PATENT DOCUMENT

Publication Number: US-10461131-B2
Application Number: US-201816219898-A
Country: US
Kind Code: B2

Title: Quantum dot LED and OLED integration for high efficiency displays

Abstract:
Displays including hybrid pixels including an OLED subpixel and QD-LED subpixel are described. In an embodiment, OLED and QD-LED stacks are integrated into the same pixel with multiple common layers shared by the OLED and QD-LED stacks.

Claims:
What is claimed is: 
     
       1. A display comprising:
 a tandem hybrid pixel including an organic light emitting diode (OLED) subpixel and a quantum dot light emitting diode (QD-LED) subpixel; 
 a common hole transport layer in the OLED subpixel and the QD-LED subpixel; 
 a common quantum dot layer over the common hole transport layer in the QD-LED subpixel and in the OLED subpixel; 
 a semi-common charge generation layer over the common quantum dot layer in the OLED subpixel; 
 a first cathode over the common quantum dot layer in the QD-LED subpixel; 
 a semi-common hole transport layer over the semi-common charge generation layer in the OLED subpixel; 
 an organic emission layer over the semi-common hole transport layer in the OLED subpixel; 
 a semi-common electron transport layer over the organic emission layer in the OLED subpixel; and 
 a semi-common second cathode over the semi-common electron transport layer in the OLED subpixel. 
 
     
     
       2. The display of  claim 1 , further comprising:
 a common nanoparticle electron transport layer comprising metal-oxide nanoparticles over the common quantum dot layer in the QD-LED subpixel and in the OLED subpixel; 
 wherein the semi-common charge generation layer is over the common nanoparticle electron transport layer in the OLED subpixel, and the first cathode is over the common nanoparticle electron transport layer in the QD-LED subpixel. 
 
     
     
       3. The display of  claim 1 , wherein the organic emission layer is over the common quantum dot layer in the OLED subpixel. 
     
     
       4. The display of  claim 1 , further comprising a first anode under the common hole transport layer in the QD-LED subpixel, and a second anode under the common hole transport layer in the OLED subpixel. 
     
     
       5. The display of  claim 1 , wherein the organic emission layer comprises a phosphorescent material. 
     
     
       6. A display comprising:
 a tandem hybrid pixel including an organic light emitting diode (OLED) subpixel and a quantum dot light emitting diode (QD-LED) subpixel; 
 a common hole transport layer in the OLED subpixel and the QD-LED subpixel; 
 a common quantum dot layer over the common hole transport layer in the QD-LED subpixel and in the OLED subpixel; 
 a common charge generation layer over the common quantum dot layer in the OLED subpixel and in the QD-LED subpixel; 
 a second common hole transport layer over the common charge generation layer in the OLED subpixel and in the QD-LED subpixel; 
 an organic emission layer over the second common hole transport layer in the OLED subpixel; 
 a common electron transport layer over the second common hole transport layer in the OLED subpixel and in the QD-LED subpixel, the common electron transport layer additionally over the organic emission layer in the OLED subpixel; and 
 a common cathode over the common electron transport layer in the OLED subpixel and in the QD-LED subpixel. 
 
     
     
       7. The display of  claim 6 , further comprising:
 a common nanoparticle electron transport layer comprising metal-oxide nanoparticles over the common quantum dot layer in the QD-LED subpixel and in the OLED subpixel; 
 wherein the common charge generation layer is over the common nanoparticle electron transport layer in the OLED subpixel and in the QD-LED subpixel. 
 
     
     
       8. The display of  claim 6 , wherein the organic emission layer is over the common quantum dot layer in the OLED subpixel. 
     
     
       9. The display of  claim 6 , further comprising a first anode under the common hole transport layer in the QD-LED subpixel, and a second anode under the common hole transport layer in the OLED subpixel. 
     
     
       10. The display of  claim 6 , wherein the organic emission layer comprises a phosphorescent material. 
     
     
       11. A display with tandem QD-LED and OLED tandem stack comprising:
 a common anode; 
 a common hole transport layer over the common anode; 
 a common quantum dot layer over the common hole transport layer; 
 a common charge generation layer over the common quantum dot layer; 
 a second common hole transport layer over the common charge generation layer; 
 a common organic emission layer over the second common hole transport layer; 
 a common electron transport layer over the common organic emission layer; and 
 a common cathode over the common electron transport layer. 
 
     
     
       12. The display of  claim 11 , further comprising a second common organic emission layer between the common organic emission layer and the common electron transport layer. 
     
     
       13. The display of  claim 12 , further comprising:
 a second common electron transport layer over the common organic emission layer; 
 a second charge generation layer over the second common electron transport layer; and 
 a third common hole transport layer over the second charge generation layer; 
 wherein the second common organic emission layer is over the third common hole transport layer. 
 
