A SOLID POLYMER COMPOSITION, A SELF-SUPPORTING FILM AND A LIGHT EMITTING DEVICE

Abstract

The invention refers in a first aspect to self-supporting film comprising green luminescent crystals (1), red luminescent crystals (2), and a polymer (3). The green luminescent crystals (1) are perovskite crystals. The red luminescent crystals (2) are zincblende or wurzite, preferably zincblende, crystals. A second aspect of the invention refers to a solid polymer composition (100). A third aspect of the invention refers to a light emitting device comprising either the solid polymer composition (100) or the self-supporting film.

Claims

1. A self-supporting film comprising green luminescent crystals red luminescent crystals, and a polymer, wherein the green luminescent crystals are perovskite crystals selected from compounds of formula (I):
[M.sup.1A.sup.1].sub.aM.sup.2.sub.bX.sub.c(I), wherein: A.sup.1 represents one or more organic cations, in particular formamidinium (FA), M.sup.1 represents one or more alkaline metals, in particular Cs, M.sup.2 represents one or more metals other than M1, in particular Pb, X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfides, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M.sup.1, or A.sup.1, or M.sup.1 and A.sup.1 being present; wherein the red luminescent crystals are zincblende or wurzite, preferably zincblende, crystals selected from compounds of formula (II)
[M.sup.3M.sup.3][YY](II), wherein: M.sup.3, M.sup.3 represent Al, Ga, In, in particular In and Y, Y represent N, P, As, Sb, in particular P and M.sup.3, Y may or may not be present, or M.sup.3, M.sup.3 represent Zn, Cd, Be in particular Cd, and Y, Y represent S, Se, Te in particular Se, and M.sup.3, Y may or may not be present, and wherein a concentration of M.sup.2 is 5-200 mg/m.sup.2, preferably 10-100 mg/m.sup.2, very preferably 20-80 mg/m.sup.2.

2. The self-supporting film according to claim 1, wherein a concentration of M.sup.3+M.sup.3 is 30-250 mg/m.sup.2.

3. The self-supporting film according to claim 1, having a haze h.sub.1 of 10?h.sub.1?80%.

4. The self-supporting film according to ne claim 1, comprising scattering particles selected from the group consisting of metal oxide particles and polymer particles.

5. The self-supporting film according to claim 1, wherein the solid polymer composition is sandwiched between two barrier layers.

6. The self-supporting film according to claim 1, wherein the green luminescent crystals are perovskite crystals of formula (I):
FAPbBr.sub.3(I).

7. The self-supporting film according to claim 1, wherein the red luminescent crystals are of the core-shell type, wherein the core is as defined in formula (II) and wherein the shell comprises compounds of formula (III)
M.sup.4Z(III), wherein: M.sup.4 represents Zn or Cd, preferably Zn, and Z represents S, Se, Te, and wherein compounds of formula (III) and formula (II) differ.

8. The self-supporting film according to claim 1, wherein the red luminescent crystals comprise a core selected from the group consisting of InP and CdSe, and comprise a shell or a multishell selected from the group consisting of ZnS, ZnSe, ZnSeS, and ZnTe, and combinations thereof.

9. The self-supporting film according to claim 1, wherein the polymer comprises an acrylate.

10. The self-supporting film according to claim 1, wherein the green luminescent crystals are arranged in a first region of the self-supporting film and the red luminescent crystals are arranged in a second region of the self-supporting film.

11. A solid polymer composition, comprising green luminescent crystals, red luminescent crystals, and a polymer, wherein the green luminescent crystals are perovskite crystals selected from compounds of formula (I):
[M.sup.1A.sup.1].sub.aM.sup.2.sub.bX.sub.c(I), wherein: A.sup.1 represents one or more organic cations, in particular formamidinium (FA), M.sup.1 represents one or more alkaline metals, in particular Cs, M.sup.2 represents one or more metals other than M1, in particular Pb, X represents one or more anions selected from the group consisting of halides, pseudohalides and sulfides, in particular Br, a represents 1-4, b represents 1-2, c represents 3-9, and wherein either M.sup.1, or A.sup.1, or M.sup.1 and A.sup.1 being present; wherein the red luminescent crystals are zincblende or wurzite, preferably zincblende, crystals selected from compounds of formula (II)
[M.sup.3M.sup.3][YY](II), wherein: M.sup.3, M.sup.3 represent Al, Ga, In, in particular In and Y, Y represent N, P, As, Sb, in particular P and M.sup.3, Y may or may not be present, or M.sup.3, M.sup.3 represent Zn, Cd, Be in particular Cd, and Y, Y represent S, Se, Te in particular Se, and M.sup.3, Y may or may not be present and wherein the concentration of M.sup.2 is 100-1000 ppm, preferably 300-1000 ppm, very preferably 500-1000 ppm.

