Charge Extraction by Linearly Increasing Voltage (CELIV) Method for Investigation of Charge Carrier Transport and Recombination in Disordered Materials

The technique of charge carrier extraction by linearly increasing voltage (CELIV) and its variations have been proposed as a powerful tool to characterize charge transport in disordered semiconductors including inorganic and organic materials and to overcome certain limitations of the traditionally used time-of-flight technique, especially when charge transport is highly dispersive. In the original version of CELIV (often referred to as dark-CELIV), a linearly increasing voltage (triangular pulse) is applied to extract thermally generated carriers and the mobility is obtained from the time it takes to reach the peak of the extraction transient. In organic semiconductors or wide-bandgap inorganic semiconductors, where the concentration of thermally generated carriers is low, either photogeneration of charge carriers or charge injection is used. These variations are called photo-CELIV and i-CELIV, respectively. This chapter discusses the principles of the CELIV techniques and provides an overview of the applicability of different variations for different materials and structures, including dark-CELIV for the determination of mobility, bulk conductivity, and density of equilibrium charge carriers, photo-CELIV for the investigation of the relaxation of both the mobility and density of photogenerated charge carriers, and i-CELIV for the independent investigation of transport peculiarities of both injected holes and electrons in bulk heterojunctions.