Patent Publication Number: US-2012038265-A1

Title: Organic electroluminescence display device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device incorporating an organic electroluminescence (EL) device and, more particularly, to a display device incorporating an organic EL device capable of enhancing light utilization efficiency from the top of the display device. 
     2. Description of the Related Art 
     One problem concerning organic EL devices, such as organic light-emitting diodes (OLEDs), is low light extraction efficiency. Light extraction efficiency may be generally defined as the fraction of light radiated outside of the organic EL device out of the total optical power generated in the active layer (light-emitting layer) of the organic EL device. In these terms, the extraction efficiency of an organic EL device is low because, since light is emitted at various angles from a light emitting layer in the organic EL device, total reflection components often appear at the interface between a protective layer and an external space and thereby the emitted light is trapped inside the organic EL device. Various configurations have been proposed to overcome this problem. Japanese Patent Laid-Open No. 2004-39500 discloses a configuration for enhancing the light extraction efficiency from the top of an organic EL device by disposing a resin-made lens array on an oxidized silicon nitride (SiNxOy) film which seals the organic EL device. 
     In the configuration in which a lens array is situated on an organic EL device disclosed in Japanese Patent Laid-Open No. 2004-39500, a light collecting effect may be produced in addition to an extraction effect of the total reflection components. These effects can enhance brightness at the top (i.e., light emission efficiency) of the display device incorporating an organic EL device. In the form disclosed in Japanese Patent Laid-Open No. 2004-39500, however, brightness of the display device in oblique directions is low and therefore no wide radiation angle characteristics is achieved. 
     SUMMARY OF THE INVENTION 
     The present invention provides a display device with wide radiation angle characteristics and improved light utilization efficiency in an organic EL display device. 
     The embodiments of present invention are directed to an organic electroluminescence display device which includes a plurality of pixels each of which includes at least one organic electroluminescence device and a lens, wherein each pixel includes a light emitting region provided with a lens and a light emitting region provided with no lens; and an area of the light emitting region provided with a lens is smaller than an area of the light emitting region provided without a lens. 
     According to the present invention, in an organic EL display device provided with a lens, a lens diameter can be increased for the enhanced light collection efficiency. It is therefore possible to provide an organic EL display device with wide radiation angle characteristics kept by a lens and with improved light utilization efficiency. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic sectional view illustrating a pixel configuration of an organic EL display device according to the present invention. 
         FIG. 1B  is a schematic sectional view illustrating a pixel configuration of an organic EL display device according to the present invention. 
         FIG. 2  illustrates view-angle dependence of brightness in accordance with the existence of a lens in the organic EL display device according to the present invention. 
         FIG. 3A  is a schematic plan view illustrating a lens arrangement of an embodiment of the organic EL display device according to the present invention. 
         FIG. 3B  is a schematic plan view illustrating a lens arrangement of an embodiment of the organic EL display device according to the present invention. 
         FIG. 4  is a schematic plan view of another embodiment of the organic EL display device according to the present invention. 
         FIG. 5A  is a schematic plan view of an embodiment of the organic EL display device according to the present invention. 
         FIG. 5B  is a pixel circuit diagram of an embodiment of the organic EL display device according to the present invention. 
         FIG. 6A  is a schematic plan view of another embodiment of the organic EL display device according to the present invention. 
         FIG. 6B  is a pixel circuit diagram of another embodiment of the organic EL display device according to the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An organic electroluminescence display device (an organic EL display device) according to the present invention includes a plurality of pixels each of which includes an organic electroluminescence device (an organic EL device) and a lens. Each pixel includes a light emitting region provided with a lens and a light emitting region provided with no lens. An area of the light emitting region provided with a lens is smaller than that of the light emitting region provided with no lens. The present invention is embodied in the following two configurations in terms of correspondence relationship between the lens and the organic EL device. 
     In a first form, a single pixel is constituted by a single organic EL device; each organic EL device includes a light emitting region provided with a lens and a light emitting region provided with no lens. 
