Design And Synthesis Of 1,10-phenanthroline Based Organic Small Molecule Electron-transport Materials For Organic Light-emitting Device

Organic light-emitting diodes tend to be a new generation of display technology for the advantages of spontaneous light,fast response,light weight and flexible display,possessing great application potential in solid-state lighting and displays.One of the key OLEDs functional layers,electron transporting/hole blocking layer help to balance charge carriers,enhance electron injection and block excitons,which is significant to improve device efficiency and stability.Rigid and electron-deficient 1,10-phenathroline is widely used as electron transporting/hole blocking materials.Unfortunately,due to low glass transition temperatures,the typical electron transporting materials BPhen and BCP are not applicable for practical OLEDs.Based on this,a series of 1,10-phenathroline based electron transporting materials has been designed,synthesized and characterized.（1）We designed and synthesized a new electron transporting material PBI-p-Phen by introducing benzimidazole group to 1,10-phenathroline through simple synthesis and purification.The material possesses good thermal property with a T_g of 125℃.Based on our previous work,we apply PBI-p-Phen as hole blocking material to pin structure green and red PHOLEDs in comparison with TPBI.Because of deeper LUMO/HOMO levels（-2.98/-6.16eV）,PBI-p-Phen devices provide higher efficiency than TPBI in both green and red PHOLEDs,with the current efficiency of 52.3 cd A^–11 and EQE of 15%in the green PHOLED,and 13.5 cd A^–1and 10.3%in the red PHOLED.The further test of device stability indicates that PBI-p-Phen provides greater stability than TPBI in both green and red PHOLEDs.At a luminance of 1000 cd m^–2,a lifetime of t₉₀0 of 176 h was found for PBI-p-Phen vs t₉₀0 of 76 h for TPBI in green PHOLED and t₉₅5 of 202 h for PBI-p-Phen vs t₉₀0 of 74 h for TPBI in red PHOLED,driven at a constant current density.（2）The low triplet energy level of PBI-p-Phen（2.26 eV）limits further application to some extent.We introduce tetrahedral TPPO group to 1,10-phenathroline in order to improve the triplet energy level and design a new electron transporting material Phen-p-PhDPO with a high triplet energy level（2.51 eV）and glass transition temperature（T_g=106℃）.Relative to Cs₂CO₃,Liq can be deposited at a low sublimation temperature.Moreover the Liq doped ETM may reduce the polaron-exciton annihilation and further increase OLED device stability.In this paper,Phen-p-PhDPO is doped with Liq and applied to pin structure red PHOLED in comparison with Phen-NaDPO.Phen-p-PhDPO and Phen-NaDPO produced similar current and power efficiency with about,9.7 cd A^–11 and 6.1 lm W^–11 at a luminance of 1000 cd m^–2,respectively.Besides,the high triplet energy of Phen-p-PhDPO indicates potential application in the green PHOLEDs.The further test shows that both of Phen-p-PhDPO and Phen-NaDPO show potential in device stability:at a luminance of 1000 cd m^–2,the device including Phen-p-PhDPO shows good stability with t₉₅5 of 240 h vs.232 h for Phen-NaDPO OLED,driven at a constant current density.