Master thesis defence by Jason Röhr – Københavns Universitet

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Master thesis defence by Jason Röhr

Novel symmetric polymer electron-only devices were realised using Caesium carbonate as electron injecting interlayers spun from solution. Steady-state space-charge-limited currents in the dark were observed for both the symmetric and asymmetric single-carrier devices. A novel method for correctly determining the built-in potential arising from asymmetry in contact work functions is reported. It is shown that the built-in potential can be determined directly from the space-charge-limited current measurements by considering both the forward and reverse bias. From a combination of drift-diffusion simulations and experimental data, the unified Gaussian nature of acceptor like traps in polymers, reported by Nicolai et al, is questioned from the considerations of the thickness dependence of the slopes of Gaussian trap states and exponential tail states. From considerations based on drift-diffusion simulations it is shown that the well known Mark-Helfrich equation, which is an analytic equation frequently used to SCLC data in the presence of exponential tail states, cannot be correctly applied. Finally, it is shown that the Mott-Gurney law can not be applied to polymer devices of low thicknesses.

Master thesis by Jason Röhr