12. The solid polymer composition according to claim 11, wherein the green luminescent crystals are perovskite crystals of formula (I):
FAPbBr.sub.3(I).

13. The solid polymer composition according to claim 11, wherein the red luminescent crystals are of the core-shell type, and wherein the shell comprises compounds of formula (III)
M.sup.4Z(III), wherein: M.sup.4 represents Zn or Cd, preferably Zn, and Z represents S, Se, Te, and wherein compounds of formula (III) and formula (II) differ.

14. The solid polymer composition according to claim 11, wherein the red luminescent crystals comprise a core selected from the group consisting of InP and CdSe, and comprise a shell or a multishell selected from the group consisting of ZnS, ZnSe, ZnSeS, and ZnTe, and combinations thereof.

15. The solid polymer composition according to claim 11, wherein the concentration of M.sup.3+M.sup.3 is 300-2500 ppm, preferably 600-2000 ppm, very preferably 1200-1700 ppm, and/or the red core-shell quantum dots have a platelet structure.

16. The solid polymer composition according to claim 11, wherein the polymer has a molar ratio of the sum of (oxygen+nitrogen) to carbon z, wherein z?0.9, z?0.75 in particular z?0.4.

17. The solid polymer composition according to claim 11, wherein the polymer comprises an acrylate.

18. The solid polymer composition according to claim 11, wherein the solid polymer composition has a glass transition temperature T.sub.g of T.sub.g?120? C.

19. The solid polymer composition according to claim 11, wherein the solid polymer composition comprises scattering particles selected from the group consisting of metal oxide particles and polymer particles.

20. A light emitting device, in particular a liquid crystal display (LCD), comprising the self-supporting film according to claim 1.

21. The light emitting device according to claim 20 comprising an array of more than one blue LED, wherein the array of LEDs covers essentially the full liquid crystal display area, and wherein a diffusor plate is arranged between the array of more than one blue LED and the self-supporting film.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0103] The invention will be better understood and objects other than those set forth above will become apparent from the following detailed description thereof.

[0104] Such description makes reference to the annexed drawings, wherein:

[0105] FIG. 1 shows a schematic of a solid polymer composition according to an embodiment of the invention;

[0106] FIG. 2 shows a schematic of a self-supporting film according to an embodiment of the invention;

[0107] FIG. 3 shows a light emitting device according to an embodiment of the invention; and

[0108] FIG. 4 shows a schematic of a self-supporting film according to a further advantageous embodiment of the invention.

MODES FOR CARRYING OUT THE INVENTION

[0109] Embodiments, examples, experiments representing or leading to embodiments, aspects and advantages of the invention will be better understood from the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:

[0110] FIG. 1 shows a schematic of a solid polymer composition 100 according to an embodiment of the first aspect, wherein the solid polymer composition comprises green luminescent crystals 1 of formula (I), red luminescent crystals 2 of formula (II), and a polymer 3.

[0111] Further embodiments of the solid polymer composition in FIG. 1 might comprise further features according to the first aspect of the invention.

[0112] FIG. 2 shows a schematic of an embodiment of a self-supporting film according to the second aspect of the invention. In an advantageous embodiment as demonstrated in the figure, the self-supporting film might comprise barrier layers 4 that sandwich the solid polymer composition 100.

[0113] FIG. 3 shows a schematic of an embodiment of a light emitting device, in particular a liquid crystal display (LCD) according to the third aspect of the invention. Advantageously, the light emitting device comprises a solid polymer composition 100 as shown in FIG. 1 or a self-supporting film as shown in FIG. 2. Advantageously, the light emitting device comprises more than one blue LED 6, wherein the LEDs covers essentially the full liquid crystal display area 5. In particular, a diffusor plate is arranged between the array of more than one blue LED and the self-supporting film (the diffusor plate is not shown in the figure).

