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The temperature dependence of the conductivity of conducting polymers is different because they are disordered systems. The charge transport is dominated by the interchain charge hopping. In general, the conductivity of conducting polymers follows the one‐dimensional variable range hopping model,

(1.17)

In terms of this model, the resistivity increases with the increasing temperature. The kT ₀ value suggests the energy barrier for the charge hopping. It decreases with the increasing crystallinity. It is easy to confuse the charge hopping mechanism with the metallic band structure of conducting polymers. At high doping level, the conducting polymers can have energy band structure like metals. This picture is applicable for an individual chain. For a conducting polymer sample, the charge transport is dominated by interchain charge hopping.

Figure 1.16 Temperature dependence of the resistance of a PEDOT:PSS treated with H₂SO₄.

Source: Xia et al. [21]. © John Wiley & Sons.

However, semimetallic or metallic behavior, that is, the conductivity is insensitive to temperature or decreases with the increasing temperature, was reported on a few conducting polymers with high conductivity. For example, H₂SO₄ treatment can enhance the conductivity of a PEDOT:PSS film prepared from the Clevious PH1000 aqueous dispersion from ~0.2 S cm⁻¹ to >3000 S cm⁻¹ [21]. As shown in Figure 1.16, when the temperature is lower than 230 K, the temperature dependence of the resistance still follows the one‐dimensional variable range hopping model. Nevertheless, when the temperature is higher than 230 K, the thermal energy can overcome the energy barrier for the interchain charge hopping. As a result, the resistance becomes insensitive to temperature. This indicates semimetallic or metallic behavior. Metallic or semimetallic behavior was also observed on highly conductive polyaniline [27].