Crystal-Domain Orientation and Boundary in Highly Ordered Organic Semiconductor Thin Film

Conduction of electric charges is often done in polycrystalline materials. Unavoidably, the crystallite size, orientation, and domain boundaries (DBs) affect the transport of the charge carriers. It is particularly so for organic semiconductors known to be highly anisotropic and strongly dependent on DBs. Understanding those effects will have a strong impact on improving the performance of organic electronic and optoelectronic devices. Herein, we report our investigation on the crystal-domain orientation and boundary on the charge transport of operating device with copper phthalocyanine (CuPc) thin films grown on p -sexiphenyl ( p -6P) by Kelvin probe force microscopy. In CuPc intradomains, the voltage drop increases as the angle increases between the domain orientation and the source-drain electric field. In DBs, the potential wells and steep voltage drops were observed. The increase of the DBs width and the angle between the orientations of neighboring domains results in the raise of voltage drop across the DBs, which restrict the charge transport in DBs simultaneously. The mobility of CuPc thin films increases with the domain size, resulting from the reduction of the mismatched orientation degree and the number of DBs.