     
     
       14. The display of  claim 11 , further comprising a second common electron transport layer between the common quantum dot layer and the common charge generation layer. 
     
     
       15. The display of  claim 14 , wherein the second common electron transport layer comprises metal-oxide nanoparticles.

Description:
This application is a divisional of U.S. patent application Ser. No. 15/244,906 filed on Aug. 23, 2016 now U.S. Pat. No. 10,192,932, issued Jan. 29, 2019, which claims the priority of U.S. Provisional Application No. 62/290,423 filed on Feb. 2, 2016, both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments described herein relate to display systems. More particularly, embodiments relate to display systems with hybrid emissive light emitting diodes (LEDs). 
     Background Information 
     State of the art displays for phones, tablets, computers and televisions utilize glass substrates with thin-film transistors (TFT) to control transmission of backlight through pixels based on liquid crystals. More recently emissive displays such as those based on organic light emitting diodes (OLED) have been introduced because they can have a faster response time, and be more power efficient, allowing each pixel to be turned off completely when displaying black or dark colors, and be compatible with plastic substrates. Even more recently, quantum dot light emitting diodes (QD-LEDs) have been introduced as an alternative display technology, potentially being more power efficient that OLEDs. 
     SUMMARY 
     Display systems and hybrid pixel arrangements are described. In an embodiment, a display includes a hybrid pixel with an OLED subpixel and a QD-LED subpixel. A common hole transport layer is in the OLED subpixel and the QD-LED subpixel. A quantum dot layer is over the common hole transport layer in the QD-LED subpixel, and an organic emission layer that includes a phosphorescent material is over the common hole transport layer in the OLED subpixel. A common electron transport layer is over the quantum dot layer in the QD-LED subpixel, and over the organic emission layer in the OLED subpixel. A common top electrode layer is over the common electron transport layer in the OLED subpixel and the QD-LED subpixel. 
     In an embodiment, a method of forming a display includes forming a common hole transport layer over a display backplane in using a first solution technique, where the common hole transport layer is formed over the display backplane in an OLED subpixel and a QD-LED subpixel. A quantum dot layer is then formed over the common hole transport layer in the QD-LED subpixel. An organic emission layer including a phosphorescent material may then be evaporated over the common hole transport layer in the OLED subpixel. A common electron transport layer may be evaporated over the quantum dot layer in the QD-LED subpixel, and over the organic emission layer in the OLED subpixel, A common top electrode layer may then be formed over the common electron transport layer in the OLED subpixel and the QD-LED subpixel. 
     In an embodiment, a display includes a tandem hybrid pixel including an OLED subpixel and a QD-LED subpixel. A common hole transport layer is in the OLED subpixel and the QD-LED subpixel. A common quantum dot layer is over the common hole transport layer in the QD-LED subpixel and in the OLED subpixel. A semi-common charge generation layer is over the common quantum dot layer in the OLED subpixel. A first cathode is over the common quantum dot layer in the QD-LED subpixel. A semi-common hole transport layer is over the semi-common charge generation layer in the OLED subpixel. An organic emission layer is over the semi-common hole transport layer in the OLED subpixel. A semi-common electron transport layer is over the organic emission layer in the OLED subpixel, and a semi-common second cathode is over the semi-common electron transport layer in the OLED subpixel. In an embodiment, a common nanoparticle electron transport layer including metal-oxide nanoparticles is over the common quantum dot layer in the QD-LED subpixel and in the OLED subpixel, the semi-common charge generation layer is over the common nanoparticle electron transport layer in the OLED subpixel, and the first cathode is over the common nanoparticle electron transport layer in the QD-LED subpixel. 
     In an embodiment, a display includes a tandem hybrid pixel including an OLED subpixel and a QD-LED subpixel. A common hole transport layer is in the OLED subpixel and the QD-LED subpixel. A common quantum dot layer is over the common hole transport layer in the QD-LED subpixel and in the OLED subpixel. A common charge generation layer is over the common quantum dot layer in the OLED subpixel and in the QD-LED subpixel, and a common hole transport layer is over the common charge generation layer in the OLED subpixel and in the QD-LED subpixel. An organic emission layer is over the common hole transport layer in the OLED subpixel. A common electron transport layer is over the common hole transport layer in the OLED subpixel and in the QD-LED subpixel, and the common electron transport layer is additionally over the organic emission layer in the OLED subpixel. A common cathode is over the common electron transport layer in the OLED subpixel and in the QD-LED subpixel. In an embodiment, a common nanoparticle electron transport layer including metal-oxide nanoparticles is over the common quantum dot layer in the QD-LED subpixel and in the OLED subpixel, and the common charge generation layer is over the common nanoparticle electron transport layer in the OLED subpixel and in the QD-LED subpixel. 
