Abstract:
A method for synthesizing a quantum dot light emitting diode by providing a glass substrate. A QD-LED stack is formed upon the glass substrate. This QD-LED stack is diffused with an active reagent. The QD-LED stack is encapsulated with a curable resin. The curable resin is cured with UV light.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/915,268 filed Dec. 12, 2013, the contents of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention is directed to an encapsulated quantum dot light emitting diode (QD-LED), and in particular, an encapsulation structure and method of manufacture which promotes a beneficial aging effect in the quantum dot light emitting diode. 
         [0003]    Quantum dot light emitting diodes are well known in the art. The basic structure for a bottom-emitting device is a glass substrate and a QD-LED stack which includes a quantum dot light emitting layer, nanoparticle layers and the like. The QD-LED stack is made of sensitive materials and therefore needs to be protected from the environment. As known in the art, protective encapsulation layers are disposed over the sensitive materials as a protective cover. This encapsulation has taken the form of a curable resin. 
         [0004]    Loctite 349 curable resin has been used to encapsulate organic LEDs (OLED). Loctite 349 is just one of many curable resins utilized to encapsulate OLED, and has not been used to encapsulate QD-LEDs which are made of inorganic or a combination of inorganic and organic materials. Some QD-LEDs exhibit a “positive aging effect” in which the various efficiencies (current, power or external quantum efficiencies) improve over time. The positive aging effect can be contrasted to degradation of QD-LED&#39;s to lower brightness and lower efficiencies, sometimes called the negative aging effects. However, no such positive aging effect has been observed in OLEDs using Loctite 349. 
         [0005]    Because the prior art structures do not promote the positive aging effect as defined above, a structure and/or a method of manufacture which further promotes the aging effect is desired. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A QD-LED is manufactured by providing a glass substrate. A QD-LED stack is formed on the substrate. An active reagent; such as an acid is incorporated (diffused) into the QD-LED stack. A curable resin sufficient to encapsulate the QD-LED stack is dropped onto the QD-LED stack and then compressed with a glass cover. The curable resin is then cured with ultraviolet light for about three minutes. 
         [0007]    In one embodiment, the acid is an acrylic acid contained in the curable resin. In another embodiment the QD-LED is baked at a temperature of about 50° C. or more for about four hours or more to achieve higher and stable efficiencies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present disclosure is better understood by reading the written description with reference to the accompanying drawings/figures, in which the reference numerals denote the similar structure referred to the elements throughout in which: 
           [0009]      FIG. 1  shows steps in the formation of a QD-LED in accordance with the invention; 
           [0010]      FIG. 2  is a schematic diagram of a QD-LED constructed in accordance with the invention illustrating the diffusion of the Acrylic Acid in accordance with the invention; 
           [0011]      FIGS. 3 a  and 3 b    are graphs showing current efficiency as a function of the luminance for a QD-LED having Acrylic Acid doped curable resin\ ( FIG. 3 a   ) in accordance with the invention, and a curable resin not doped with Acrylic Acid ( FIG. 3 b   ), in accordance with the prior art; 
           [0012]      FIG. 4  is a comparison of a QD-LED constructed in accordance with the invention and a prior art QD-LED; 
           [0013]      FIG. 5  is a graphical representation of current efficiency as a function of—luminance for red and blue QD-LEDs constructed in accordance with the invention; 
           [0014]      FIGS. 6 a -6 c    show the positive aging effect for a red QD-LED utilizing an encapsulation curable resin having different concentrations of Acrylic Acid in—accordance with the invention; 
