Improved Electrical Ideality and Photoresponse in Near Infrared Phototransistors Realized by Incorporating a Bulk Heterojunction Channel

Simultaneous increase in electrical ideality and near infrared (NIR) response in the organic phototransistors (OPTs) is realized by applying a donor/acceptor bulk heterojunction (BHJ) channel layer. A comprehensive analysis has been carried out to understand the effects of the miscibility between the donor and acceptor in the BHJ channel, and the morphology of the channel layer on the electrical charge transport and optical response of the OPTs. The presence of the acceptors in the channel layer helps to trap the undesirable injected electrons, avoiding the accumulation of the electrons at the active channel/dielectric interface, and thereby improving the hole transporting in the p-type channel. The electrical stability is then improved with mitigated dependence of charge mobility on gate voltage in the saturation region. The use of a BHJ channel in the OPTs also offers an improved photoresponse through enhanced exciton dissociation at the donor/acceptor interface and the stable mobility in the saturation region, leading to more than one order of magnitude increase in responsivity than that in a conventional OPT with a single p-type semiconductor channel layer. The OPTs with a BHJ channel layer exhibit an excellent hole mobility of 1.0 cm2V-1s-1, a high photoresponsivity of the 104 A/W and a high specific detectivity of 1.2×1012 Jones in the NIR wavelength.