Understanding Mass Transport in Copper Electrolyte-Based Dye-Sensitized Solar Cells
Jayadev Velore, Sourava C. Pradhan, Thomas W. Hamann, Anders Hagfeldt, K. N. Narayanan Unni, Suraj Soman
Abstract
Copper redox shuttles, particularly [Cu(tmby)2]2+/1+ (tmby = bis(4,4′,6,6′-tetramethyl-2,2′-bipyridine)), proved to be among the best electrolytes for dye-sensitized solar cells (DSCs), realizing higher power conversion efficiencies both under full sun and indoor illumination than conventional iodide/triiodide and cobalt electrolytes. Even though [Cu(tmby)2]2+/1+ renders a relatively higher performance, this metal complex is bulky and is limited by mass transport. Since the regeneration of the dye ground state by CuI and the reaction of CuII at the counter electrode are comparatively faster processes, the efficiency of DSC involving CuI/CuII electrolytes under relatively high light intensities is largely governed by the diffusion of CuI/CuII species. Understanding mass transport in these solar cells will enable further improvements in the performance of such copper-based DSCs. In the present study, the role of illumination intensity on the photogenerated current and its relationship to mass transport is evaluated using the best cosensitized dye (D35:XY1) and copper electrolyte ([Cu(tmby)2]2+/1+) combination.