We describe a defect generation phenomenon that is new to organic semiconductors. A defect in pentacene single crystals can be created by bias-stress and persists at room temperature for an hour in the dark but only seconds with 420 nm illumination. The defect gives rise to a hole trap at $E_v+0.38\mathrm{e}\mathrm{V}$ and causes metastable transport effects at room temperature. Creation and decay rates of the hole trap have a 0.67 eV activation energy with a small (${10}^8{\mathrm{s}}^{\mathrm{-}\mathrm{1}}$) prefactor, suggesting that atomic motion plays a key role in the generation and quenching process.

• Received 17 December 2003

DOI:https://doi.org/10.1103/PhysRevLett.93.076601