Patent Publication Number: US-9406884-B2

Title: Method for making organic light emitting diode array

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 201310724055.2 filed on Dec. 25, 2013 in the China Intellectual Property Office, the contents of which are incorporated by reference herein. 
     FIELD 
     The subject matter herein generally relates to organic light emitting diode (OLED) arrays and method for making the same. 
     BACKGROUND 
     Organic light emitting diodes are a type of light emitting diode that is made of thin films of organic molecules. A display screen using the organic light emitting diodes need no back light source, can save electric energy, and has greater angle of visibility. Thus, the organic light emitting diodes attract more and more attention. 
     A conventional method for making the organic light emitting diodes is to make a plurality of organic light emitting diodes on a substrate to form an array. The method includes: forming a thin-film transistor (TFT) array on the substrate; applying a first insulative layer on the thin-film transistor array; forming a plurality of first electrodes on the first insulative layer; applying a second insulative layer on the first insulative layer to cover the edges of each of plurality of first electrodes to expose the middle portion of each of plurality of first electrodes; depositing an organic light emitting layer on the middle portion of each of plurality of first electrodes; and making a second electrode on the organic light emitting layer. However, the organic light emitting layer is formed usually by vacuum evaporation which needs mask, high temperature, and vacuum device. Thus, the method is complicated and high cost. 
     What is needed, therefore, is to provide an organic light emitting diode arrays and method for making the same which can overcome the shortcomings as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures, wherein: 
         FIG. 1  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 2  is a schematic view of one embodiment of a plurality of convexities arranged in a two-dimensional array. 
         FIG. 3  is a schematic view of one embodiment of a plurality of strip-shaped convexities arranged in a one-dimensional array. 
         FIG. 4  is a flow chart of one embodiment of a method for making a first electrode of an organic light emitting diode array. 
         FIG. 5  is a flow chart of one embodiment of a method for making an organic light emitting layer of an organic light emitting diode array. 
         FIG. 6  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 7  is a schematic view of one embodiment of an organic light emitting layer. 
         FIG. 8  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 9  is a flow chart of one embodiment of a method for making an organic red light emitting layer of an organic light emitting diode array. 
         FIG. 10  is a flow chart of one embodiment of a method for making an organic green light emitting layer of an organic light emitting diode array. 
         FIG. 11  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 12  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 13  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 14  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 15  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 16  is a top view of the flow chart of  FIG. 15 . 
         FIG. 17  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 18  is a flow chart of one embodiment of a method for making a hole transport layer with different thickness by transfer printing once time. 
         FIG. 19  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 20  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 21  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 22  is a flow chart of one embodiment of a method for making a hole injection layer and a hole transport layer with different thickness by transfer printing once time. 
         FIG. 23  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 24  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 25  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 26  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 27  is a schematic view of one embodiment of an organic light emitting diode array. 
         FIG. 28  is an exploded view of one embodiment of the organic light emitting diode array of  FIG. 27 . 
         FIG. 29  is a flow chart of one embodiment of a method for making an organic light emitting diode array. 
         FIG. 30  is an exploded view of one embodiment of an organic light emitting diode array. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The term “outside” refers to a region that is beyond the outermost confines of a physical object. The term “inside” indicates that at least a portion of a region is partially contained within a boundary formed by the object. The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     The present disclosure is described in relation to organic light emitting diode arrays and methods for making the same. The organic light emitting diode array includes a base having a plurality of convexities, and a plurality of organic light emitting diodes located on the plurality of convexities. Each of the plurality of organic light emitting diodes can include a hole injection layer (HIL), a hole transport layer (HTL), an electroluminescent layer (EL), an electron transport layer (ETL), and an electron injection layer (EIL) stacked with each other in that order. The hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer are optional. The plurality of organic light emitting diodes can share a common hole injection layer, hole transport layer, electron transport layer, and/or the electron injection layer. The organic light emitting diode array can be an active matrix type or passive matrix type. The number of the organic light emitting diodes in each organic light emitting diode array is not limited. Each of the plurality of organic light emitting diodes can be used as a pixel unit. Each of the plurality of organic light emitting diodes can also be used as a sub-pixel, and three of the plurality of organic light emitting diodes form a pixel unit. 
     The plurality of organic light emitting diodes can be made on the plurality of convexities by transfer printing. In some embodiments, at least one of the hole injection layer, the hole transport layer, the electroluminescent layer, the electron transport layer, and the electron injection layer can be made by transfer printing. Especially, the hole injection layer, the hole transport layer, the electroluminescent layer are made by transfer printing, and the electron transport layer and the electron injection layer are made by vacuum evaporation because the wetting process may change the property of the electron injection layer. The material for transfer printing is coated on a template first and then transfer printed from the template to the plurality of convexities to form a plurality of layer-shaped elements. The material for transfer printing can be transfer printed to form a plurality of layer-shaped elements with the same or different thickness or heights. The plurality of layer-shaped elements can be transfer printed on all of the plurality of convexities once time, twice time, or more than twice time. 
       FIG. 1  illustrates a method of one embodiment for making an organic light emitting diode array  10 . The method includes following steps: 
     step (S 10 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; the first insulative layer  106  defines a plurality of convexities  108  on a surface opposite to the plurality of thin-film transistors  104 ; 
     step (S 11 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein each of the plurality of first electrodes  110  is located on and electrically connected to one of the plurality of thin-film transistors  104 ; 
     step (S 12 ), applying a plurality of organic light emitting layers  120  on the plurality of first electrodes  110 ; 
     step (S 13 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  and expose part of each of the plurality of organic light emitting layers  120 ; and 
     step (S 14 ), electrically connecting a second electrode  130  to the plurality of organic light emitting layers  120 . 
     In step (S 10 ), the material of the substrate  102  can be glass, ceramic, silicon dioxide (SiO 2 ), silicon nitride (SiN) or polymer. The plurality of thin-film transistors  104  can be made of semiconductor such as silicon, gallium arsenide (GaAs), gallium nitride (GaN), or carbon nanotubes (CNTs). In one embodiment, the substrate  102  is a silicon dioxide layer on a wafer, and the plurality of thin-film transistors  104  are made on the wafer similar to that used to make semiconductor device. 
     The first insulative layer  106  covers all of the plurality of thin-film transistors  104 . The first insulative layer  106  can be configured to provide a smooth surface for making the plurality of organic light emitting diodes and insulate the plurality of organic light emitting diodes from the plurality of thin-film transistors  104 . The first insulative layer  106  can be made of organic insulative material or inorganic insulative material. The thickness of the first insulative layer  106  can be in a range from about 1 micrometer to about 50 micrometers. In one embodiment, the thickness of the first insulative layer  106  is in a range from about 1 micrometer to about 15 micrometers. The first insulative layer  106  can be made by depositing, transfer printing or spin coating. 
