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 FeCl3-doped poly(2-methoxy-5-(2′-ethyl)hexyloxy-p-phenylene vinylene) [MEH-PPV] film. The measured data fit well to Lorentz oscillator (LO) model indicating that free carriers are negligible though the system is fairly conducting (∼0.1 S/cm) at room temperature. The large value of the coupling constant (Ωp1/2π = 14.7 THz) in LO model indicates that intra-chain localization of carriers is rather strong and the inter-chain transport is quite weak.