Quantum dot device and display device

Abstract

A quantum dot device includes: a first electrode and a second electrode facing each other; a quantum dot layer between the first electrode and the second electrode, and an electron auxiliary layer between the quantum dot layer and the second electrode, the electron auxiliary layer including a first nanoparticle and a second nanoparticle which is larger than the first nanoparticle, wherein a work function of the first electrode is greater than a work function of the second electrode, and wherein a difference between a lowest unoccupied molecular orbital energy level of the quantum dot layer and a lowest unoccupied molecular orbital energy level of the electron auxiliary layer is less than about 1.1 electronvolts.

What is claimed is: 
     
         1 . A quantum dot device, comprising:
 a first electrode and a second electrode facing each other;   a quantum dot layer between the first electrode and the second electrode; and   an electron auxiliary layer between the quantum dot layer and the second electrode, the electron auxiliary layer comprising a first nanoparticle and a second nanoparticle which is larger than the first nanoparticle,   wherein a work function of the first electrode is greater than a work function of the second electrode, and   wherein a difference between a lowest unoccupied molecular orbital energy level of the quantum dot layer and a lowest unoccupied molecular orbital energy level of the electron auxiliary layer is less than about 1.1 electronvolts.   
     
     
         2 . The quantum dot device of  claim 1 , wherein each of the first nanoparticle and the second nanoparticle comprises a zinc-containing oxide. 
     
     
         3 . The quantum dot device of  claim 2 , wherein
 the first nanoparticle is represented by Chemical Formula 1, and   the second nanoparticle is ZnO:
   Zn 1-x M x O  Chemical Formula 1
 
   
       wherein, in Chemical Formula 1,
 M is Mg, Ca, Zr, W, Li, Ti, or a combination thereof, and 
 0.01≤x<0.5. 
 
     
     
         4 . The quantum dot device of  claim 1 , wherein the electron auxiliary layer comprises
 a first electron auxiliary layer comprising the first nanoparticle, and   a second electron auxiliary layer comprising the second nanoparticle,   wherein the first electron auxiliary layer is closer to the quantum dot layer than the second electron auxiliary layer, and   wherein the second electron auxiliary layer is closer to the second electrode than the first electron auxiliary layer.   
     
     
         5 . The quantum dot device of  claim 4 , wherein the first electron auxiliary layer contacts the quantum dot layer. 
     
     
         6 . The quantum dot device of  claim 4 , wherein
 a difference between a lowest unoccupied molecular orbital energy level of the quantum dot layer and the a lowest unoccupied molecular orbital energy level of the first electron auxiliary layer is less than about 1.1 eV, and   a difference between a lowest unoccupied molecular orbital energy level of the first electron auxiliary layer and a lowest unoccupied molecular orbital energy level of the second electron auxiliary layer is less than or equal to about 0.5 electronvolts.   
     
     
         7 . The quantum dot device of  claim 6 , wherein
 the lowest unoccupied molecular orbital energy level of the quantum dot layer is in a range from about 2.5 electronvolts to about 3.6 electronvolts,   the lowest unoccupied molecular orbital energy level of the first electron auxiliary layer is in a range from about 3.2 electronvolts to about 4 electronvolts, and   the lowest unoccupied molecular orbital energy level of the second electron auxiliary layer is in a range from about 3.9 electronvolts to about 4.3 electronvolts.   
     
     
         8 . The quantum dot device of  claim 1 , wherein the electron auxiliary layer comprises the first nanoparticle and the second nanoparticle. 
     
     
         9 . The quantum dot device of  claim 1 , wherein
 an average particle size of the first nanoparticle is in a range from about 1.5 nanometers to about 3.3 nanometers, and   an average particle size of the second nanoparticle is in a range from about 3.5 nm to about 5 nanometers.   
     
     
         10 . The quantum dot device of  claim 1 , wherein a bandgap energy of the quantum dot layer is in a range from about 2.4 electronvolts to about 2.9 electronvolts. 
     
     
         11 . The quantum dot device of  claim 1 , wherein the quantum dot layer comprises a quantum dot which does not comprise cadmium. 
     
     
         12 . The quantum dot device of  claim 1 , wherein the quantum dot layer comprises a blue light-emitting quantum dot having a peak emission wavelength of less than or equal to about 470 nanometers. 
     
     
         13 . The quantum dot device of  claim 12 , wherein the quantum dot comprises zinc, tellurium, and selenium. 
     
     
         14 . The quantum dot device of  claim 13 , wherein
 the quantum dot comprises a core comprising zinc, tellurium, and selenium, and   a shell on at least a part of the core, the shell having a different composition than that of the core.   
     
     
         15 . The quantum dot device of  claim 14 , wherein the shell comprises ZnSeS, ZnS, or a combination thereof. 
     
     
         16 . The quantum dot device of  claim 12 , wherein
 the quantum dot comprises indium, zinc, and phosphorus, and   a mole ratio of the zinc relative to the indium is greater than or equal to about 25:1.   
     
     
         17 . The quantum dot device of  claim 16 , wherein the quantum dot comprises
 a core comprising indium, zinc, and phosphorus, and   a shell on at least a part of the core, the shell having a different composition than that of the core.   
     
     
         18 . The quantum dot device of  claim 17 , wherein the shell comprises ZnSeS, ZnS, or a combination thereof. 
     
     
         19 . The quantum dot device of  claim 1 , wherein
 a work function of the first electrode is about 4.5 electronvolts to about 5 electronvolts, and   a work function of the second electrode is greater than or equal to about 4 electronvolts and less than about 4.5 electronvolts.   
     
     
         20 . A display device comprising the quantum dot device of  claim 1 . 
     
     
         21 . A quantum dot device, comprising:
 a first electrode and a second electrode facing each other, wherein a work function of the first electrode is greater than a work function of the second electrode;   a quantum dot layer between the first electrode and the second electrode, the quantum dot comprising zinc, tellurium, selenium, sulfur, or a combination thereof, the quantum dot comprising a core and a shell on at least a part of the core, the shell having a different composition than that of the core; and   an electron auxiliary layer between the quantum dot layer and the second electrode, the electron auxiliary layer comprising a first nanoparticle comprising a compound represented by Chemical Formula 1 and a second nanoparticle comprising ZnO,
   Zn 1-x M x O  Chemical Formula 1
 
   
       wherein, in Chemical Formula 1,
 M is Mg, Ca, Zr, W, Li, Ti, or a combination thereof, and 
 0.01≤x<0.5.