Analysing space charge limited currents in organic light emitting diodes

The error in making a mean field approximation when analysing space charge limited currents in organic light emitting diodes has been assessed. Using a Poole Frenkel-like, exp(γE), field dependent mobility, space charge limited currents have been simulated using zero field mobilities from 10−10 m2/V s to 10−4 m2/V s and field dependent parameter γ from 10−7 (m/V)0.5 to 10−2 (m/V)0.5. The simulated current–voltage data has been fitted using a mean field approximation to a modified Mott–Gurney equation and the deviation of zero field mobility and γ from the real values has been calculated. It was found that for a significant range of the simulations the error in both the zero field mobility and the γ factor was invariant, but systematically underestimated by 2% and 15% respectively. We conclude that the mean field approximation is a useful method with which to assess mobility using space charge limited currents in organic semiconductor devices, but the accuracy of such an analysis can be improved by accounting for the systematic error.