Development and Demonstration of Charge Transfer Devices With Aligned Polymer Chains

The work presents first-of-its-kind acoustic charge transfer devices (CTDs) using an organic semiconductor, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinylene] (MEH-PPV), with aligned polymer chains and demonstrates efficient charge transport over a distance of 3 mm using surface acoustic waves (SAWs). The aligned chains of MEH-PPV provide a conducive medium for the discrete and directed transfer of charges along the chains. Acoustic CTDs have traditionally used inorganic semiconductors as active materials. This work demonstrates experimentally the SAW-controlled intrachain and interchain transport of optically excited charge carriers in MEH-PPV with aligned chains. The device structure comprises an aligned MEH-PPV film on a piezoelectric YZ lithium niobate substrate, a pair of orthogonal interdigital transducers (IDTs), and corresponding collector diodes. The long-range alignment of the MEH-PPV chains has been achieved using a DC electric field (EF). The pair of IDTs emits SAWs in orthogonal directions, one in the direction of chain alignment and the other across the direction of chain alignment. Furthermore, an analysis of the performance of CTD is carried out using another device structure consisting of a single IDT, aligned MEH-PPV film, and two collector diodes separated with a gap facing opposite to the IDT within its aperture width. An experimental demonstration of the directed charge transfer shows a charge leakage of less than 5% of direct charge transport. The work offers a foundational framework for the future design and development of potential organic semiconductor devices for imaging and other optoelectronic applications.