Origin of Bias-Stress Induced Instability in Organic Thin-Film Transistors with Semiconducting Small-Molecule/Insulating Polymer Blend Channel

摘要

The stabilities of a blending type organic thin-film transistor with phase-separated TIPS-pentacene channel layer were characterized under the conditions of negative-bias-stress (NBS) and positive-bias-stress (PBS). During NBS, threshold voltage (V_(th)) shifts noticeably. NBS-imposed devices revealed interfacial trap density-of-states (DOS) at 1.56 and 1.66 eV, whereas initial device showed the DOS at only 1.56 eV, as measured by photoexcited charge-collection spectroscopy (PECCS) method. Possible origin of this newly created defect is related to ester group in PMMA, which induces some hole traps at the TIPS-pentacene/ i-PMMA interface. PBS-imposed device showed little V_(th) shift but visible off-current increase as "back-channel" effect, which is attributed to the water molecules trapped on the TFT surface.