           [0015]      FIGS. 7 a -7 b    show a comparison of current efficiency as a function of luminescence for QD-LEDs encapsulated in a curable resin being doped with Methyl Methacrylate ( FIG. 8 a   ) and an encapsulation curable resin doped with poly-Acrylic Acid ( FIG. 8 b   ) in accordance with the invention; 
           [0016]      FIGS. 8 a -8 c    show the current efficiency as a function of luminescence over time for QD-LEDs constructed in accordance with the invention; 
           [0017]      FIGS. 9 a -9 b    are graphs showing current efficiency, at two points in time, for QD-LEDs constructed in accordance with the invention in which the encapsulation curable resin has 7.5% Acrylic Acid by weight in accordance with the invention; 
           [0018]      FIGS. 10 a -10 b    are graphs showing current efficiency, at two points in time, for QD-LEDs constructed in accordance with the invention in which the encapsulation curable resin has 15% Acrylic Acid by weight in accordance with the invention; 
           [0019]      FIGS. 11 a -11 b    are graphs showing current efficiency, at two points in time, for QD-LEDs constructed in accordance with the invention in which the encapsulation curable resin has 23% Acrylic Acid by weight in accordance with the invention; 
           [0020]      FIGS. 12 a -12 b    show current efficiency as a function of luminance for a plurality of QD-LEDs formed in accordance with the invention with a variety of Acrylic Acid concentrations and exposed to heat over time. 
           [0021]      FIGS. 13 a -13 b    show current efficiency as a function of luminance for a plurality of QD-LEDs formed in accordance with the invention with a variety of Acrylic Acid concentrations and heated at 70° C.; 
           [0022]      FIGS. 14 a -14 b    show current efficiency as a function of luminance for a plurality of QD-LEDs formed in accordance with the invention with a variety of Acrylic Acid concentrations and heated at 90° C.; and 
           [0023]      FIGS. 15 a -15 b    are graphs showing the current efficiency as a function of luminance for a QD-LED in which the encapsulating curable resin is doped with a variety of additives as a control. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0024]    The inventors have created a method for building an encapsulated QD-LED and resulting structure which promotes the desirable positive aging effect in QD-LED. Applicants found that diffusing a reactive reagent, such as an acid by way of non-limiting example, into the QD-LED stack promotes the positive aging effect for that QD-LED. A preferred method of delivering the acid is by doping an encapsulation layer with an acid; preferably but not limited to Acrylic Acid. By exposing the QD-LED constructed in accordance with the invention to heat, the positive aging effect may be accelerated and stabilized. 
         [0025]    More specifically, as shown in  FIG. 1 , in step  1 ( a ), a glass substrate  102  is provided and a QD-LED stack  104  is deposited thereon as known in the art. A QD-LED stack as known in the prior art will generally include a cathode, electron transport layer, a quantum dot emitting layer, a hole transport layer, a hole injection layer, and an anode. In a step  1 ( b ), an encapsulating curable resin  106  is deposited onto the QD-LED stack to encapsulate the QD-LED stack  104 . In a preferred, but non-limiting embodiment, the curable resin is doped with Acrylic Acid at a concentration of about 7.5 percent or more by weight by way of non-limiting example. In step  1 ( c ), a cover glass  108  presses the curable resin droplet  106  to spread over the entire QD-LED stack  104 . Steps  1 ( b ) and  1 ( c ) are performed in a glove box. In step  1 ( d ), QD-LED is exposed to ultraviolet light at a wavelength of about 365 nm as known in the art, for about three minutes in the glove box or in air, but for a time period sufficient to cure the curable resin encapsulating a QD-LED  110 . 
