Effects of interfacial tension and molecular dipole moment on the electrical characteristics of low-voltage-driven organic electronic devices

In organic electronic/photonic devices, numerous types of interfaces and their properties exhibit profound correlation with device performance. For optimizing the performance of organic electronic/photonic devices, appropriate and effective interface engineering needs to be developed. In this study, a high dielectric constant material, hafnium dioxide (HfO2), and an organic semiconductor, N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) were adopted as the dielectric and active layers, respectively, to fabricate low-voltage-driven organic thin-film transistors. Three kinds of insulating polymers were selected to serve as buffer layers (BLs) to modify HfO2. After the addition of BLs onto HfO2, the insulating properties of HfO2 and the microstructures of PTCDI-C13 active layers improved, resulting in considerably enhanced electrical characteristics and stability of the devices. Among different polymeric BLs, the BL polymer exhibiting smaller interfacial tension with PTCDI-C13 can induce PTCDI-C13 to form better microstructures and generate lower interfacial trap density despite the rougher topography of polymeric BL, leading to improved electrical characteristics of the corresponding device. However, we observed that BL polymer with larger dipole moment of side groups can yield better electrical stability of the corresponding device under continuous operation compared with polymers with smaller interfacial tension. During long-term operation, the dipoles can be aligned by an electric field and form a strong dipole layer to facilitate charge accumulation and alleviate device degradation caused by bias-stress-induced trap/defect states. We further adopted a BL polymer with both small interfacial tension and large dipole moment to fabricate low-voltage-driven organic complementary inverters. The inverter can exhibit high electrical characteristics and stability during continuous operation. Interfacial tension and molecular dipole moment are possible important issues for effective interface engineering.