Abstract
Establishing fundamental relationships between strain and work function (WF) in organic
semiconductors is important not only for understanding the electrical properties of organic
thin films, which are subject to both intrinsic and extrinsic strains, but also for developing
flexible electronic devices. Here we investigate tensile and compressive strain effects on the
WF of rubrene single crystals. Mechanical strain induced by thermal expansion mismatch
between the substrate and rubrene is quantified by X-ray diffraction. The corresponding
WF change is measured by scanning Kelvin probe microscopy. The WF of rubrene
increases (decreases) significantly with in-plane tensile (compressive) strain, which agrees
qualitatively with density functional theory calculations. An elastic-to-plastic transition,
characterized by a steep rise of the WF, occurs at ~0.05% tensile strain along the rubrene
π-stacking direction. The results provide the first concrete link between mechanical strain
and the WF of an organic semiconductor and have important implications for
understanding the connection between structural and electronic disorder (charge traps) in
soft organic electronic materials.