A Study Of Solution-Processed Hole Injection And Transport Materials

Solution-processed organic light-emitting diode（OLED）offers an opportunity to significantly lower the fabrication costs and also enables the application on large area and flexible substrates,causing extensive attention.However,the efficiency and lifetime of solution-processed OLED are commonly low,and it is difficult to fabricate multilayer structures.Therefore,many researchers propose new solution processable materials,and optimize the fabrication technology and the structure of device to improve the performance.To realize the solution-processed OLED with high performance,we systematically study the solution-processed hole injection and transport materials.Firstly,we have demonstrated that the work function of solution-processed molybdenum trioxide（s-MoO₃）can be increased by UV-ozone treatment,which improves the hole injection from the anode to hole transport layer.And the phosphorescent green OLED with UV-ozone treated s-MoO₃ shows a maximum current efficiency of 48.3 cd/A,which is comparable to the device with evaporated MoO₃.It is expected that UV-ozone treated s-MoO₃ can be widely applied in simple and low-cost solution processed OLED as an excellent hole injection layer.Secondly,we have investigated multiple solution-processed hole transport materials,and found out that the hole transport abilities of solution-processed materials can be enhanced by annealing in the air,which are comparable to those of the corresponding evaporated materials.However,those materials are easy to dissolved by the solvents of emitting materials,which restrain the application in solution-processed OLED.To improve the anti-solubility of hole transport layer,we blend the hole transport material with high hole transport ability and cross-link polymer material.The fabricated mixing hole transport layer is hardly dissolved in common solvents,and a good hole transport property is obtained as well.When the blending layer is applied in a phosphorescent red device,the maximum current efficiency is up to 11.2 cd/A with very low efficiency roll-off.