Compositions comprising quantum dots

Abstract

A composition is provided, including one or more quantum dots and at least one organic emitter. Further, a formulation including the composition, a use of the formulation and a device comprising the composition or formulation is provided.

Claims

1. An electroluminescent device comprising a light emitting layer consisting of one type of quantum dot and one type of organic emitter, wherein said organic emitter is a phosphorescent, non-conjugated polymeric compound that includes at least one unit comprising a host compound, and a metal complex, the metal selected from a transition, a rare earth, a lanthanide, or an actinide metal, and the concentration of the quantum dots in the composition is in a range from 0.1 to 20 wt %; wherein the quantum dot is selected from the group consisting of CdSe, CdS, CdTe, ZnSe, ZnS, ZnTe, alloys thereof, combinations thereof, core/shell structures thereof, and core multi-shell layered structures thereof, with a trioctylphosphine oxide coating the surface of the quantum dot; wherein the one organic emitter is a phosphorescent, non-conjugated polymer that includes a repeat unit selected from formula (77) or (78) ##STR00034## wherein X and Y are independently selected from H, F, an alkyl group with 1 to 40 carbon atoms, an alkenyl group with 2 to 40 carbon atoms, an alkynyl group with 2 to 40 carbon atoms, a substituted or unsubstituted aryl group with 6 to 40 carbon atoms, and a substituted or unsubstituted heteroaryl group, wherein the heteroaryl group has 5 to 25 ring members.

2. The electroluminescent device of claim 1, wherein the metal is selected from the group consisting of Ir, Ru, Os, Eu, Au, Pt, Cu, Zn, Mo, W, Rh, Pd, and Ag.

3. The electroluminescent device of claim 1, wherein the one quantum dot has an emission wavelength that is longer than the emission wavelength of said at least one organic emitter.

4. The electroluminescent device of claim 1 further comprising at least one organic functional material selected from a host material, hole transport material, hole injection material, hole blocking material, electron transport material, electron injection material, electron blocking material, and emitter material, wherein said at least one organic functional material is selected from the group consisting of small molecules, conjugated polymers, non-conjugated polymers, oligomers, and dendrimers.

5. The electroluminescent device of claim 1, wherein said phosphorescent, non-conjugated polymeric compound includes at least one further organic functional group selected from a host material, hole transport material, hole injection material, electron transport material, and electron injection material.

6. The electroluminescent device of claim 1, wherein said electroluminescent device is a light emitting diode comprising an anode, a cathode, and the light emitting layer, wherein the emitting layer is positioned between said anode and said cathode.

7. The electroluminescent device of claim 1, wherein said electroluminescent device emits either white light or emits in at least one wavelength range chosen from the blue wavelength range, the green wavelength range, the red wavelength range, and the infrared wavelength range.

8. The device of claim 1, wherein the non-conjugated polymer further includes a repeat unit selected from the group consisting of formulae (79) to (92) ##STR00035## ##STR00036## wherein R.sup.1 to R.sup.4 are independently from each other selected from H, F, an alkyl group with 1 to 40 carbon atoms, an alkenyl group with 2 to 40 carbon atoms, an alkinyl group with 2 to 40 C-atoms, a substituted or unsubstituted aryl group with 6 to 40 carbon atoms, and a substituted or unsubstituted heteroaryl group, wherein the heteroaryl group has 5 to 25 ring members.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The FIGURE: Absorption spectrum of QD1, electroluminescence spectra of OLED1 to OLED4, and photoluminescence spectrum of QD1.

WORKING EXAMPLES

Example 1

(2) Materials

(3) The following materials can be used in the present invention as examples.

(4) ##STR00028## ##STR00029##

(5) The polymer P1 can be synthesized by radical polymerization of the corresponding monomers in the given ratio.

(6) ##STR00030##

(7) The monomers are dissolved in 200 ml dry toluene and degassed with argon. The reaction is started by adding AlBN as initiator. The reaction mixture is then heated to 75 C. for 16 hours and is stopped by adding 10 ml methanol. The solvent is removed in the vacuum and the residue is dissolved in THF. The polymer is isolated by precipitation in methanol and dry in vacuum.

(8) ##STR00031##

(9) The synthesis of P2 is described in detail in DE 102009023154.4.

(10) ##STR00032##

(11) The synthesis of polymer P3 is described in detail in DE 102010006377.0. Interlayer polymer P4

(12) ##STR00033##

(13) The polymer P4 is synthesized by Suzuki coupling as disclosed in WO 03/048225.

(14) Red quantum dot QD1 is a core-shell type quantum-dot which can be purchased from Plasmachem GmbH, Berlin, Germany. QD1 has a CdSe spherical core capped with epitaxial ZnS shell. QD1 has a hydro-phobic surface layer comprising of mostly trioctylphosphine oxide. The emission maximum of QD1 is 630 nm+/5 nm. The emission FWHM of QD1 is smaller than 35 nm and its core diameter is approximately 5.4 nm.

