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The charge extraction (of injected carriers) by linearly increasing voltage in metal-insulator-semiconductor structures, or MIS-CELIV, is based on the theory of space-charge-limited currents. In this work, the validity of MIS-CELIV for mobility determination in organic thin-film devices has been critically examined and clarified by means of drift-diffusion simulations. It is found that depending on the applied transient voltage, the mobility might be overestimated by several orders of magnitude in the case of an ohmic injecting contact. The shortcomings of the MIS-CELIV theory can be traced back to the underlying assumption of a drift-dominated transport. However, the effect of diffusion can be taken into account by introducing a correction factor. In the case of non-ohmic injecting contacts, the extracted mobility becomes strongly dependent on device parameters, possibly leading to large deviations from the actual mobility.

We present charge extraction by a linearly increasing voltage measurements on diodes based on an n-channel naphthalenetetracarboxylic acid diimide semiconductor and an aluminum oxide blocking layer. Results show a large displacement current (roughly 15 times that expected from the geometrical capacitance), which we associate with trap filling in the oxide. The trap density is calculated to be on the order of 1019 cm−3, in agreement with preceding work. We present a way of using the displacement current as a tool for probing the vacuum level shift caused by modifying the oxide surface with self-assembled monolayers in operating devices.