Purity-Sensitive Dark and Photoconductivity in Trans-Polyacetylene

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Abstract
The photoinduced current was measured in the range 0.5–3.4 eV in undoped trans-polyacetylene of various grades of sample quality. It is shown that careful purification of acetylene gas and distillation of Ti(OBu)4 greatly decrease the photoinduced current as well as the dark current. The lowest dark conductivity obtained is 2×10-8 Ω-1cm-1, which is two orders of magnitude lower than that reported as the room-temperature conductivity. The peak at 1.4 eV in the photoinduced current spectrum is conspicuous in better samples, and its origin is regarded as intrinsic. The temperature dependences of the dark and the photoinduced current were measured, and from this the existence of a bolometric spectral region was confirmed.