Organic semiconductors with bipolar (electron and hole) transport capability play a crucial role in electronic and
optoelectronic devices such as organic light-emitting diodes (OLEDs), bipolar transistors and photovoltaic cells.
Recently, a considerable amount of work has been devoted to the characterization of ambipolar transport in organic
materials, allowing for a better understanding of their properties as well as the physical processes, which take place in
materials and devices [1-4]. The experimental methods used to obtain information about charge transport in organic
semiconductors - time-of-flight (TOF) transient photoconductivity , charge extraction by linearly increasing voltage
(CELIV) , current-voltage measurements in space charge limited current regime , and field effect transistor (FET)
measurements [8, 9] are mostly focused on determination of charge carrier mobility. On the other hand, for many devices
(e.g. organic photovoltaic solar cells or light emitting diodes) the knowledge of the transport and recombination
characteristics of both carriers (electron and hole), and specifically their diffusion LD = the square root of Dτ (here D is the diffusion
coefficient and τ is the photocarriers lifetime) and drift lengths L0 = μτE0 (here μ is the carrier's mobility and E0 is
the electric dc field) is important.