Partial carbonization of aromatic polyimide films—aiming at solar cells

Aromatic polyimide films are partially carbonized between 700 and 1000 °C in an atmosphere of hydrogen. Electrical conductivity and Hall coefficient have been measured. Electrical conductivity increases with measuring temperatures. The electrical conductivity σ can be expressed as σ=σ0 exp(−Eσ/kT), where k is the Boltzmann constant.T is the measuring temperature in K. E depends upon the carbonized temperature. The experimental data show the Hall coefficient RH is negative, and this implies the majority carriers are negatively charged, i.e. electrons. Thus the specimens are n-type semiconductors. The carrier density η can be expressed by η=Aη exp (−Eη/kT) and carrier mobility μ can be expressed by μ=Aμ exp(Eμ/kT). Eσ, Eη and Eμ depend upon the carbonized temperature.