Previous work revealed that electron traps in pentacene formed in air cause hysteresis in thin-film transistor characteristics. Here, we experimentally showed that water vapor, rather than oxygen, is responsible for these hysteresis-causing trap states. Photogenerated and injected electrons are trapped at the pentacene-dielectric interface under positive gate bias, and induce extra holes, resulting in the observed extra drain current. The electron detrapping causes the decay of the extra hole population with time under negative gate bias and, therefore, that of the drain current.
The irradiance on the device under test was measured by a Hamamatsu S2281-04 Si photodiode. The light sources are typical fluorescent lamps (for spectra, see for example, http://en.wikipedia.org/wiki/Fluorescent_lamps). Due to the broadband illumination spectrum, we specify the irradiance in photons/. The irradiances are and , respectively, for the in-air and glovebox measurements.