Intrinsic Mobility-Strain Relationship in Flexible Organic Semiconductor Crystals via Hall Effect and Raman Spectroscopy
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Here we report the first measurements of Hall effect and low-frequency Raman modes of a crystalline organic semiconductor (rubrene) as a function of calibrated uniaxial mechanical strain. Our measurements reveal a strong and reversible modulation of the intrinsic (trap-free) charge carrier mobility of crystalline rubrene with strain, showing that the effective mobility can be enhanced by 70 - 110% with only 1% of compressive strain. Consistently, Raman spectroscopy reveals shifts of the low-frequency Raman modes to higher (lower) frequencies with compressive (tensile) strain, which is in line with the strain-dependent carrier mobility measurements. These studies significantly contribute to our fundamental understanding of the relationship between the carrier mobility, molecular vibrations and strain in organic semiconductors and are thus important for the foundations of strain engineering and flexible organic electronics.