Synthesis Of Bipolar Host Materials And Corresponding Oleds In Panchromatic Range

Compared with traditional displays, organic light-emitting devices(OLEDs) as a new generation of display technology not only overcome the narrow viewing angle, low brightness, complex process and other shortcomings, but also have fast response, low power consumption, full solid-state, independent luminous, wide operation condition and other advantages. Despite the rapid development of OLEDs, device performances, such as efficiency and lifetime, etc, are still need to be improved. Therefore, developing good functional materials and device structure are demanding. Among them, using a single host for panchromatic phosphors is an important topic, because in this way, device structure can be significantly simplified, benifical to mass production. This work focuses on the synthesis of bipolar host materials and study their OLED application in full-color(red, green, blue) devices, which comprises the following contents:First, a bipolar host material 2,4,6-tris(3-(carbazol-9-yl)phenyl)-triazine(TCPZ) was synthesized according to literature, and then based on this method, two additional host materials(H2 and H3) were synthesised by replacing carbazole in TCPZ with naphthylamine or diphenylamine. Then they were characterized by NMR and mass spectrometry, confirming their molecular structure. In addition, their photophysical properties were characterized. The triplet of TCPZ is slight lower than that of blue phosphor, but it holds small singlet-triplet splitting as well as large spectra overlap between the fluorescence and phosphorescence. Thus, it can be expected to be the host of blue phosphor. However, it was found that the later two materials(H2 and H3) are not suitable for blue phosphor due to their relatively low triplet.Second, starting with the synthesis of our previously reported phosphors of Ir(BPPa)3(red) and Ir(BPPya)3(green), based on host TCPZ, green(Ir(BPPya)3) and red(Ir(BPPa)3) phosphorescent OLEDs were studied. In this part we optimized the thickness of the electron transport layer for the purpose of balance charge carrier in the emitting layer. As a result, excellent performance of green and red devices were achieved, with efficiencies of 81.0 cd/A(23.1%) for green, 9.3 cd/A(13.2%) for red. Particularly, our red PhOLED presents a much saturated red emission, with peak up to 644 nm and Commission International de L’Eclairage(CIE) coordinates of(0.69, 0.30). The high efficiency of 13.2% is rare for deep red in literature due to the instability of red emission material with low bandgap.Third, FIrpic(blue) phosphorescent OLEDs based on host TCPZ were studied. Due to the additional EL from the electron transport layer when applied the previously red or green device structure in blue phosphorescent OLEDs, we changed the electron transport layer and pure EL from the phosphor was successfully achieved. In addition, we optimized the doping concentration, founding that at the doping 9% presented the best performance, with efficiencies of 17.0 cd/A(10.4%) at maximum. These results indicate that in our blue PhOLEDs, efficient energy transfer from the host to the dopant does occur, though the triplet of TCPZ is slightly lower than FIrpic. This can be explained by its small singlet-triplet splitting as well as large spectra overlap between the fluorescence and phosphorescence in TCPZ transfer energy, in such, thermal activated energy transfer from triplet to singlet in TCPZ may occur. Therefore, energy transfer from host triplet to host singlet then to the phosphor can be realized, improving the harvesting of the electrical energy in triplet host hence benefiting device performance. At this point, full-color efficient devices based on a single host material achieved all.