Working Principle of Hydrogen Sensor Based on Pentacene Thin-Film Transistor

A hydrogen sensor based on pentacene organic thin-film transistor (OTFT) with palladium (Pd) source and drain (S/D) electrodes is analyzed in detail. When exposed to H2 with different concentrations, the sensor shows a clear change in drain current due to three reasons: work-function change of the source electrode induced by hydrogen absorption; reduced carrier mobility; and increased S/D series resistance both caused by the expansion of the S/D electrodes after absorbing hydrogen. Analysis of the data demonstrates that the first two are the dominant mechanisms. Without the need of heating, rapid, reversible, and concentration-dependent response of the OTFT is observed upon introduction and removal of H2 with concentration ranging from 200 to 17 000 ppm.