**3. QLED fabrication by spin coating**

### **3.1 Experimental chemicals**

Detergent TFD4 was purchased from BioLab, PEDOT:PSS 4083 from Heraeus, poly-TPD (LT-N149) from Luminescence Technology Corp Ltd., patterned ITO glass from Xinyan Technology Ltd., green (CdZnSeS/ZnS) quantum dots from Suzhou Mesolight Inc., and zinc acetate dihydrate powder, potassium hydroxide flakes, acetone, isopropyl alcohol, methyl alcohol, chloroform, and chlorobenzene all from Aldrich.

### **3.2 Synthesis of ZnO nanoparticles**

The uncleation-dissolution-recrystallization growth method [16] was applied to synthesize the ZnO nanoparticles. Firstly 0.37 g potassium hydroxide was dissolved in 16.25 ml methyl alcohol. Then zinc acetate dihydrate solution was prepared by adding 0.74 g zinc acetate dihydrate in 31.25 ml methyl alcohol at 60°C under vigorous stirring. Then the potassium hydroxide solution was jetted into the zinc acetate dihydrate solution at the rate of 0.8 ml/min. The reaction takes around 1.7 h under N2 protection condition. After the reaction, the solution was allowed to sit for another 2 h to let the ZnO nanoparticles settle at the bottom of the reaction flask. The ZnO nanoparticles were washed twice by methyl alcohol. Then the ZnO

**73**

**Figure 5.**

*Quantum Dot Light-Emitting Diode: Structure, Mechanism, and Preparation*

nanoparticles were dispersed in chloroform and isopropyl alcohol mix solution at

Transmission electron microscopy (TEM, JEOL JEM 2010) was applied to

The patterned ITO glass was cleaned by detergent, methyl alcohol, acetone, and isopropyl alcohol in turn, each sonication for 20 minutes. After cleaning, UV ozone plasma was applied for surface energy modification. PEDOT:PSS was spin-coated on the cleaned ITO surface at 3000 rpm for 30 s and then baked under vacuum at 150°C for 30 min. Then hole transport layer (HTL) was prepared by spin coating poly-TPD on the annealed PEDOT:PSS surface at 3000 rpm for 60 s and baking at 100°C for 30 min under vacuum protection. Quantum dots were also deposited on the annealed poly-TPD surface by spin coating at 3000 rpm for 30 s. Then the synthesized ZnO nanoparticle solution was spin-coated at 1500 rpm for 60 s. The baking temperature is 60°C for 30 min. The cathode was deposited by vapor deposition method. A more detailed QLED device fabrication process was mentioned in previous work [2].

The concentration of precursor, evaporation rate, and the time of reaction were all significant synthetic parameters, which affected the growth of ZnO nanoparticel dimensions and structures. **Figure 5** shows the TEM images of the as-synthesized

*TEM images of two different sizes of ZnO NPs. (a, b) reaction times of 105 min and (c, d) 80 min.*

*DOI: http://dx.doi.org/10.5772/intechopen.91162*

characterize the morphology of the nanoparticles.

the concentration of 35 mg/ml.

**3.3 QLED device preparation**

**3.4 Results and discussion**

*3.4.1 ZnO nanoparticle analysis*

*Quantum Dot Light-Emitting Diode: Structure, Mechanism, and Preparation DOI: http://dx.doi.org/10.5772/intechopen.91162*

nanoparticles were dispersed in chloroform and isopropyl alcohol mix solution at the concentration of 35 mg/ml.

Transmission electron microscopy (TEM, JEOL JEM 2010) was applied to characterize the morphology of the nanoparticles.
