Doping and photo-induced current in discotic liquid crystals thin films: Long-time and temperature effects

Here we address the problem of time and temperature instability of the electrical current related to parasitic doping effects in discotic liquid crystals (DLCs). We investigated the electrical transport in thin films of a phthalocyanine-based DLC in-dark and upon laser irradiation during long thermal cycles. Measuring the electrical transport between two electrodes we observed that in-dark the current is mostly due to doping levels while, upon laser irradiation, the photocurrent reflects the diffusion length of the photogenerated charge carriers and it is limited by the coherence length of a column. We prove here that the two contributions are completely independent. Our result experimentally supports the theoretical studies performed at the molecular level on discotic liquid crystals.

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► Measure in the same experiment of the photo-conductivity and the conductivity in-dark vs. time and temperature during long time experiments.
► Direct experimental evidence that the two contributions are completely independent.
► Evidence that the photocurrent is limited by the coherence length of the columns.