Strain effects on the energy level alignment at metal/organic semiconductor interfaces.

Flexible and wearable devices are growing sectors of the opto-electronics market. Nevertheless, bendable devices should possess the same efficiency and stability as their rigid analogs. It is well known that the energy barriers between the Fermi energy of a metal and the molecular levels of an conducting organic semiconductor play a fundamental role in the performance of organic based electronic devices. Therefore, it is critical to understand how the energy barriers at metal/organic semiconductor interfaces change with bending. In this work we experimentally measure the interfacial energy barriers between a metallic contact and small semiconducting molecules. The measurements are performed while the devices are operating as the samples are bent by a controlled applied mechanical strain. We determine that the energy barriers are not sensitive to sample bending, but we observe that the hopping transport of charges in flat molecules can be tuned by mechanical strain. The theoretical model developed for this work confirms our experimental observations.