Taichiro Morimune

Photoresponse Properties of a High-Speed Organic Photodetector Based on Copper–Phthalocyanine Under Red Light Illumination

For this letter, carrier generation and charge transfer characteristics in an organic photodetector under forward and reverse bias conditions were analyzed. For the forward bias condition, holes are dominantly injected into the highest occupied molecular orbital states of copper-phthalocyanine from an indium tin-oxide electrode and flow into the Au electrode. However, under a reverse bias condition, the photocurrent is generated at the hetero interface and removed by both electrodes. A cutoff frequency of 70 MHz was observed under a reverse bias of 7V and clear response pulses at 100 MHz were observed using a sinusoidally modulated laser (lambda=650 nm)

Polymer Device of Poly(3-hexylthiophene) with a Cathode Fabricated from Silver Nanoparticles by Wet Processing

The fabrication and characteristics of a polymer device of poly(3-hexylthiophene) (PAT6) with a cathode fabricated from silver (Ag) nanoparticles were investigated. As the formation temperature is 210°C, the cathode electrode can be formed by wet processing on the organic layer with an amorphous carbon nitride buffer layer and a bank to prevent Ag nanoparticles from penetrating into the organic layer. The PAT6 device with a cathode fabricated from Ag nanoparticles shows a photo-response and a red emission in the reverse and forward bias regions, respectively. We demonstrated the possibility of a polymer photodiode and an organic light-emitting diode with a cathode utilizing Ag nanoparticles.

Improved characteristics of P3HT:PCBM photodetectors with indium-tin-oxide electrodes modified by self-assembled monolayers

The mixed self-assembled monolayers (SAMs) serve to tune the work function of ITO by varying the blend ratio. P3HT:PCBM device with indium-tin-oxide modified by short treatment time of 1H,1H,2H,2H -perfluorooctanephosphonic acid exhibits the incident-photon -to-current conversion efficiency of 55 % at -2V., high on/off ratio and improved durability.

Organic photo sensors operating at high speed utilizing poly(9,9-dioctylfluorene) derivative and fullerene derivative fabricated by solution process

Organic photodiodes have been discussed as high-speed photo sensors fabricated by solution process. Poly(9,9- dioctylfluorene) (PFO) or poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) mixed with [6-6]phenyl-C61-butyric acid methylester (PCBM) were used as photo sensitive materials. The device shows high photosensitive characteristics in the visible region. The photocurrent and photo response speed increases as increasing the reverse bias voltage. Both the devices have a cut-off frequency of approximately 60 MHz under reverse bias of 10 V. Clear response pulse signals at 80 MHz were received using a sinusoidally modulated laser light illumination. The printable organic photo sensors have a huge potential in a field of arrayed photo sensors in a large area, scanners and so on.

Organic photonic devices utilizing nano-structured materials

The characteristics of organic photonic devices with various kinds of geometrical nano-structures at the interface between organic materials, and also between the organic layer and metal electrode are investigated. A cutoff frequency of more than 20 MHz was observed for single-layer heterostructure organic photodetector (OPD) by applying a reverse bias electric field under the illumination of the red repetition pulse light. The mixed-layer heterostructure OPD with high photocurrent and high speed photoresponse is suitable for the application of optical link devices. An organic light-emitting diode (OLED) with a partial doping layer at the interface of heterostructure device can be expected to improve the modulation characteristics. The existence of interface between the organic layer and Cs or CsF results in low turn-on voltage for OLEDs. To achieve the efficient electron injection, it is necessary to exist Cs layer just on the organic layer. The efficient electron injection and the low turn-on voltage result from the coexistence of MgAg and CsF at the position of approximately 1 nm from organic layer. The poly(3-hexylthiophene) device with a cathode fabricated from Ag nanoparticles shows a photoresponse and a red emission in the reverse and forward bias regions, respectively. We demonstrated the possibility of polymer OLEDs using a cathode fabricated from Ag nanoparticles by wet processing.

High-speed response properties of organic photo-detector as an opto-electrical conversion device

Organic photo-detectors (OPDs) were examined as receivers for display systems. The cut-off frequency of more than 20 MHz bandwidth was obtained. The OPDs were demonstrated as a receiver of transmitting picture signals.