     The plurality of convexities  108  can be arranged in a two-dimensional array as shown in  FIG. 2 . The shape of the convexity  108  can be selected according to need, as long as the convexity  108  has a smooth top surface  109 . Each of the plurality of convexities  108  can be a frustum of a cone, a cuboid, or a cube, namely, the smooth top surface  109  can be circular, square, or rectangular. The smooth top surface  109  can be a planar surface or a curved surface such as concave spherical or convex spherical. When the smooth top surface  109  is a curved surface, the organic light emitting layer  120  can have a greater area, and the angle of the emergent light of the organic light emitting layer  120  can be adjusted by changing the curvature of the smooth top surface  109 . The size of the convexity  108  can be selected according to pixel unit of the organic light emitting diode array  10 , for example, from tens micrometers to hundreds micrometers. The plurality of convexities  108  can be made by printing, etching, or stamping. When the first insulative layer  106  is made of organic insulative material, the plurality of convexities  108  can be made by stamping. When the first insulative layer  106  is made of inorganic insulative material, the plurality of convexities  108  can be made by etching. The plurality of convexities  108  can also be arranged in a one-dimensional array as shown in  FIG. 3 . Each of the plurality of convexities  108  is strip-shaped, and the plurality of convexities  108  are in parallel with each other. In one embodiment, the plurality of convexities  108  are a plurality of cuboids arranged in a two-dimensional array, and the plurality of convexities  108  are located corresponding to the plurality of thin-film transistors  104  in a one-to-one manner. 
     In step (S 11 ), the plurality of first electrodes  110  are paced and insulated from each other. The plurality of first electrodes  110  are electrical conductive layers and made of conductive oxide, such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO) or tin oxide (TO), or metal such as gold, silver, aluminum, magnesium or alloy thereof. Each of the plurality of first electrodes  110  is located at least on the smooth top surface  109  of the corresponding convexity  108 . In one embodiment, each of the plurality of first electrodes  110  is coated on both the smooth top surface  109  and side surfaces of the corresponding convexity  108 . The plurality of first electrodes  110  can be formed by directly depositing through a mask. The plurality of first electrodes  110  can also be formed by depositing a continuous conductive layer to cover all the plurality of convexities  108  first, and then patterning the continuous conductive layer by etching to obtain the plurality of first electrodes  110 . At least part of each of the plurality of first electrodes  110  is located on the smooth top surface  109  of the corresponding convexity  108  so that each first electrode  110  has a protrudent surface. The protrudent surface can be used to transfer print the plurality of organic light emitting layers  120 . 
       FIG. 4  illustrates a method of one embodiment for making the plurality of first electrodes  110 . The method includes following steps: 
     step (S 110 ), exposing part of each of the plurality of thin-film transistors  104  by etching the base  100  from the first insulative layer  106 ; 
     step (S 111 ), depositing a continuous conductive layer  112  to cover all the plurality of convexities  108  and electrically connect to the plurality of thin-film transistors  104 ; 
     step (S 112 ), patterning the continuous conductive layer  112  to obtain the plurality of first electrodes  110  spaced from each other, wherein each of the plurality of first electrodes  110  corresponds to and is electrically connected to one of the plurality of thin-film transistors  104 ; and 
     step (S 113 ), making a patterned third insulative layer  142  between the plurality of first electrodes  110  so that adjacent two of the plurality of first electrodes  110  are insulated from each other and the part of the plurality of first electrodes  110  on the smooth top surfaces  109  are exposed. 
     In step (S 110 ), the etching method can be selected according to the material of the first insulative layer  106  and the thin-film transistors  104 . A plurality of openings  107  are formed to corresponding the plurality of thin-film transistors  104  so that at least part of each of the plurality of thin-film transistors  104  is exposed. 
     In step (S 111 ), the method for depositing the conductive layer  112  can be selected according to need, for example, sputtering, chemical vapor deposition, or thermal deposition. The conductive layer  112  can be deposited in to the plurality of openings  107  to electrically connect to the plurality of thin-film transistors  104 . In one embodiment, the depositing the conductive layer  112  includes: depositing a first indium tin oxide layer; applying a silver layer on the first indium tin oxide layer; and depositing a second indium tin oxide layer on the silver layer. Thus, an ITO/Ag/ITO composite conductive layer  112  is formed. Because the silver metal layer is sandwiched between two indium tin oxide layers, the metal layer can prevent oxidation. 
     In step (S 112 ), the patterning the continuous conductive layer  112  can be performed by etching through a mask. The pattern of the plurality of first electrodes  110  can be designed according to need. 
     In step (S 113 ), the patterned third insulative layer  142  can be formed by directly depositing through a mask. The patterned third insulative layer  142  can be formed by depositing a continuous insulative layer to cover the plurality of first electrodes  110  and then removing part of the continuous insulative layer to expose the part of the plurality of first electrodes  110  on the smooth top surfaces  109 . When the conductive layer  112  is ITO/Ag/ITO composite, the metal layer will be exposed on edge during patterning the conductive layer  112 . The patterned third insulative layer  142  can cover the edge of the plurality of first electrodes  110  to protect the exposed metal layer of the ITO/Ag/ITO composite. The patterned third insulative layer  142  can also prevent the plurality of first electrodes  110  from being broken or electrically connected with each other in following process. The step (S 113 ) is optional. 
     In step (S 12 ), the plurality of organic light emitting layers  120  are made my transfer printing. In one embodiment, as shown in  FIG. 5 , each of the plurality of organic light emitting layers  120  only includes an electroluminescent layer  125 . The plurality of organic light emitting layers  120  are made by following steps: 
     step (S 120 ), applying an organic electroluminescent film  1252  on a surface  1502  of a first template  150 ; 
     step (S 121 ), contacting the protrudent surfaces of the plurality of first electrodes  110  with the organic electroluminescent film  1252 ; and 
     step (S 122 ), separating the plurality of first electrodes  110  from the first template  150 . 
     In step (S 120 ), the material, size and shape of the first template  150  can be selected or designed according to need. The material of the organic electroluminescent film  1252  can be any organic electroluminescent high or low molecular materials that can be made in to solution, such as polyfluorene (PF). The thickness of the organic electroluminescent film  1252  can be in a range from about tens nanometers to about hundreds nanometers, for example, from about 50 nanometers to about 300 nanometers. The organic electroluminescent film  1252  can be applied on the surface  1502  of the first template  150  by spin-coating, spray-coating, brush-coating, or immerse-coating. In one embodiment, the first template  150  is a planar polydimethylsiloxane (PDMS) substrate with low surface free energy, and the organic electroluminescent film  1252  is coated on the entire surface  1502 . 
