Hiroyuki Uchiuzou

Lateral organic light-emitting diode with field-effect transistor characteristics

We succeeded in observing bright electroluminescence (EL) from 1wt%-rubrene doped tetraphenylpyrene (TPPy) as an active layer in a lateral organic light-emitting diode structure that allowed field-effect transistor operation. This device configuration provides an organic light-emitting diode structure where the anode (source) and cathode (drain) electrodes are laterally arranged, providing us a chance to control the EL intensity by changing the gate bias. We demonstrated that TPPy provides compatible transistor and EL characteristics. Further, not only rubrene doping into the TPPy host but also adjusting the source-drain channel length significantly improved the EL characteristics. We observed a maximum EL quantum efficiency (ηext) of ∼0.5% with a Cr∕Au source (S)-drain (D) electrode and a slightly higher ηext of ∼0.8% with S-D electrodes of MgAu∕Au, Al∕Au, Cr∕YAu∕Au, and MgAl∕Au multilayers, aiming for simultaneous hole and electron injection.

Ambipolar light-emitting organic field-effect transistors using a wide-band-gap blue-emitting small molecule

The authors applied a wide-band-gap (2.9eV) molecule of 4,-4′-bis(styryl)biphenyl (BSBP) as an active layer in light-emitting organic field-effect transistors. They found that BSBP provided both relatively high field-effect hole mobility of 0.01cm2∕Vs and photoluminescence efficiency of 20% in thin film. They achieved ambipolar operation by without breaking vacuum through devices’ preparation and measurements, applying aluminum contacts, and inserting a hydroxyl-free poly(methylmethacrylate) layer, and light emission was observed when the device was operated in the ambipolar mode. The results presented here will open the way to fabricating efficient light-emitting transistors with high mobility.

Blue‐to‐red electroluminescence from organic light‐emitting field‐effect transistor using various organic semiconductor materials

— We succeeded in observing visible bright electroluminescence from blue to red in an organic field-effect-transistor structure. In particular, tetraphenylpyrene (TPPy) demonstrated a high photoluminescence efficiency of φPL ∼ 70% and a maximum electroluminescence efficiency of ηEL ∼ 10−2%. The electroluminescence efficiency (ηEL) was enhanced by using a short source-to-drain channel length (LSD < 1 μm). In addition, doping the TPPy layer with highly fluorescent rubrene molecules led to an #PL of ∼100% and a maximum ηEL of 0.8%.

Optical and Electrical Properties of Bis(4-(phenylethynyl)phenyl)ethynes and Their Application to Organic Field-Effect Transistors

We demonstrate that bis(4-(phenylethynyl)phenyl)ethynes (BPEPEs) have high potential as organic field-effect transistors (FETs). We observed a p-type transistor operation in FETs with BPEPE derivatives having electron-donating substituents. The devices showed FET hole mobilities in the range of µh = 10-3–10-5 cm2/(V s), depending on the substituents. Further, bis(4-(4-trifluoromethylphenylethynyl)phenyl)ethyne (4-CF3-BPEPE), which has an electron-withdrawing group, indicated n-type operation.