THz time domain spectroscopy of doped poly p-phenylene vinylene (MEH-PPV)

An optoelectronic contactless method by THz time domain spectroscopy(THz-TDS, in the frequency range 0.5-3.0 THz) has been used to measure the absorption, dispersion, and reflectance of $FeCl_{3}-dopedpoly(2-methoxy-5-(2'-ethyl)hexyloxy-p-phenylene vinylene)$ [MEHPPV]film. The measured data fit well to Lorentz oscillator (LO) model indicating that free carriers are negligible though the system is fairly conducting (similar to 0.1 S/cm) at room temperature. The large value of the coupling constant $(\Omega_{p1}/2 \pi = 14.7 THz)$ in LO model indicates that intra-chain localization of carriers is rather strongand the inter-chain transport is quite weak.