     In an embodiment a display with a tandem QD-LED and OLED tandem stack includes a common anode, a common hole transport layer over the common anode, a common quantum dot layer over the common hole transport layer, a common charge generation layer over the common quantum dot layer. a common hole transport layer over the common charge generation layer, a common organic emission layer over the common hole transport layer, a common electron transport layer over the common organic emission layer, and a common cathode over the common electron transport layer. In an embodiment, the tandem QD-LED and OLED tandem stack further includes a second common organic emission layer between the common organic emission layer and the common electron transport layer. In an embodiment, the tandem QD-LED and OLED tandem stack further includes a second common electron transport layer over the common organic emission layer, a second charge generation layer over the second common electron transport layer, and a second hole transport layer over the second charge generation layer, where the second common organic emission layer is over the second hole transport layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an energy diagram of the layers in a QD-LED stack in accordance with an embodiment. 
         FIG. 2  is an energy diagram of the layers in a QD-LED stack including a metal oxide nanoparticle electron transport layer in accordance with an embodiment. 
         FIG. 3  is an energy diagram of the layers in a QD-LED stack including an insulating layer between a quantum dot layer and a metal oxide nanoparticle electron transport layer in accordance with an embodiment. 
         FIG. 4  is an energy diagram of the layers in a QD-LED stack including a hole transport layer with modified energy levels in accordance with an embodiment. 
         FIG. 5  is an energy diagram of the layers in a QD-LED stack including a metal oxide nanoparticle hole transport layer in accordance with an embodiment. 
         FIG. 6  is a schematic cross-sectional side view illustration of a hybrid pixel including a patterned quantum dot layer in accordance with an embodiment. 
         FIGS. 7-10  are schematic cross-sectional side view illustrations of hybrid pixels including a common quantum dot layer in accordance with embodiments. 
         FIG. 11  is a schematic cross-sectional side view illustration of an inverted hybrid pixel including a common quantum dot layer in accordance with an embodiment. 
         FIGS. 12-18  are schematic cross-sectional side view illustrations of hybrid pixels including tandem structure stacks in accordance with embodiments. 
         FIGS. 19-20  are schematic cross-sectional side view illustrations blended emission tandem structure stacks in accordance with embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe display systems with hybrid pixels. In an embodiment, a display includes a hybrid pixel including an OLED subpixel and a QD-LED subpixel. A common hole transport layer is in the OLED subpixel and the QD-LED subpixel with commonly shared layers. A quantum dot (QD) layer is over the common hole transport layer in the QD-LED subpixel. In some embodiments, the QD layer is a common layer over the common hole transport layer in the OLED subpixel and the QD-LED subpixel. An organic emission layer is over the common hole transport layer in the OLED subpixel. In some embodiments the organic emission layer is over the common QD layer in the OLED subpixel. A common electron transport layer is over the QD layer in the QD-LED subpixel and over the organic emission layer in the OLED subpixel. A common top electrode layer is over the common electron transport layer in the OLED subpixel and the QD-LED subpixel. 
     While power efficiency for OLEDs is a potential benefit of OLED displays, conventional fluorescent OLEDs are known to have a maximum internal quantum efficiency (IQE) of around 25%. Phosphorescent OLED systems may be more efficient, and can have IQE values approaching 100%. As such, it may be advantageous to employ phosphorescent OLED materials in displays. Red and green phosphorescent OLED devices have high efficiencies, saturated colors, and acceptable lifetimes. For blue phosphorescent materials, however, available materials tend to have unacceptably short lifetime, unsaturated colors, or both. As such, there is a need to improve the blue emitter system in an OLED display, while maintaining the acceptable performance of red and green phosphorescent materials. 
     In an embodiment, a hybrid pixel includes a blue-emitting QD-LED pixel and one or more emitting OLED subpixels, such as a green-emitting OLED subpixel and a red-emitting OLED subpixel in a RGB hybrid pixel layout. In a specific embodiment, the red OLED subpixel and green OLED subpixel include phosphorescent OLED materials. It is to be appreciated that an RGB hybrid pixel layout is exemplary, and embodiments are not so limited. Other exemplary pixel arrangements include red-green-blue-yellow-cyan (RBGYC), red-green-blue-white (RGBW), or other sub-pixel matrix schemes where the pixels have a different number of sub-pixels. 
     In various embodiments, description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions and processes, etc., in order to provide a thorough understanding of the embodiments. In other instances, well-known display processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the embodiments. Reference throughout this specification to “one embodiment” means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The terms “above”, “over”, “to”, “between”, and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “above”, “over”, or “on” another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers. 
