent or similar feature.
(35) All features of the present invention can be combined with one another in any way, unless certain features and/or steps are mutually exclusive. This applies, in particular, to preferred features of the present invention. Equally, features of non-essential combinations can be used separately (and not in combination).
(36) It should furthermore be pointed out that many of the features, and in particular those of the preferred embodiments of the present invention, are themselves inventive and are not to be regarded merely as part of the embodiments of the present invention. For these features, independent pro-tection can be sought in addition or as an alternative to each invention presently claimed.
(37) The teaching on technical action disclosed in the present invention can be abstracted and combined with other examples.
(38) The invention is explained in greater detail below with reference to working examples, but without being restricted thereby.
WORKING EXAMPLES
Example 1
(39) A device having only a blue pixel is produced having a blue emission layer which is obtained by a vacuum deposition process. The thickness of the cathode is 100 nm, the thickness of the ETL is 20 nm, the thickness of the blue common layer is 25 nm, the thickness of the blue HTL (B-HTL) is 40 nm, the thickness of the HIL is 30 nm, the thickness of the ITO anode is 50 nm.
(40) The used ink set 1 has the following features:
(41) TABLE-US-00001 Concentration Viscosity Surface tension Layer Ink code (g/L) (cp) (mN/m) HIL MBL3- 16 3.6 33 6300 B-HTL MHL3- 8.5 3.3 33 2973 The inks used, are commercially available products of Merck KGaA
(42) The following devices are obtained by the following annealing temperatures
(43) TABLE-US-00002 LT95 at Anneal Temperature EQE (%) @ 1,000 (° C.) ∧max @ 10000 cd/m.sup.2 Device T1 T2 T3 (nm) cd/m.sup.2 (hrs) remark A 180 210 200 na na na No emission B 180 230 150 447 7.23 69 Spots in the devices C 180 210 150 447 7.45 216 D 200 210 150 447 7.54 286 E 200 200 150 447 7.09 425 F 200 190 150 447 6.89 495 G 200 180 150 447 6.42 592 Very good lifetime
(44) These data clearly show that Device A does not provide an acceptable performance, while Device B has a low performance. The other devices have a good or excellent performance.
(45) The measurements of Amax (nm), EQE (%)@1000 cd/m.sup.2 and LT95@1,000 cd/m.sup.2 (hrs) are achieved with the following methods:
(46) The devices are driven with constant voltage provided by a Keithley 230 voltage source. The voltage over the device as well as the current through the device are measured with two Keithley 199 DMM multimeters. The brightness of the device is detected with a SPL-025Y brightness sensor, a combination of a photodiode with a photonic filter. The photo current is measured with a Keithley 617 electrometer. For the spectra, the brightness sensor is replaced by a glass fiber which is connected to the spectrometer input. The device lifetime is measured under a given current with an initial luminance. The luminance is then measured over time by a calibrated photodiode.
Example 2
(47) A device as mentioned in
(48) TABLE-US-00003 Red Green Blue Cathode (AI) 100 nm 100 nm 100 nm ETL 20 nm 20 nm 20 nm BCL 25 nm 25 nm 25 nm EML 60 nm 60 nm — HTL 20 nm 20 nm 40 nm HIL 60 nm 30 nm 30 nm Anode (ITO) 50 nm 50 nm 50 nm
(49) The used ink set 1 has the following features:
(50) Ink Set 1
(51) TABLE-US-00004 Ink set 1 Concentration Viscosity Surface tension Layer Ink code (g/L) (cp) (mN/m) HIL MBL3- 16 3.6 33 6300 RG-HTL MHL3- 5.5 6 38 1484 B-HTL MHL3- 8.5 3.3 33 2973 G-EML MRE3- 19.5 4.7 38 2502 R-EML MRE3- 15.5 4.6 38 4067 The inks used, are commercially available products of Merck KGaA
(52) The device is prepared as mentioned as follows:
(53) Glass substrates covered with pre-structured ITO and bank material were cleaned using ultrasonication in isopropanol followed by de-ionized water, then dried using an air-gun and a subsequent annealing on a hot-plate at 230° C. for 2 hours.
(54) HIL inks were printed and vacuum dried. The HIL was then annealed at 210° C. for 30 minutes in air.
(55) On top of the HIL for green and red devices, green and red hole-transport layer (G-HTL and R-HTL) was inkjet-printed, dried in vacuum and annealed at 210° C. for 30 minutes in nitrogen atmosphere.
(56) For green and red devices, the green and red emissive layer (G-EML and R-EML) were also inkjet-printed, vacuum dried and annealed at 140° C. for 10 minutes in nitrogen atmosphere. For blue device, the blue hole-transport layer (B-HTL) was inkjet-printed, vacuum dried and annealed at 140° C. for 10 minutes in nitrogen atmosphere.
(57) All inkjet printing processes were performed under yellow light and under ambient conditions.
(58) The devices were then transferred into a vacuum deposition chamber where the deposition of a common blue emissive layer (BCL), an electron-transport layer (ETL), electron injection layer (EIL) and a cathode (Al) was done using thermal evaporation (see
(59) In the ETL, ETM-1 was used as a hole-blocking material. The material has the following structure:
(60) ##STR00026##
(61) In the electron transport layer (ETL) a 50:50 mixture of ETM-1 and LiQ was used. LiQ is lithium 8-hydroxyquinolinate.
(62) Finally, the Al electrode is vapor-deposited. The devices were then encapsulated in a glove box and physical characterization was performed in ambient air.
(63) The following performance is measured using the methods mentioned above.
(64) Device Performance:
(65) TABLE-US-00005 LT80 at EQE (%) @ 1,000 Anneal Temperature (° C.) ∧max @ 1000 cd/m.sup.2 Device T1 T2 T3 (nm) cd/m.sup.2 (hrs) R 210 210 140 621 16.8 4,700 G 210 210 140 520 17 20,500 B 210 210 140 448 8 740
Example 3
(66) Example 2 is essentially repeated but the following ink set is used:
(67) Ink Set 2
(68) TABLE-US-00006 Ink set 2 Concentration Viscosity Surface tension Layer Ink code (g/L) (cp) (mN/m) HIL MBL3- 16 3.6 33 1156 RG-HTL MHL3- 7 4.4 33 6989 B-HTL MHL3- 11 3.4 33 1927 G-EML MGE3- 20 4.7 38 9186 R-EML MRE3- 20 4.7 38 3846 The inks used, are commercially available products of Merck KGaA
(69) The following performance is measured using the methods mentioned above.
(70) Device Performance:
(71) TABLE-US-00007 LT80 at EQE (%) @ 1,000 Anneal Temperature (° C.) ∧max @ 1000 cd/m.sup.2 Device T1 T2 T3 (nm) cd/m.sup.2 (hrs) R 225 225 150 621 16.5 20,000 G 225 225 150 520 17 40,000 B 225 225 180 448 8.2 1,000
(72) The person skilled in the art will be able to use the descriptions to produce further inks and electronic devices according to the present invention without the need to employ inventive skill and thus can carry out the invention throughout the claimed range.