Organic semiconductor gas sensor is one of the promising candidates of room temperature operated gas sensors with high selectivity. However, for a long time the performance of organic semiconductor sensors, especially for the detection of oxidizing gases, is far behind that of the traditional metal oxide gas sensors. Although intensive attempts have been made to address the problem, the performance and the understanding of the sensing mechanism are still far from sufficient. Herein, an ultrasensitive organic semiconductor NO sensor based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-petacene) is reported. The device achieves a sensitivity over 1000%/ppm and fast response/recovery, together with a low limit of detection (LOD) of 20 ppb, all of which reach the level of metal oxide sensors. After a comprehensive analysis on the morphology and electrical properties of the organic films, it is revealed that the ultrahigh performance is largely related to the film charge transport ability, which was less concerned in the studies previously. And the combination of efficient charge transport and low original charge carrier concentration is demonstrated to be an effective access to obtain high performance organic semiconductor gas sensors.

Articles you may be interested inMolecular structure of extended defects in monolayer-scale pentacene thin films Scanning tunneling microscopy with high impedance has been used to image the growth of pentacene thin films on Au͑111͒. Instead of the herringbone structure in bulk solid, pentacene molecules in these thin films form a cofacial, -stacked crystalline phase with their molecular planes parallel to the surface. The growth of this crystalline phase is attributed to the formation of a close-packed, crystalline monolayer which seeds the growth of the -stacked multilayer film.

Petacene is one of the most promising organic semiconductors for thin-film transistors. Transport measurements in the past have established the presence of shallow traps but their origins have remained a mystery. Here we show that shallow traps in vapor-deposited crystalline pentacene thin films are due to local defects resulting from the sliding of pentacene molecules along their long molecular axis, while two-dimensional crystalline packing is maintained. Electronic structural calculation confirms that these sliding defects are shallow-charge traps with energies ⩽100meV above (below) the valence band maximum (conduction band minimum).

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Pentacene, as well as other polyacenes, is known to adsorb on metal surfaces in a lying-down geometry, that is, with the molecular plane parallel to the surface. Here we show using scanning tunneling microscopy that the lying-down pentacene monolayer seeds the growth of a multilayer polycrystalline film in a layerby-layer fashion, with the molecular planes parallel to the substrate surface. Growth in the submonolayer region is characterized by a large number of ordered molecular structures as coverage increases. The saturated monolayer structure remains approximately the same throughout multilayer coverages studied. Statistical analysis of molecular domain orientation reveals that the ordered pentacene structures are incommensurate with the Au(111) substrate and growth beyond the monolayer region is a mixture of epitaxy and nonepitaxy. We conclude that the relatively large footprint of a lying-down pentacene molecule smoothes out lateral corrugation in the adsorption energy landscape on the Au(111) surface, leading to the growth of an incommensurate, polycrystalline, and partially nonepitaxial thin film.