     Furthermore, a wetting layer (not shown) can be applied on the surface  1502  of the first template  150  before applying the organic electroluminescent film  1252 . Thus, the organic electroluminescent film  1252  is easy to be coated and transferred. The wetting layer can be a high volatile solvent coated on the surface  1502 , such as toluene. The wetting layer can also be a plurality of high reactive functional groups formed by treating the surface  1502 . For example, a plurality of carboxyl group (—COOH) or hydroxyl group (—OH) can be formed on the surface  1502  of the polydimethylsiloxane first template  150  by oxygen plasma treating. 
     In step (S 121 ), a pressure can be applied on the base  100  in the process of contacting the protrudent surfaces of the plurality of first electrodes  110  with the organic electroluminescent film  1252 . Because the plurality of first electrodes  110  are located on the plurality of convexities  108  and the organic electroluminescent film  1252  is formed on the planar surface  1502 , it is easy to transfer print and does not need to align the plurality of first electrodes  110  with the organic electroluminescent film  1252 . 
     In step (S 122 ), a plurality of electroluminescent layers  125  are formed on the protrudent surfaces of the plurality of first electrodes  110  and used as the plurality of organic light emitting layers  120 . 
     Furthermore, a heating can be applied on the first template  150  in the process of separating the plurality of first electrodes  110  from the first template  150 . Thus, the plurality of first electrodes  110  and the first template  150  may have different temperature, and the adhesion strength between the organic electroluminescent film  1252  and the plurality of first electrodes  110  is stronger than the adhesion strength between the organic electroluminescent film  1252  and the first template  150 . 
     Because the plurality of electroluminescent layers  125  have the same material, the organic light emitting diode array  10  is a monochromatic organic light emitting diode array. Each of the plurality of organic light emitting layer  120  can be a single layer of organic electroluminescent material that can luminesce red light, green light, blue light, or white light. Each of the plurality of organic light emitting layer  120  can also be a multi-layer structure of different organic electroluminescent materials that can be made by repeating embodiment of the method of  FIG. 5 . For example, each of the plurality of organic light emitting layer  120  includes red light electroluminescent layer, a green light electroluminescent layer, and a blue light electroluminescent layer stacked with each other. 
     Furthermore, a hole injection layer  122  and a hole transport layer  124  can be formed on the plurality of first electrodes  110  before the transfer printing the plurality of electroluminescent layers  125 . Also, an electron transport layer  126  and an electron injection layer  128  can be formed on surfaces of the plurality of electroluminescent layers  125  after the transfer printing the plurality of electroluminescent layers  125 . The hole injection layer  122 , the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  can be made by the transfer printing method of  FIG. 5 , or by the vacuum evaporation. The material of the hole injection layer  122  suitable for transfer printing can be PEDOT:PSS. The PEDOT:PSS is a water solution of a polymer consisting of PEDOT and PSS. The PEDOT is Poly(3,4-ethylenedioxythiophene). The PSS is poly(styrenesulfonate). The material of the hole transport layer  124  suitable for transfer printing can be polyaniline (PAN). 
     When the hole injection layer  122 , the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  are made by the vacuum evaporation, the hole injection layer  122 , each of the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  can be a continuous layer. Namely, the plurality of organic light emitting layers  120  have a common hole injection layer  122 , a common hole transport layer  124 , a common electron transport layer  126 , and a common electron injection layer  128 . When the hole injection layer  122 , the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  are made by the transfer printing method of  FIG. 5 , each of the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  is a patterned structure with a plurality of layers spaced from each other. Namely, each of the plurality of organic light emitting layers  120  has an independent hole injection layer  122 , an independent hole transport layer  124 , an independent electron transport layer  126 , and an independent electron injection layer  128 . 
     In step (S 13 ), the patterned second insulative layer  140  can be formed by directly depositing through a mask. The patterned second insulative layer  140  can also be formed by depositing a continuous insulative layer to cover the plurality of first electrodes  110  and the plurality of organic light emitting layers  120 , and then removing the part of the continuous insulative layer to expose a part of each of the plurality of organic light emitting layers  120 . The patterned second insulative layer  140  can be made of the same or different material as the first insulative layer  106 . The patterned second insulative layer  140  can insulate adjacent two of the plurality of first electrodes  110  and prevent the plurality of first electrodes  110  from being electrically connected with the second electrode  130  in following process. Because the plurality of first electrodes  110  are covered by the plurality of organic light emitting layers  120 , the patterned second insulative layer  140  only need to be coated on the first electrode  110  between adjacent two of the plurality of convexities  108  or on the side surfaces of the plurality of convexities  108 . In one embodiment, the patterned second insulative layer  140  and the plurality of organic light emitting layers  120  have a common planar surface so that the second electrode  130  is easy to be formed. 
     In step (S 14 ), the second electrode  130  is an electrical conductive layer and made of conductive oxide, such as indium tin oxide, indium zinc oxide, aluminum zinc oxide, zinc oxide or tin oxide, or metal such as gold, silver, aluminum, magnesium or alloys thereof. The second electrode  130  can be a continuous conductive layer, namely, the organic light emitting diode array  10  shares a common second electrode. The second electrode  130  can also be a patterned structure, namely, a plurality of second electrodes  130  are located. Each of the plurality of second electrodes  130  is located corresponding to a single one of the plurality of organic light emitting layers  120  or one row of the plurality of organic light emitting layers  120 . The second electrode  130  can be formed by sputtering, vacuum evaporation, transfer printing, or spin coating to cover all of the patterned second insulative layer  140  and the plurality of organic light emitting layers  120 . The second electrode  130  can also be formed on the corresponding one of the plurality of organic light emitting layers  120  by screen printing or mask depositing. In one embodiment, the second electrode  130  is a continuous indium tin oxide film with a thickness of about 100 micrometers. 
     Furthermore, a step of applying an insulative protecting layer on the second electrode  130  to package the organic light emitting diode array  10  can be performed. 
       FIG. 6  illustrates an organic light emitting diode array  10  of one embodiment. The organic light emitting diode array  10  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140 , and a second electrode  130 . The base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 . The first insulative layer  106  defines a plurality of convexities  108  on a surface opposite to the plurality of thin-film transistors  104 . The plurality of first electrodes  110  and the plurality of thin-film transistors  104  are located and electrically connected with each other in a one-to-one manner. Each of the plurality of first electrodes  110  is located on the top surface and side surfaces of the corresponding one of the plurality of convexities  108 . Part of the plurality of first electrodes  110  extend to the surface of the first insulative layer  106  exposed from adjacent two of the plurality of convexities  108 . The plurality of organic light emitting layers  120  are located on the surfaces of the plurality of first electrodes  110  and electrically connected with the plurality of first electrodes  110  in a one-to-one manner. The patterned second insulative layer  140  cover the plurality of first electrodes  110  and expose the plurality of organic light emitting layers  120 . The second electrode  130  covers the patterned second insulative layer  140  and the plurality of organic light emitting layers  120 . 
