Memory effects are commonly seen in organic thin-film transistor (OTFT) characteristics. In the absence of memory
effects associated with the gate dielectric, the hysteresis in p-channel pentacene-based OTFTs, as measured in air and
under illumination, was found to be dominated by trapped electrons, rather than trapped holes, in the semiconductor.
The responsible acceptor type traps have very long lifetime. The immobile, previously stored negative charge requires
extra holes to balance it, resulting in early establishment of the channel and extra drain current. This model is unique in
that it discusses the majority carrier population influenced by trapped charge opposite in sign to the majority carriers in
a simple electrostatic manner, to explain history dependence. The model was supported by drain current transient decay
data. This memory effect is ambient and illumination sensitive. We studied the presence or absence of this effect under
various ambient and illumination conditions, and found the responsible acceptor type traps mostly extrinsic and their
formation reversible. Efforts were taken in the quantitative analysis to exclude the bias stress effect from the memory
effect due to the charged acceptors.