Hydrostatic pressure was applied to single-crystal rubrene photoconductors and p channel field-effect transistors. Under illumination from a GaInN light-emitting diode, we observed linear increases in photoconductivity, by up to a factor of 2.1 at 0.43 GPa. We also measured increases in the drain current of the single-crystal rubrene organic field-effect transistors (OFETs) with increasing pressure up to 0.52 GPa. Analyzing the transfer characteristics of the OFETs, we extracted the pressure dependence of the field-effect hole mobility. The different OFETs examined showed similar hole mobility increase ratios with pressure, although their atmospheric pressure mobilities varied by more than a factor of two. Threshold voltages shifts with pressure were small. All results were reversible, i.e., the measured currents returned to their atmospheric pressure values upon release of pressure unless complete device failure occurred at the highest pressure.

Pentacene and tetracene show readily observable photoconductivity when illuminated with light in the blue part of the visible spectrum. We measured the change of photoconductivity with hydrostatic pressure in single-crystal samples of both materials. Possible mechanisms for the observed increase in photoconductivity with pressure are discussed. We conclude that a carrier-mobility increase under pressure is most likely to cause the increase in photoconductivity in the case of pentacene. For tetracene, changes in the absorption spectrum in the range of the excitation wavelengths may also be significant. We also observe a phase transition near 0.3 GPa in tetracene, in agreement with previous results.

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We report results of electrical output and transfer characteristics for two top-contact pentacene thin-film transistors under hydrostatic pressure at room temperature. Strong reversible increases of the drain current and the field-effect hole mobility with increasing pressure were observed, in particular for a device with relatively low current at atmospheric pressure.

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