         [0026]    Reference is now made to  FIG. 2  in which a schematic sectional view of QD-LED constructed in accordance with the invention is provided. QD-LED  110  includes a glass substrate  102 , and an anode  122  is disposed on glass substrate  102  as known in the art. As discussed above, a QD-LED stack  104  is assembled on anode  122  and as known in the art, includes a cathode  114 , supported by an electron transport layer  116 , which in turn is disposed upon a quantum dot emitting layer  118 , which in turn is disposed upon a hole transport layer  120 , which in turn is disposed on a hole injection layer  122  which lies upon anode  124 . QD-LED stack  104  is encapsulated by curable resin  106 . As known in the art, at least quantum dot emitting layer  118  is formed of inorganic materials. The curable resin is doped with Acrylic Acid molecules  130  in an amount between 0.1% to 99% by weight, but preferably between 7.5% and 30% by weight. Glass cover plate  108  is provided on the encapsulation curable resin  106  to promote flow of the curable resin  106  about QD-LED stack  104  so that the QD-LED stack  104  is disposed between two glass layers. 
         [0027]    In the above embodiment, the Acrylic Acid is delivered by the doped encapsulation layer  106 . However, the active reagent may also be diffused by gas phase annealing, solution doping with active reagents, or washing of QD-LED stack  104  with an active reagent solution prior to encapsulation. 
         [0028]    As will be demonstrated below, Applicants have discovered that unlike OLEDs, the use of an encapsulating resin doped with Acrylic Acid promotes the positive aging effect in QD-LEDs. The Acrylic Acid molecules  130  is thought to diffuse into the QD-LED stack  104  as simplistically shown for ease of description, by way of non-limiting example, by arrows A and B in  FIG. 2 . It is believed that the Acrylic Acid molecules  130  interact with the device layers of QD-LED stack  104  and the interfaces between the layers by diffusing through the top and sides of the device layers. It is believed that it is this process which promotes the positive aging effect in QD-LEDs where no such effect was found in OLEDs. 
         [0029]    The inventors created a green QD-LED as shown in  FIG. 2  and a QD-LED as known in the prior art (without Acrylic Acid in the curable resin) and compared current efficiencies as a function of luminance for the two QD-LEDs. As shown in  FIG. 3   a,  a green QD-LED is formed in accordance with  FIG. 1  utilizing an encapsulating resin  106  having about 7.5% Acrylic Acid by weight, by way of example, Loctite 349 manufactured by Henkel Corporation. Luminance was tested each day for four days and current efficiency was determined each day for four days. 
         [0030]    In  FIG. 3   b,  a green QD-LED was constructed utilizing an encapsulation curable resin having no Acrylic Acid therein, by way of non-limiting example, QG142 manufactured by Epoxy Technology, Inc. Again, luminance and current efficiency were determined each day. As can be seen, there is a significant improvement in current efficiency for the green QD-LED formed with an Acrylic Acid doped encapsulating curable resin  106 . The current efficiency at a luminescence of 10,000 cd/m 2 , on the fourth day for the QD-LED constructed in accordance with the invention ( FIG. 3 a   ) is more than triple that of the current efficiency for the similarly constructed green QD-LED using a prior art encapsulation resin; without Acrylic Acid ( FIG. 3 b   ). 
         [0031]    Furthermore, as seen in  FIG. 4 , the inventors also discovered that the T50 lifetime (negative aging effect) for the QD-LED constructed having an encapsulating curable resin layer  106  doped with Acrylic Acid is significantly greater than the T50 lifetime for the QD-LED having an encapsulation layer that is not doped with Acrylic Acid. The acrylic acid doped QD-LED has a T50 lifetime of about 320 hours. In contrast thereto, the T50 lifetime for the device having an encapsulation layer not doped with Acrylic Acid is less than 100 hours. 
         [0032]    As seen in  FIGS. 3   a,    3   b,  the current efficiency increases each day over the three to four day period from the device fabrication. This is the exhibition of the positive aging effect in the QD-LED having the Acrylic Acid doped encapsulation layer. The efficiency of the green QD-LED increases from about 20 cd/A on the first day of the test to 55 cd/A by the third day of testing. In contrast, the green QD-LED constructed in accordance with the prior art never reaches a maximum efficiency greater than 20 cd/A. 
