Reflectance of conducting poly(3,4-ethylenedioxythiophene)

We present the reflectance spectrum of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with PF6 with dc conductivity of 230 S/cm at room temperature, measured over a wide frequency range from 50 to 5×104 cm−1 (0.006–6 eV). The reflectance, R(ω), of PEDOT-PF6 is characterized by metal-like signatures in the infrared (IR), including high R(ω) in the far-IR and a plasma frequency of approximately 1.2 eV. The optical conductivity, σ(ω), is dominated by intraband contributions below 1 eV, characteristic of a disordered metal near the metal–insulator (M–I) transition. The reflectance spectrum is in good quantitative agreement with the “localization-modified Drude (LMD) model”. Since the onset of the interband absorption (below 1.5 eV) is at lower energy than in other conducting polymers, PEDOT-PF6 shows low absorption in the visible range between 2 and 3 eV. Our spectroscopic results demonstrate that this doped PEDOT system can be utilized as a transparent electrode for optoelectronic devices.