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

Hiroyuki Shimada¹, Shigeki Naka^1,2, Hiroyuki Okada^1,2, and Hiroyoshi Onnagawa^1,2

(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, σ_R, was approximately 10³ for both BA- and TA-OPDs. In a TA-type Al/td-PTC/α-NPD/CuPc/IZO device, the σ_R and the short-circuit photocurrent I_P were 3.4×10² and 5.3×10^-2 mA/cm², respectively. The lower value of σ_R 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.

URL: http://jjap.jsap.jp/link?JJAP/44/2830/
DOI: 10.1143/JJAP.44.2830
KEYWORDS:organic devices, organic photodiode, organic material

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