Abstract
Organic semiconductors 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 layer. Field-effect transistors of single-crystal organic semiconductors with the new electrodes of M/pc-OSC/TTC (M: Ca or Au) show both highly efficient electron and hole injection. Contact resistance for electron injection from Au/pc-OSC/TTC and hole injection from Ca/pc-OSC/TTC are comparable to those for electron injection from Ca and hole injection from Au, respectively. Furthermore, the highest field-effect mobilities of holes (22 cm2 V–1 s–1) and electrons (5.0 cm2 V–1 s–1) are observed in rubrene among field-effect transistors with electrodes so far proposed by employing Ca/pc-OSC/TTC and Au/pc-OSC/TTC electrodes for electron and hole injection, respectively.
Highlights
Organic semiconductors have attracted much attention for low-cost, flexible and humanfriendly optoelectronics
EF of Au is generally located near valence band maximum (VBM) while that of Ca is near conduction band minimum (CBM) of organic semiconductors (OSCs), and hitherto hole injection has been more popularly observed when Au electrode is employed, but efficient electron injection needs air-unstable metals with high EF, such as Ca8–16
A barrier height for carrier injection is nearly independent of EF for inorganic semiconductors (ISCs) owing to the disorder-induced gap states (DIGS) and metal-induced gap states (MIGS) inside a band gap made by disorder/dangling bonds on the surface and MS interface structure[6, 7]
Summary
Organic semiconductors have attracted much attention for low-cost, flexible and humanfriendly optoelectronics. We can consider two types of states inside the band gap of the pc-OSC, and each of them plays very important roles in a different manner in the new electrodes of M/pc-OSC/TTC and can offer higher ambipolar injection than any other electrodes so far reported.
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