     In a second form, a single pixel includes a plurality of organic EL devices which emit the same colored light; one of the plurality of organic EL devices is situated in the light emitting region provided with a lens and one of other organic EL devices is situated in the light emitting region provided with no lens. 
     The lens is situated on a light emitting surface side of the organic EL device. The light emitted by the organic EL device is extracted from the light emitting surface. In a typical organic EL display device, display signals in accordance with gradation are applied to the organic EL device; the minimum unit to which the same display signal is applied is a single pixel. Multicolor display is usually achieved by a combination of the color of red (R), green (G) and blue (B). The organic EL device is provided with a light emitting layer which emits light of either of the colors R, G and B. The pixel as a display unit is the minimum unit to which the display signal representing R, G or B is applied; predetermined hues are displayed by combinations of a red pixel for the R display, a green pixel for G display and a blue pixel for B display. 
     Hereinafter, the organic EL display device according to the present invention will be described with reference to the embodiments. 
       FIGS. 1A and 1B  are fragmentary sectional views of portions corresponding to a single pixel related to an embodiment of the organic EL display device according to the present invention;  FIG. 1A  illustrates the first form and  FIG. 1B  illustrates the second form. The first and second forms each include a substrate  10 , organic EL devices  17   a ,  17   b  or  17  and partitions  12  which separate the organic EL devices  17   a ,  17   b  or  17  from one another. The partitions  12  separates the organic EL devices  17   a ,  17   b  or  17  from one another to define apertures (i.e., light emitting regions) of the organic EL devices  17   a ,  17   b  or  17 . In the first form of the present invention, a single pixel  18  is constituted by a single organic EL device  17  as illustrated in  FIG. 1A . In the second form, a single pixel  18  is constituted by a plurality of organic EL devices; in the example of  FIG. 1B , the single pixel  18  is constituted by two organic EL devices  17   a  and  17   b.    
     Each of the organic EL devices  17   a ,  17   b  and  17  is provided with an organic compound layer  13  which is situated between a pair of electrodes  11  and  14  and includes a light emitting layer. In particular, each of the organic EL devices  17   a ,  17   b  and  17  is provided with a first electrode  11  situated on the substrate  10 , the organic compound layer  13  situated on the first electrode  11  and a second electrode  14  situated on the organic compound layer  13 . The organic compound layer  13  is a layered product constituted by a single layer or a plurality of layers including a light emitting layer. In particular, for example, the organic compound layer  13  may be four-layered product constituted by a hole transport layer, a light emitting layer, an electron transport layer and an electron injection layer or a three-layered product constituted by a hole transport layer, a light emitting layer and an electron transport layer. Any known materials may be used for the organic compound layer  13  (i.e., an organic light emitting material, a hole transport material, an electron transport material and an electron injection material). Color display is achieved by employing a red light emitting material, a green light emitting material and a blue light emitting material in the light emitting layer. 
     In the organic EL devices  17   a ,  17   b  and  17 , the first electrode  11  is provided in each of the devices along a surface direction of the substrate  10 ; and the second electrode  14  is provided continuously across a plurality of devices. The organic compound layer  13  includes a light emitting layer which differs in configuration in accordance with the color of the emitted light. Accordingly, if adjacent organic EL devices emit light of the same color, the organic EL devices  17   a ,  17   b  and  17  have a common light emitting layer; other layers than the light emitting layer are common in the entire organic EL devices. For example, if the pixels of R, G and B are arranged in a striped pattern, the light emitting layers are formed in accordance with the striped pattern. In an arrangement with adjacent organic EL devices being different in color of emitted light, each of the devices includes a light emitting layer. 
     The substrate  10  is provided with a driving circuit (not illustrated) which actively drives the organic EL devices  17   a ,  17   b  and  17 . A protective film  15  is provided on the second electrode  14 . The protective film  15  is a light transmissive film and may be formed of an inorganic material, such as SiO and SiN or an organic material, such as thermosetting resin and photo-setting resin. 
