A Wide Band Gap Naphthalene Semiconductor for Thin-Film Transistors

This study reports a new simple organic semiconductor 2,6-bis(4-methoxyphenyl) naphthalene (BOPNA) with unprecedentedly large band gap of 3.35 eV and an apparent hole mobility of approximate to 1 cm(2) V-1 s(-1) measured in thin-film organic field-effect transistors in a saturation regime. This large band gap leads to complete optical transparency in the visible range (>370 nm), very high stability and independence of the device current with illumination conditions; this is in contrasts to the behavior of common organic semiconductors that have the band gap in the visible or near-IR range of the spectrum. Crystal structure of BOPNA reveals a highly isotropic electronic coupling in two directions of a herringbone-packing plane. A uniform, nearly single crystalline morphology can be achieved in highly crystalline BOPNA films through a rapid thermal annealing. Temperature-dependent studies reveal increase of the hole mobility as the temperature is reduced from +25 to -25 degrees C, suggesting a band-like transport, followed by a nearly temperature-independent mobility down to at least -150 degrees C.