Gas Phase Electrodeposition: A Programmable Localized Deposition Method for Rapid Combinatorial Investigation of Nanostu
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Gas Phase Electrodeposition: A Programmable Localized Deposition Method for Rapid Combinatorial Investigation of Nanostuctured Devices and 3D Bulk Heterojunction Photovoltaic Cells En-Chiang Lin, Jun Fang and Heiko O. Jacobs Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455 ABSTRACT This article applies a recently discovered gas phase nanocluster electrodeposition process to the formation and combinatorial improvement of 3D bulk heterojunction photovoltaic cells. The gas phase deposition process used here is a single reactor system that forms charged nanoclusters (gold, silver, tungsten, and platinum) at atmospheric pressure. The clusters deposit onto selected surface areas with sub 100 nm lateral resolution using a programmable concept similar to liquid phase electrodeposition such that biased electrodes turn ON or OFF deposition in selected areas. Continued deposition of the nanoparticles results in a tower array with different lengths and density on a single substrate which is used as contacts to the active organic layer of 3D bulk heterojunction photovoltaic cells. Applying a combinatorial approach identifies in a massively parallel way electrode designs and topologies that improve light scattering, absorption, and minority carrier extraction. We report photovoltaic cells with higher and denser nanocluster tower arrays that improve the power conversion efficiency of bulk heterojunction photovoltaic cells by approximately 47.7%. INTRODUCTION Inorganic nanomaterials have recently attracted tremendous attention due to their unusual properties such as high surface area to volume ratio, quantum size effects, and increased catalytic activity. These interesting properties have found use in several unique applications such as optoelectronics, photovoltaics, photodetectors, DNA screening, nanoxerography, and environmental protection [1-5]. There are various synthesis techniques available to form inorganic nanomaterials which can be grouped into liquid phase and gas phase methods. Gas phase methods such as thermal flow synthesis [6-8], laser ablation [9], sputtering [10], plasma induced synthesis, [11] and arc discharge [12, 13] can produce nanoparticles, nanotubes, nanobelts, and quantum wells with higher purity and throughput rates than their liquid phase counterparts. Typically gas phase methods involve either high vacuum environments or high temperatures which are incompatible with applications in flexible electronics. Among these synthesis methods, the atmospheric pressure arc discharge method is a viable candidate for mass production of nanoparticles as it provides a low temperature process, a high mass flow rate, inexpensive production setups, and a variety of selections for conductive material including metals and semiconductors [12, 13]. While most prior studies focused on the size or shape properties of nanoparticles synthesized by arc discharge, few studies discussed integrating those nanoparticles into locations on a substrate by self assembly [14] for fabricating functional d
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