ELECTRONIC ELEMENT AND DISPLAY

Abstract

The present invention relates inter alia to a color display comprising nanoparticles and color filters.

Claims

1. Electronic element comprising a) a pixelated organic electroluminescent device 100 comprising a first 101, a second 102, and a third 103 light emitting pixel that are identical, but that are electronically controlled separately. b) a first color converter layer 201 disposed in the light output path 151 of the first pixel 101, wherein the color converter layer 201 comprises at least one light emitting semiconducting nanoparticle acting as first color converter; c) a first color filter layer 301 disposed in the light output path 251 of the first color converter layer 201 comprising a first color filter.

2. The electronic element according to claim 1, characterized in that the first color filter layer 301 comprises a red color filter as first color filter and the first color converter layer 201 comprises a red light emitting semiconducting nanoparticle as first color converter.

3. The electronic element according to claim 1, characterized in that a second color filter layer 302 comprising a second color filter is disposed in the light output path of the second pixel 102, preferably the second color filter is a green color filter.

4. The electronic element according to claim 1, characterized in that a third color filter layer 303 comprising a third color filter is disposed in the light output path of the third pixel 103, preferably the third color filter is a blue color filter.

5. The electronic element according to claim 1, characterized in that the first color filter and the first color converter are located in the same layer as first combined layer 501.

6. The electronic element according to claim 1, characterized in that the display comprises a fourth pixel 104.

7. The electronic element according to claim 1, characterized in that the pixels of the pixelated organic electroluminescent device emit white light.

8. The electronic element according to claim 1, characterized in that the device comprises in the light output path 152 of the second pixel 102 between the second pixel 102 and the second color filter layer 302 a second color converter layer 202 comprising a second color converter, preferably the second color converter is a light emitting semiconducting nanoparticle, very preferably the second color converter emits green light.

9. The electronic element according to claim 8, characterized in that the first color converter layer 201 and the second color converter layer 202 are represented by a single common color converter layer 212 being disposed in the light output paths of the first 101 and the second 102 pixel, wherein the common color converter layer 212 comprises a composition of the first color converter and the second color converter.

10. The electronic element according to claim 1, characterized in that the organic electroluminescent device emits blue light.

11. The electronic element according to claim 1, characterized in that the device comprises a common color filter layer 523 in the light output paths of the second 152 and a third 153 pixel, wherein the common color filter layer comprises a composition of the second and third color filter.

12. The electronic element according to claim 1, characterized in that the organic electroluminescent device emits bluish-green light.

13. The electronic element according to claim 1, characterized in that the concentration of the light emitting semiconducting nanoparticle in the first, second or third color converter layer is in the range between 10 mg/m.sup.2 and 1 g/m.sup.2, preferably between 20 mg/m.sup.2 and 500 mg/m.sup.2, very preferably between 50 mg/m.sup.2 and 300 mg/m.sup.2 and particularly preferably between 100 mg/m.sup.2 and 200 mg/m.sup.2.

14. The electronic element according to claim 1, characterized in that the light emitting semiconducting nanoparticle(s) is(are) selected from quantum dots, core shell type quantum dots, quantum rods, core shell type quantum rods and combinations thereof.

15. The electronic element according to claim 1, characterized in that the light emitting semiconducting nanoparticle(s) is(are) selected from InGaP, CdSe, CdS, CdTe, ZnO, ZnSe, ZnS, ZnTe, HgSe, HgTe, CdZnSe, InP, InN, GaN, InSb, InAsP, InGaAs, GaAs, GaP, GaSb, AlP, AlN, AlAs, AlSb, CdSeTe, ZnCdSe, PbSe, PbTe, PbS, PbSnTe, and Tl.sub.2SnTe.sub.5 and combinations thereof.

16. The electronic element according to claim 1, characterized in that the color filters are selected from dyes and pigments.

17. The electronic element according to claim 1, characterized in that the device further comprises a planarization layer 150 between the pixelated organic electroluminescent device 100 and the color converter layer(s) or if no color converter layer is present between the pixelated organic electroluminescent device 100 and the color filter layer(s).

18. Color display comprising at least one of the electronic elements according to claim 1.

19. The color display according to claim 18, characterized in that the color display comprises a TFT backplane 600.

20. A method for generating red emission which comprises incorporating a red light emitting semiconducting nanoparticle in combination with a red color filter in color displays comprising organic electroluminescent devices.

21. Layer comprising at least one red light emitting semiconducting nanoparticle and at least one red color filter.

22. Method for the preparation of the electronic element according to claim 1, characterized in that the color converter layer comprising the quantum rod, core shell type quantum rod or combination thereof is, at least in part, oriented, preferably by oriented deposition or by stretching before it is deposited onto the pixelated organic electroluminescent device.

