Jpn. J. Appl. Phys. 44 (2005) pp. 2830-2832 |Previous Article| |Next Article| |Table of Contents|
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Top-Absorption Organic Photodiodes Suitable for Device Integration
1Faculty of Engineering, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan
2Innovation Plaza Tokai, Japan Science and Technology Agency, 23-1 Ahara-cho, Minami-ku, Nagoya 457-0063, Japan
(Received September 21, 2004; revised December 7, 2004; accepted December 15, 2004; published April 21, 2005)
We have fabricated top-absorption organic photodiodes (TA-OPDs) using sputtered indium zinc oxide (IZO) electrodes and compared their photodiode characteristics with conventional bottom-absorption organic photodiodes (BA-OPDs). In poly ([2-methoxy-5-(2'-ethylhexyloxy)]-1,4-phenylenevinylene) (MEH-PPV) films sandwiched between Al and IZO electrodes, the ratio of photoconductivity to dark conductivity, σR, was approximately 103 for both BA- and TA-OPDs. In a TA-type Al/td-PTC/α-NPD/CuPc/IZO device, the σR and the short-circuit photocurrent IP were 3.4×102 and 5.3×10-2 mA/cm2, respectively. The lower value of σR in TA-OPDs compared to BA-OPDs in this structure is ascribed to sputtering damage during IZO film preparation. We were able to prevent successfully this damage by inserting the MoO3 hole-injecting and sputter buffer layer instead of the CuPc layer. We have also investigated the frequency characteristics of several TA-OPDs and obtained relatively good response in the TA-OPDs with a MoO3 buffer layer. In terms of frequency characteristics, the cut-off frequency of the TA-OPDs with a MoO3 buffer layer was as high as 300 kHz.
KEYWORDS:organic devices, organic photodiode, organic material
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