Abstract:
An organic light emitting element according to an exemplary embodiment includes: a first electrode; a hole injection layer contacting the first electrode; a first emission layer comprising at least two sublayers emitting different color lights and contacting the hole injection layer; a first impurity layer of a first conductive type contacting the first emission layer; a second impurity layer of a second conductive type contacting the first impurity layer; a second emission layer comprising at least two sublayers emitting different color lights and contacting the second impurity layer; a electron injection layer contacting the second emission layer; and a second electrode contacting the electron injection layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application relies upon and claims priority to Korean Patent Application No. 10-2007-0036442 filed in the Korean Intellectual Property Office on Apr. 13, 2007, the contents of which are incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The disclosure relates to an organic light emitting element and in particular, an organic light emitting element and an organic light emitting device including a white organic light emitting member. 
         [0004]    (b) Description of the Related Art 
         [0005]    An organic light emitting device includes a plurality of organic light emitting elements that include an anode, a cathode, and an organic light emitting member disposed between the anode and the cathode. 
         [0006]    An organic light emitting element emits white light or primary-color light, and includes a light emission layer and auxiliary layers such as an electron injection layer, a hole injection layer, an electron transport layer, and a hole transport layer. A light emitting layer for an organic light emitting element generating white light has a layered structure of a plurality of light emitting materials respectively emitting three primary colors such as red, green, and blue lights. 
         [0007]    However, such a white organic light emitting element has a low emission efficiency. 
       SUMMARY OF THE INVENTION 
       [0008]    An organic light emitting element according to one embodiment of the subject matter disclosed includes: a first electrode; a hole injection layer contacting the first electrode; a first emission layer comprising at least two sublayers emitting different color lights and contacting the hole injection layer; a first impurity layer of a first conductive type contacting the first emission layer; a second impurity layer of a second conductive type contacting the first impurity layer; a second emission layer comprising at least two sublayers emitting different color lights and contacting the second impurity layer; a electron injection layer contacting the second emission layer; and a second electrode contacting the electron injection layer. 
         [0009]    The lights emitted by the at least two sublayers in each of the first and the second emission layers may be synthesized to form a white light. 
         [0010]    At least one of the at least two sublayers in each of the first and the second emission layers may have a hole transport characteristic or an electron transport characteristic. 
         [0011]    The at least two sublayers in each of the first and the second emission layers may include a first sublayer, a second sublayer, and a third sublayer that are deposited in sequence, and the second sublayer may have an emission efficiency less than the first sublayer and the third sublayer. 
         [0012]    The first sublayer may have a hole transport characteristic and the third sublayer has an electron transport characteristic. 
         [0013]    The first electrode may be an anode, the second electrode may be a cathode, and the first sublayer may be closer to the first electrode than the third sublayer. 
         [0014]    The second sublayer may emit blue light, and the first sublayer and the third sublayer may emit red and green lights, respectively, or green and red lights, respectively. 
         [0015]    The hole injection layer may include an impurity of the second conductive type and the electron injection layer comprises an impurity of the first conductive type. 
         [0016]    The first conductive type may be n-type and the second conductive type may be p-type. 
         [0017]    The first impurity layer may serve as an electron injection layer and the second impurity layer may serve as a hole injection layer. 
         [0018]    An organic light emitting device according to one embodiment of the subject matter disclosed includes: an organic light emitting element comprising an anode, a cathode, and an organic light emitting member disposed between the anode and the cathode; a driving transistor connected to the organic light emitting element; a switching transistor connected to a driving transistor; a gate line connected to the switching transistor; and a data line connected to the switching transistor and insulated from the gate line, wherein the organic light emitting element comprises: a multi-layered first emission layer, a multi-layered second emission layer, a impurity junction layer disposed between the first emission layer and the second emission layer; a hole injection layer that has a first surface contacting the anode and a second surface contacting the first emission layer; and an electron injection layer that has a first surface contacting the first emission layer and a second surface contacting the cathode. 
         [0019]    Each of the first emission layer and the second emission layer emits white light. 
         [0020]    Each of the first emission layer and the second emission layer may include a first sublayer, a second sublayer, and a third sublayer that are deposited in sequence, and the second sublayer may have an emission efficiency less than the first sublayer and the third sublayer. 
