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/cm2 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.

This work reports for the first time acoustoelectric charge transport in an organic semiconductor, regioregular poly(3hexylthiophene), (rrP3HT) deposited as thin films on surface acoustic wave (SAW) devices generating shear horizontal and Rayleigh SAW. With the propagation of SAW, an enhancement in current was observed, especially when the applied bias field was in the direction of wave propagation. The momentum and energy transfer from SAW helped to reduce charge trapping at trap states and increase the free charge density, assisting the drift current. The mechanical and electrical effects of the acoustic wave were independently studied by using a non-piezoelectric substrate and by screening the mechanical deformations of SAW, respectively, in order to support the observations. The devices displayed high stability on repeated exposure of the SAW while they were monitored for 1 week under ambient conditions (temperature at around 24 °C and humidity at around 44% RH).

Demonstration of acoustically improving charge transport characteristics of regioregular poly(3-hexylthiophene) (rrP3HT) based organic field effect transistor (OFET) fabricated on YZ lithium niobate piezoelectric substrate has been presented and analyzed. Owing to the acoustoelectric (AE) effect, a surface acoustic wave (SAW) propagating through the substrate transfers its momentum and energy to the charges in the rrP3HT channel, reducing the effective energy gap between the charge hopping states, which leads to a decrease in charge trapping and an increase in path conductivity and number of paths for charge transport. Hence, a significant increase in drain current and mobility and a substantial reduction in gate voltage were observed in the presence of SAW. The AE effect has been especially predominant in devices with smaller channel width, depicting that gate voltage brought down by 30 V provided drain current equivalent to that obtained in the absence of SAW. The bias stress analysis of the devices showed an increase in current instead of the decrease, generally seen with respect to time, reinforcing that the long term charge trapping effect in OFETs can be compensated with the propagation of SAW leading to enhanced device stability.

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An organic semiconductor, regioregular poly­(3-hexylthiophene) (rrP3HT), based excitonic transistor on a piezoelectric YZ lithium niobate substrate is reported for the first time. The propagating surface acoustic wave (SAW) field ionizes the excitons, stores the charge pair in the SAW modulated potential field in the semiconductor, and carries them forward. A long-range transport ∼4.7 mm at room temperature has been demonstrated. The electrical control of the exciton flux was achieved with SAW propagating through a dual metal–insulator–semiconductor (MIS) structure. The working of the device has been demonstrated using white and green light. A threshold voltage of −20.65 V was observed, and the working mechanism of the proposed device has been verified through numerical analysis using MATLAB. The potential use of the proposed device structure as an all optical device was verified electrically with additional electrode terminals at the output end.