A new concept of electrodes for ambipolar carrier injection in organic semiconductors*

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 (pcOSC) covered by a metal (M) thin film layer. Field effect transistors of single crystal organic semiconductors (scOSCs) with the new electrodes of M/pcOSC/TTC (M: Ca or Au) show both highly efficient electron and hole injection. Contact resistances of electron and hole injection from Ca/pcOSC/TTC and Au/pcOSC/TTC are fascinatingly 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) can be observed in a rubrene single crystal, which are the highest among field effect transistors so far proposed. Higly efficient light emission will be demonstrated via amipolar carrier injection.