     Referring to  FIG. 7 , each of the plurality of organic light emitting layers  120  can include a hole injection layer  122 , a hole transport layer  124 , an electroluminescent layer  125 , an electron transport layer  126 , and an electron injection layer  128 . The hole injection layer  122 , the hole transport layer  124 , the electroluminescent layer  125 , the electron transport layer  126 , and the electron injection layer  128  are stacked with each other in that order from the first electrode  110  to the second electrode  130  or from the second electrode  130  to the first electrode  110 . Each of the hole injection layer  122 , the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  can be located only corresponding to one of the plurality of first electrodes  110 . Each of the hole injection layer  122 , the hole transport layer  124 , the electron transport layer  126 , and the electron injection layer  128  can also be a continuous layer to cover all of the plurality of first electrodes  110 . 
     The organic light emitting diode array  10  is a monochromatic organic light emitting diode array. Embodiments of full color organic light emitting diode array are provided below. Only one pixel unit is shown in the FIGS. Each of the pixel unit includes a red light organic light emitting diode, a green light organic light emitting diode, and a blue light organic light emitting diode. The red light organic light emitting diode, the green light organic light emitting diode, and the blue light organic light emitting diode are used as three sub-pixels. 
       FIG. 8  illustrates a method of one embodiment for making an organic light emitting diode array  20 . The method includes following steps: 
     step (S 20 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; and the first insulative layer  106  defines a plurality of convexities  108  on a surface opposite to the plurality of thin-film transistors  104 ; 
     step (S 21 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein each of the plurality of first electrodes  110  is located corresponding to and electrically connected to one of the plurality of thin-film transistors  104 ; 
     step (S 22 ), applying a plurality of organic light emitting layers  120  on the plurality of first electrodes  110 , wherein adjacent three of the plurality of organic light emitting layers  120  have different organic electroluminescent materials; 
     step (S 23 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  and expose part of each of the plurality of organic light emitting layers  120 ; and 
     step (S 24 ), electrically connecting a second electrode  130  to the plurality of organic light emitting layers  120 . 
     The method for making the organic light emitting diode array  20  is similar to the method for making the organic light emitting diode array  10  except that in step (S 22 ), three organic light emitting layers  120  of the same pixel unit have different organic electroluminescent materials that can luminesce light of different color. In one embodiment, a red light organic light emitting layer  120 , a green light organic light emitting layer  120 , and a blue light organic light emitting layer  120  are transfer printed on adjacent three of the plurality of first electrodes  110 . Thus, the organic light emitting diode array  20  can achieve full color display. 
     In one embodiment, the red light organic light emitting layer  120 , the green light organic light emitting layer  120 , and the blue light organic light emitting layer  120  of the same pixel unit can have different thickness. In one embodiment, one of the red light organic light emitting layer  120 , the green light organic light emitting layer  120 , and the blue light organic light emitting layer  120  of the same pixel unit can have different thickness with the other two. Because the red light, green light and the blue light have different transmittance through the organic light emitting layer  120 , the second electrode layer  130  and other package layer, the different thickness of the organic light emitting layers  120  allows the red light, the green light and the blue light to be mixed uniformly. 
       FIGS. 9-10  illustrates a method of one embodiment for transfer printing three different color organic light emitting layers  120  on three adjacent first electrodes  110 . The method includes following steps: 
     step (S 220 ), applying a red light organic electroluminescent film  1252  on a surface of a second template  152 ; 
     step (S 221 ), contacting the first one of the three first electrodes  110  with the red light organic electroluminescent film  1252 ; 
     step (S 222 ), separating the first one of the three first electrodes  110  from the second template  152  so that a red light organic light emitting layer  120  is formed on the first one of the three first electrodes  110 ; 
     step (S 223 ), applying a green light organic electroluminescent film  1252  on a surface of a third template  154 ; 
     step (S 224 ), contacting the second one of the three first electrodes  110  with the green light organic electroluminescent film  1252 ; 
     step (S 225 ), separating the second one of the three first electrodes  110  from the third template  154  so that a green light organic light emitting layer  120  is formed on the second one of the three first electrodes  110 ; and 
     step (S 226 ), transfer printing a blue light organic light emitting layer  120  on the third one of the three first electrodes  110  by the process above. 
     In step (S 221 ), the second one and third one of the three first electrodes  110  are not in contact with the red light organic electroluminescent film  1252 . The step (S 221 ) can be achieved by only applying the red light organic electroluminescent film  1252  on part of the second template  152  corresponding to the first one of the three first electrodes  110 , covering the red light organic electroluminescent film  1252  corresponding to the second one and third one of the three first electrodes  110 , or allowing red light organic electroluminescent film  1252  have different heights. In one embodiment, the second template  152  has a first surface  1522  and a second surface  1524 . The first surface  1522  and the second surface  1524  have different heights so that the red light organic electroluminescent film  1252  on the second template  152  has different heights. Because the red light organic electroluminescent film  1252  has a uniform thickness, the red light organic electroluminescent film  1252  on the first surface  1522  is higher than the red light organic electroluminescent film  1252  on the second surface  1524 . When the first one of the three first electrodes  110  touches the red light organic electroluminescent film  1252  on the first surface  1522 , the second one and third one of the three first electrodes  110  are spaced from the red light organic electroluminescent film  1252  on the second surface  1524 . 
     In step (S 224 ), the red light organic light emitting layer  120  and the third one of the three first electrodes  110  are not in contact with the green light organic electroluminescent film  1252 . In one embodiment, the third template  154  has a third surface  1542  and a fourth surface  1544 . The third surface  1542  and the fourth surface  1544  have different heights so that the green light organic electroluminescent film  1252  on the third template  154  has different heights. Because the green light organic electroluminescent film  1252  has a uniform thickness, the green light organic electroluminescent film  1252  on the third surface  1542  is higher than the green light organic electroluminescent film  1252  on the fourth surface  1544 . When the second one of the three first electrodes  110  touches the green light organic electroluminescent film  1252  on the third surface  1542 , the red light organic light emitting layer  120  and the third one of the three first electrodes  110  are spaced from the green light organic electroluminescent film  1252  on the fourth surface  1544 . The height difference between the third surface  1542  and the fourth surface  1544  is greater than the height difference between the first surface  1522  and the second surface  1524 . 
