Copper Phthalocyanine Nanowire Based Solar Cells
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Copper Phthalocyanine Nanowire Based Solar Cells Vijay Singh, Suresh Rajaputra, Sovannary Phok, Goutham Chintakula, and Gayatri Sagi Department of Electrical & Computer Engineering, University of Kentucky, 453 Anderson Hall, Lexington, KY, 40506-0046 ABSTRACT Photovoltaic devices based on organic semiconductors are of interest because of their potential as flexible, lightweight and inexpensive devices. One of the promising devices, involves the heterojunction between copper phthalocyanine (CuPc) and 3,4,9,10perylenetetracarboxylic bis-benzimidazole (PTCBI). Earlier, we reported, the highest Voc (1.125V) in a single organic heterojunction solar cell in an ITO/PEDOT:PSS/CuPc/PTCBI/Al structure. Results were interpreted in terms of a modified CuPc-Al Schottky diode for this thin PTCBI layer case and a CuPc-PTCBI heterojunction for the thick PTCBI case. We also reported the device characteristics of Copper phthalocyanine (CuPc)/Aluminum (Al) Schottky diode solar cells. Here, open circuit voltages (Voc) increased from 220 mV at 15 nm to 907 mV at 140 nm. Analysis of the current-voltage characteristics indicated that tunneling and interface recombination mechanisms are important components of the current transport at the CuPc/Al junction. In this paper, we report the fabrication, materials and electrical characterization of Schottky diode solar cells based on electro-deposited CuPc nanowires. The nanowires were characterized by XRD, UV-Vis absorption spectroscopy, electron microscopy and electrical measurements. Effect of the PEDOT: PSS buffer layer on the nanowire based device characteristics was also investigated. INTRODUCTION The development of plastic electronics into a well established technology is a goal currently pursued by many research groups worldwide. The success of plastic electronics depends critically on significant improvements in devices based on organic semiconductors [1,2]. Organic semiconductors like copper phthalocyanine (CuPc) are finding more and more applications in many optoelectronic devices including light emitting diodes [3,4] and solar cells [5-12]. CuPc based solar cells are of interest because of their potential as flexible, lightweight and inexpensive devices. High open circuit voltages have been obtained in Schottky diode solar cells on thermally evaporated films of CuPc [5,6]. However short circuit current densities (Jsc) in these cells as in organic semiconductor cells (OSC), in general, are low. The major reason for low Jsc in organic semiconductor cells is the small exciton diffusion length of a few nm. Nanowire cell designs [7] offer a way out of this serious limitation and thus a path to high efficiency OSCs. Many promising nanowire fabrication techniques however depend on the technology of electrodepositing organic semiconductors into nanoporous structures like alumina templates. Thus electrodeposition of organic semiconductor films is not only a less expensive technology than deposition by vacuum evaporation, but it is indispensable for fabricating many nanoscale devic
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