Characterization Of The Ambipolar Transport Properties Of Polymer-Based Organic Photoconductor By Non-Steady-State Photo-Emf Technique

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 [5], charge extraction by linearly increasing voltage (CELIV) [6], current-voltage measurements in space charge limited current regime [7], 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 L-D = root D tau (here D is the diffusion coefficient and tau is the photocarriers lifetime) and drift lengths L-0 -mu tau E-0 (here mu is the carrier's mobility and E-0 is the electric dc field) is important.