Photo-carrier transport in disordered organic TPD films

Abstract Steady state and transient photo-carrier transports in disordered tri-methylphenyl diamine (TPD) films have been studied at relatively high temperatures (200–300 K). Hopping transport of holes occurs through localized centers with a Gaussian energy distribution. The steady state photo-conductivity is proportional to Gγexp[−(σ/kT)2/2] (with γ ≈ 0.5), where G is the number of absorbed photons and σ (≈0.07 eV) the standard deviation of the Gaussian distribution. The residual decay of photo-conductivity is nearly proportional to t−β (β ≈ 0.25). We have formulated the hopping photo-conductivity and reasonable physical parameters, such as hopping relaxation time, recombination time, and diffusion coefficient (and hence mobility) of charge carriers, are estimated for the TPD films.