     Referring now to  FIGS. 1-5  various cross-sectional side view illustrations are provided of QD-LED stacks in accordance with embodiments. In the particular embodiments illustrated (including those illustrated in  FIGS. 6-9 ), a dashed outline is provided around a group of layers that may be fabricated using solution-based processing. These groupings are exemplary, and intended to visually illustrate the potential impact of solution-based processing, however, the embodiments are not limited to solution-based processing. In one aspect, increasing the ratio of solution-based processed layers can potentially lead to increased performance and reduced cost of fabrication. For example, solution-based processing may have a reduced time of production compared to evaporation techniques. Solution-based processing of layers may potentially reduce the number of processing steps, and increase yield. For example, solution-based process may negate concerns with exposing evaporated species to air, solvent, etc. In some embodiments, solution-based processing is implemented only prior to the formation of an organic layer by thermal evaporation. 
       FIG. 1  is an energy diagram of the layers in a QD-LED stack in accordance with an embodiment. As shown, the QD-LED stack may include an anode  110 , a hole injection layer (HIL)  120  on/over the anode  110 , a hole transport layer (HTL)  130  on/over the HIL  120 , a QD layer  140  on/over the HTL  130 , an electron transport layer (ETL)  150  on/over the QD layer  140 , an electron injection layer (EIL)  160  on/over the ETL  150 , and a cathode  170  on/over the EIL  160 . As described and illustrated herein a layer on/over another layer may be directly on (in contact) with the other layer or may have or more intervening layers. In operation, a voltage is applied across the QD-LED stack such that the anode is positive with respect to the cathode. Current flows through the QD-LED stack from the cathode to anode, as electrons are injected from the cathode  170  into the lowest unoccupied molecular orbital (LUMO) of the QD layer  140 , while electrons are withdrawn toward the anode  110  from the highest occupied molecular orbital (HOMO) of the QD layer  140  (alternately described as hole injection into the HOMO of the QD layer  140 ). Recombination of electrons and holes in the QD layer  140  is accompanied by emission of radiation, the frequency of which dependent upon the band gap of the QDs, or the difference in energy (eV) between the HOMO and LUMO. It is to be appreciated that the particular energy levels illustrated in  FIGS. 1-5  are exemplary, and that the energy levels are variable. Accordingly, the particular energy levels illustrated are provided for illustrative purposes only, and embodiments are not limited to the specific energy levels illustrated. 
     Still referring to  FIG. 1 , an anode  110  is formed on a display substrate, such as a TFT substrate, or substrate including redistribution lines. Anode  110  may be formed of a variety of electrically conductive materials. In an embodiment, anode  110  is formed of indium-tin-oxide (ITO). For example, ITO may be formed by sputtering or thermal evaporation. In an embodiment, an array of anodes  110  is sputtered onto a display substrate through a mask, such as a fine metal mask, with a separate anode  110  formed in each subpixel. 
     As shown, a HIL  120  is formed on the anode  110 . In accordance with embodiments, the HIL  120  may be a common layer shared by multiple subpixels within a pixel, and may be a common layer across multiple pixels. The HIL  120  facilitates the injection of positive charge (holes) from the anode  110  into the HTL  130 . The HIL  120  may be formed of materials such as conductive polymer-based materials (e.g. poly thiophenes, poly anilines), combination of arylamine based hole transport host and electron accepting dopant (e.g. charge transfer salts), strongly electron accepting small organic molecules, metal oxides. The HIL  120  may be formed using techniques such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, any solution printing technology, as well as thermal evaporation. 
     As shown, a HTL  130  is formed on the HIL  120 . In accordance with embodiments, the HTL  130  may be a common layer shared by multiple subpixels within a pixel, and may be a common layer across multiple pixels. The HTL  130  transports positive charge (holes) to the QD layer  140 , the emissive layer in the QD-LED stack, and physically separates the HIL  120  from the QD layer  140 . HTL  130  may be formed of electron rich materials such as arylamines, polyfluorene derivatives, and nanoparticle metal oxides (e.g. NiO). The HTL  130  may be formed using techniques such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, any solution printing technology, as well as thermal evaporation. 
     As shown, a QD layer  140  is formed on the HTL  130 . In accordance with embodiments, the QD layer  140  may be formed or patterned only in a QD-LED subpixel, or the QD layer  140  may be a common layer shared by multiple subpixels within a pixel, or may be a common layer across multiple pixels. The QD layer  140  may be formed of light emitting semiconductor nanoparticles that emit light at desired wavelength and full width at half max. Exemplary nanoparticles include spherical, rod shaped, platelet (2D quantum well) including semiconductor materials such as CdSe, InP, GaSe, etc. The QD layer  140  may be formed using techniques such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, and any solution printing technology. In an embodiment QD layer  140  may be formed by transfer printing an array of QD layers  140  into an array of subpixels. 
