Charge Conductivity in Donor-Acceptor Polymer Dispersions Measured with Time-Resolved Terahertz Spectroscopy

Ultrafast Time-Domain and Time-Resolved Terahertz (TDS/TRTS) spectroscopic methods are utilized to explore photoconductive properties of five conjugated donor-acceptor co-polymers (PCDTPT, CDTBTZ, IDTBT, PBDTTPD and N2200) dispersed in room temperature toluene, a nonpolar dielectric solvent. TRTS provides an effective non-contact handle to interrogate localized relative conductivity of dispersed co-polymers. Conductivity dynamics are contrasted among disparate polymer structures and between their photoconductive peak and thermalized time-delayed signatures. Photoconductivity kinetics, relative levels of real/imaginary conductivity, and carrier properties are summarized with higher energy photoexcitation increasing the real photoconductivity by up to three-fold. Molecular orbital pictures and donor-acceptor twisting mode frequencies ascertained through ab initio calculations (via Density Functional Theory) support descriptions of the relative efficacies of charge transfer from the perspective of the localized THz method.