# Synthesis and Electrical Properties of a New Bipolar Material Using Spacer Moiety
## 3 Results and Discussion
### Electroluminescence Properties
Additionally, all fabricated devices adequately maintained their carrier balance, even at high luminance, beginning at 20 mA/cm\({}^{2}\); the maximum CE was 50 mA/cm\({}^{2}\), and the current density was high. The 10 wt% doped devices showed only a slight roll-off effect. The roll-off values of devices doped with 20 and 30 wt% showed 9.0% and 6.9%, respectively (Figure 7b). The small roll-off of less than 10% observed in these materials is a key characteristic of materials with bipolar properties, as it helps maintain carrier balance within the device. To further confirm this, hole-only devices (HOD) and electron-only devices (EOD) of DTTCZ were fabricated. The structures of HOD and EOD are as follows: ITO/molybdenum trioxide (MoO\({}_{3}\)) (1 nm)/EML (50 nm)/MoO\({}_{3}\) (10 nm)/Al (100 nm) and ITO/TPBi (40 nm)/EML (50 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm). As a result, it was confirmed that the mobility of both holes and electrons was similar, exhibiting good bipolar characteristics (Figure S5). All doped devices showed the same ELmax peak  
Figure 5: Thermal properties of DTTCZ and poly DTTCZ: (**a**) TGA analysis and (**b**) DSC results. of 430 nm and a FWHM value of 61 nm. The CIE values were identical (0.16, 0.06) in 10- and 20-wt%-doped devices; however, the CIE y-value increased to (0.17, 0.09) in the 30 wt% doped device. Therefore, a doping concentration of 20 wt% provided the optimal results and showed the highest EL efficiency, as well as a CIE y-value of deep-blue emission--this was better than the mobile specification value of approximately 0.15 while satisfying the television specification value of 0.08 [31; 32]. Moiety composed of donor-acceptor types, such as DTPCZ, exhibits TADF properties and can also demonstrate high OLED efficiency. However, in the case of DTPCZ, it does not possess TADF characteristics and showed low efficiency due to exciplex in the non-doped device structure. Nonetheless, by utilizing a doping system, we enhanced EQE by approximately 1.4 times. We will report on the synthesis of various new derivatives in the future. Polymer deposition devices could not be manufactured because of their high molecular weight. Thus, OLEDs were fabricated using a solution process. The devices were fabricated with the configuration ITO/poly(2,3-dihydro-1,4-dioxin):polystyrene sulfonate (PEDOT:PSS) (40 nm)/CBP: 5 wt% poly DTPCZ (20 nm)/TPBi (40 nm)/LiF (1 nm)/Al (200 nm). PEDOT:PSS was included for hole injection, and CBP was used as the host material. TPBi was used as an electron-transporting and hole-blocking layer (Figure 56a). As shown in the J-V curves, the device operated normally, and the EL maximum peaks occurred at 465 nm, with energy transfer from the host to the dopant (Figure 56b,c). However, because of the low PLQY of poly DTPCZ, EQEmax exhibited a low device efficiency of approximately 0.6%. Further improvements in device fabrication for both DTPCZ and poly DTPCZ are  
Figure 6: EL characteristics of non-doped DTPCZ devices: (**a**) J-V-L curve, (**b**) CE versus current density, (**c**) PE versus current density, (**d**) EQE versus current density, (**e**) EL spectrum at 9.0 V, and (**f**) the band diagram of the materials in OLED devices. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**@ 10 mA/cm\({}^{2}\)** & **V\({}_{\text{on}}\)****a** & **CE** & **EQE** & **PE** & **EL\({}_{\text{max}}\) (nm)** & **FWHM** & **CIE** \\  & **(V)** & **(cd/A)** & **(\%)** & **(Im/W)** & **EL\({}_{\text{max}}\) (nm)** & **(nm)** & **(x, y)** \\ \hline CBP: 10\% DTPCZ & 3.9 & 0.48 & 1.07 & 0.30 & 430 & 61 & (0.16, 0.06) \\ CBP: 20\% DTPCZ & 3.9 & 1.17 & 2.32 & 0.68 & 430 & 61 & (0.16, 0.06) \\ CBP: 30\% DTPCZ & 3.9 & 0.97 & 2.05 & 0.59 & 430 & 61 & (0.17, 0.09) \\ \hline \hline \end{tabular}  
* Operating voltage of 10 mA/cm\({}^{2}\).  
\end{table} 
Table 3: EL performances of doped OLED devices at 10 mA/cm\({}^{2}\). possible by optimizing the solution process and the device structure.