A new electrode design for ambipolar carrier injection in organic semiconductors and its applications to light emitting diodes

Organic semiconductors (OSCs) have attracted much attention for low-cost, flexible and human-friendly optoelectronics. However, achieving high electron injection efficiency is difficult from air-stable electrodes and cannot be equivalent to that of holes. Here, we present a novel concept of electrode composed of a bilayer of tetratetracontane (TTC) and polycrystalline organic semiconductors (pc-OSC) covered by a metal (M) thin film layer. Field-effect transistors of single crystal organic semiconductors (sc-OSCs) with the new electrodes of M/pc-OSC/TTC (M: Ca or Au) show both highly-efficient electron and hole injection. Contact resistances of electron and hole injection from Ca/pc-OSC/TTC and Au/pc-OSC/TTC are lower than those from pure Ca for electrons and Au for holes, respectively. Equivalent high field-effect mobilities of holes (22 cm²V^–1s^–1) and electrons (5.0 cm²V^–1s^–1) were observed in a rubrene single crystal, which are the highest among field-effect transistors with electrodes so far proposed. The new electronde are useful in high performance and air stable lihgt emitting field-effect transistors.