Mechanical properties and interfacial reliability of organic electronic materials

Abstract

Organic electronics have been highlighted because of their outstanding advantages such as solution process, light weight, fast and flexibility compared with conventional electronics. Therefore, conventional electronics have been transformed to organic material based electronics which can endure various mechanical loadings. However, current organic electronics have critical problems with their low fracture resistance, environmental stability and defects evolution under mechanical loadings. In this dissertation, I have focused on evaluation of the weak interfacial reliability of organic electronic materials and the simultaneous improvement with efficien-cy. To investigate the interfacial reliability, double cantilever beam (DCB) fracture mechanics testing was employed. Also, four different enhancing methods are introduced. First method is a using an additive into organic electronic material in the state of solution to change the polymer conformation. Second method is surface treatments on the spin coated organic electronic material thin films to alter the surface energies. Third method is introduction of adhesive layer at the weak interface. The last is a method of strengthening by forming fibrils in an organic electronic material. Through adopting the enhancing methods, the cohesion and electrical conductivity of conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) which has low cohesion by weak hy-drogen bonding were improved by adding dimethyl sulfoxide (DMSO) and $H_2SO_4$ treatment. Also the significant changes in the mechanical and electrical properties that are dependent on the concentration of DMSO and $H_2SO_4$ were demonstrated. In addition, the enhancement mechanism of adhesion and efficiency in PCDTBT-based organic solar cells (OSCs) was studied by controlling the surface wettability at the interface between buffer and active layers. Depending on surface treatments on ZnO layer, adhesion and crack path are changed indicating that surface wettability affects to interfacial characteristics. In perovskite solar cells, mechanical stability of perovskite solar cell was investigated through the adhesion changes by ion additives under humid environments and the correlation between additives, adhesion and delamination was demonstrated. Also, to make difficult the crack propagation at the weak interface, surface roughness control of perovskite layer and fibril formation in organic electronic materials were conducted.