# Quantum Dot-Based White Organic Light-Emitting Diodes Excited by a Blue OLED
## 3 Results and Discussion
### Blue OLED (BOLED) Devices  
Blue OLED devices are fabricated through the adjustment of the hole injection layer (HIL) thickness and the effects of HIL thickness on the device characteristics are observed. In the beginning, we chose an ETL (TPBi) thickness, such as 30 nm. To obtain the optimal device structure, the HIL thickness needed to be adjusted to 10 and 20 nm, respectively. The structure of the blue OLED device was ITO/HATCN (Y nm)/TAPC (30 nm)/MADN: \(\
u\)-DABA (40 nm)/TPBi (30 nm)/LiF (0.8 nm)/Al (150 nm). Figure 11a depicts the energy band diagram of the blue OLED, and Figure 11b shows a photo of the blue emission. The device parameters of blue OLEDs are listed in Table 3. Figure 12a,b shows the current density-voltage and luminance-voltage characteristics, respectively. From the results, it was found that with an HATCN thickness of 10 nm the device had a current density of 45.29 mA/cm\({}^{2}\) and luminance of 746.8 cd/m\({}^{2}\) at 8 V. When the HATCN thickness was adjusted to 20 nm, the current density and luminance increased to 87.68 mA/cm\({}^{2}\) and 963.9 cd/m\({}^{2}\), respectively, at 8 V. Therefore, an HATCN of 20 nm was determined to be the best thickness.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Device**} & \multicolumn{2}{c}{**ITO**} & **HIL** & **HTL** & **EIL** & **Cathode** \\ \cline{2-6}  & **UV Treatment** & **HATCN** & **X** & **LiF** & **Al** \\ \hline TAPC & Yes & & & & \\ \hline TAPC (\(w\)/\(o\) UV) & \(w\)/\(o\) & & & & \\ \hline mCP & Yes & & & & \\ \hline mCP (\(w\)/\(o\) UV) & \(w\)/\(o\) & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Structural parameters of the hole-only devices with different HTL materials (unit: nm).  
Figure 10: Comparison of current density–voltage characteristics of hole-only devices with different HTL materials.  
The UV laser-excited photoluminescence (PL) analysis of the TADF host material MADN and the doped material v-DABNA is shown in Figure 13a,b, respectively. This demonstrated that the host material MADN had a PL peak at about 423 nm, while the dopant peak v-DABNA was at about 460 nm. The electroluminescence (EL) spectrum of the blue OLED Z-1 is shown in Figure 13c. From the EL spectrum in Figure 13c, it was apparent that the emission peak of an MADN doped with 10% v-DABNA as the emitting layer was at 456 nm, and the full width at half maximum was only 28 nm. Based on Figure 13d, which shows the CIE coordinates, when MADN:v-DABNA was used as the emitting layer, the CIE coordinates were fixed at (0.14, 0.07) when biased at 5-8 V, which was a pure blue device.  
Figure 11: (a) Energy band diagram; (b) the photo of blue emission of the BOLED.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & **HIL** & **HTL** & **EML** & **ETL** & **EIL** & **Cathode** \\ \hline NO & HATCN & TAPC & MADN: v-DABNA (10\%) & TPBi & LiF & Al \\ S-1 & 10 & 30 & 40 & 30 & 0.8 & 150 \\ Z-1 & 20 & 30 & 40 & 30 & 0.8 & 150 \\ \hline \end{tabular}
\end{table}
Table 3: The device parameters of the blue OLED with its HATCN thickness adjusted (unit: nm).  
Figure 12: The blue OLED device: (a) current density–voltage characteristic curve; (b) luminance–voltage characteristic curve.