Effects of Molecular Weight and Annealing on Charge Carrier Concentration in Thin PANI-CSA Films

PANI-CSA thin films have shown promising results like higher temperature sensitivities (Ahmad et al, J. Appl. Polym. Sci. 2013) and overcoming limitations of Wiedemann-Franz law (Jin et al, J. Phys. D: Appl. Phys. 2010) hence, can be used in flexible wearable sensors, thermoelectric devices. However, charge transport in PANI-CSA thin films is not very well understood. Effect of doping on electrical conductivity (σ) in PANI-CSA, effect of molecular weight (M_W) on mobility (μ) in RR-P3HT (Zhang et al, Jour. of Amer. Chem. Soc. 2006) and change in grain size on annealing in P3HT:PCBM (Beal et al, Macromolecules 2010) have been reported. However, there is no study on effect of M_W on charge carrier concentration (n) in annealed PANI-CSA thin films. PANI-CSA thin films (~50-70nm) were fabricated with different M_W of PANI-EB. Their σ was checked before and after annealing which showed a strong dependence on M_W. Annealing decreased σ for all films but effect was more prominent at lower M_W. AFM was done to map morphological changes with M_W and annealing. DC Hall measurements were done to measure μ but were inconclusive due to low μ (Yamada et al, Synth. Met. 2019) hence, AC Hall measurements were done which indicated that the change in σ has two contributors; change in μ and change in n.