Looks to me that the the key to this Apple patent is blue QDs, since it appears that the red and green are produced with the organics (organic emission layers 200-R, 200-G) and the blue with QDs (the blue-emitting QD-LED subpixel includes a QD layer 140).
[0022] 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.
[0040] 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 150, 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.
[0041] 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.
[0042] 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.
[0022] 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.
[0040] 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 150, 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.
[0041] 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.
[0042] 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.
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