     As shown, an ETL  150  is formed on the QD layer  140 . In accordance with embodiments, the ETL  150  may be a common layer shared by multiple subpixels within a pixel, and may be a common layer across multiple pixels. The ETL  150  may be a high electron mobility layer that transports negative charge (electrons) into the QD layer  140  and physically separates the EIL  160  from the QD layer  140 . ETL  150  may be formed of electron deficient materials such as organometallic compounds, organic small molecules (e.g. substituted benzimidazoles), and nanoparticle metal oxides (e.g. ZnO). The ETL  150  may be formed using techniques such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, any solution printing technology, as well as thermal evaporation. 
     As shown, an EIL  160  is formed on the ETL  150 . In accordance with embodiments, the EIL  160  may be a common layer shared by multiple subpixels within a pixel, and may be a common layer across multiple pixels. The EIL  160  facilitates the injection of negative charge (electrons) from the electrode into the ETL  150 . EIL  160  may be formed of alkali metal salts such as LiF, low work function metals such as Ca, Ba, and n-doped material (e.g. combination of electron transport material and electron donating material). In an embodiment, the EIL  160  is formed by thermal evaporation. 
     As shown, a cathode  170  is formed on the EIL  160 . Cathode  170  may be formed of a variety of electrically conductive materials, including transparent or semi-transparent materials. In accordance with embodiments, the cathode  170  may be a common layer shared by multiple subpixels within a pixel, and may be a common layer across multiple pixels. In an embodiment, cathode  170  is formed of materials such as Ca/Mg, Sm/Au, Yb/Ag, Ca/Ag, Ba/Ag, and Sr/Ag. For example, in a double layer Ca/Mg the Ca layer has a low work-function for electron injection, whereas a Mg capping layer improves electrical conductance of the cathode  170 . In an embodiment, cathode  170  is formed by thermal evaporation. 
     Referring now to  FIG. 2 , an energy diagram similar to  FIG. 1  is provided with the addition of a nanoparticle ETL  180  formed between the QD layer  140  and the ETL  150  in accordance with an embodiment. In an embodiment, nanoparticle ETL  180  includes an assembly of metal oxide nanoparticles, such as ZnO nanoparticles. In the embodiment illustrated, nanoparticle ETL  180  facilitates the transport of electrons from ETL  150  to the QD layer  140  and physically separates the QDs within QD layer  140  from an organic ETL  150 . In an embodiment, ETL  180  is formed using a technique such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, and any solution printing technology. In an embodiment ETL  180  may be formed by transfer printing an array of ETLs  180  into an array of subpixels. In an embodiment, transfer printing includes transferring an ETL  180 /QD layer  140  stack. 
     Referring now to  FIG. 3 , an energy diagram similar to  FIG. 2  is provided with the addition of an insulating layer  185  formed between the QD layer  140  and the nanoparticle ETL  180  in accordance with an embodiment. The insulating layer  185  may function to modulate electron current into the QD layer  140 , or more specifically electron injection from the nanoparticle ETL  180  to the QD layer  140  in order to mitigate excess electron current. This modulation may be adjusted by composition and thickness of the insulating layer  185 . In an embodiment, the insulating layer is nanometers to tens of nanometers thick. In an embodiment, insulating layer  185  is formed of poly (methyl methacrylate) (PMMA). In an embodiment, insulating layer  185  is formed using a technique such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, and any solution printing technology. In an embodiment insulating layer  185  may be formed by transfer printing an array of insulating layers  185  into an array of subpixels. In an embodiment, transfer printing includes transferring an ETL  180 /insulating layer  185 /QD layer  140  stack. 
     Referring now to  FIG. 4 , an energy diagram similar to  FIG. 2  is provided with modified energy levels of the HTL  130  in accordance with an embodiment. For example, the HOMO and LUMO energy levels of the HTL  130  may be modified by the use of non-traditional deep HOMO based compounds to more closely match the QD HOMO energy level. In an embodiment, the energy difference between the HTL  130  HOMO energy level and the QD layer  140  HOMO energy level is less than 0.5 eV with the inclusion of non-traditional deep HOMO based compounds for HTL  130 . Exemplary materials include nanoparticle metal oxides (e.g. NiO), and organic based molecules (e.g. acene and carbazole derivative based compounds, carbizole derivative based polymers, polyphenylenes, derivatized triphenylenes). In an embodiment, HTL  130  is formed using any technique previously described for HTL  130 . 