       FIG. 11  illustrate an organic light emitting diode array  20  of one embodiment. The organic light emitting diode array  20  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140 , and a second electrode  130 . The organic light emitting diode array  20  is similar to the organic light emitting diode array  10  except that three organic light emitting layers  120  of the same pixel unit includes a red light organic light emitting layer  120 , a green light organic light emitting layer  120 , and a blue light organic light emitting layer  120 . Thus, the organic light emitting diode array  20  can achieve full color display. 
     In one embodiment, the red light organic light emitting layer  120 , the green light organic light emitting layer  120 , and the blue light organic light emitting layer  120  of the same pixel unit can have different thickness. Because the protrudent surfaces of the three first electrodes  110  have the same height, the surfaces of the red light organic light emitting layer  120 , the green light organic light emitting layer  120 , and the blue light organic light emitting layer  120  that is opposite to the three first electrodes  110  have different heights. The surface of the patterned second insulative layer  140  that is opposite to the base  100  can be flushed with any one of the surfaces of the red light organic light emitting layer  120 , the green light organic light emitting layer  120 , and the blue light organic light emitting layer  120  that is opposite to the three first electrodes  110 . In one embodiment, the surface of the patterned second insulative layer  140  that is opposite to the base  100  is flushed with the surface of the red light organic light emitting layer  120 . The green light organic light emitting layer  120  and the blue light organic light emitting layer  120  extends out of the patterned second insulative layer  140  and are embedded in to the second electrode  130 . 
       FIG. 12  illustrate an organic light emitting diode array  20 A of another embodiment. In the organic light emitting diode array  20 A, the organic light emitting layer  120  includes a hole injection layer  122 , a hole transport layer  124 , an electroluminescent layer  125 , an electron transport layer  126 , and an electron injection layer  128 . The hole injection layer  122  and the hole transport layer  124  are located between the first electrode  110  and the electroluminescent layer  125 . The hole injection layer  122  and the hole transport layer  124  have the same thickness and heights. The electroluminescent layers  125  have different thickness and heights. The electron transport layer  126  and the electron injection layer  128  are located between the electroluminescent layer  125  and the second electrode  130 . The electron transport layer  126  and the electron injection layer  128  have the same thickness and different heights. The surface of the patterned second insulative layer  140  that is opposite to the base  100  is flushed with the highest surface of the electron injection layer  128 . A part of the second electrode  130  is embedded in to the patterned second insulative layer  140  and in direct contact with the other two electron injection layers  128 . The organic light emitting layer  120  of  FIG. 12  can be made by making the hole injection layer  122  and the hole transport layer  124  on the first electrodes  110  via the method of  FIG. 5  or vacuum evaporation; transfer printing the electroluminescent layers  125  by the method of  FIGS. 9-10 ; and making the electron transport layer  126  and the electron injection layer  128  by or vacuum evaporation. 
     Referring to  FIG. 13  illustrates a method of one embodiment for making an organic light emitting diode array  30 . The method includes following steps: 
     step (S 30 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; the first insulative layer  106  defines a plurality of convexities  108  on a surface opposite to the plurality of thin-film transistors  104 ; 
     step (S 31 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein each of the plurality of first electrodes  110  is located corresponding to and electrically connected to one of the plurality of thin-film transistors  104 ; 
     step (S 32 ), making a patterned second insulative layer  140  to cover parts of the plurality of first electrodes  110  between the plurality of convexities  108  and expose protrudent surfaces of the plurality of first electrodes  110  on the smooth top surfaces  109  of the plurality of convexities  108 ; 
     step (S 33 ), applying a plurality of organic light emitting layers  120  on the plurality of first electrodes  110 , wherein adjacent three of the plurality of organic light emitting layers  120  have different organic electroluminescent materials; and 
     step (S 34 ), electrically connecting a second electrode  130  to the plurality of organic light emitting layers  120 . 
     The method for making the organic light emitting diode array  30  is similar to the method for making the organic light emitting diode array  20  except that the patterned second insulative layer  140  is applied before the plurality of organic light emitting layers  120 , and the three organic light emitting layers  120  of the same pixel unit have the same thickness. 
     In step (S 32 ), because the patterned second insulative layer  140  is applied before the plurality of organic light emitting layers  120 , it can prevent the plurality of organic light emitting layers  120  from being damaged and polluted when the patterned second insulative layer  140  is made by etching. The surface of the patterned second insulative layer  140  can be flushed with the smooth top surfaces  109  of the plurality of convexities  108 . 
     In step (S 33 ), because parts of the plurality of first electrodes  110  on the smooth top surfaces  109  of the plurality of convexities  108  are exposed and protruded out of the patterned second insulative layer  140 , the plurality of organic light emitting layers  120  can be transfer printed on the plurality of first electrodes  110  easily. The plurality of organic light emitting layers  120  can be transfer printed by the method of  FIGS. 9-10 . 
     In step (S 34 ), the second electrode  130  is formed by coating an electrically conductive film  1304  on a surface of a free standing support  1302 , and then placing the electrically conductive film  1304  on the plurality of organic light emitting layers  120 . The electrically conductive film  1304  is in direct contact with the plurality of organic light emitting layers  120 . Because part side surfaces of the plurality of first electrodes  110  are exposed from both the patterned second insulative layer  140  and the plurality of organic light emitting layers  120 , if the second electrode  130  is formed by directly depositing, it will cause the first electrodes  110  and the second electrode  130  being in contact with each other and short. Parts of the second electrode  130  are suspended between adjacent two of the plurality of organic light emitting layers  120 . The support  1302  can be a glass plate or a polymer sheet. 
       FIG. 14  illustrates an organic light emitting diode array  30  of one embodiment. The organic light emitting diode array  30  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140 , and a second electrode  130 . The organic light emitting diode array  30  is similar to the organic light emitting diode array  20  except that parts of the plurality of first electrodes  110  on the smooth top surfaces  109  of the plurality of convexities  108  are protruded out of the patterned second insulative layer  140 , the second electrode  130  includes a free standing support  1302  and an electrically conductive film  1304 . The support  1302  is a glass, and the electrically conductive film  1304  is a continuous indium tin oxide film. 
       FIGS. 15-16  illustrates a method of one embodiment for making an organic light emitting diode array  40 . The method includes following steps: 
     step (S 40 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; the first insulative layer  106  defines a plurality of convexities  108  on a surface opposite to the plurality of thin-film transistors  104 ; 
     step (S 41 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein each of the plurality of first electrodes  110  is located corresponding to and electrically connected to one of the plurality of thin-film transistors  104 ; 
     step (S 42 ), applying a plurality of organic light emitting layers  120  on the plurality of first electrodes  110 , wherein adjacent three of the plurality of organic light emitting layers  120  have different organic electroluminescent materials; 
     step (S 43 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  between the plurality of convexities  108  and expose each of the plurality of organic light emitting layers  120 ; and 
     step (S 44 ), electrically connecting a second electrode  130  to the plurality of organic light emitting layers  120 . 
