Field and temperature dependent transport properties of undoped and doped polyaniline films

The low and high electric field conductivity measurements were carried out in undoped and (±)-10-camphor sulfonic acid (CSA) dopedpolyaniline (PANI) film samples in the temperature range 173 ≤ T ≤ 303 K and 303 ≤ T ≤ 383 K, respectively. In the undoped and doped polyaniline films one and three dimension variable range hopping (VRH) type is identified, respectively, at low electric field (1 × 10³ V/cm) in the temperature range 173 ≤ T ≤ 303 K. The VRH parameters such as localization length (α^-1), hopping range (R_hop) and hopping energy (W) are calculated and the influence of doping on these parameters is discussed. The current - voltage (I - V) characteristics studied at high field (< 10 ⁴ V/cm) for the undoped and doped polyaniline films in the temperature range 303 ≤ T ≤ 383 K exhibit the space charge limited current (SCLC) conduction mechanism. The activation energy (E_α) calculated from the plot in θ versus T^-1 of the doped sample is reduced to nearly half of the undoped. The hole mobility (μ) value 7.06 × 10^-8 m²V^-1 s^-1 for UP and 2.37 × 10^-9 m²V^-1 s^-1 for DP calculated at 303 K are well within the limits of reported conjugated polymers. A high value of trap density (N_t = 1.28 × 10²¹ m^-3) is found for doped polyaniline film supports the 1D variable hopping in DP film. The trap parameters such as the trap filled limit voltage (V_TFL), the depth of the dominant trap level (E_t - E _v), the density of states within the hole mobility edge (N _v) are also calculated and their dependence on doping is discussed. The traps exponentially distributed in energy and a single discrete trapping level is found for undoped and doped polyaniline films respectively.