[0114] In particular, the light emitting device might emit light in RGB colours (aa, bb, cc).

[0115] FIG. 4 shows a further advantageous embodiment of the self-supporting film according to the second aspect of the invention. The green luminescent crystals 1 in this embodiment are arranged in a first region 11 of the self-supporting film. The red luminescent crystals 2 are arranged in a second region 21 of the self-supporting film.

[0116] The first region 11 and the second region 21 form layers adjacent to each other.

EXPERIMENTAL SECTION

Example 1: Preparation of a Self-Supporting Film with a Polymer Having a Low Glass Transition Temperature and Low Haze

[0117] Green perovskite luminescent crystals with composition formamidinium lead tribromide (FAPbBr.sub.3) are synthesized in toluene as following: Formamidinium lead tribromide FAPbBr.sub.3) was synthesized by milling PbBr.sub.2 and FABr. Namely, 16 mmol PbBr.sub.2 (5.87 g, 98% ABCR, Karlsruhe (DE)) and 16 mmol FABr (2.00 g, Greatcell Solar Materials, Queanbeyan, (AU)) were milled with Yttrium stabilized zirconia beads (5 mm diameter) for 6 h to obtain pure cubic FAPbBr.sub.3, confirmed by XRD. The orange FAPbBr.sub.3 powder was added to Oleylamine (80-90, Acros Organics, Geel (BE)) (weight ratio FAPbBr.sub.3:Oleylamine=100:15) and toluene (>99.5%, puriss, Sigma Aldrich). The final concentration of FAPbBr.sub.3 was 1 wt %. The mixture was then dispersed by ball milling using yttrium stabilized zirconia beads with a diameter size of 200 ?m at ambient conditions (if not otherwise defined, the atmospheric conditions for all experiments are: 35? C., 1 atm, in air) for a period of 1 h yielding an ink with green luminescence.

[0118] Film formation: 0.1 g of the green ink was mixed with an UV curable monomer/crosslinker mixture (0.7 g FA-513AS, Hitachi Chemical, Japan/0.3 g Miramer M240, Miwon, Korea) containing 1 wt % photoinitiator Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TCI Europe, Netherlands) and 2 wt % polymeric scattering particles (Organopolysiloxane, ShinEtsu, KMP-590) and red luminescent crystals being isometric core-shell QDs having an InP core and a ZnS shell suspended in toluene in a speed mixer and the toluene was evaporated by vacuum (<0.01 mbar) at room temperature. The resulting mixture was then coated with 50 micron layer thickness on a 100 micron barrier film (supplier: I-components (Korea); Product: TBF-1007), then laminated with a second barrier film of the same type. Afterwards the laminate structure was UV-cured for 60 s (UVAcube100 equipped with a mercury lamp and quartz filter, Hoenle, Germany). The concentration of Pb in the cured layer (without the barriers) was 500 ppm Pb and the Pb loading per area was 30 mg Pb/m.sup.2. The concentration of In in the cured layer (without the barriers) was 1300 ppm In and the In loading per area was 80 mg In/m.sup.2. The initial performance of the as obtained film showed a green emission wavelength of 526 nm with a FWHM of 22 nm and a red emission wavelength of 630 nm with a FWHM of 20 nm. The color coordinates (CIE1931) of the film were x=0.25 and y=0.20 when placed on a blue LED light source (450 nm emission wavelength) with two crossed prism sheets (X-BEF) and one brightness enhancement film (DBEF) on top of the QD film (optical properties measured with a Konica Minolta CS-2000). The haze of the obtained film was 50% and the transmittance was 85% (measured with BYK Gardner haze meter). The light conversion factor of the film was 49% (LCF; LCF=emitted green intensity (integrated emission peak) divided by the reduction of the blue intensity (integrated emission peak); measured with perpendicular emission of green and blue from the QD film by using a Konica Minolta CS-2000). The glass transition temperature Tg of the UV-cured solid polymer composition was determined by DSC according to DIN EN ISO 11357-2:2014-07 with a starting temperature of ?90? C. and an end temperature of 250? C. and a heating rate of 20 K/min in nitrogen atmosphere (20 ml/min). The purging gas was nitrogen (5.0) at 20 ml/min. The DSC system DSC 204 F1 Phoenix (Netzsch) was used. The T.sub.g was determined on the second heating cycle (the first heating from ?90? C. to 250? C. showed overlaying effects besides the glass transition). For the DSC measurement, the solid polymer composition was removed from the film by delaminating the barrier films. The measured Tg of the UV-cured resin composition was 75? C.