         [0021]    The first sublayer may have a hole transport characteristic and the third sublayer may have an electron transport characteristic, and the first sublayer may have closer to the anode than the third sublayer. 
         [0022]    The electron injection layer and the hole injection layer may include impurity. 
         [0023]    The impurity junction layer may include a p-type impurity layer and an n-type impurity layer contacting the p-type impurity layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is an equivalent circuit of an organic light emitting device according to an exemplary embodiment; 
           [0025]      FIG. 2  is a layout view of a pixel of an organic light emitting device according to an exemplary embodiment; 
           [0026]      FIG. 3  is a sectional view of the organic light emitting device shown in  FIG. 2  taken along line III-III; and 
           [0027]      FIG. 4  is a schematic sectional view of an organic light emitting element according to exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0028]    The subject matter of the disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown. 
         [0029]    In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numerals refer to like elements throughout. It will be understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. 
         [0030]    An organic light emitting device according to an exemplary embodiment will now be described in detail with reference to  FIG. 1 . 
         [0031]      FIG. 1  is an equivalent circuit for an organic light emitting device according to an exemplary embodiment. 
         [0032]    Referring to  FIG. 1 , an organic light emitting device includes a plurality of signal lines  121 ,  171  and  172 , and a plurality of pixels PX connected to the signal lines  121 , 171  and  172  and arranged in a matrix. 
         [0033]    The signal lines includes a plurality gate lines  121  transmitting gate signals (or scanning signals), a plurality of data lines  171  transmitting data signals, and a plurality of driving voltage lines  172  transmitting a driving voltage. The gate lines  121  extend approximately in a row direction and parallel to each other. The data lines  171  and the driving voltage lines  172  extend approximately in a column direction and parallel to each other. 
         [0034]    Each pixel PX includes a switching transistor Qs, a driving transistor Qd, a storage capacitor Cst and an organic light emitting diode (OLED) LD. 
         [0035]    The switching transistor Qs has a control terminal, an input terminal, and an output terminal. The control terminal is connected to a gate line  121 , the input terminal is connected to a data line  171 , and the output terminal is connected to the driving transistor Qd. The switching transistor Qs transmits data signals received from the data line  171  to the driving transistor Qd in response to a scanning signal from the gate lines  121 . 
         [0036]    The driving transistor Qd also has a control terminal, an input terminal, and an output terminal. The control terminal is connected to the switching transistor Qs, the input terminal is connected to the driving voltage lines  172 , and the output terminal is connected to the OLED LD. The driving transistor Qd generates an output current I LD  having a magnitude depending on the voltage difference between the control terminal and the output terminal. 
         [0037]    The capacitor Cst is connected between the control terminal and the input terminal of the driving transistor Qd. The capacitor Cst stores the data signals applied to the control terminal of the driving transistor Qd and maintains the signals after the switching transistor Qs turns off. 
         [0038]    The OLED LD has an anode connected to the output terminal of the driving transistor Qd and a cathode connected to a common voltage Vss. The OLED LD emits light having an intensity depending on the output current I LD  of the driving transistor. This light is used to display images. 
         [0039]    The switching transistor Qs and the driving transistor Qd are n-channel field effect transistors (FETs). However, at least one of the switching transistor Qs and the driving transistor Qd may be a p-channel FET. Moreover, relative positions of the transistors Qs and Qd, the capacitor Cst, and the OLED LD may be varied. 
         [0040]    Now, a detailed structure of the organic light emitting device is described in detail with reference to  FIGS. 2 and 3  as well as  FIG. 1 . 
         [0041]      FIG. 2  is a layout view of a pixel of an organic light emitting device according to an exemplary embodiment, and  FIG. 3  is a sectional view of the organic light emitting device shown in  FIG. 2  taken along line III-III. 
         [0042]    A plurality of semiconductor islands  154   b  for driving transistors (referred to as “driving semiconductor islands” hereinafter) are formed on a substrate  110 . The driving semiconductor islands  154   b  may be made of crystalline semiconductor such as microcrystalline silicon and polycrystalline silicon. 