         [0033]    The initial comparison between QD-LEDs constructed with Acrylic Acid doped encapsulating layers  106  and the prior art devices was done with a green QD-LED. However, as seen in  FIG. 5 , the positive aging effect may also be promoted in red and blue QD-LEDs constructed with Acrylic Acid doped encapsulating resin. However, the positive aging effect of the red QD-LED is exhibited to a lesser extent compared to the green QD-LED. The positive aging effect in the blue QD-LEDs is also not as significant as the green QD-LEDs. This is attributable to the relatively fast efficiency degradation known to occur in blue QD-LEDs which counteracts any efficiency increase induced by the positive aging effect. 
         [0034]    The effect of different formulations of Acrylic Acid based encapsulation curable resin were studied to confirm that Acrylic Acid is the primary contributor to promoting the positive aging effect in the QD-LED. While the tested curable resin for the QD-LED constructed in accordance with the invention was known to contain Acrylic Acid as compared to the prior art encapsulation resin (OG142), a series of studies were performed to confirm and determine the contributing factor(s) to promoting the positive aging effect with QD-LEDs. Accordingly, as seen in  FIGS. 6 a -6 c    red QD-LEDs were constructed with various formulations utilizing known Acrylic Acid resins of 7.5%, 15%, 23%, respectively. As can be seen in  FIGS. 6 a -6 c    that even with different formulations, the positive aging effect was experienced to varying degrees in each QD-LED at three days from fabrication. In other words, the current efficiency as a function of luminance substantially increased by the third day after encapsulation for all Acrylic Acid formulations tested. 
         [0035]    In order to confirm what factor promoted the positive aging effect, the inventors further studied formulations. The inventors discovered at least one difference between the formulation that promoted the positive aging effect and prior art encapsulation material (OG142) is that the OG142 resin did not include Acrylic Acid or Methyl Methacrylate (MMA). Accordingly, as seen in  FIGS. 7 a    and  7   b,  green QD-LEDs having MMA doped encapsulation layers ( FIG. 7 a   ) were compared to green QD-LEDs having an Acrylic Acid doped encapsulation layer. As seen when comparing  FIGS. 7 a    to  7   b,  the QD-LEDs with the Acrylic Acid doped encapsulation layer show improved current efficiency which are greater than ten times the current efficiencies exhibited by the same green QD-LED structure having an MMA doped encapsulation layer. This confirms that the addition of Acrylic Acid to the encapsulation layer promotes the positive aging effect. 
         [0036]    After confirmation that Acrylic Acid doped encapsulation layers promote the positive aging effect, formulations were tested. The inventors created a QD-LED having an encapsulation layer containing 7.5% Acrylic Acid by weight, a second QD-LED having an encapsulation layer which is 15% Acrylic Acid by weight; a third QD-LED having an encapsulation layer which is 23% Acrylic Acid by weight and a fourth QD-LED having an encapsulation layer which is 30% Acrylic Acid by weight, a fifth QD-LED was formed in accordance with the invention as described in  FIG. 1  doped with Acrylic Acid of 23% by weight, and additionally baked at 50° C. for 18 hours. 
         [0037]    As seen in  FIGS. 8 a   - 8   c,  representing current efficiency as tested on the first day, third day and fourth day respectively, the positive aging effect occurs in those QD-LEDs having Acrylic Acid doped encapsulation layers of 7.5%, 15% and 23%. They all reach the same general maximum current efficiency. However, the QD-LED having encapsulation layer doped with 30% Acrylic Acid by weight actually showed no positive aging effect. The maximum efficiency is decreased. Furthermore, as seen in  FIG. 8   a,  baking the QD-LED accelerates the time period in which the positive aging effect is realized. The baked QD-Led reached its maximum efficiency in the first day, while it took three to four days for the remaining QD-LED to attain their maximum current efficiency. A summary of the results is shown in Table 1 below where t 1 . 1  designates aging for one day, t 2 . 3  for 2 to 3 days, and t 3 . 4  for 3 to 4 days. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Additive 
                 CE t1.1 (cd/A) 
                 CE t2.3 (cd/A) 
                 CE t3.4 (cd/A) 
               