[0119] The stability of the film was tested for 150 hours under blue LED light irradiation by placing the film into a light box with high blue intensity (supplier: Hoenle; model: LED CUBE 100 IC) with a blue flux on the film of 410 mW/cm.sup.2 at a film temperature of 50? C. Furthermore the film was also tested for 150 hours in a climate chamber with 60? C. and 90% relative humidity. The change of optical parameters after stability testing of the film for was measured with the same procedure as for measuring the initial performance (described above). The change of optical parameters were as following:

TABLE-US-00001 x-value y-value Luminanance test condition () () (%) initial 0.25 0.20 100% 150 h 0.24 0.19 95% high flux (410 mW/cm.sup.2) 150 h 0.235 0.19 93% 60? C./90% r.H.
These results show that a self-supporting luminescent film could be obtained whereby the green perovskite crystals and red core-shell quantum dots both show a good chemical compatibility and high stability when tested under high blue flux and high temperature/humidity.

[0120] Comparative example 1 for example 1: Preparation of a self-supporting film with a polymer having a low glass transition temperature and high haze.

[0121] The procedure was the same as in the previous procedure in example 1, except the following parameters were changed: [0122] Only 50% of the green perovskite QDs and the red core-shell InP quantum dots were used [0123] 12 wt % scattering particles KMP-590 were mixed into the UV curable acrylate mixture to increase the haze of the final QD film.

[0124] The as-obtained self-supporting film showed similar optical properties and Tg as in example 1 but with a haze of 95%, a transmittance of 80% and an LCF of 41%.

[0125] It can be seen that the LCF is lower than in experiment 1. A higher haze leads to a lower LCF and a lower haze leads to a higher LCF. Therefore, a lower haze of the QD film is beneficial to have a higher LCF and in turn a higher display efficiency (at specific comparable white point colour coordinates).

[0126] The concentration of Pb in the cured layer (without the barriers) was 250 ppm Pb and the Pb loading per area was 15 mg Pb/m.sup.2. The concentration of In in the cured layer (without the barriers) was 650 ppm In and the In loading per area was 40 mg In/m.sup.2.

[0127] The same stability tests were done again as in example 1 and the change of optical parameters were as following:

TABLE-US-00002 x-value y-value Luminanance test condition () () (%) initial 0.25 0.20 100% 150 h 0.24 0.17 75% high flux (410 mW/cm.sup.2) 150 h 0.235 0.19 93% 60? C./90% r.H.

[0128] These results show that a higher haze of the QD film leads to lower stability of the green perovskite crystals under high blue flux (decrease of green intensity as seen by the decrease of the y-value) compared to example 1, especially the green perovskite crystals are less stable under high blue flux. Therefore, it is advantageous to have a low haze of the QD film which leads to improved QD film stability under high blue flux in order to have stable colour coordinates and a stable white point during the operating lifetime of the display device.

[0129] Comparative example 2 for example 1: Preparation of a self-supporting film with a polymer having a high glass transition temperature and low haze.

[0130] The procedure was the same as in the procedure of example 1, except the acrylate monomer mixture (0.7 g FA-513AS, Hitachi Chemical, Japan/0.3 g Miramer M240, Miwon, Korea) was replaced by the following acrylate monomer mixture: [0131] 0.7 g FA-DCPA, Hitachi Chemical, Japan/0.3 g FA-320M, Hitachi Chemical, Japan

[0132] The as-obtained self-supporting film showed similar optical properties and haze as in example 1 but with a Tg of 140? C.

[0133] The concentration of Pb and In in the cured layer (without the barriers) was the same as in example 1.