         [0043]    A plurality of pairs of ohmic contact islands  163   b  and  165   b  for driving transistors (referred to as “driving ohmic contacts” hereinafter) are formed on the driving semiconductor islands  154   b . The driving ohmic contacts  163   b  and  165   b  have island shapes and may be made of n+ crystalline silicon, such as microcrystalline silicon or polysilicon, heavily doped with n type impurity such as phosphorous. 
         [0044]    A plurality of gate lines  121 , a plurality of input electrodes for driving transistors (referred to as “driving input electrodes” hereinafter), and a plurality of output electrodes for driving transistors  175   b  (referred to as “driving output electrodes” hereinafter) are formed on the substrate  110  and the driving ohmic contacts  163   b  and  165   b.    
         [0045]    The gate lines  121 , disposed on the substrate  110 , transmit gate signals and extend approximately in a transverse direction. Each gate line  121  includes a plurality of control electrodes  124   a  for switching transistors (referred to as “switching control electrodes” hereinafter), which extend upward, and an end portion  129  having a large area for connection with other layer of external driving circuits. 
         [0046]    The driving input electrodes  173   b  and the driving output electrodes  175   b  are separated from the gate lines  121  and disposed on the driving ohmic contacts  163   b  and  165   b  and the substrate  110 , respectively. 
         [0047]    A gate insulating layer  140  that may be made of silicon dioxide SiO 2  or silicon nitride SiN x  is formed on the gate lines  121 , the driving input electrodes  173   b , the driving output electrodes  175   b , and exposed portions of the driving semiconductor islands  154   b.    
         [0048]    A plurality of semiconductor islands  154   a  for switching transistors (referred to as “switching semiconductor islands” hereinafter), which may be made of hydrogenated amorphous silicon, are formed on the gate insulating layer  140 . The switching semiconductor islands  154   a  are disposed on the switching control electrodes  124   a.    
         [0049]    A plurality of pairs of ohmic contact islands  163   a  and  165   a  for switching transistors (referred to as “switching ohmic contacts” hereinafter) are formed on the switching semiconductor islands  154   a . The switching ohmic contacts  163   a  and  165   a  have island shapes and may be made of n+ hydrogenated amorphous silicon heavily doped with n type impurity such as phosphorous. 
         [0050]    A plurality of data lines  171 , a plurality of driving voltage lines  172 , and a plurality of electrode members  176  are formed on the switching ohmic contacts  163   a  and  165   a  and the gate insulating layer  140 . 
         [0051]    The data lines  171  transmit data signals and extend approximately in a longitudinal direction to intersect the gate lines  121 . Each of the data lines  171  includes a plurality of input electrodes  173   a  for switching transistors (referred to as “switching input electrodes” hereinafter), which extend toward the switching control electrodes  124   a , and an end portion  179  having a large area for connection with other layer of external driving circuits. 
         [0052]    The driving voltage lines  172  transmit a driving voltage and extend approximately in the longitudinal direction to intersect the gate lines  121 . 
         [0053]    The electrode members  176  are separated from the data lines  171  and the driving voltage lines  172 . Each of the electrode members  176  includes an output electrode  175   a  for a switching transistor (referred to as “switching output electrode” hereinafter) and a control electrode  124   b  for a driving transistor (referred to as “driving control electrode” hereinafter). 
         [0054]    The switching output electrode  175   a  is disposed on a switching ohmic contact  165   a  and the driving control electrode  124   b  is disposed on a driving semiconductor island  154   b.    
         [0055]    The gate lines  121 , the data lines  171 , the driving voltage lines  172 , and the electrode members  176  may be made of the same material. 
         [0056]    A plurality of color filters  230  are formed on the data lines  171 , the driving voltage lines  172 , the electrode members  176 , and exposed portions of the switching semiconductor islands  154   a . However, when the organic light emitting device includes white pixels, the white pixels have no color filter or have transparent white filters (not shown). 
         [0057]    The color filters  230  have a plurality of through holes  232   b ,  233   b ,  235   b . The through holes  232   b  expose the driving voltage lines  172 , the through holes  233   b  exposed the driving input electrodes  173   b , and the through holes  235   b  expose the driving output electrodes  175   b.    