               
                   
               
             
             
               
                 Control 
                 29.6 
                 56.3 
                 60.4 
               
               
                 15% AA 
                 25.2 
                 55.3 
                 58.0 
               
               
                 23% AA 
                 22.4 
                 50.9 
                 62.1 
               
               
                 23% AA with 18 hr 
                 52.0 
                 54.4 
                 56.7 
               
               
                 bake 
               
               
                 30% AA 
                 16.5 
                 28.5 
                 38.8 
               
               
                   
               
             
          
         
       
     
         [0038]    To confirm that baking (heating the QD-LED over time) at fabrication, promotes the positive aging factor, QD-LEDs were constructed in which the encapsulated layer was doped with different amounts of Acrylic Acid and then baked for anywhere from one-half hour to four hours and compared to a control QD-LED which is not baked. Reference is made to  FIGS. 9 a  and 9 b    in which the positive aging effect is shown over time after baking for a QD-LED having an encapsulation layer containing 7.5% Acrylic Acid by weight. A significant increase in current efficiency is produced by the second day, particularly for that QD-LED which is baked for four hours. Little difference is seen when the control (baked for 0 hours) is compared to devices baked for one-half hour, one hour or two hours. Similarly, as seen in  FIGS. 10 a    and  10   b,  for the QD-LEDs having encapsulation layers of 15% Acrylic Acid by weight, baking for four hours significantly increases the current efficiency in the first day. The same is true for QD-LEDs having 23% by weight Acrylic Acid doped encapsulation layers as seen in  FIGS. 11 a    and  11   b.  Those QD-LEDs baked the longest show the quickest exhibition of the positive aging effect as seen in  FIG. 11   a.  Tables 2-4 summarize the results below: 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Additive 
                 CE t1.1 (cd/A) 
                 CE t2.2 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
                 7.5% AA 
                 30.8 
                 58.8 
               
               
                   
                 7.5% AA 0.5 hrs 
                 31.0 
                 59.0 
               
               
                   
                 7.5% AA 1 hr 
                 33.3 
                 60.2 
               
               
                   
                 7.5% AA 2 hrs 
                 32.5 
                 55.9 
               
               
                   
                 7.5% AA 4 hrs 
                 39.6 
                 57.4 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Additive 
                 CE t1.1 (cd/A) 
                 CE t2.2 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
                 15% AA 
                 24.0 
                 46.6 
               
               
                   
                 15% AA 0.5 hrs 
                 24.0 
                 46.1 
               
               
                   
                 15% AA 1 hr 
                 24.3 
                 45.4 
               
               
                   
                 15% AA 2 hrs 
                 26.4 
                 47.8 
               
               
                   
                 15% AA 4 hrs 
                 32.3 
                 48.8 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Additive 
                 CE t1.1 (cd/A) 
                 CE t2.2 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
                 23% AA 
                 22.1 
                 46.9 
               
               
                   
                 23% AA 0.5 hrs 
                 22.7 
                 46.6 
               
               
                   
                 23% AA 1 hr 
                 25.9 
                 45.4 
               
               
                   
                 23% AA 2 hrs 
                 26.6 
                 46.6 
               
               
                   
                 23% AA 4 hrs 
                 30.6 
                 50.6 
               
               
                   
                   
               
             
          
         
       
     
         [0039]    Having determined that baking can accelerate the aging process, the inventors performed studies to determine whether baking temperature would further affect the acceleration of the aging process. QD-LEDs having an encapsulation layer having 7.5%, 15% and 23% Acrylic Acid by weight, were baked at fabrication for 0 hours, 24 hours and 48 hours. One sample was baked at 50° C. for the time periods, one at 70° C. for the time periods, and one at 90° C. for the time periods. The results confirmed that in a preferred, but non-limiting embodiment, the QD-LED should be baked for 50° C. for 24 hours in order to maximize throughput for QD-LED while promoting an accelerating aging process in the QD-LED. As seen in  FIGS. 12   a,  and  12   b,  the current efficiencies maximized for the QD-LEDs baked for 48 hours as compared to 24 hours when tested on the second day. However, the increment for baking an additional 24 hours is not nearly as significant as the increase in current efficiency compared to baking for 24 hours when compared with baking for 0 hours. In each instance, the first 24 hours of baking at 50° C. resulted in over 50% increase in current efficiency, whereas an additional 24 hours of baking resulted in an additional 10% to 20% increase in current efficiency. The results are summarized in Table 5 below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Encapsulant 
                   