     Referring now to  FIG. 5 , an energy diagram similar to  FIG. 4  is provided with the addition of a metal oxide nanoparticle HTL  190  between the QD layer  140  and the HTL  130  in accordance with an embodiment. In an embodiment, metal oxide nanoparticle HTL  190  includes an assembly of metal oxide nanoparticles, such as NiO nanoparticles. In the embodiment illustrated, nanoparticle HTL  190  facilitates the transport of holes from HTL  130  to the QD layer  140  and physically separates the QDs within QD layer  140  from an organic HTL  130 . The HTL  190  may be formed using techniques such as spin coating, ink jet printing, slot die coating, nozzle printing, contact printing, gravure printing, and any solution printing technology. In an embodiment HTL  190  may be formed by transfer printing an array of HTLs  190  into an array of subpixels. In an embodiment, transfer printing includes transferring an HTL  190 /QD layer  140  stack. In an embodiment, transfer printing includes transferring an HTL  190 /QD layer  140 /ETL  180  stack. In an embodiment, transfer printing includes transferring an HTL  190 /QD layer  140 //insulating layer  185 /ETL  180  stack. 
     Referring now to  FIGS. 6-9  various hybrid pixel layouts are provided to illustrate the integration of QD-LED and OLED subpixels within a display. In particular, the illustrated hybrid pixel layouts are based upon the QD-LED stack structures illustrated and described with regard to  FIGS. 1, 2 and 4 . However, these illustrations are exemplary and may include additional layers, such as insulating layer  185  and HTL  190 . Accordingly, the implementation of insulating layer  185  and HTL  190  is not limited to the embodiments illustrated and described with regard to  FIGS. 3 and 5 . 
     In the case of electroluminescent displays, the red, green, and blue subpixels within a single display pixel are comprised of an assembly of layers common to all three subpixels and layers specific to a particular subpixel. In accordance with some embodiments, the common layers in the hybrid pixel may include the HIL  120 , HTL  130 , and ETL  150 , EIL  160 , and cathode  170  layer. In some embodiments, the layers specific to each subpixel may include the buffer transport layers (BTLs)  210  and the emissive layers (e.g. organic emission layers  200 -R,  200 -G, and QD layer  140 ). In some embodiment, the BTL  210  and/or QD layer  140  may be common layers. The thickness of the common layers and BTLs  210  are selected to ensure specific micro cavity design for each of the red, green, and blue subpixels. In the hybrid pixel assembly, the BTLs  210  have two roles- one is to further adjust the cavity strength as well as to ensure that the layer next to the emissive layer has a band gap higher than that of the emissive species itself. In the case of the red and green phosphorescent organic emission layers  200 -R,  200 -G, the BTL  210  should have a triplet energy that is higher than the triplet energy of the emitter material. Furthermore, the BTL  210  energy levels (HOMO, LUMO) may be selected to facilitate hole or electron blocking functionality next to the emissive layer. 
       FIG. 6  is a schematic cross-sectional side view illustration of a hybrid pixel including a patterned QD layer  140  in accordance with an embodiment. In the embodiment illustrated, separate anodes  110 -R,  110 -G,  110 -B are provided for each separate subpixel (e.g. RBG). A common HIL  120  and common HTL  130  are formed over the separate anodes  110 -R,  110 -G,  110 -B. 
     In the particular embodiment illustrated in  FIG. 6 , the blue-emitting QD-LED subpixel includes a QD layer  140  formed on the common HTL  130 , and a nanoparticle ETL  180  (e.g. ZnO nanoparticles) formed on the QD layer  140 . In one embodiment, the QD layer  140  and nanoparticle ETL  180  are formed using any of the previously described solution-based techniques. In another embodiment, the QD layer  140  and nanoparticle ETL  180  are transfer printed either separately, or together as a layer stack. Following the formation of the QD layer  140  and nanoparticle ETL  180 , the remainder of the layers may be fabricated, for example, by thermal evaporation. 
     Still referring to  FIG. 6 , buffer transport layers  210 -R,  210 -G are formed on the common HTL  130 , followed by the formation of red and green emitting organic emission layers  200 -R,  200 -G on the BTLs  210 -R,  210 -G. In the arrangement illustrated in  FIG. 6, 210 -R.  210 -G are BTLs in the red and green OLED subpixels, and are both serving as electron blocking layers. Exemplary materials may include carbazole and triphenylene based organic compounds, which may be formed by thermal evaporation. A common ETL  150  may then be formed on the organic emission layers  200 -R,  200 -G, and the nanoparticle ETL  180 . A common EIL  160  may then be formed over the common ETL  150 , followed by the formation of a common cathode  170  layer. 
     As shown in  FIG. 6 , the hybrid pixel arrangement includes a QD-LED stack structure similar to that illustrated in  FIG. 2  or  FIG. 4 . In other embodiments, the hybrid pixel arrangement may optionally include an insulating layer  185 , and/or HTL  190  as previously described with regard to  FIGS. 3 and 5 . Additionally, the nanoparticle ETL  180  may optionally be removed. 
     Referring now to  FIGS. 7-9  additional hybrid pixel arrangements are illustrated including a common QD layer  140  in accordance with embodiments. In such arrangements, additional processing operations associated with patterning the QD layer  140  may be removed, which may reduce time of production. This may additionally eliminate resolution (e.g. pixels per inch) constraints related to patterning or printing. 