[0134] The same stability tests were done again as in example 1 and the change of optical parameters were as following:

TABLE-US-00003 x-value y-value Luminanance test condition () () (%) initial 0.25 0.20 100% 150 h 0.24 0.15 52% high flux (410 mW/cm.sup.2) 150 h 0.235 0.19 94% 60? C./90% r.H.

[0135] These results show that a high T.sub.g of the solid polymer of the self-supporting film leads to lower stability of the green perovskite crystals under high blue flux (decrease of green intensity as seen by the decrease of the y-value) compared to example 1. Therefore it is advantageous to have a low T.sub.g of the QD film which leads to improved QD film stability under high blue flux in order to have stable colour coordinates and a stable white point during the operating life-time of the display device.

Example 2: Preparation of a Self-Supporting Film with a Low Haze and Whereby the Red Core-Shell Quantum Dots and the Green Perovskite Crystals are Spatially Separated

[0136] The green perovskite QDs were used from example 1.

[0137] Film formation: 0.1 g of the green ink from example 1 was mixed with an UV curable monomer/crosslinker mixture (0.7 g FA-513AS, Hitachi Chemical, Japan/0.3 g Miramer M240, Miwon, Korea) containing 1 wt % photoinitiator Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TCI Europe, Netherlands) and 2 wt % polymeric scattering particles (Organopolysiloxane, ShinEtsu, KMP-590) in a speed mixer and the toluene was evaporated by vacuum (<0.01 mbar) at room temperature. The resulting mixture was then coated with 50 micron layer thickness on a 100 micron barrier film (supplier: I-components (Korea); Product: TBF-1007), then UV cured in a nitrogen atmosphere. Then a red coating formulation was prepared by mixing the red core-shell quantum dots with InP core and ZnS shell from experiment 1 (suspended in toluene) with an UV curable monomer/crosslinker mixture (0.7 g FA-DCPA, Hitachi Chemical, Japan/0.3 g Miramer M240, Miwon, Korea) containing 1 wt % photoinitiator Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TCI Europe, Netherlands) and 2 wt % polymeric scattering particles (Organopolysiloxane, ShinEtsu, KMP-590) in a speed mixer and the toluene was evaporated by vacuum (<0.01 mbar) at room temperature. The resulting mixture was then coated with 50 micron layer thickness on the previously deposited green layer, then a second barrier film was laminated on top and the total sandwich structure was UV-cured for 60 s (UVAcube100 equipped with a mercury lamp and quartz filter, Hoenle, Germany).

[0138] The final self-supporting film showed optical properties comparable to experiment 1.

[0139] The concentration of Pb in the cured green layer (without the barriers) was 500 ppm Pb and the Pb loading per area was 30 mg Pb/m2. The concentration of In in the cured red layer (without the barriers) was 1300 ppm In and the In loading per area was 80 mg In/m.sup.2.

[0140] The change of optical parameters were as following:

TABLE-US-00004 x-value y-value Luminanance test condition () () (%) initial 0.25 0.20 100% 150 h 0.24 0.19 95% high flux (410 mW/cm.sup.2) 150 h 0.24 0.19 96% 60? C./90% r.H.

[0141] These results show that a self-supporting luminescent film could be obtained with a separated green layer and red layer whereby the green perovskite crystals and red core-shell quantum dots both show a high stability when tested under high blue flux and high temperature/humidity.

Example 3: Preparation of a Self-Supporting Film as in Example 1 but with Red Core-Shell Quantum Dot Platelets with a CdSe Core and a ZnS Shell

[0142] The same experimental procedure was used as described in example 1, but with red core-shell quantum dot platelets with a CdSe core and a ZnS shell.

[0143] The concentration of Pb in the cured layer (without the barriers) was 500 ppm Pb and the Pb loading per area was 30 mg Pb/m.sup.2. The concentration of Cd in the cured layer (without the barriers) was 500 ppm Cd and the Cd loading per area was 30 mg Cd/m.sup.2.

[0144] The result was an optical performance and stability comparable to example 1.

Example 4: Preparation of a Self-Supporting Film as in Example 2 but with Red Core-Shell Quantum Dot Platelets with a CdSe Core and a ZnS Shell

[0145] The same experimental procedure was used as described in example 2, but with red core-shell quantum dot platelets with a CdSe core and a ZnS shell.

[0146] The result was an optical performance and stability comparable to example 2.