Electric field induced phototransport in dye-doped semiconducting polymer

Electric field induced phototransport of regioregular poly(3-hexylthiophene) [P3HT] and squaraine (SQ) dye-sensitized samples are studied in this paper. The relative variation of photoresponse spectra shows that the trap energetics and charge transport are modified in the presence of $1\phantom{\rule{0.16em}{0ex}}\mathrm{wt}%$ SQ dye. In the doped sample, the $S(V)/S(60V)$ ratio at 2.1 eV increases by a factor of 21 at 1800 V/cm, with a substantial increase in the photoresponse. The redistribution of the trap energy levels and enhancement in transport is associated with the variations in transit and relaxation times of carriers in the presence of the dye. The phase part of the signal consisting of photocapacitance is reduced and becomes less dependent on the optical energy in the doped sample. This is consistent with the absence of space charge contribution in dye-doped samples. The deconvoluted photoresponse signal by using Gaussian functions indicates that the trapping-detrapping processes are altered by the dye since only three Gaussian peaks are observed in the dye-doped sample. The deconvoluted photoresponse in the dye-doped sample indicates that the modified trapping-detrapping processes have enhanced the transport, which results in three Gaussian peaks.