         [0058]    An interlayer film (not shown) may be formed under the color filters  230 . The interlayer film may prevent the pigments in the color filters  230  from intruding the switching semiconductor islands  154   a.    
         [0059]    A passivation layer  180  is formed on the color filters  230 , the data lines  171 , the driving voltage lines  172 , and the electrode members  176 . 
         [0060]    The passivation layer  180  has a plurality of contact holes  182  exposing the end portions  179  of the data lines  171  and a plurality of contact holes  182   b  exposing the driving voltage lines  172  through the through holes  232   b . The passivation layer  180  and the gate insulating layer  140  has a plurality of contact holes  181  exposing the end portions  129  of the gate lines  121 , a plurality of contact holes  183   b  exposing the driving input electrodes  173   b  through the through holes  233   b , and a plurality of contact holes  185   b  exposing the driving output electrodes  175   b  through the through holes  235   b.    
         [0061]    A plurality of pixel electrodes  191 , a plurality of connecting members  85 , and a plurality of contact assistants  81 ,  82  are formed on the passivation layer  180 . 
         [0062]    The pixel electrodes  191  are connected to the driving output electrodes  175   b  through the contact holes  185   b.    
         [0063]    The connecting members  85  are connected to the driving voltage lines  172  and the driving input electrodes  173   b  through the contact holes  182   b  and  183   b . The connecting members  85  may overlap the driving control electrodes  124   b  in part to form storage capacitors Cst. 
         [0064]    The contact assistants  81  and  82  are connected to the end portions  129  of the gate lines  121  and the end portions  179  of the data lines  171  through the contact holes  181  and  182 . The contact assistants  81  and  82  enhances the adhesion between an external device and the end portions  129  and  179  of the gate lines  121  and the data lines and protects the end portions  129  and  179 . 
         [0065]    The pixel electrode  191 , the connecting members  85 , and the contact assistants  81  and  82  may be made of transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). 
         [0066]    An insulating bank  361  is formed on the pixel electrodes  191  and the connecting members  85 . The bank  361  surrounds boundaries of the pixel electrodes  191  to form openings  365 . 
         [0067]    A plurality of organic light emitting members  370  emitting white light are formed on the bank  361  and the pixel electrode  191 , and a common electrode  270  supplied with a common voltage Vss is formed thereon. 
         [0068]    Referring to  FIG. 4 , the organic light emitting element  370  includes a lower emitting member  380  and an upper emitting member  390 . 
         [0069]    The lower emitting member  380  includes a hole injection layer (HIL)  381 , an impurity layer  382 , and an emission layer  383  interposed between the EIL  381  and the impurity layer  382 . The upper emitting member  390  includes an electron injection layer (EIL)  391 , an impurity layer  392 , and an emission layer  393  interposed between the EIL  391  and the impurity layer  392   
         [0070]    The HIL  381  of the lower emitting member  380  is adjacent to the pixel electrode  191  and may be doped with a p-type impurity. The impurity layer  382  is disposed opposite the HIL  381  and may be doped with an n-type impurity. The EIL  391  of the upper emitting member  390  is disposed adjacent to the common electrode  270  and may be doped with an n-type impurity. The impurity layer  392  is disposed opposite the EIL  391  and may be doped with a p-type impurity. The n-type impurity layer  382  of the lower emitting member  380  and the p-type impurity layer  392  of the upper emitting member  390  contact each other to form a impurity junction. 
         [0071]    The p-type impurity layer  392  serves as a hole injection layer, and the n-type impurity layer  382  serves as an electron injection layers. 
         [0072]    The HIL  381  and the p-type impurity layer  392  may be made of the same material or different materials. Likewise, the n-type impurity layer  382  and the EIL  391  may be made of the same material or different materials. 
