Low-voltage organic phototransistors based on naphthyl end-capped oligothiophene nanofibers

Abstract Organic crystalline semiconductors with highly ordered molecular packing could be vital components in novel low power consumption light sensors due to their unique light absorption and charge carrier transport properties. In this work, we show that nanofibers made from naphthyl end-capped bithiophenes can be used for low-voltage, high responsivity organic phototransistors (OPTs). Density functional theory (DFT) calculations have been carried out to estimate the device properties related to charge transport and photon absorption. In terms of the calculation of the reorganization energy upon charge transfer, we used an extended method to include inter-molecule interactions. Experimentally, the device performance of the 5,5-bis(naphthyl)-2,2′-bithiophene (NaT2) nanofiber OPTs has been compared with that of a thin film OPT with inferior molecular ordering. The better photoresponsivity of the nanofiber OPT compared with the thin film OPT under monochromatic illumination at various wavelengths suggests that the NaT2 nanofiber-based OPTs have great potential to be used as high performance nano-scale light detectors. Moreover, the absorption of the nanofiber-based OPTs is also polarization sensitive, which provides another advantage of nanofiber-based devices in terms of potential novel sensor design.