     The organic EL devices  17   a ,  17   b  and  17  illustrated in  FIGS. 1A and 1B  are top-emitting devices in which light is extracted from an upper surface of the substrate  10 . Accordingly, the first electrode  11  can be formed of a light reflecting electrode material and the second electrode  14  can be formed of a light transmissive or semitransmissive electrode material. Note that the present invention is also applicable to bottom-emitting organic EL devices in which light is extracted from a back surface of the substrate  10 . In this case, the first electrode  11  is a light transmissive or semitransmissive electrode and the second electrode  14  is a light reflecting electrode. The lens  16  is formed on the substrate  10  side. 
     The organic EL display device according to the present invention is manufactured by a known method. The lens  16  illustrated in  FIGS. 1A and 1B  is situated on the light emitting surface side via the protective film  15 . The lens  16  may have any shape including a spherical shape and a semicylindrical shape. The lens  16  may be formed by processing such materials as transparent thermosetting resin, light curing resin and thermoplastic resin. In particular, the lens  16  may be formed by, for example, embossing. In addition to the embossing, the lens  16  may be formed by either of the following methods (i) to (v): 
     (i) heat-treating a resin layer which has been patterned through, for example, photolithography, followed by reflowing the resin layer into a lens shape; 
     (ii) exposing a light curing resin layer of uniform thickness with light distributed in the surface direction, followed by developing the resin layer to form a lens; 
     (iii) processing a surface of a resin material of uniform thickness into a lens shape using, for example, an ion beam, an electron beam and laser; 
     (iv) adding a proper amount of resin dropwise to each pixel to form a lens in a self-aligning manner; and 
     (v) preparing a resin sheet on which a lens has been formed, aligning the resin sheet with a substrate on which an organic EL device is formed, and then bonding the resin sheet and the substrate together. 
     A sealing structure may be achieved by a protective film  15  which has sealability or a sealing film formed on an upper surface of the lens  16 . Alternatively, a hollow sealing structure may be employed which is achieved by bonding a sealing housing and the substrate  10  which are provided separately. 
     In the organic EL devices  17  and  17   a , the light emitted from the organic compound layer  13  passes through the second electrode  14  and then the protective film  15  and the lens  16 , and exits the organic EL display device.  FIG. 2  illustrates radiation angle distribution of brightness in the light emitting region with the lens  16  situated on the organic EL device  17  illustrated in  FIG. 1A  (i.e., the lens region) and in the light emitting region without a lens  16  (i.e., the non-lens region). Specifically, in  FIG. 2 , the “lens region” curve corresponds to a brightness distribution as function of radiation angle in the region where the lens  16  is situated on the organic EL device  17 ; and the “non-lens region” curve corresponds to a brightness distribution in the light emitting region with no lens  16 . An exit angle of the light becomes closer to a direction vertical to the substrate when the light exits the device from the outermost layer via the lens  16  as compared with a structure in which no lens  16  is provided. Accordingly, the lens region has a higher light collection effect in the vertical direction than the non-lens region does. That is, light utilization efficiency from the top of the organic EL display device can be enhanced. Note that the extent to which the light is collected depends on the lens shape, the curvature, the distance from the light emitting surface to the lens and the light emitting region. 
     In the organic EL device  17 , the light emitted in oblique directions from the organic compound layer  13 , meanwhile, exits the device in more oblique directions; this phenomenon is an aid to a further increase in brightness for tilted visual fields. 
       FIG. 3A  is a schematic plan view of an organic EL display device having a pixel configuration illustrated in  FIG. 1B . In this example, multicolor display is achieved by combining the R, G and B colors and the pixels emitting light of each color are arranged in a striped pattern extending the vertical direction of the page. In  FIG. 3A ,  17 Ra and  17 Rb represent the organic EL devices for the R display,  17 Ga and  17 Gb represent the organic EL devices for the G display and  17 Ba and  17 Bb represent the organic EL devices for the B display;  17 Ra and  17 Rb,  17 Ga and  17 Gb and  17 Ba and  17 Bb each constitutes a single pixel. 