                   
               
               
                   
                 and bake time 
                 CE t1.2 (cd/A) 
                 CE t2.3 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Loctite 349 0 hrs 
                 25.4 
                 42.5 
               
               
                   
                 Loctite 349 
                 41.7 
                 52.7 
               
               
                   
                 24 hrs 50 C. 
               
               
                   
                 Loctite 349 
                 48.2 
                 57.3 
               
               
                   
                 48 hrs 50 C. 
               
               
                   
                 Loctite 352 0 hrs 
                 26.6 
                 44.6 
               
               
                   
                 Loctite 352 
                 42.5 
                 50.3 
               
               
                   
                 24 hrs 50 C. 
               
               
                   
                 Loctite 352 
                 42.6 
                 48.4 
               
               
                   
                 48 hrs 50 C. 
               
               
                   
                 Loctite 366 0 hrs 
                 31.4 
                 44.5 
               
               
                   
                 Loctite 366 
                 48.9 
                 47.0 
               
               
                   
                 24 hrs 50 C. 
               
               
                   
                 Loctite 366 
                 52.1 
                 39.9 
               
               
                   
                 48 hrs 50 C. 
               
               
                   
                   
               
             
          
         
       
     
         [0040]    When the temperature was increased to 70° C. and sampled on the third and fourth day, the positive aging effect was promoted, but not to the same extent as for baking at 50° C. as seen by comparing 0 hours of baking with the initial 24 hours of baking, both in Table 6 below and comparing the results of 50° C. as shown in Table 5 for the same test. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Encapsulant 
                   
                   
               
               
                   
                 and bake time 
                 CE t1.3 (cd/A) 
                 CE t2.4 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
                 Loctite 349 0 hrs 
                 30.7 
                 49.5 
               
               
                   
                 Loctite 349 
                 46.0 
                 53.2 
               
               
                   
                 24 hrs 70 C. 
               
               
                   
                 Loctite 349 
                 46.4 
                 51.2 
               
               
                   
                 48 hrs 70 C. 
               
               
                   
                 Loctite 352 0 hrs 
                 30.2 
                 45.2 
               
               
                   
                 Loctite 352 
                 41.2 
                 44.4 
               
               
                   
                 24 hrs 70 C. 
               
               
                   
                 Loctite 352 
                 43.8 
                 46.8 
               
               
                   
                 48 hrs 70 C. 
               
               
                   
                 Loctite 366 0 hrs 
                 86.4 
                 50.2 
               
               
                   
                 Loctite 366 
                 39.8 
                 39.4 
               
               
                   
                 24 hrs 70 C. 
               
               
                   
                 Loctite 366 
                 41.8 
                 39.6 
               
               
                   
                 48 hrs 70 C. 
               
               
                   
                   
               
             
          
         
       
     
         [0041]    Similarly, baking the QD-LEDs at 90° C. did not show significant improvement when compared to 70° C. as seen in  FIGS. 14   a,    14   b,  and summarized in Table 7 below. Again, there was a significant increase between baking for at least 24 hours; while the additional 24 hours (for a total of 48 hours) did not show an equally significant increase in the positive aging effect and did not show a significantly appreciable promotion of the positive aging effect when compared to the more energy efficient baking at 50° C. Results of baking the QD-LEDs at 90° C. are summarized in Table 7 below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Encapsulant 
                   
                   
               
               
                   
                 and bake time 
                 CE t1.3 (cd/A) 
                 CE t2.4 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Loctite 349 0 hrs 
                 32.0 
                 47.4 
               
               
                   
                 Loctite 349 
                 45.2 
                 50.9 
               
               
                   
                 24 hrs 90 C. 
               