23. Electronic element obtainable according to the method of claim 22.

Description

BRIEF DESCRIPTION OF THE FIGURES:

[0114] FIG. 1 depicts in a) and b) different arrangements of an electronic device according to the present invention. The electronic device comprises an organic electroluminescent device 100 comprising a first pixel 101, a second pixel 102, a third pixel 103 and optionally a fourth pixel 104. The pixels emit the same light, but are electronically controlled separately. The device comprises in the light output path of the first pixel 151 a color converter layer 201 comprising a first light emitting semiconducting nanoparticle. In the light output path 251 of the first color converter layer 201 the electronic device further comprises a first color filter layer 301. The first color filter layer 301 finally emits light 351. The light output paths of the second 102, third 103 and fourth 104 pixels are denoted by 152, 153 and 154, respectively. Light emitted to the outside of the electronic devices either by the pixels directly or by color filter layers is denoted by 351, 352, 353 and 354. In b) a second color filter layer 302 and a third color filter layer 303 are disposed in the light output paths of the second pixel 102 and the third pixel 103, respectively.

[0115] FIG. 2 shows an electronic device according to the present invention wherein the first color converting light emitting semiconducting nanoparticle and the first color filter are employed as composition in a single layer 501.

[0116] FIG. 3 shows another electronic device according to the present invention wherein a second color converter layer 202 is disposed in the light output path 152 of the second pixel 102. The second color filter layer 302 is disposed in the light output path 252 of the color converter layer 202.

[0117] FIG. 4 shows a pixelated device according to the present invention having a common color converter layer 212 for the first and second pixel

[0118] FIG. 5 shows another electronic device according to the present invention wherein a common color filter layer 523 is disposed in the light output paths 152 and 153 of the second and third pixel 102 and 103.

[0119] FIG. 6 depicts an example of a full color display comprising a pixelated tandem OLED as white light emitting organic electroluminescent device 100, wherein the numbers have the following meaning: 201—first color converter layer comprising at least one red light emitting semiconducting nanoparticle; 301—first color filter which is a red color filter; 302—second color filter which is a green color filter; 303—third color filter which is a blue color filter; 10—cathode layer for the first second, third and (optional) fourth pixel; 20—electron transport layer (ETL) for the first, second, third and fourth pixel; 30—red/green or yellow light emitting emissive layer for the first, second, third and fourth pixel; 40—hole transport layer (HTL) for the first, second, third and fourth pixel; 50—charge generation layer for the first, second, third and fourth pixel; 60—blue light emitting emissive layer for the first, second, third and fourth pixel; 70—hole transport layer (HTL) for the first, second, third and fourth pixel; 90—anode (e.g. ITO) for the first, second, third and fourth pixel; 150—planarization layer; 600—TFT backplane:oxide, LTPS (low temperature polycrystalline silicon); 700—glass.

[0120] FIG. 7 shows the electroluminescence spectrum of the white OLED used in Example 3.

[0121] FIG. 8 shows transmission spectrum of the red color filter used in Example 3.

WORKING EXAMPLES

Example 1

[0122] Preparation of Light Emitting Semiconducting Nanoparticles

[0123] Preparation of CdSe Cores for red light emitting nanorods: A 3 neck flask containing 0.06 g cadmium oxide, 0.28 g octadecyl-phosphonic acid (ODPA) and 3 g of trioctylphosphine oxide (TOPO) is degassed at 150° C. for an hour and a half. The selenium precursor is prepared in a glove box by dissolving 58 mg of elemental Se in 0.36 g of tri-n-octylphosphine (TOP) in a 20 mL vial. 1.5 g of TOP are put in a second vial. After degassing, the flask is flushed with argon, and heated to about 300° C., when an optical clarity is achieved. At this point 1.5 g TOP is slowly injected into the flask. The flask is further heated to 350° C., at which point, the TOP:Se is quickly injected into the flask. The reaction time depends on the desired size of the cores. The reaction is stopped by removing the heating source. The cores are dissolved and precipitated by 1:1 toluene:methanol mixture. In this first step, CdSe cores with diameter of 3.4 nm are synthesized.

[0124] Preparation of CdSe/CdS Red Light Emitting Nanorods: A 3 neck flask containing 0.12 g cadmium oxide, 0.16 g hexaphosphonic acid (HPA), 0.56 g octadecylphosphonic acid (ODPA) and 3 g of trioctylphosphine oxide (TOPO) is degassed at 150° C. for an hour and a half. The sulfur precursor is prepared dissolving 0.12 g of elemental Sulfur in 1.5 g of tri-n-octylphosphine (TOP) in a 20 mL vial. 1.5 g of TOP are put in a second vial. The required amount of cores depends on the desired length of the nanorods. For 23 nm long rods, 2.3*10.sup.−7 mol of CdSe are needed. After the sulfur has dissolved, the TOP:S is poured onto the purified cores and mixed until complete dissolvent of the cores is achieved. After degassing, the flask is flushed with argon and heated to about 300° C., when an optical clarity is achieved. At this point 1.5 g TOP is slowly injected into the flask. The flask is further heated to 360° C., at which point, the TOP:S:CdSe is quickly injected into the flask. The reaction is allowed to stand for 8 minutes. The reaction is stopped by removing the heating source. The resulting nanorods synthesized using the CdSe cores with diameter of 3.4 nm described above have dimensions of 23×7 nm with an emission maximum at 628 nm and full width halve maximum (FWHM) of 24 nm when measured in a toluene solution.

