Organic photoconductive materials can be used to create novel imaging systems on non-traditional substrates. Our research focuses on using different materials, device architectures, and fabrication techniques to produce application specific imaging systems.
Materials
Phthalocyanines are a class of organic photoconductive materials with interesting optical, magnetic, catalytic, semiconductive, and photoconductive properties. Titanyl pthalalocyanine (TiOPc) is extensively used in photocopier drums and has a response closely matches that for the human eye, with a maximum near 555nm.
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| TiOPc Structure |
TiOPc Device EQE [1] |
Bulk heterojunction based on polymer semiconductors have been extensively studied for use in organic photovoltiacs and organic photodetectors. We are currently investigating photodetectors based on a Poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) blend.
P3HT:PCBM Structure
Device Architectures
Our group is exploring two different devices architectures. The first approach, adopted by Street et al., creates photodetectors using a vertical "sandwich" geometry [2]. The second approach, adopted by Kymissis et al., creates photodetectors using a lateral geometry [3]. The lateral geometry, which uses lateral contacts, also known as interdigitated electrodes or "fingers", to form the photodetector, is better suited to applications involving organic electronics. The channel resistance organic field effect transistor (OFET) is typically quite large, and therefore it is necessary to use a high-impedance photodetector.
Left: Vertical Architecture; Right: Horizontal Architecture
Fabrication
Device performance depends on the thickness and morphology of the photoconductive layer. TiOPc can be deposited at low temperatures using a variety of techniques such as evaporation, spin-coating, inkjetting, or micro-dot dispensing. For more information see the Precision Dispencing Sytem page.
Applications
One exciting application is a collaboration with the Columbia Vision Laboratory to develop a flexible imaging array backplane for 3D imaging applications. The first generation of this backplane is a 16 x 16 array addressed using a passive matrix configuration. The arrays are currently being characterized and integrated with the imaging system.
[1] I. Nausieda, K. Ryu, I. Kymissis, A.I. Akinwande, V. Bulovic, and C.G. Sodini, "An Organic Active-Matrix Imager", IEEE Transactions on Electron Devices, vol. 55, no. 2, 2008
[2] R. A. Street, J. Graham, Z. D. Popovic, A. Hor, S. Ready, and J. Ho, “Image sensors combining an organic photoconductor with a-si : H matrix addressing,” Journal of Non-Crystalline Solids, vol. 299, pp. 1240-1244, 2002.
[3] I. Kymissis, C.G Sodini, A.I. Akinwande, and V. Bulovic, "An organic semiconductor based process for photodetecting applications," Electron Devices Meeting, 2004.
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