Mobility and dynamics of charge carriers in rubrene single crystals studied by flash-photolysis microwave conductivity and optical spectroscopy

The optoelectronic properties of single-crystal rubrene were studied by investigating the charge-carrier dynamics and mobility, by flash-photolysis time-resolved microwave conductivity (TRMC) and transient optical microscopy (TOS). The emission maximum located at 630 nm shows a red-shift of about 60 nm relative to solution. The single-crystal nature is anticipated to account for the clear dependence on photon density, while various grain boundaries and chemical/physical defects hide this dependence. The TMRC mobility of holes obtained at a 10μs delay is found to be (3.6∓0.8)×10 ^-2cm²V^-1s^-1, which is 70% of that at the pulse end. The anisotropic conductivity of single-crystal rubrene with charge-carrier motion on the nanoscale is achieved on the micrometer scale.