Example 2

(15) OLED Preparation from Solution

(16) OLEDs with the layer structure:1. cathode; 2. EML; 3. Interlayer; 4. HIL; 5. ITO) using corresponding solutions shown in Table 1, are prepared according to the following procedure: 1. Deposition of 80 nm PEDOT (Baytron P AI 4083) as HIL onto an ITO coated glass substrate by spin coating; 2. Deposition of 20 nm interlayer by spin coating from toluene solution of P4 having a concentration of 0.5% wt/l in glovebox; 3. Heating interlayer at 180 C. for 1 hour in glovebox; 4. Deposition of the EML from a solution to a desired thickness by using doctor blade technique (dip-coating may also be used here); the materials for EMLs, the corresponding solutions and the thickness of EMLs are listed in Table 1. The different thickness for EML for different colors is mainly due to the cavity effect. The optimal thickness for blue is found to be 65 nm, for green and red the optimal thickness is 80 nm. Spin-coating is not the optimal method to coat EML, because the quantum dots are much heavier than other organic compounds, most of them may be lost by the centrifugal force during the spin-coating; 5. Heating the device to remove residual solvent; the heating conditions are listed in Table 1. The different conditions result from the different glass transition temperatures T.sub.9 or different melting points T.sub.m of the EML materials. Heat-treatment shouldn't lead to re-crystallization in EML; 6. Deposition of a Ba/Al cathode (3 nm/150 nm) over the emissive layer by vacuum thermal evaporation; 7. Encapsulation of the device using an UV cured resin.

(17) TABLE-US-00001 TABLE 1 EML materials and process parameters EML Conc. Heating thickness Composition for EML [wt %] Solvent [mg/ml] [min/ C.] [nm] OLED1 40% TMM1:40% TMM2:20% TEG1 T 24 10/180 80 QD-LED1 30% TMM1:30% TMM2:20% TEG1:20% QD1 T 24 10/180 80 OLED2 P1 T 24 60/140 80 QD-LED2 80% P1:20% QD1 T 24 60/140 80 OLED3 80% P2:20% TEG1 T 12.5 10/180 80 QD-LED3 60% P2:20% TEG1:20% QD1 T 12.5 10/180 80 OLED4 95% SMB1:5% SEB1 C 16 30/120 65 QD-LED4 90% SMB1:5% SEB1:5% QD1 C 16 30/120 80 OLED5 95% P3:5% SEB1 T 10 10/180 65 QD-LED5 90% P3:5% SEB1:5% QD1 T 10 10/180 80 Solvent: T = toluene; C = chlorbenzene. Conc. = concentration. Heating [min/ C.] stands for minutes heating at the temperature in C., e.g. 10/180 means 10 minutes heating at 180 C.

(18) The terms OLED1 to OLED5 in Table 1 correspond to reference OLEDs without quantum dots in the emissive layer whereas QD-LED1 to QD-LED5 represent OLEDs according to the present invention having quantum dots in the emissive layer.

Example 3

(19) OLED Characterization

(20) In order to characterize the OLEDs according to the present invention, the following properties are recorded: VIL (voltage-current-luminance) characteristics, EL spectrum and color coordinates, efficiency, driving voltages.

(21) The FIGURE depicts the absorption and photoluminescence (PL) spectrum of QD1 and electroluminescence (EL) spectrum of OLED1 to OLED4. The PL-spectrum of QD1 overlaps with the EL-spectrum of OLED1 to OLED4, whereby the overlap is particularly significant with the EL-spectrum of the blue emitting OLED4. The EL-spectrum of OLED5, which is not shown in the FIGURE, is very similar to the EL-spectrum of OLED4.

(22) Table 2 summarizes the results employing OLED1 as control. Uon stands for turn-on voltage, U(100) for voltage at 100 nits (1 nits=cd/m.sup.2), and EQE for external quantum efficiency. The theoretical maximal external quantum efficiency (Max. EQE) for the QD-LED is calculated by PLQE multiplied with Max. EQE of the corresponding OLED.

(23) QD-LED1 to QD-LED5 show the same CIE coordinates in the deep red region. Maximal external quantum efficiencies of more than 1% are achieved with combination of triplet green/yellow and QDs (QD-LED1 to QD-LED3), which represent significant improvements as compared to max. EQEs reported for QDs in light emitting diodes. The combination of triplet OLEDs with quantum dots is, thus, very beneficial.

(24) TABLE-US-00002 TABLE 2 Max. Eff. Uon U(100) CIE @ Max. Theoretical Device [cd/A] [V] [V] 100 cd/m.sup.2 EQE Max EQE OLED1 27.0 2.6 3.7 0.33/0.63 7.45% QD-LED1 2.2 4.0 5.8 0.67/0.33 1.53% 2.23% OLED2 41.5 3.6 5.9 0.48/0.52 12.91% QD-LED2 1.9 3.9 5.6 0.67/0.33 1.35% 3.87% OLED3 31.2 3.3 5.8 0.34/0.62 8.66% QD-LED3 2.5 3.5 6.0 0.67/0.33 1.80% 2.60% OLED4 2.0 5.5 8.7 0.14/0.19 1.42% QD-LED4 0.5 5.7 9.3 0.67/0.33 0.39% 0.42% OLED5 1.0 11.5 13.9 0.14/0.19 0.71% QD-LED5 0.3 12.1 14.2 0.67/0.33 0.18% 0.21%

(25) Further improvement can easily be achieved without being inventive by 1) concentration optimization; 2) using QDs having stronger absorption in green and yellow wavelength ranges; 3) using QDs having high PLQE; 4) using higher efficiency OLEDs; For triplet OLEDs, the max. theoretical EQE can be as high as 20%.

(26) The max. EQEs of QD-LED4 and QD-LED5 are high if the low max. EQEs of the reference devices OLED4 and OLED5 are taken into account., i.e. QD-LED4 and QD-LED5 QD-LED4 and QD-LED5QD-LED4 and QD-LED5 show efficient energy transfer from singlet blue to QD. Employing a singlet blue with an improved performance in OLED4 and/or OLED5, one skilled in the art is able based on the present invention to get, without being inventive, a high performance red QD-LED.