Origin of Nonlinear Device Performance with Illuminated Sun Intensity in Mesoscopic Sb2S3-sensitized Photoelectrochemical Solar Cells using Cobalt Electrolyte
ABSTRACT: The mesoscopic Sb 2 S 3 -sensitized photoelectrochemical solar cells using cobalt redox electrolyteexhibit nonlinear behavior of power conversion efficiency with illuminated sun intensity. From themeasurement of bulk diffusion and electrochemical impedance spectroscopy studies, we suggestthat the nonlinearity of device performance with illuminated sun intensity is attributed not to theslow bulk diffusion problem of cobalt electrolyte but to the limited mass transport in narrowed porevolume in mesoscopic TiO 2 electrode.Keywords : Sb 2 S 3 , Photoelectrochemical solar cell, TiO 2 , Cobalt electrolyte Received September 15, 2011: Accepted September 29, 2011 1. Introduction Since Gratzel et al. 1) reported a mesoscopic dye-sensitized photoelectrochemical solar cell with highpower conversion efficiency over 11% at 1 sun illumination,the sensitized photoelectrochemical solar cells have beenintensively studied due to their distinguished device structurefrom conventional p-n heterojunction solar cells. The sensi-tized solar cells are comprised to mesoscopic photoanode,sensitizer, and redox electrolyte which has correspondingrole of electron conductor, light absorber, and hole con-ductor, respectively. This unique device architecture enablesthe sensitized solar cells to hold cost-effectiveness.Recently inorganic semiconductors have been con-sidered as a promising alternative of conventional dyesbecause of their peculiar properties such as easy chargeseparation by higher dipole moment, ~10 fold higherextinction coefficient than Ru/organic dyes, convenientbandgap tunability by size control, and multiple excitongeneration.