       FIG. 7  is a schematic cross-sectional side view illustration of a hybrid pixel similar to  FIG. 6 , with common QD layer  140 , and no nanoparticle ETL  180 . Additionally, the optional BTLs  210 -R,  210 -G are removed. In the embodiment illustrated, the common ETL  150  is formed on organic emission layers  200 -R,  200 -G in the OLED subpixels, and on the common QD layer  140  in the QD-LED subpixel. 
       FIG. 8  is a schematic cross-sectional side view illustration of a hybrid pixel similar to  FIG. 6 , with common QD layer  140 , and common nanoparticle ETL  180  formed on the common QD layer  140 . In the embodiment illustrated, the common ETL  150  is formed on organic emission layers  200 -R,  200 -G in the OLED subpixels, and on the common nanoparticle ETL  180  in the QD-LED subpixel. 
       FIG. 9  is a schematic cross-sectional side view illustration of a hybrid pixel similar to  FIG. 7 , with BTLs  210 -R,  210 -G formed on the organic emission layers  200 -R,  200 -G, respectively. The BTLs  210 -R,  210 -G in  FIG. 9  are distinguishable from the BTLs illustrated in  FIGS. 6 and 8 , in that the BTLs  210 -R,  210 -G in  FIG. 9  serve as hole blocking layers as opposed to electron blocking layers. Exemplary materials for BTLs serving as hole blocking layers may include organometallic wide band gap compounds (hole blocking) and other organic compounds (e.g. substituted benzimidazoles), which may be formed by thermal evaporation. 
       FIG. 10  is a schematic cross-sectional side view illustration of a hybrid pixel similar to  FIG. 9 , with a common BTL  210  being formed on the organic emission layers  200 -R,  200 -G and common QD layer  140 , as opposed to separate BTLs being formed in each OLED subpixel 
     In other embodiments, the hybrid pixel arrangements illustrated in  FIGS. 7-9  may optionally include a common insulating layer  185 , and/or common HTL  190  as previously described with regard to  FIGS. 3 and 5 . 
       FIG. 11  is a schematic cross-sectional side view illustration of an inverted hybrid pixel including a common QD layer  140  in accordance with an embodiment. In the embodiment illustrated, separate cathodes  170 -R,  170 -G,  170 -B are provided for each separate subpixel (e.g. RBG). In an embodiment, the cathodes  170 -R,  170 -G,  170 -B are formed of ITO. A common nanoparticle ETL  180  is formed over the separate cathodes  170 -R,  170 -G,  170 -B, followed by the formation of a common QD layer  140  over the common nanoparticle ETL  180 . Similar to the arrangements illustrated in  FIGS. 7-10 , the arrangement in  FIG. 11  may eliminate the resolution constraints associated with patterning or printing. Still referring to  FIG. 11 , organic emission layers  200 -R,  200 -G are formed on the QD layer  140 , followed by the formation of BTLs  210 -R,  210 -G on the organic emission layers  200 -R,  200 -G, respectively, for example using thermal evaporation. A common HTL  130  is then formed on the BTLs  210 -R,  210 -G in the OLED subpixels, and the common QD layer  140  in the QD-LED subpixel. A common HIL  192  may then be formed over the common HTL  130 , for example, using thermal evaporation. Exemplary materials of HIL  192  include hexaazatriphenylene-hexacarbonitrile (HAT-CN) or molybdenum oxide (MoOx). A common anode  110  layer is then formed over the common HIL  192 . In an embodiment, the common anode  110  layer is formed of aluminum. 
     Referring now to  FIGS. 12-18  various configurations of hybrid pixels including tandem structure stacks are provided in accordance with embodiments, in which multiple emitting units are stacked vertically. Referring to  FIG. 12 , a QD layer  140 , HTL  130 , HIL  120  may be formed over separate anodes  110 -R,  110 -G,  110 -B similarly as previously described with regard to  FIG. 7 , followed by the formation of a common ETL  150  over the common QD layer  140  in the OLED subpixels and the QD-LED subpixel. A separate cathode  170 -B may then be formed on the common ETL  150  in the QD-LED subpixel, while a semi-common charge generation layer (CGL)  220  is formed on the common ETL  150  in the OLED subpixels. As illustrated, the semi-common CGL  220  is common to the OLED subpixels only. 
     In accordance with embodiments, the CGL  220  is used to connect an assembly of two emissive layers in tandem with each other. It provides positive (hole) current to the upper (with reference to the figures) emissive layers (e.g.  200 -R,  200 -G) and negative (electron) current to the lower emissive layer (e.g. QD layer  140 ). Typically a CGL  220  is comprised of two distinct layers. For example, the electron current can be provided by a layer comprised of alkali metal salts such as LiF, low work function metals such as Ca, Ba, and n-doped material (e.g. combination of electron transport material and electron donating material). The hole current can be provided by a layer comprised of combination of arylamine based hole transport host and electron accepting dopant (e.g. charge transfer salts), strongly electron accepting small organic molecules, metal oxides. In accordance with embodiments, CGL  220  is formed by thermal evaporation. 
     A semi-common HIL  120  may then be formed on the semi-common CGL  220 , followed by the formation of a semi-common HTL  130  on the semi-common HIL  120 . Organic emission layers  200 -R,  200 -G may then be formed on the semi-common HTL  130  in separated OLED subpixels. A semi-common ETL  150  may then be formed over both organic emission layers  200 -R,  200 -G, followed by the formation of a semi-common EIL  160 , and a semi-common cathode  170  in both OLED subpixels. A red color filter  230 -R may optionally be formed over the semi-common cathode  170  in the red emitting OLED subpixel, and a green color filter  230 -G may optionally be formed over the semi-common cathode  170  in the green emitting OLED subpixel. 