     The method for making the organic light emitting diode array  40  is similar to the method for making the organic light emitting diode array  20  except that the plurality of convexities  108  are strip-shaped and arranged in a one-dimensional array as shown in  FIG. 3 , each of the plurality of convexities  108  corresponds to a row of the plurality of thin-film transistors  104 , and the second electrode  130  is comb-shaped. 
     In step (S 41 ), a plurality of first electrodes  110  are located on a surface of each of the plurality of convexities  108  and spaced from each other. In step (S 42 ), a strip-shaped organic light emitting layers  120  is transfer printed on entire surface of each of the strip-shaped convexity  108  to cover all of the corresponding strip-shaped convexity  108  and the plurality of first electrodes  110  on the corresponding strip-shaped convexity  108 . The organic light emitting diodes corresponding to the same strip-shaped convexity  108  share the common strip-shaped organic light emitting layers  120  and luminesce light of the same color. In step (S 44 ), the comb-shaped second electrode  130  includes a plurality of first strip-shaped conductors parallel with and spaced from each other, and a second strip-shaped conductors perpendicular with and connecting the plurality of first strip-shaped conductors. Each of the plurality of first strip-shaped conductors is located on the corresponding strip-shaped organic light emitting layers  120 . 
       FIG. 17  illustrates a method of one embodiment for making an organic light emitting diode array  50 . The method includes following steps: 
     step (S 50 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; the first insulative layer  106  defines a plurality of convexities  108  on a surface opposite to the plurality of thin-film transistors  104 ; 
     step (S 51 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein each of the plurality of first electrodes  110  is located corresponding to and electrically connected to one of the plurality of thin-film transistors  104 ; 
     step (S 52 ), applying a plurality of hole injection layers  122  on the plurality of first electrodes  110 ; 
     step (S 53 ), transfer printing a plurality of hole transport layers  124  on the plurality of hole injection layers  122 , wherein adjacent three of the plurality of hole transport layers  124  of the same pixel unit have different thickness; 
     step (S 54 ), making a plurality of electroluminescent layers  125  on the plurality of hole transport layers  124 , wherein adjacent three of the plurality of electroluminescent layers  125  of the same pixel unit have different organic electroluminescent materials; 
     step (S 55 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  between the plurality of convexities  108  and expose each of the plurality of electroluminescent layers  125 ; and 
     step (S 56 ), electrically connecting a second electrode  130  to the plurality of electroluminescent layers  125 . 
     The method for making the organic light emitting diode array  50  is similar to the method for making the organic light emitting diode array  20  except that the plurality of hole injection layers  122  and the plurality of hole transport layers  124  are applied on the plurality of first electrodes  110  before the plurality of electroluminescent layers  125 . The plurality of hole injection layers  122  have the same thickness, and the plurality of hole transport layers  124  have different thickness. Each of the organic light emitting layers  120  includes the hole injection layer  122 , the hole transport layer  124 , and the electroluminescent layer  125 . The plurality of hole injection layers  122  can be made by the method of  FIG. 5  or vacuum evaporation, and the plurality of electroluminescent layers  125  can be made by the method of  FIGS. 9-10  or vacuum evaporation. 
       FIG. 18  illustrates a method for transfer printing the plurality of hole transport layers  124  with different thickness once time. The method includes following steps: 
     step (S 530 ), forming a hole transport film  1242  on a surface of a fourth template  156 , wherein the hole transport film  1242  has different thickness corresponding to the plurality of hole injection layers  122  of the same pixel unit; 
     step (S 531 ), contacting the plurality of hole injection layers  122  with the hole transport film  1242 ; and 
     step (S 532 ), separating the plurality of hole injection layers  122  from the fourth template  156 . 
     In step (S 530 ), the hole transport film  1242  can be made by spin-coating, spray-coating, brush-coating, or immerse-coating. The fourth template  156  has a fifth surface  1562  and a sixth surface  1564 , and a seventh surface  1566 . The fifth surface  1562 , the sixth surface  1564 , and the seventh surface  1566  have different heights. In one embodiment, the fifth surface  1562  is higher than the sixth surface  1564 , and the sixth surface  1564  is higher than the seventh surface  1566 . When the hole transport film  1242  is applied on the fourth template  156 , the surface of the hole transport film  1242  that is opposite to the fourth template  156  is a planar. Thus, the hole transport film  1242  on the fifth surface  1562 , the hole transport film  1242  on the sixth surface  1564 , and the hole transport film  1242  on the seventh surface  1566  have different thickness. The method of  FIG. 18  can also be used to make the plurality of hole injection layers  122 , the plurality of electroluminescent layers  125 , the plurality of electron transport layers  126  and the plurality of electron injection layers  128 . 
       FIG. 19  illustrates an organic light emitting diode array  50  of one embodiment. The organic light emitting diode array  50  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140 , and a second electrode  130 . The organic light emitting diode array  50  is similar to the organic light emitting diode array  20  except that each of the organic light emitting layers  120  includes the hole injection layer  122 , the hole transport layer  124 , and the electroluminescent layer  125  stacked with each other. The plurality of hole injection layers  122  have the same thickness, the plurality of electroluminescent layers  125  have the same thickness, and the plurality of hole transport layers  124  have different thickness. Because the plurality of hole transport layers  124  have different thickness, the surfaces of the plurality of hole transport layers  124  that are opposite to the plurality of hole injection layers  122  have different heights. The surfaces of the plurality of electroluminescent layers  125  that are opposite to the plurality of hole injection layers  122  have different heights. Thus, the red light, the green light and the blue light can be mixed uniformly. 
       FIG. 20  illustrates an organic light emitting diode array  50 A of another embodiment. In the organic light emitting diode array  50 A, the hole injection layer  122  is a continuous layer and covers all of the plurality of first electrodes  110 . The organic light emitting diode array  50 A shares a common hole injection layer  122 . The continuous hole injection layer  122  can be made by vacuum evaporation or immerse-coating. 
       FIG. 21  illustrates a method of one embodiment for making an organic light emitting diode array  60 . The method includes following steps: 
     step (S 60 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; the first insulative layer  106  defines a plurality of convexities  108  with different heights; 
     step (S 61 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein each of the plurality of first electrodes  110  is located corresponding to and electrically connected to one of the plurality of thin-film transistors  104 ; 
     step (S 62 ), applying a plurality of hole injection layers  122  and a plurality of hole transport layers  124  on the plurality of first electrodes  110 ; 
     step (S 63 ), making a plurality of electroluminescent layers  125  on the plurality of hole transport layers  124 , wherein adjacent three of the plurality of electroluminescent layers  125  of the same pixel unit have different organic electroluminescent materials; 
     step (S 64 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  between the plurality of convexities  108  and expose each of the plurality of electroluminescent layers  125 ; and 
     step (S 65 ), electrically connecting a second electrode  130  to the plurality of electroluminescent layers  125 . 