     In this example, areas of apertures defined by the partitions of the organic EL devices  17 Ra,  17 Ga and  17 Ba provided with the lenses  16  are smaller than those of the organic EL devices  17 Rb,  17 Gb and  17 Bb provided with no lens  16 . With this configuration, it is possible to reduce the areas of the apertures defined by the partitions with respect to the diameter of lens  16  in the organic EL devices  17 Ra,  17 Ga and  17 Ba provided with the lenses  16 ; thus the light emitted from the organic EL devices  17 Ra,  17 Ga and  17 Ba can be collected effectively. This is because this configuration is similar to that in which lenses are provided at point light sources. An increase in the areas of the apertures defined by the partitions of the organic EL devices  17 Rb,  17 Gb and  17 Bb is advantageous for a longer lifetime of the organic EL display device according to the present invention. This is because, if the areas of the apertures of the partitions of the organic EL devices  17 Rb,  17 Gb and  17 Bb are increased, desired brightness can be achieved with a reduced driving current. Accordingly, in this example, the light collection efficiency of the lens  16  is enhanced while the lifetime of the organic EL display device becomes long. 
       FIG. 3B  is a schematic plan view of the organic EL display device which has the pixel configuration illustrated in  FIG. 1A . Also in this example, pixels of R, G and B are arranged in a striped pattern extending in the vertical direction of the page. In  FIG. 3B ,  17 R represents the organic EL device for the R display,  17 G represents the organic EL device for the G display and  17 B represents the organic EL device for the B display. In this example, as illustrated in  FIG. 3B , a single pixel includes a single organic EL device and a lens  16  is formed on a light emitting surface side of a part of the organic EL device. In this example, widths t 1  of apertures defined by partitions in regions provided with lenses  16  are narrower than widths t 2  of apertures defined by partitions in regions provided with no lenses  16  in the organic EL devices  17 R,  17 G and  17 B. With this configuration, an area of the light emitting region provided with the lens is smaller than that of the light emitting region provided with no lens. It is therefore possible, also in this example, to enhance light collection efficiency of the lens  16  in the region provided with the lens  16  as in the example illustrated in  FIG. 3A . Note that, in the present invention, the width of the aperture defined by the partition is the length of the aperture defined by the partition in the direction perpendicular to the direction in which the region provided with the lens  16  and the region provided with no lens  16  are arranged, i.e., the length of the aperture defined by the partition in the horizontal direction of the page of  FIG. 3B . The light emitting region provided with the lens  16  and the light emitting region provided with no lens  16  may be separated from each other. In this configuration, since edges of the lens  16  are situated on the partitions  12 , the difference in level existing at the edges of the lens  16  is reduced and thereby distortion of the lens shape is avoided. It is to be noted that, although the area of the light emitting region provided with a lens and the area of the light emitting region provided with no lens are controlled by adjusting the widths of these regions in this example, the present invention is not limited to the same. 
       FIG. 4  is a schematic plan view of another embodiment of the organic EL display device having the pixel configuration illustrated in  FIG. 1B . In this example, areas of apertures defined by partitions of organic EL devices  17 Ra,  17 Ga and  17 Ba in which lenses  16  are provided are smaller than those of the example illustrated in  FIG. 3A . Moreover, areas of apertures defined by partitions of organic EL devices  17 Ra,  17 Ga and  17 Ba in which lenses  16  are provided are not limited to being smaller than the areas on which lenses are not provided. One of ordinary skill in the art may readily understand that the opposite may be true. Thus, embodiments of the present invention are directed to arrangement where an area of the light emitting region provided with a lens is of a different size than an area of the light emitting region provided with no lens regardless of shape thereof. 
       FIG. 5A  is a schematic plan view of an organic EL display device having the pixel configuration illustrated in  FIG. 1A .  FIG. 5B  is a circuit diagram of a single pixel of this organic EL display device. In  FIG. 5B , C 1  represents capacity and M 1  and M 2  represent thin-film transistors (TFTs). An organic EL display device  21  of this example includes n scanning lines  26 , m data lines  25 , and (m×n) pixel circuits  24  situated at intersections of the scanning lines  26  and the data lines  25  (x represents the scanning line number and y represents the data line number). The scanning lines  26  are driven by a scanning line driving circuit  23 . A data line driving circuit  22  applies predetermined information signals (i.e., display signals) to the data lines  25  which, in turn, apply the information signals to the pixel circuits  24 . 