       FIG. 13  is a schematic cross-sectional side view illustration of a hybrid pixel including a tandem structure stack similar to that provided in  FIG. 12  with one difference being the substitution of nanoparticle ETL  180  in place of ETL  150 . Additionally, nanoparticle ETL  180  may be fabricated using a solution-based technique. 
       FIG. 14  is a schematic cross-sectional side view illustration of a hybrid pixel including a tandem structure stack similar to that provided in  FIG. 13  with one difference being the addition of semi-common ETL  150  between the semi-common CGL  220  and the semi-common HIL  120 . 
     Referring now to  FIG. 15  a schematic cross-sectional side view illustration of a hybrid pixel including a tandem structure stack is provided in accordance with an embodiment in which the QD-LED subpixel is inverted. As shown, a common nanoparticle ETL  180  may be formed over separate anodes  110 -R,  110 -G, and cathode  170 -B. In an embodiment, anodes  110 -R,  110 G, and cathode  170 -B are formed of the same material, such as ITO. A common QD layer  140  may then be formed over the common nanoparticle ETL  180 . The common nanoparticle ETL  180  and common QD layer  140  may be formed using solution-based techniques. A common HTL  130  may then be formed over the common QD layer  140 , followed by the formation of a common HIL  192  over the common HTL  130 , for example by thermal evaporation. An anode  110 -B may then be formed on the common HIL  192  in the QD-LED subpixel, while a semi-common HTL  130  is formed on the common HIL  192  in the OLED subpixels. 
     BTLs  210 -R,  210 -G are then formed on the semi-common HTL  130  in the red-emitting and green-emitting OLED subpixels, followed by the formation of organic emission layers  200 -R,  200 -G on the BTLs  210 -R,  210 -G. In the arrangement illustrated in  FIG. 15, 210 -R,  210 -G are BTLs in the red and green OLED subpixels, and are both serving as electron blocking layers. Exemplary materials may include carbazole and triphenylene based organic compounds, which may be formed by thermal evaporation. A semi-common ETL  150  is then formed over the organic emission layers  200 -R,  200 -G, followed by the formation of a semi-common EIL  160  on the semi-common ETL  150 , and a semi-common cathode  170  on the semi-common EIL  160 . 
     Referring now to  FIGS. 16-18 , schematic cross-sectional side view illustrations of hybrid pixels including tandem structure stacks are provided similar to those in  FIGS. 12-14  with one difference being that a separate cathode  170  is not provided for the QD-LED subpixel, and the previously described and illustrated semi-common layers are now common layers across both the OLED subpixels and the QD-LED subpixel. Additionally, a blue color filter  230 -B may be formed over the common cathode  170  layer in the QD-LED subpixel. 
       FIGS. 19-20  are schematic cross-sectional side view illustrations blended emission tandem structure stacks in accordance with embodiments. As such, the structures illustrated in  FIGS. 19-20  may be utilized to emit a blended spectrum, such as white light. As illustrated in  FIGS. 19-20 , each layer may be a common layer formed on top of another common layer. In both embodiments illustrated in  FIGS. 19-20 , the ETL  150  formed above the solution-based layers may be substituted with a solution-based nanoparticle ETL  180 , or ETL  150  may be formed on top of a solution-based nanoparticle ETL  180 . 
     In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for forming hybrid OLED/QD-LED pixels. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration.

Metadata:
Filing Date: 20181213
Publication Date: 20191029
Grant Date: 20191029
Priority Date: 20160202
Inventors: Steckel, Jonathan S.
MATHAI, MATHEW K.
DRZAIC, PAUL S.
YAMAMOTO, HITOSHI
Assignee: APPLE INC
CPC Classifications: [{"code": "H01L51/0003", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L27/3211", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2251/5369", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L51/5278", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5044", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/502", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/3209", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L51/5072", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/0013", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L51/5016", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K71/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K71/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/115", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/32", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/32", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/131", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K2102/331", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/115", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/18", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K2101/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K2101/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K2102/331", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/19", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/131", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/16", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 59385685