We demonstrate the operation of an organic switching device using a uniform poly-crystalline Cu:7, 7, 8, 8-Tetracyanoquinodimethane ͑TCNQ͒ charge transfer ͑CT͒-complex thin film that is prepared by vacuum vapor codeposition. Characteristic CT-absorption at ϭ600-1200 nm was observed in the complex film in the UV-visible spectrum and the cyano stretching peak in the IR spectrum shifted to a higher ͑more than 29 cm Ϫ1) wave number than that of a pristine TCNQ film, suggesting the formation of a CT-complex in the evaporated thin film. Reproducible electrical switching characteristics were observed in the indium tin oxide/Al/(Al 2 O 3)/Cu:TCNQ/Al structure. The device exhibited a clear threshold from low impedance to high impedance at an applied voltage of 10.0Ϯ2.0 V and a reverse phenomenon at a negative bias of Ϫ9.5Ϯ2.0 V. In this study, we demonstrate that a thin Al 2 O 3 layer between the aluminum ͑Al͒ anode and Cu:TCNQ layers creates reproducible switching.
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.
A unique method of material synthesis based on vacuum co‐deposition is reported. A Eu complex was formed by co‐deposition of bis(dipivaloymethanato)europium (Eu(DPM)3) and 2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (BCP), which both showed excellent volatility during vacuum deposition. Photoexcitation of the BCP led to intense emission from the Eu3+ ions, verifying efficient exciton energy transfer and therefore complex formation.
We succeeded in observing electroluminescence ͑EL͒ of 2,4-bis͑4-͑2Ј-thiophene-yl͒phenyl͒thiophene ͑TPTPT͒ as an active layer in an organic field-effect transistor ͑OFET͒. In particular, an OFET with a short channel of d SD = 0.8 m demonstrated higher EL efficiency than one with a much longer channel ͑d SD = 9.8 m͒. We observed a maximum EL quantum efficiency ͑ max ͒ of 6.4 ϫ 10 −3 % in the short-channel-length device at an applied source-drain voltage of V d = −100 V and a gate voltage of V g = −40 V. From the OFET characteristics, although the TPTPT layer demonstrated typical p-type operation, the occurrence of EL clearly indicated simultaneous hole and electron injection from the source and drain electronics, respectively, under high V d and V g .
We demonstrated efficient electron injection and transport in organic light-emitting diodes using an electron-transport layer (ETL) composed of a Cs and phenyldipyrenylphosphine oxide (POPy2) co-deposited layer. In particular, an ETL composed of a Cs:POPy2 layer with an atom:molar ratio of 1:2 demonstrated an extremely low driving voltage, resulting in a high current density of 100mA∕cm2 at an applied voltage of only 3.9 V. The results of Kelvin probe and absorption measurements indicated that the formation of a CsAl alloy layer at the Cs:POPy2/Al cathode interface and the charge-transfer complex between the Cs and POPy2 contributed to enhancing the efficiency of electron injection and transport, respectively.
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