Example 2

[0125] Preparation and Characterisation of Color Converting Films

[0126] Films which are not stretched are prepared following similar procedures to those disclosed in WO 2011/092646 (LIGHTING DEVICES WITH PRESCRIBED COLOUR EMISSION). Two different films are prepared, one scattering (called QFilm2) and one non-scattering (called QFilm1). The preparation of the nanorods used for preparing the films is described above.

[0127] Preparation of the Non-Scattering Film (QFilm1):

[0128] A nanorod solution is prepared. For this, a certain amount of nanorods is added to 4 ml toluene. The amount is chosen so that when the solution is diluted 50 times, an optical density of 0.27 for a 10 mm path quartz cuvette at is obtained at 450 nm. Next, 1.1 g of of Poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB), available e.g. from Sigma-Aldrich, is dissolved in 15 ml toluene. 25% of this PVB solution is added to the nanorod solution while stirring. The resulting solution of nanorods and PVB is placed on a 6 cm by 6 cm glass plate, inserted into a dessicator and vacuumed for 15 hours after which the mixture is solid and the resulting film can be removed from the glass plate.

[0129] Preparation of the Scattering Film (QFilm2):

[0130] The scattering film (QFilm2) is prepared in the same way with the exception that an additional 55 mg of BaSO4 is added to the PVB solution. The Quantum Yield of the films is measured with a Hamamatsu Quantaurus QY C11347-11 and a value of 63% is obtained for the non-scatterring film, 66% for the scattering film. The optical density of the non-scattering film is measured using a Shimadzu UV-1800 spectrophotometer and a value of 1.28 is obtained.

[0131] Stretched films (called QFilm3) are prepared following the procedures described in WO 2012/059931, (POLARIZING LIGHTING SYSTEMS, Example 1) with a stretching ratio of 4. The films before stretching are prepared following the same procedure as describe above for the non-scattering film. The polarization ratio is obtained by dividing the intensity of the emission polarized parallel to the stretching axis by the emission perpendicular to the stretching axis. The stretched films of the example exhibit a polarization ratio of 2.7. The Quantum Yield of the films is measured with a Hamamatsu Quantaurus QY C11347-11 and a value of 64% is obtained. The optical density of the films is measured using Shimadzu UV-1800 spectrophotometer and a value of 0.75 is obtained.

Example 3

[0132] Device Fabrication and Characterization

[0133] Determination of Performance Data:

[0134] The current efficiency (in cd/A) is calculated from the luminance and the current density. The luminance is measured in forward direction with a calibrated photodiode. Electroluminescence spectra are recorded for a luminance of 1000 cd/m.sup.2. CIE 1931 x and y color coordinates are calculated from these spectra. The external quantum efficiency (EQE, measured in percent) is calculated under the assumption of lambertian emission from a measurement of the current efficiency, voltage and the electroluminescence spectra for 1000 cd/m.sup.2.

[0135] For the following examples, a white emitting OLED is used. The electroluminescence spectrum is shown in FIG. 7. The OLED has an EQE of 29.3%.

[0136] As comparative example according to the state of the art, a red color filter (Lee Filter 106, “Primary red”) is put on the OLED. The transmission spectrum of the filter is shown in FIG. 8. As immersion oil between the OLED and the filter, C.sub.14H.sub.12O.sub.2 is used. The resulting device shows red emission, CIE 1931 color coordinates x=0.67, y=0.32 and an EQE of 4.7%.

[0137] As inventive example, a film containing nanorods (QFilm) is put between the color filter and the OLED. C.sub.14H.sub.12O.sub.2 is applied as immersion oil between the OLED and the QFilm and between the QFilm and the red color filter.

[0138] If the non scattering QFilm1 is used, the EQE increases to 7.1% which corresponds to a 50% improvement compared to the state of the art. The color coordinates of this device are x=0.68, y=0.32 and thus virtually identical to that of the device from the comparative example.

[0139] If the scattering QFilm2 is used, the EQE increases to 8.0% which corresponds to a 70% improvement. The color coordinates of this device are x=0.68, y=0.32 and thus almost identical to that of the device from the comparative example.

[0140] If the stretched, non scattering QFilm3 is used, the EQE increases to 5.8% which corresponds to an improvement of about 20%. The color coordinates of this device are x=0.68, y=0.32 and thus almost identical to that of the device from the comparative example.

[0141] If two instead of one QFilm3 are used and immersion oil is applied between the two films, the EQE increases to 6.3% which corresponds to an improvement of 35%. The color coordinates of this device are x=0.68, y=0.32 and thus virtually identical to that of the device from the comparative example.