# Quantum Dot-Based White Organic Light-Emitting Diodes Excited by a Blue OLED
## 3 Results and Discussion
### White OLED (WoLED) Devices
Nevertheless, due to the energy gap architecture between BOLED\(\rightarrow\)RQD\(\rightarrow\)GQD, as shown in Figure 17a, most of the blue light energy from blue OLED was absorbed by the RQD because it was first excited, so the amount of blue light that reached the green QD was minimal. In addition, the excited red emission penetrated the GQD without exciting it. Therefore, pure white light was not able to be achieved since the green spectrum could not be excited as the red emission. The result is shown as the red curve in Figure 16b. If the RQD-GQD order was reversed, the blue OLED first excited the GQD then the RQD, which resulted in three peaks emitting at 460, 530, and 620 nm at 8 V, as shown in Figure 16b. Due to the energy gap architectures between BOLED\(\rightarrow\)GQD\(\rightarrow\)RQD, as shown in Figure 17b, the green QD absorbed part of the blue light emitted from the BOLED, and  
Figure 16: (**a**) Luminance–voltage curves; (**b**) EL spectra of BOLED\(\rightarrow\)GQD\(\rightarrow\)RQD and BOLED\(\rightarrow\)RQD\(\rightarrow\)GQD. Figure 17: Energy band diagram of light excitation architectures: (**a**) BOLED\(\rightarrow\)RQD\(\rightarrow\)GQD; (**b**) BOLED\(\rightarrow\)GQD\(\rightarrow\)RQD. the remaining blue light penetrated the GQD to reach the RQD. These excited spectra were very close to the white light, as the black square curve shows in Figure 16b. The original blue CIE coordinates were (0.15, 0.07). After using the excitation combination BOLED\(\rightarrow\)GQD\(\rightarrow\)RQD, the CIE coordinates were (0.42, 0.33), as shown in Figure 18, which was very close to the white light position and independent of the applied voltage. QD (CdSe/ZnS)-based LEDs have been extensively studied in recent years, but very few approaches have been detailed for QD (CdSe/ZnS) PR-based white OLEDs. In the literature review, [PERSON] et al., from Jilin University, used CdSe/ZnS quantum dot material mixed with polymethylmethacrylate (PMMA) to create a separate composite film to convert a blue OLED to white color, producing a white OLED with a maximum luminance of 10,250 cd/m\({}^{2}\) and maximum current efficiency of 20.6 cd/A. In the case of the white OLED, the CIE coordinates shifted only from (0.291, 0.406) at 4 V to (0.288, 0.405) at 8 V. [PERSON] et al. from YONSEI University, South Korea, used red and green quantum dot materials mixed with PGMEA and positive photoresist and exposed and developed technology on the glass substrate to create a full-color OLED display. [PERSON] et al. Hongik University in South Korea investigated the color conversion properties of QD/OLEDs using the microcavity effect, with an OLED fabricated on a WO\({}_{3}\)/Ag/WO\({}_{3}\) (WAW) anode. Some fabrication methods, such as drop casting, air-gapped bridges, QD dispersed PR films, and flat and patterned QD down-conversion films have been recognized for the development of the QD PR-based top and bottom emission white OLED on glass and PET substrates. In the development of QD PR-based WOLEDs, BLOEDs have played an important role. From the literature, all the research has been successful in achieving the white light. The QD nanoimprinting methods were introduced in this study to achieve QD PR-based white light emission. In that, the patterned sapphire was used as the master mold to prepare PDMS to be attached to spin-coated QD PR glass substrates to perform the nanoimprinting process. In that, the back side of a blue OLED was attached to nanoimprinted RQD and GQD photoresists, which were excited by blue OLEDs to achieve the white light. As a result of this process, we successfully fabricated GQD and RQD (CdSe/ZnS) PR-based bottom emission white OLEDs. Figure 18: CIE coordinates of device assembly of BOLED\(\rightarrow\)GQD\(\rightarrow\)RQD.