Photo-stable organic thin-film transistor utilizing a new indolocarbazole derivative for image pixel and logic applications

Small molecule pentacene layer has been a representative among many organic thin-film transistor (OTFT) channels with decent p-type mobilities, but it is certainly light-sensitive due to its relatively small highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (1.85 eV). Although a few other small molecule-based layers have been reported later, their photo-stabilities or related device applications have hardly been addressed. Here, a new photostable organic layer is reported, heptazole (C ₂₆H₁₆N₂), which has almost the same HOMO level as that of pentacene but with a higher HOMO-LUMO gap (≈2.95 eV). This heptazole OTFT displays a decent mobility comparable to that of conventional amorphous Si TFTs, showing good photostability unlike pentacene OTFTs. An image pixel driving the photostable heptazole OTFT connected to a pentacene/Al Schottky photodiode is demonstrated. This heptazole OTFT also conveniently forms a logic inverter coupled with a pentacene OTFT, sharing Au for source/drain. A new indolocabazole derivative (heptazole) possessing a HOMO-LUMO gap of ≈2.95 eV is synthesized and shows good photo-stability unlike old pentacene. An image pixel driving our photostable heptazole OTFT connected to a pentacene/Al Schottky photodiode is demonstrated. The heptazole OTFT also conveniently forms a logic inverter coupled with a pentacene OTFT, sharing Au for source/drain.