     The method for making the organic light emitting diode array  60  is similar to the method for making the organic light emitting diode array  50  except that the plurality of convexities  108  have different heights, the plurality of hole injection layers  122  have the same thickness, and the plurality of hole transport layers  124  have the same thickness. In step (S 62 ), the plurality of hole injection layers  122  and the plurality of hole transport layers  124  can be made by vacuum evaporation or transfer printing. 
       FIG. 22  illustrates a method for transfer printing the plurality of hole injection layers  122  and the plurality of hole transport layers  12  once time. The method includes following steps: 
     step (S 620 ), forming a hole transport film  1242  on a surface of a fifth template  158 , wherein the hole transport film  1242  has different heights corresponding to adjacent three of the plurality of first electrodes  110  of the same pixel unit; 
     step (S 621 ), forming a hole injection film  1222  on a surface of the hole transport film  1242 , wherein the hole injection film  1222  also has different heights corresponding to adjacent three of the plurality of first electrodes  110  of the same pixel unit; 
     step (S 622 ), contacting the plurality of first electrodes  110  with the hole injection film  1222 ; and 
     step (S 623 ), separating the plurality of first electrodes  110  from the fifth template  158 . 
     In step (S 620 ), the fifth template  158  has an eighth surface  1582 , a ninth surface  1584 , and a tenth surface  1586 . The eighth surface  1582 , the ninth surface  1584 , and the tenth surface  1586  have different heights. The height differences of the eighth surface  1582 , the ninth surface  1584 , and the tenth surface  1586  are designed according to the height differences of the plurality of convexities  108 . The highest convexity  108  corresponds to the lowest one of the eighth surface  1582 , the ninth surface  1584 , and the tenth surface  1586 . When the plurality of first electrodes  110  closes to the hole injection film  1222  on the fifth template  158 , each of the plurality of first electrodes  110  can be in direct contact with the hole injection film  1222 . 
     Both the hole injection film  1222  and the hole transport film  1242  has uniform thickness, so that the hole injection film  1222  and the hole transport film  1242  on the eighth surface  1582 , the ninth surface  1584 , and the tenth surface  1586  have different heights. The adhesion strength between the hole injection film  1222  and the hole transport film  1242  is greater than the adhesion strength between the hole transport film  1242  and the fifth template  158 . Thus, the hole injection film  1222  and the hole transport film  1242  can be transferred from the fifth template  158  to the first electrodes  110  together. A wetting layer can be applied between the hole transport film  1242  and the fifth template  158 . In one embodiment, the hole transport film  1242  is baked before applying the hole injection film  1222  so that the hole transport film  1242  would not be damaged in the wet membrane process of making the hole injection film  1222 . The baked hole transport film  1242  can also be further wetted in the wet membrane process of making the hole injection film  1222 . Furthermore, the hole injection film  1222  and the hole transport film  1242  can be made by transfer printing twice via the method of  FIG. 22 . The method of  FIG. 22  can also be used to made the plurality of electroluminescent layers  125 , the plurality of electron transport layers  126  and the plurality of electron injection layers  128 . 
       FIG. 23  illustrates an organic light emitting diode array  60  of one embodiment. The organic light emitting diode array  60  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140 , and a second electrode  130 . The organic light emitting diode array  60  is similar to the organic light emitting diode array  50  except that the plurality of convexities  108  have different heights, the plurality of hole injection layers  122  have the same thickness, the plurality of hole transport layers  124  have the same thickness, and the plurality of electroluminescent layers  125  have the same thickness. 
       FIG. 24  illustrates an organic light emitting diode array  60 A of another embodiment. In the organic light emitting diode array  60 A, a continuous electron transport layer  126  and a continuous electron injection layer  128  are located between the plurality of electroluminescent layers  125  and the second electrode  130 . The organic light emitting diode array  60 A share a common electron transport layer  126  and a common electron injection layer  128 . The electron transport layer  126  and the electron injection layer  128  can be made by vacuum evaporation or coating. 
       FIG. 25  illustrates a method of one embodiment for making an organic light emitting diode array  70 . The method includes following steps: 
     step (S 70 ), providing a base  100 , wherein the base  100  includes a substrate  102 , a plurality of thin-film transistors  104  located on a surface of the substrate  102  and arranged to form an array, and a first insulative layer  106  located on a surface of the plurality of thin-film transistors  104 ; the first insulative layer  106  defines a plurality of convexities  108 ; 
     step (S 71 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein the plurality of first electrodes  110  are located corresponding to and electrically connected to the plurality of thin-film transistors  104  in a one-to-one manner; 
     step (S 72 ), transfer printing a plurality of blue light electroluminescent layers  125  on the plurality of first electrodes  110 , wherein one of the plurality of blue light electroluminescent layers  125  are higher than the other two of the plurality of blue light electroluminescent layers  125  in each pixel unit; 
     step (S 73 ), making a red light electroluminescent layers  125  and a green light electroluminescent layers  125  on the lower two of the plurality of blue light electroluminescent layers  125 ; 
     step (S 74 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  between the plurality of convexities  108  and expose the blue light electroluminescent layer  125 , the red light electroluminescent layer  125 , and the green light electroluminescent layer  125  of each pixel unit; and 
     step (S 75 ), electrically connecting a second electrode  130  to the blue light electroluminescent layer  125 , the red light electroluminescent layer  125 , and the green light electroluminescent layer  125  of each pixel unit. 
     The method for making the organic light emitting diode array  70  is similar to the method for making the organic light emitting diode array  20  except that the plurality of blue light electroluminescent layers  125  with different thickness are transfer printed on the plurality of first electrodes  110  directly by the method of  FIG. 18 , and then the red light electroluminescent layer  125  and the green light electroluminescent layer  125  are applied on the lower two of the plurality of blue light electroluminescent layers  125  respectively. The red light electroluminescent layer  125  and the green light electroluminescent layer  125  can be made by vacuum evaporation, or transfer printing method of  FIGS. 9-10 . The red light electroluminescent layer  125 , the green light electroluminescent layer  125  and the highest blue light electroluminescent layer  125  have the same height. The blue light electroluminescent layers  125  of the organic light emitting diode array  70  can play the function of hole injection and hole transport. Furthermore, in step (S 72 ), a plurality of red light or green light electroluminescent layers  125  with different heights can be applied first, and then, in step (S 73 ), the other two kinds of different color electroluminescent layers  125  are formed on the lower two of the plurality of electroluminescent layers  125 . 
