Enhanced electrical conductivity of polydiacetylene crystals by chemical doping and ion implantation

The conductivity enhancement in polydiacetylene (PDA) crystals due to chemical doping and ion implantation was measured and analyzed in relation to their spin concentration and photocurrent decay based on the structural and optical information obtained through infrared and visible reflectivity spectra. A conductivity jump was observed upon slight increase of the spin concentration at low doping levels of chemically doped PDAs, suggesting the formation of spinless carriers in chemically doped PDAs, as in trans-polyacetylene and poly(p-phenylene). In contrast, in ion-implanted samples, a great difference in the magnitudes (by more than five orders of magnitude) was observed between the conductivity enhancement for two PDAs having different side chain species. Furthermore, the photocurrent decay time measurements reveal different distributions of implantation-induced trap levels between ion-implanted poly [2,4-hexadiyne-1,6-diol-bis-(p-toluene sulfonate)] (PTS) and poly[2,4-hexadiyne-1,6-di(N-carbazolyl)] (DCH). A conduction mechanism which could explain the significant difference in conductivity enhancement between PTS and DCH is suggested. Because the enhanced conductivity by ion-implanted PTS showed no orientational effect associated with the polymer chain direction, a conductive path and network formation by the implantation-induced defects is more plausible for the conduction mechanism than carrier introduction into the backbone chain band from side chain defect levels.