Tuning charge transfer at the electron donor/acceptor assembly through vibration-induced aggregation of P3HT chains in solution

Abstract

In this report, we developed a test platform to probe charge transfer at a model electron donor/acceptor system in which charge transfer rate is investigated through electrical contact resistance in a metal oxide/organic semiconductor/metal oxide structure using transmission line method (TLM). Aluminum (Al)-doped zinc oxide (AZO) films were adopted as source and drain electrodes. Molecular ordering of the organic semiconductor was systematically varied through vibration-induced aggregation (VIA) treatment of poly(3-hexylthiophene) (P3HT) polymer chains in solution to probe the effect of molecular ordering of P3HT (donor) in contact with AZO (acceptor) on interfacial charge transfer at the electron donor (P3HT)/acceptor (AZO) interface crucial in determining device performance of optoelectronic devices. Enhanced charge transfer at the donor/acceptor interface containing P3HT film treated with VIA process was demonstrated by reduction of the contact resistance via TLM. More efficient charge transfer at the AZO/sonicated-P3HT/AZO compared with AZO/pristine-P3HT/AZO results from enhanced charge carrier mobility of P3HT near the interface, blocking back-transfer of injected holes from P3HT to the AZO electrode, as demonstrated by theoretical prediction. Effect of VIA treatment on charge transfer at the electron donor/acceptor interface is confirmed through comparing the AZO/P3HT contact resistance depending on the degree of VIA for P3HT polymer chains by varying sonication time. Our work presented here demonstrates that improvement in structural arrangement of polymer chains leads to efficient charge transfer at interface.