Acoustic charge transport in organic semiconductor films

Abstract

Abstract We demonstrate the acoustic charge transport of optically induced excitons in two organic semiconductors, P3HT and MEH-PPV, up to a distance of 3 mm. The device consists of a surface acoustic wave (SAW) resonator transmitting SAW through a polymer layer where acoustic charge transport takes place and a polymer diode at the end to collect the charges. The voltage excitation is provided using an interdigital transducer (IDT) on a piezoelectric YZ lithium niobate substrate producing Rayleigh SAW at 42 MHz. Optical illumination up to 15 mW cm−2 intensity is applied to induce excitons in the polymer layer deposited on the lithium niobate substrate. The photogenerated excitons in the polymer are ionized by SAW field resulting in free carriers that are transported to the polymer diode by the travelling SAW. A surge in photovoltaic current in the diode is observed in the presence of SAW when the carriers are optically generated away from the diode. The maximum charge capacity and transfer efficiency of the acoustic transport are calculated for various SAW power and illumination intensities. A theoretical analysis of charge carrier dynamics in the presence of a moving SAW field is also performed using a semi-classical Hamiltonian of the system.