A Robust, High-Temperature Organic Semiconductor

Abstract

We introduce a new pentacene-based organic semiconductor, 5,6,7-trithiapentacene-13-one (TTPO). TTPO is a small-molecule organic semiconductor that is simple to synthesize and purify, readily crystallizes, melts in air from 386–388 °C without decomposition, and is indefinitely stable against degradation in acid-free solution. TTPO has a high molar absorptivity, optical and electrochemical HOMO–LUMO gaps of 1.90 and 1.71 eV, respectively, and can be thermally evaporated to produce highly uniform thin films. Its cyclic voltammogram reveals one reversible oxidation and two reversible reductions between +1.5 and −1.5 V. The crystal structure for TTPO has been solved and its unique parallel displaced, and head-to-tail packing arrangement has been examined and explained using high-level density functional theory. High-resolution scanning tunneling microscopy (STM) was used to image individual TTPO molecules upon assembly on a pristine Au(111) surface in ultrahigh vacuum. STM images reveal that vapor-deposited TTPO molecules nucleate in a unique stacked geometry with a small acute angle with respect to Au(111) surface. Preliminary TTPO-based bilayer photovoltaic devices show increases in short circuit current density upon heating from 25 to 80 °C with a concomitant 4–160-fold increase in power conversion efficiencies. TTPO has the potential to be used in thin-film electronic devices that require operation over a wide range of temperatures such as thin-film transistors, sensors, switches, and solar cells.