A novel one-dimensional (1D) polymeric heterojunction based on weak-acceptor-polyacrylonitrile/donor-polyaniline core-shell nanofibers is designed for photoconductive devices through electrospinning followed by solution polymerization. Such 1D heterojunction can not only provide the large phase-separated nano-interface for effective charges separation between the cores and shells, but also facilitate the mass charge collection and transport along the nanofiber structure, resulting in greatly enhanced optoelectronic performance. The short 0.1 s response time upon irradiation is among the fastest values, as is the short 0.1 s time for return to the non-irradiated state. Extremely high on-off resistivity ratios (exceeding 4 x 10(4)) can be obtained under the drive voltage of only 0.01 V, indicating the energy required for electrical input is very small. Higher drive voltages (a modest 10 V) can provide a very high responsivity of 20 A W-1 driven by 365 nm UV irradiation. Moreover, the as-prepared flexible photoconductive device maintains performance even after bending fatigue tests for bending angles as large as 180 degrees. (C) 2012 Elsevier B.V. All rights reserved.