A series of new p-type polymers, PNDT-T and PNDT-TT, with enforced coplanar structure for effective πelectron delocalization, having naphtho[2,1-b:3,4-b′]dithiophene and thiophenes as main core units, were successfully synthesized by Stille coupling reaction. The naphtho[2,1-b:3,4-b′]dithiophene unit of the polymer main chain enhances charge carrier mobility by extending πconjugation length and rigidly enforced coplanar structure. Both polymers, PNDT-T and PNDT-TT, have high thermal stability up to 250 °C with a high T g of 402 °C. On the basis of AFM and XRD results, it was found that PNDT-TT showed relatively more highly ordered intermolecular structures than did PNDT-T, with thiophene unit and high field-effect mobility, because the bithiophene unit provides crystallinity with increasing planarity and enough space for interdigitation of the long alkyl side chains for high order. These new p-type polymers PNDT-T and PNDT-TT exhibit high carrier mobilities of 0.01 and 0.076 cm 2 /(V s) and on/off ratios of 4 × 10 5 and 7 × 10 6 , respectively. The above results indicate that the plate structure with a sulfur-containing fully aromatic system, which has the upper direction extended, could enhance the thermal stability and charge transport characteristics for OTFT applications.

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We demonstrate the synthesis of a new copolymer which is composed of dialkyl thienylated benzodithiophene and perfluororalkyl-carbonyl thienothiophene (DTBDT-TTFO) and the characterization of its optoelectronic properties. The introduction of thienyl groups enabled the extended delocalization of π electrons in the DTBDT-TTFO backbone and efficient intermolecular charge transport as proved by the fairly high field effect mobility of 0.02 cm(2)/(V s). The introduction of perfluororalkyl-carbonyl side chains resulted in a significant red-shift of DTBDT-TTFO in the absorption spectra and a decrease in the HOMO and LUMO levels. The resulting energy levels of DTBDT-TTFO were not satisfactory for solar cell applications, especially in terms of charge separation at the polymer/PCBM interfaces. Rather, the DTBDT-TTFO showed better energy level matching with the colloidal nanocrystals (NCs) of CdSe. A photodetector based on the bulkheterojunction of DTBDT-TTFO and CdSe NCs with coplanar device geometry resulted in a high photoconductive gain (responsivity higher than 1A/W under a low operating voltage of 1 V), possibly arising from electron trapping at CdSe NCs such that the hole can travel along the detector and its surrounding circuit. More importantly, the photodetector revealed a time constant of a few hundreds of microseconds, which means that the response speed of the photodetector is fast enough for lag-free imaging applications.

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