     In the organic EL display device of this example, a single organic EL device  17  corresponds to a single pixel  18  as illustrated in  FIG. 1A . Accordingly, a single organic EL device  17  is connected to a single pixel circuit  24  as illustrated in  FIG. 5B . 
       FIG. 6A  is a schematic plan view of an organic EL display device having the pixel configuration illustrated in  FIG. 1B .  FIG. 6B  is a circuit diagram of a single pixel of this organic EL display device. In  FIG. 6B , C 1  represents capacitance and M 1  to M 4  represent thin-film transistors (TFTs). This example includes, in addition to the configuration illustrated  FIG. 5A , selection control lines  37  and  38  which are parallel to the scanning lines  26  and a selection control line driving circuit  34  which drives the selection control lines  37  and  38 . Two organic EL devices  17   a  and  17   b  are connected to the pixel circuit  24  to be driven independently. 
     It is also possible in the organic EL display device having the pixel configuration illustrated in  FIG. 1B  to include the pixel circuits illustrated in  FIG. 5B  one on each side of the data lines  25 . One of the pixel circuits drives the organic EL device  17   a  and the other drives the organic EL device  17   b . It is also possible, as the first form of the present invention, to electrically connect the first electrodes  11  of the organic EL devices  17   a  and  17   b  which are separated by the partition  12  as illustrated in  FIG. 1B  and connect one of the first electrodes  11  to the pixel circuit illustrated in  FIG. 5B  to thereby drive the organic EL devices  17   a  and  17   b  simultaneously. In this manner, since the lens regions and the non-lens regions are separated by the partitions  12  and edges of the lens  16  are situated on the partitions  12 , the difference in level existing at the edges of the lens  16  is reduced and thereby distortion of the lens shape is avoided. 
     Next, an operation of the organic EL display device according to the present invention will be described. 
     In the first form of the present invention, the lens region and the non-lens region are driven simultaneously. In the second form, an organic EL device provided with a lens and an organic EL device provided with no lens can be driven simultaneously in an integrated manner as in the first form, and can also be driven independently. Hereinafter, for ease of description, simultaneous driving and independent driving of the organic EL device provided with a lens (i.e., a lens region) and the organic EL device provided with no lens (i.e., a non-lens region) in the second form will be described. 
     If both the lens region and the non-lens region are driven in an integrated manner, with the optical properties illustrated in  FIG. 2 , the lens region increases brightness at the top and the non-lens region reduces the decrease in brightness in oblique directions; as a result, the radiation angle characteristics are improved. It is therefore possible to keep the radiation angle characteristics while enhancing light utilization efficiency. 
     If the two regions are driven independently, e.g., if only the non-lens region is turned on, an organic EL display device with wide radiation angle characteristics is achieved. If only the lens region is turned on, an organic EL display device with narrow radiation angle characteristics but high in brightness at the top is achieved. If the brightness of the lens region is substantially the same as that of the non-lens region, the lens region can be driven with a lower current than that required for driving the non-lens region. Thus the device of low power consumption is achieved. Accordingly, either of “wide radiation angle characteristics,” “priority on the brightness at the top” or “priority on the low power consumption” can be selected as the characteristics of the organic EL display device in accordance with the purpose. 
     Hereinafter, specific driving methods will be described. 
     First Driving Method 
     A first driving method is an exemplary method of driving the organic EL display device illustrated in  FIG. 5A  which includes the pixel configuration illustrated in  FIG. 1A  and the pixel circuit illustrated in  FIG. 5B . In the circuit illustrated  FIG. 5B , M 1  and M 2  are nMOS transistors, that is, transistors that conduct when the gate is low. If M 1  and M 2  are pMOS transistors, the high level (H level) and the low level (L level) should be inverted. 
     In  FIG. 5B , scanning selection signals are input from the scanning lines  26  and information signals (i.e., voltage data, Vdata) representing predetermined gradation are input to the data lines  25  in synchronization with the scanning selection signals. The first electrode  11  of the organic EL device  17  is connected to a drain terminal of M 2  and the second electrode  14  is connected to ground potential CGND. 
