Charge transport studies in thermally evaporated 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-MeOTAD) thin film

Charge transport mechanism in 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenyl amino)-9,9′-spirobifluorene (spiro-MeOTAD) has been investigated as a function of temperature and organic layer thicknesses. Hole only devices of different thicknesses were fabricated in configuration ITO/spiro-MeOTAD/Au by vacuum evaporation technique. The hole current is space charge limited which provides a direct measurement of the hole mobility μ as a function of electric field and temperature. Gaussian disorder model has been used to explain the temperature and field dependent behavior of mobility. The values of energetic disorder (σ = 0.088 eV), positional disorder (Σ = 3.35) and mobility prefactor (μ0 = 0.0147 cm2/V s) have been evaluated using this model.