         [0073]    The emission layer  383 / 393  includes a red sublayer  383 R/ 393 R, a blue sublayer  383 B/ 393 B, and a green sublayer  383 G/ 393 G. The red sublayer  383 R/ 393 R, the blue sublayer  383 B/ 393 B, and the green sublayer  383 G/ 393 G are arranged differently according to their characteristics. Among the sublayers  383 R,  383 B,  383 G/ 393 R,  393 B,  393 G, one having the lowest emission efficiency may be disposed in the middle, another sublayer having a good hole-transport characteristic may be disposed adjacent to the pixel electrode  191 , while another sublayer having a good electron-transport characteristic may be disposed adjacent to the common electrode  270 . For obtaining good emission efficiency in a layered structure, the charge carriers such as electrons and holes may be distributed uniformly in the emission layer as a whole. Since the probability for finding the charge carriers is high in a middle portion, the placement of the lowest-efficiency layer in the middle can yield relatively uniform charge distribution and thus the whole emission efficiency can be made high. 
         [0074]      FIG. 4  shows that the blue sublayer  383 B/ 393 B is disposed in the middle, because the commercially available material for the blue sublayer  383 B/ 393 B has emission efficiency lower than materials for other sublayers in the current stage. However, this structural arrangement is optional. 
         [0075]    The positions of the red sublayer  383 R/ 393 R and the green sublayer  383 G/ 393 G shown in  FIG. 4  may be exchanged, and the positions of the red sublayer  383 R/ 393 R and the green sublayer  383 G/ 393 G are different in the lower emitting member  380  and the upper emitting member  390 . For example, the red sublayer  383 R in the lower emitting member  380  may be disposed in the lower portion, while the red sublayer  393 R in the upper emitting member  390  may be disposed in the upper portion. The opposite arrangement is also allowed. 
         [0076]    As described above, since two emission layers  383  and  393  are layered, the emission efficiency is high. 
         [0077]    In addition, there is no hole transport layer and no electron transport layer, and thus the structure is simple. Instead of the omission of the hole transport layer and the electron transport layer, the sublayer adjacent to the pixel electrode  191  in one of the lower and the upper emission members  380  and  390  may have a hole transport characteristic, and the sublayer close to the common electrode  270  may have an electron transport characteristic. For example, in  FIG. 4 , the red sublayers  383 R,  393 R may be made of materials having a hole transport characteristic, and the green sublayer  383 G/ 393 G may be made of materials having a electron transport characteristic. 
         [0078]    In this organic light emitting device, the pixel electrode  191 , the organic light emitting element  370 , and the common electrode  270  form an OLED LD that has the pixel electrode  191  as an anode and the common electrode  270  as a cathode. However, the pixel electrode  191  may be a cathode, while the common electrode  270  may be an anode, and in this case, the internal structure of the organic light emitting element  370  is reversed relative to that shown in  FIG. 4 . 
         [0079]    A switching control electrode  124   a  connected to a gate line  121 , a switching input electrode  173   a  connected to a data line  171 , and a switching output electrode  175   a  along with a switching semiconductor island  154   a  form a switching thin film transistor (TFT) Qs that has a channel in the switching semiconductor island  154   a  disposed between the switching input electrode  173   a  and the switching output electrode  175   a.    
         [0080]    A driving control electrode  124   b  connected to a switching output electrode  175   a , a driving input electrode  173   b  connected to a driving voltage line  172 , and a driving output electrode  175   b  connected to the pixel electrode  191  along with the driving semiconductor islands  154   b  form a driving TFT Qd that has a channel in the driving semiconductor island  154   b  disposed between the driving input electrode  173   b  and the driving output electrode  175   b.    
         [0081]    As described above, the switching semiconductor islands  154   a  are made of amorphous silicon, and the driving semiconductor islands  154   b  are made of crystalline semiconductor, thereby satisfying characteristics required by the TFTs. However, the semiconductor types included in the driving TFTs Qd and the switching TFTs Qs may be different from those described above. For example, both the two TFTs Qd and Qs may include amorphous silicon only or crystalline silicon only. 
         [0082]    The driving TFTs Qd shown in  FIGS. 2 and 3  have a top gate structure, and the switching TFTs Qs have a bottom gate structure. However, this structural arrangement is optional. 
         [0083]    According to another embodiment of the present invention, each pixel PX may further include other transistors for preventing or compensating for the degradation of the OLED LD and the driving transistor Qd as well as a switching transistor Qs and a driving transistor Qd. 
         [0084]    The subject matter disclosed herein can be employed in other types of organic light emitting devices. 
         [0085]    Although preferred embodiments have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.