# Highly Efficient Blue Host Compound Based on an Anthracene Moiety for OLEDs
## 3 Results and Discussion
### Electroluminescence Properties  
Non-doped OLED devices were fabricated using 2-NaAn-1-PNa as the emitting layer. As shown in Figure 5, the non-doped device was prepared as follows: ITO (150 nm)/2-TNATA (60 nm)/NPB (20 nm)/2-NaAn-1-PNa (35 nm)/Alq\({}_{3}\) (15 nm)/LiF (1 nm)/Al (200 nm). 2-TNATA, NPB, and Alq\({}_{3}\) were utilized as the HIL, HTL, and ETL, respectively. Chemical structures of materials for non-doped OLED devices are depicted in Figure S7. Figure 5a-d illustrate the current density (J)-voltage (V)-luminance (L) curves, CE-J, EQE-J, and EL spectrum of the fabricated non-doped OLED devices. The EL characteristics of the non-doped device are summarized in Table 2. The non-doped OLED device exhibited typical J-V-L curves and an operating voltage (O.V.) of approximately 8.1 V at 10 mA/cm\({}^{2}\). As shown in Figure 5d, the EL spectrum emitted light with a maximum peak at 457 nm and CIE (x, y) values of (0.150, 0.113). The CE was 3.4 cd/A, EQE was 3.9%, and luminance was 335 cd/m\({}^{2}\). Consequently, it was confirmed that 2-NaAn-1-PNa can emit blue light as a host material. The non-doped and doped devices fabricated in this study used different structures to meet their respective purposes. The HIL and HTL used in the non-doped device were configured to verify the EL wavelength and I-V-L characteristics of the host material itself, and this device structure is well-known for evaluating blue emissive materials. The doped device structure, using different HIL and HTL compared to the non-doped device, was optimized for high efficiency and long device lifetime, using a structure that our lab has previously reported to be optimized for the dopant. Therefore, even if similar HIL and HTL were used in both structures, the efficiency of the non-doped device would be lower than that of the doped device due to the absence of a dopant. If an EBL with suitable energy levels is introduced into the non-doped device, it is possible to form an increased recombination zone and decreased polaron-induced stress at the interface [29]. Figure 4: Thermal properties of 2-NaAn-1-PNa: (**a**) TGA and (**b**) DSC in 1 st heating (inset: Expansion of the T\({}_{\text{g}}\) region in 2 nd heating). Figure 5: EL characteristics of non-doped device using 2-NaAn-1-PNa: (**a**) J-V-L curve (left arrow: current density, right arrow: luminance), (**b**) luminance efficiency versus current density, (**c**) external quantum efficiency versus current density, (**d**) EL spectrum of OLED non-doped device at 10 mA/cm\({}^{2}\), and (**e**) band diagrams of the fabricated non-doped OLED device. To verify the potential of 2-NaAn-1-PNa as a blue host, doped devices were fabricated, and the EL characteristics of the OLED doped device are shown in Figure 6 and Table 2. Utilizing a doped device has the advantage of achieving higher efficiency by suppressing luminescence quenching caused by molecular packing, which typically occurs in non-doped devices [30]. The doped device was composed of ITO (150 nm)/HAT-CN (10 nm)/MHT210 (100 nm)/MEB310 (10 nm)/2-NaAn-1-PNa: 4% 3 Me-1 Bu-TPPDA (20 nm)/LG201 + 80% Liq (24 nm)/LiF/Al. The HIL, HTL, and EBL-HTL utilized HAT-CN, MHT210, and MEB310, respectively, with LG201 and Liq serving as the ETL. We verified the thickness of the EML films using the thickness monitor of the evaporation equipment during film and device fabrication. Additionally, we cross-checked the thickness of the films produced under the same conditions as the devices using an alpha step instrument (Figure S8). The doped device also exhibited typical J-V-L curves and a low O.V. of 3.9 V at 10 mA/cm\({}^{2}\). When using the optimized structure of the doped device, the operating voltage decreased by approximately 50%, from 8.1 V to 3.9 V, due to the lower energy barrier compared to the non-doped device. Additionally, it showed CIE (x, y) values of (0.134, 0.139), CE of 9.3 cd/A, EQE of 8.3%, and luminance of 934 cd/m\({}^{2}\) (Figure 6).