Increasing Polymer Solar Cell Active Layer Efficiency and Organization by Adding Gold-Functionalized Reduced Graphene Ox
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Increasing Polymer Solar Cell Active Layer Efficiency and Organization by Adding Gold-Functionalized Reduced Graphene Oxide Rebecca Isseroff 1,2, Andrew Chen2, Sneha Chittabathini2, Alexandra Tse2, Cheng Pan1, 3 1 4 1 1 Benjamin Goldman , Hongfei Li , Benjamin Akhavan , Jonathan Sokolov , Miriam Rafailovich 1) Dept of Materials Science and Engineering, SBU, Stony Brook, NY 11794-2275 2) Lawrence High School, Cedarhurst, NY 11516 3) Yeshiva University, NY, NY 10033 4) Rambam High School, Lawrence, NY 11559 ABSTRACT Relatively low efficiency is one of the main obstacles to overcome in the engineering of organic bulk heterojunction (BHJ) solar cells. Reduced graphene oxide (RGO), which has high conductivity, has been proposed to enhance the function of PCBM in the interfacial dissociation of excitons, but incorporating it into the hydrophobic photoactive polymers has proved challenging. Here we describe a novel technique for incorporating Au nanoparticles (AuNp) into the structure of the RGO. The AuNps then interact with the sulfur groups on the photoactive polymer component, while the RGO interacts via π – π stacking with the chemically similar PCBM, thereby anchoring the complex to the polymer interface. Graphene oxide was synthesized and then reduced in the presence of a gold salt. The resulting gold-functionalized RGO (AuRGO) sheets were characterized using TGA, FTIR, and TEM. The AuRGO was not soluble in chlorobenzene; however, in the presence of P3HT, the AuRGO dissolved, suggesting a reaction between the gold and the sulfur of the P3HT via a metal-thiolate bond. At 2 mg/ml, AuRGO increased the solar cell efficiency approximately 50% over the control, but higher concentrations produced large, columnar structures which blocked the electrode from having a uniform contact with the active layer. INTRODUCTION Bulk heterojunction solar cells (BHJ) are an area of intense interest due to their relatively low cost and ease of fabrication into flexible shapes. Currently, most cells are constructed by blending a photoactive polymer with functionalized C60 particles such as PCBM, forming an interpenetrating network of electron donors and acceptors which allows for the dissociation of excitons (the charge-carrying species in organic solar cells) and the transport of electrons and holes to respective electrodes. This morphology can lead to the formation of interconnected though meandering domains which form lengthy and indirect pathways to the electrodes [1]. These can increase the probability of recombination of the electron and hole pairs, thereby increasing the effective resistance and lowering the efficiency of the cell. Numerous groups have proposed increasing the efficiency by providing internal templates to guide the structures more efficiently towards the electrodes [2-4]. Most, though, require some form of nanoscale lithography or etching which increases cost and makes large-scale manufacturing difficult. We propose another approach to increase the efficiency of the BHJ by producing and employing reduced graphene oxid
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