Abstract:
One of the challenges for cost e ective and e cient Dye-Sensitized Solar Cells (DSSCs) is the development of appropriate low-cost counter electrode (CE) materials. The CE is one of the crucial and indispensable components of DSSC that must be able to transport the electrons e ciently from outer circuit to redox electrolyte. The standard DSSC comprised of highly conducting and a catalytic platinum counter electrode for triiodide reduction. However, its high price and rarity on earth are the serious drawbacks in the large scale production of DSSCs. In this research work polypyrrole (PPy), polypyrrole-functionalized multiwall carbon nanotubes (PPy-FMWCNTS), silver-polypyrrole-functionalized multiwall carbon nanotubes (Ag-PPy-FMWCNTS) and PPy, PPy-FMWCNTS, copper-polypyrrole-functionalized multiwall carbon nanotubes (Cu-PPy-FMWCNTS) based nanocomposite CEs were synthesized by electrodeposition technique on a stainless steel substrate. These composites were utilized as an e cient electrocatalytic CE materials in DSSCs. The functionalization of multiwall carbon
nanotubes and successful formation of PPy-FMWCNTS nanocomposite is con rmed by FTIR
analysis. The XRD analysis revealed the presence of Ag and Cu in the PPy-FMWCNTS that describe the development of Ag-PPy-FMWCNTS and Cu-PPy-FMWCNTS nanocomposites CEs. The scanning electron microscopy (SEM) analysis con rmed the presence of uniformly dispersed Ag and Cu nanoparticles in PPy-FMWCNTS. The four probe study of these composites showed the larger electrical conductivity. The electrochemical impedance test of Ag-PPy-FMWCNTS and Cu-PPy-FMWCNTS nanocomposites CEs were performed in an electrochemical
cell and the equivalent circuit was found. The cyclic voltammetry and Tafel polymerization
measurements of Ag-PPy-FMWCNTS and Cu-PPy-FMWCNTS nanocomposites CEs
explored the larger catalytic activity for I 3 =I redox solution. As compared to bare PPy and PPy-FMWCNTS counter electrode these composites electrodes demonstrated the higher value of cathodic peak current and exchange current densities. The higher electrocatalytic activity is of great signi cance for improvement of e ciency of DSSCs. The DSSC assembled with Ag-PPy-FMWCNTS nanocomposites CE display the considerable short circuit current density and acceptable solar to electrical conversion e ciency of 7.6%. This power conversion e ciency is greater than Cu-PPy-FMWCNTS and thermally decomposed Pt based DSSC. The enhanced e ciency of the DSSC is due to following aspects: Firstly, PPy-FMWCNTS shows a strong interaction between FMWCNTS and PPy quinoid rings which facilitate the fast movement of the charges between the two components. Secondly, the high electron-transport network formed by the Ag nanoparticles on the composite surface is also responsible for enhanced e ciency.
This highlighted the importance of the large surface area, good accessibility of electrolyte into the CE and appropriate conductivity of the composite material, underlining a synergetic e ect between three constitutes. The excellent conversion e ciency, rapid charge transfer in combination with low cost and simple fabrication method of Ag-PPy-FMWCNTS nanocomposites can be exploited as an e cient and potential candidate to replace the Pt CE for large scale production of DSSC. Glass slides being used as CE substrate in the fabrication of standard DSSCs, however they are heavy, expensive and rigid. Therefore, to overcome these drawbacks glass slides have been replaced with lightweight, cost e ective and exible stainless steel foil in this research work.