     When this circuit is selected, H level signals are input to a gate terminal of M 1  as scanning signals from the scanning lines  26  and the V data produces voltage in accordance with current drive capacity of M 1  in C 1  situated between a gate terminal of M 2  and power supply potential V 1 . Next, when an electric current in accordance with the written Vdata is supplied to the organic EL device  17 , L level signals are input to the scanning lines  26 . As a result, M 1  is turned off and an electric current in accordance with current drive capacity of M 2  is supplied to the organic EL device  17  by the voltage produced in C 1 ; then the organic EL device  17  emits light of brightness in accordance with the supplied electric current. 
     Since both the lens region and the non-lens region are driven in an integrated manner in this example, with the optical properties illustrated in  FIG. 2 , the lens region increases brightness at the top and the existence of the non-lens region reduces the decrease in brightness in oblique directions; as a result, the radiation angle characteristics are improved. It is therefore possible to keep the radiation angle characteristics while enhancing light utilization efficiency. 
     Second Driving Method 
     A second driving method is an exemplary method of driving the organic EL display device illustrated in  FIG. 6A  which includes the pixel configuration illustrated in  FIG. 1B  and the pixel circuit illustrated in  FIG. 6B . M 1 , M 3  and M 4  are nMOSs. If M 1 , M 3  and M 4  are pMOSs, the H level and the L level should be inverted. 
     In  FIG. 6B , scanning selection signals are input to the scanning lines  26  and information signals (i.e., voltage data, Vdata) representing predetermined gradation are input to the data lines  25  in synchronization with the scanning selection signals. The first electrode  11  of the organic EL device  17   a  is connected to a drain terminal of M 3  and the second electrode  14  is connected to ground potential CGND. The first electrode  11  of the organic EL device  17   b  is connected to a drain terminal of M 4  and the second electrode  14  is connected to ground potential CGND. 
     When this circuit is selected, the L level signals are input to the selection control lines  37  and  38  and thus M 1  is turned on and M 3  and M 4  are turned off. Since M 3  and M 4  are not electrically conductive, no electric current flows through the organic EL devices  17   a  and  17   b . The V data applied from the data lines  25  produces voltage in accordance with current drive capacity of M 1  in C 1  situated between a gate terminal of M 2  and power supply potential V 1 . 
     Next, when an electric current in accordance with the written V data is supplied to the organic EL device  17   a , L level signals are input to the scanning lines  26 , H level signals are input to the selection control lines  37  and L level signals are input to the selection control lines  38 . At this time, M 1  is turned off, M 3  is turned on and M 4  is turned off. Since only M 3  is electrically conductive, with the voltage produced in C 1 , an electric current in accordance with the current drive capacity of M 2  is supplied to the organic EL device  17   a  and the organic EL device  17   a  emits light of brightness in accordance with the supplied electric current. 
     If an electric current is supplied only to the organic EL device  17   b , L level signal are input to the scanning lines  26 , L level signals are input to the selection control lines  37  and H level signals are input to the selection control lines  38 . At this time, M 1  is turned off, M 3  is turned off and M 4  is turned on. Since only M 4  is electrically conductive, an electric current in accordance with current drive capacity of M 2  is supplied to the organic EL device  17   b  by the voltage produced in C 1 ; then the organic EL device  17   b  emits light of brightness in accordance with the supplied electric current. 
     In this manner, the organic EL devices  17   a  and  17   b  can be controlled independently by selecting the H level signals and the L level signals as the signals input to the selection control lines  37  and  38 . It is therefore possible to control the organic EL display device  21  by selecting either of “wide radiation angle characteristic” or “priority on brightness at the top.” In this example, the current values supplied to the organic EL devices  17   a  and  17   b  are the same. 
     Since the same signals are input to the selection control lines  37  and  38 , the organic EL devices  17   a  and  17   b  can also be driven in an integrated manner; thus it is possible to select independent driving and integrated driving in accordance with the purpose. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2010-179137 filed Aug. 10, 2010, which is hereby incorporated by reference herein in its entirety.