               
                   
                 Loctite 349 
                 44.1 
                 51.8 
               
               
                   
                 48 hrs 90 C. 
               
               
                   
                 Loctite 352 0 hrs 
                 30.8 
                 49.8 
               
               
                   
                 Loctite 352 
                 44.3 
                 43.7 
               
               
                   
                 24 hrs 90 C. 
               
               
                   
                 Loctite 352 
                 45.9 
                 44.8 
               
               
                   
                 48 hrs 90 C. 
               
               
                   
                 Loctite 366 0 hrs 
                 37.5 
                 51.0 
               
               
                   
                 Loctite 366 
                 48.3 
                 42.5 
               
               
                   
                 24 hrs 90 C. 
               
               
                   
                 Loctite 366 
                 45.1 
                 39.9 
               
               
                   
                 48 hrs 90 C. 
               
               
                   
                   
               
             
          
         
       
     
         [0042]    In a preferred non-limiting embodiment in order to maximize throughput and energy costs, the optimized baking conditions would be 50° C. for 24 hours. 
         [0043]    To test whether Acrylic Acid was unique in promoting the positive aging effect, the inventors doped curable resins with benzoic acid (BA) and different types of BAderivatives. QD-LEDs were formed utilizing the methodology of  FIG. 1 , without baking. However, rather than doping the encapsulating curable resin with Acrylic Acid, a prior art non-Acrylic Acid resin was used as a control and various benzoic acids derivatives were used to dope the encapsulating curable resin. As seen in  FIGS. 14 a    and  14   b,  on the second day the current efficiency for sample BA was 60% greater than for the control sample, while the current efficiencies for all other sample were approximately equal to or less than that of the control sample for each embodiment on both the first and second day. These data suggest that doping with acids other than acrylic acids can lead to a positive aging effect. However, the embodiment of the invention using acrylic acid, shown in  FIG. 3 a    and in  FIGS. 14   a,    14   b  provide the largest improvements. The results with various acids are summarized in Table 8 below. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Additive 
                 CE t1.1 (cd/A) 
                 CE t2.3 (cd/A) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Control 
                 6.9 
                 10.9 
               
               
                   
                 BA-CF 3   
                 3.9 
                 10.3 
               
               
                   
                 BA-CN 
                 4.3 
                 7.6 
               
               
                   
                 BA-SH 
                 2.9 
                 6.7 
               
               
                   
                 BA 
                 7.1 
                 16.8 
               
               
                   
                 BA-CH 3   
                 6.0 
                 7.0 
               
               
                   
                 BA-OCH 3   
                 5.5 
                 7.8 
               
               
                   
                   
               
             
          
         
       
     
         [0044]    Accordingly, by forming a QD-LED with encapsulation layer having an active reagent therein, the positive aging effect is promoted. In other words, much greater current efficiencies are obtained than previously known. Furthermore, by baking the QD-LED at temperatures of about 50° C. or higher, for up to 48 hours from fabrication, the aging process may be accelerated and stabilized while Acrylic Acid and Benzoic Acid promote the beneficial aging effect as shown, in other embodiments, the active reagent may include one or more of methacrylic acid, 3-butenoic acid, crotonic acid and other unsaturated carboxylic acid derivatives; acetic acid, propionic acid, butyric acid, isobutyric acid and other saturated carboxylic acid derivatives. 
         [0045]    While there have been shown, described, and pointed out, novel features of the present invention, as applied to preferred embodiments thereof, it will be understood that various submissions and substitutions and changes in the form and detail are contemplated to the disclosed invention, which may be made by those skilled in the art without departing from the spirit and scope of the invention. It is the intention therefore, to be limited, only as indicated by the scope of the claims appended hereto. It is also be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all states of the scope of the invention which, as a matter of language might be said to fall therebetween.