Flexible and stable solution-processed organic field-effect transistors

Highly stable, solution-processed, small molecule-polymer blend organic field-effect transistors (OFETs) with a top-gate geometry were demonstrated on a flexible polyethersulfone (PES) substrate. The top-gate dielectric was a bi-layer comprised of CYTOP and a high-k Al2O3 layer grown by atomic layer deposition (ALD). A solution processed 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and poly(triarylamine) (PTAA) blend was used as the organic semiconductor. TIPS-pentacene and PTAA blend OFETs with the CYTOP/Al2O3 bi-layer top gate dielectric showed an averaged saturation mobility value of 0.24 ± 0.08 cm2/Vs at operation voltages below 8 V. A constant direct-current bias stress test was carried out to examine their operational stability for 2 h. Under bias stress, neither significant change in mobility nor shift in the threshold voltage has been observed in these OFETs. To evaluate the real potential of these OFETs towards the development of circuit components commonly used in electronic applications, a resistive-load inverter was implemented by connecting an OFET to an external load resistor. Excellent stability of the transistor led to electrically stable inverters with negligible variations of the voltage transfer characteristics before and after bias stress. After the operational stability test, these OFETs were exposed to air and then were subjected to bending experiments. Even after exposure to air for 4 months and bending for 30 min, no significant changes in performance were observed in either a single transistor device or in a resistive-load inverter.