The electrical and optical properties of conjugated polymers have received considerable attention in the context of potentially low-cost replacements for conventional metals and inorganic semiconductors. Charge transport in these organic materials has been characterized in both the doped-metallic and the semiconducting state, but superconductivity has not hitherto been observed in these polymers. Here we report a distinct metal-insulator transition and metallic levels of conductivity in a polymer field-effect transistor. The active material is solution-cast regioregular poly(3-hexylthiophene), which forms relatively well ordered films owing to self-organization, and which yields a high charge carrier mobility (0.05-0.1 cm2 V(-1) s(-1)) at room temperature. At temperatures below approximately 2.35 K with sheet carrier densities exceeding 2.5 x 10(14) cm(-2), the polythiophene film becomes superconducting. The appearance of superconductivity seems to be closely related to the self-assembly properties of the polymer, as the introduction of additional disorder is found to suppress superconductivity. Our findings therefore demonstrate the feasibility of tuning the electrical properties of conjugated polymers over the largest range possible-from insulating to superconducting.

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In order to prepare n-type CuGaSe2 as-grown, p-type CuGaSe2 single crystals were at first doped by Ge implantation. Thermal healing of the implantation damage in vacuum resulted in strong electrical compensation of the material, but not in n-type conduction. This limitation was overcome by annealing of implanted samples in Zn atmosphere, resulting in n-type conduction of CuGaSe2 with a carrier concentration at room temperature of up to 1016 cm−3. The samples were analyzed by photoluminescence, resistivity, and Hall effect measurements. It was found that the Zn–Ge codoping minimizes the formation of Cu vacancies, which act as acceptor levels and lead to self-compensation, by the formation of ZnCu defects. Furthermore, the number of electrically active Ge dopants is increased by a rise of the GeGa concentration compared to the GeCu defect density. The possibility of n-type conduction in Ga-rich CuIn1−xGaxSe2 compounds opens the possibility of the preparation of homojunction photovoltaic devices and might lead to improved solar cell performance of large band-gap chalcopyrites.

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