     The organic light emitting diode arrays  10 ,  20 ,  20 A,  30 ,  40 ,  50 ,  50 A,  60 ,  60 A,  70  are active matrix type organic light emitting diode arrays. The methods of  FIG. 1 ,  FIG. 8 ,  FIG. 13 ,  FIG. 15 ,  FIG. 17 ,  FIG. 21  and  FIG. 25  can also be used to make the passive matrix type organic light emitting diode array. 
       FIG. 26  illustrates a method of one embodiment for making a passive matrix type organic light emitting diode array  80 . The method includes following steps: 
     step (S 80 ), providing a base  100 , wherein the base  100  defines a plurality of convexities  108  parallel with and spaced from each other; 
     step (S 81 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein the plurality of first electrodes  110  are parallel with and spaced from each other, and each of the plurality of first electrodes  110  is located on a top surface of one of the plurality of convexities  108 ; 
     step (S 82 ), applying a plurality of organic light emitting layers  120  on the plurality of first electrodes  110 , wherein the plurality of organic light emitting layers  120  are located on a top surface of one of the plurality of first electrodes  110  in a one-to-one manner; 
     step (S 83 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  and expose part of each of the plurality of organic light emitting layers  120 ; and 
     step (S 84 ), electrically connecting a plurality of second electrodes  130  to the plurality of organic light emitting layers  120 , wherein the plurality of second electrodes  130  are parallel with, spaced from each other, and extend along a direction different from the extending direction of the plurality of first electrodes  110 . 
     The method for making the organic light emitting diode array  80  is similar to the method for making the organic light emitting diode array  10  except that the plurality of first electrodes  110  and the plurality of second electrodes  130  have different structures, so that the organic light emitting diode array  80  is passive matrix type. Furthermore, in step (S 80 ), the base  100  can be a glass substrate, a ceramic substrate, a silicon dioxide substrate, a silicon nitride substrate or a polymer substrate. The plurality of convexities  108  are strip-shaped and defined by the base  100 . 
       FIGS. 27-28  illustrate a passive matrix type organic light emitting diode array  80  of one embodiment. The organic light emitting diode array  80  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140 , and a plurality of second electrodes  130 . The plurality of convexities  108  are strip-shaped, parallel with and spaced from each other, and formed on a surface of the base  100 . The plurality of first electrodes  110  are parallel with and spaced from each other, and corresponds to the plurality of convexities  108  in a one-to-one manner. Each of the plurality of first electrodes  110  is located on both the top surface and side surface of the corresponding one of the plurality of convexities  108 , and extends to the surface of the base  100  between adjacent two of the plurality of convexities  108 . The plurality of organic light emitting layers  120  are strip-shaped, parallel with and spaced from each other, and located on the plurality of convexities  108  in a one-to-one manner. The plurality of organic light emitting layers  120  can be the same color organic light emitting layers, or different color organic light emitting layers such as a blue light, a red light, and a green light. The patterned second insulative layer  140  is located between adjacent two of the plurality of convexities  108 . The plurality of second electrodes  130  extend along a direction perpendicular with the extending direction of the plurality of first electrodes  110 . A plurality of sub-pixels are defined at the places where the plurality of second electrodes  130  across the plurality of first electrodes  110 . In work, the plurality of second electrodes  130  and the plurality of first electrodes  110  are used as an address circuit to control the plurality of sub-pixels. 
       FIG. 29  illustrates a method of one embodiment for making a passive matrix type organic light emitting diode array  90 . The method includes following steps: 
     step (S 90 ), providing a base  100 , wherein the base  100  defines a plurality of convexities  108  arranged in a two-dimensional array and spaced from each other; 
     step (S 91 ), forming a plurality of first electrodes  110  on the plurality of convexities  108 , wherein the plurality of first electrodes  110  are parallel with and spaced from each other, and each of the plurality of first electrodes  110  is located corresponding to the same row of the plurality of convexities  108 ; 
     step (S 92 ), applying a plurality of organic light emitting layers  120  on the plurality of first electrodes  110 , wherein the plurality of organic light emitting layers  120  are located corresponding to the plurality of convexities  108  in a one-to-one manner; 
     step (S 93 ), making a patterned second insulative layer  140  to cover the plurality of first electrodes  110  and expose part of each of the plurality of organic light emitting layers  120 ; and 
     step (S 94 ), electrically connecting a plurality of second electrodes  130  to the plurality of organic light emitting layers  120 , wherein the plurality of second electrodes  130  are parallel with, spaced from each other, and extend along a direction different from the extending direction of the plurality of first electrodes  110 . 
     The method for making the organic light emitting diode array  90  is similar to the method for making the organic light emitting diode array  80  except that the plurality of convexities  108  are arranged to form a two-dimensional array, each of the plurality of first electrodes  110  is located corresponding to one row of the plurality of convexities  108 , and each of the plurality of organic light emitting layers  120  is located corresponding to one of the plurality of convexities  108 . In step (S 91 ), each of the plurality of first electrodes  110  is continuous, located on both top surface and side surface of the corresponding row of the plurality of convexities  108 , and extends to the surface of the extends to the surface of the base  100  between adjacent two of the plurality of convexities  108 . 
       FIG. 30  illustrates a passive matrix type organic light emitting diode array  90  of one embodiment. The organic light emitting diode array  90  includes a base  100 , a plurality of first electrodes  110 , a plurality of organic light emitting layers  120 , a patterned second insulative layer  140  (not shown in  FIG. 30 ), and a plurality of second electrodes  130 . The plurality of convexities  108  are arranged to form a two-dimensional array. The plurality of first electrodes  110  are parallel with and spaced from each other, and each of the plurality of first electrodes  110  is located corresponding to one row of the plurality of convexities  108 . The plurality of organic light emitting layers  120  are located corresponding to the plurality of convexities  108  in a one-to-one manner and located on the protrudent surfaces of the first electrode  110  on the corresponding one of the plurality of convexities  108 . The patterned second insulative layer  140  is located between adjacent two of the plurality of convexities  108 . The plurality of second electrodes  130  extend along a direction perpendicular with the extending direction of the plurality of first electrodes  110 . A plurality of sub-pixels are defined at the places where the plurality of second electrodes  130  across the plurality of first electrodes  110 . Each of the organic light emitting layers  120  corresponds to one of the plurality of sub-pixels. The same column of organic light emitting layers  120  are the same color. In work, the plurality of second electrodes  130  and the plurality of first electrodes  110  are used as an address circuit to control the plurality of sub-pixels. 
     The embodiments shown and described above are only examples. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, including in matters of shape, size and arrangement of the parts within the principles of the present disclosure up to, and including, the full extent established by the broad general meaning of the terms used in the claims.