Quantum Dot-Single Wall Carbon Nanotube Complexes for Polymeric Photovoltaics
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Quantum Dot-Single Wall Carbon Nanotube Complexes for Polymeric Photovoltaics Brian J. Landi1, Stephanie L. Castro2, Chris M. Evans1, Herbert J. Ruf1, Sheila G. Bailey3, and Ryne P. Raffaelle1 1
NanoPower Research Laboratories, Rochester Institute of Technology, Rochester, NY 14623, USA 2 Ohio Aerospace Institute, Brookpark, OH 44142, USA 3 NASA Glenn Research Center, Cleveland, OH 44135, USA ABSTRACT The ability to dissociate the photo-generated excitons and transport the resulting charge carriers are the major impediments in improving the efficiency of polymeric solar cells. In order to simultaneously address both of these issues, we have investigated the use of quantum dotsingle wall carbon nanotube (QD-SWNT) complexes as a suitable nanomaterial dopant in these devices. The formation of CdSe-SWNT complexes occurred through covalent attachment of carboxylic acid-functionalized SWNTs with CdSe-aminoethanethiol (AET) quantum dots. An additional synthetic approach was evaluated using both electrostatic and covalent attachment schemes for CuInS2-mercaptoacetic acid (MA) quantum dots and amine terminated SWNTs. The efficacy of each approach is discussed, including the necessary transmission electron microscopy (TEM) and optical absorption spectroscopy data to probe the interactions between nanomaterials. The potential effects of charge transfer between components may have important implications in the efficiency of these materials for polymeric photovoltaic devices. INTRODUCTION Polymeric solar cells are currently being investigated as an alternative photovoltaic technology, due to the potential reduction in processing cost, improved scalability, and opportunity for lightweight, flexible devices [1]. The use of nanomaterials as an additive in these polymer systems is currently an area of very active research, with most efforts directed at semiconductor quantum dots (QDs), fullerenes, and single wall carbon nanotubes (SWNTs) [13]. Selection of the appropriate nanomaterial should maximize exciton dissociation and promote efficient carrier transport in the device. Additionally, the potential exists for a multiple-junction device that is tailored to the air mass zero (AM0) spectrum since conducting polymers, QDs, and SWNTs each absorb in a different spectral region. To better facilitate this process of photon absorption by the components and dissociation of the excitons by the highest electron affinity material nearest the exciton, we are evaluating the use of QD-SWNT complexes as an ideal nanomaterial. Quantum dot-single wall carbon nanotube (QD-SWNT) complexes represent a class of materials that can encompass both high electron affinity and high electrical conductivity. The electron affinity of the QDs can be tailored based upon the selection of semiconductor material used as well being influenced by the nanocrystal size [4, 5]. For example, CdSe QDs have a range of electron affinities reported from 3.5-4.5 eV, while bulk CuInS2 ranges from 4.1-4.9 eV [5, 6]. In addition, the low percolation threshold of SWNTs c
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