Investigation of charge carrier transport and recombination in organic semiconductors with Charge Extraction by Linearly Increasing Voltage (CELIV) technique

This study aimed to calculate the drift velocity and mobility of holes in organic semiconducting polymers by the Charge Extraction via Linearly Increasing Voltage (CELIV) technique to measure the charge carrier mobility. The charge carrier mobility is defined as carrier drift velocity v in each electric field E. This technique is complementary to Time of Flight (ToF) by providing us with an indication of the material’s properties when other methods are not applicable. Typically, Photo-CELIV is used to measure the charge carrier mobility in Organic Semiconductor (OSCs) due to large bandgap (2 eV) and few thermally generated carriers for extraction in the dark. The effect of the recombination mechanism is investigated on the carrier mobility in the organic layer. The calculation results showed that saturation of extracted charge is linearly proportional to carrier concentration at low concentrations, whereas at high density is saturated due to bimolecular carrier recombination. Langevin recombination mechanisms show that extracted demand saturates at j0, the capacitive displacement current step. Therefore, Δj/j0=1 at high light intensities, the saturation of extracted charge will start to decrease from its maximum value only when tdel is increased to be like tmax. In Langevin recombination, the bimolecular carrier lifetime is much faster than transit time at high carrier concentrations giving the saturation of extracted charge.