Polyaniline/Graphene/Multi-Walled Carbon Nanotube Composites as Counter Electrode for Dye-Sensitized Solar Cells
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Polyaniline/Graphene/Multi-Walled Carbon Nanotube Composites as Counter Electrode for Dye-Sensitized Solar Cells Yen-Chen Shih1, Hsiao-Li Lin2 and King-Fu Lin1, 2 1 Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan 2 Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan ABSTRACT To provide a counter electrode with lower-cost and simple production method for dyesensitized solar cells (DSSCs), we developed polyaniline/graphene nanoplatelet/multi-walled carbon nanotube (PANi/GNP/MWCNT) composite films growing on glass substrates by using chemical/electrochemical deposition method and on fluorine-doped tin oxide (FTO)/glass substrates by using electrochemical deposition method respectively. A proper weight ratio of PANi/GNP/MWCNT (1/0.0030/0.0045) composite film depositing on FTO substrate as counter electrode with sheet resistance of 8.25±0.13 Ω/sq for DSSCs yielded power conversion efficiency (PCE) up to 7.45±0.08%, which has potential to replace the conventional Pt cell (7.62±0.07%). In addition, we also fabricated the DSSCs composed of a proper weight ratio of PANi/GNP/MWCNTs (1/0.0045/0.0060) composite film depositing on glass substrate as counter electrode. The sheet resistance of resulting composite film was 59.34±12.34 Ω/sq. These solar cells with FTO-free counter electrode exhibited a PCE of 2.90±0.09%. INTRODUCTION The counter electrode (CE) in a dye-sensitized solar cell (DSSC) plays an important role to transport the electrons from external circuit to the electrolyte and catalyze the reduction of redox I3 to I [1,2]. Most commonly used CE in DSSCs is a Pt-deposited fluorine-doped tin oxide (FTO) glass substrate. Although Pt exhibits excellent catalytic activity for I3 reduction, high cost would obstruct its application in practice. Polyaniline (PANi) has been developed over the past decades as a promising material for CEs due to high conductivity, environmental stability, and good catalytic activity for I3 reduction [3,4]. In this work, PANi was made from aniline sulfate by electrochemical deposition (ED) on FTO glass substrates and chemical/electrochemical deposition (C/ED) on glass substrates. Graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) were incorporated as additives into PANi based composites to increase their conductivity. Thus, the influence of carbon additives on sheet resistance, redox activity and DSSCs performance was investigated. EXPERIMENT DETAILS Pt-Free CE for DSSCs PANi based films were polymerized through ED method on FTO from an aqueous solution containing 0.5 M aniline sulfate and 1 M sulfuric acid in a three-electrode system, where the cleaned FTO glass substrate, a Pt wire, and a saturated Ag/AgCl were used as the working electrode, counter electrode and reference electrode respectively. GNPs (specific surface area 2 -1 450 m g , Purity >99% , average thickness 3 nm flakes , average particle size : 0.5-40 μm, Uni-
Region) and MWCNTs (O.D. 10-15 nm, I.D. 2-6, length 0.1-10 μm, Arkema
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