Effect of the acceptor on the performance of dye-sensitized solar cells

Abstract

Three new phenothiazine dyes were designed and synthesized, utilizing different acceptor groups. Upon application to TiO₂-based solar cells, the effects of different acceptors on the photophysical and electrochemical properties of the dyes and the solar cell performance are detailed. The introduction of a pyridinium unit or 5-carboxy-1-hexyl-2,3,3-trimethyl-indolium unit into the molecular frame as the acceptor instead of cyano acrylic acid can effectively cause a red shift in the absorption spectra. Applied to DSSCs, the devices sensitized by CM502 with the pyridinium unit as the acceptor show the highest efficiency of 7.3%. The devices fabricated with dye CM501 with cyano acrylic acid as the acceptor exhibited the highest V_oc while for the devices sensitized by the dye CM503 with 5-carboxy-1-hexyl-2,3,3-trimethyl-3H-indolium unit as the acceptor, the V_oc value was the lowest, at 494 mV. The addition of TBP in the electrolyte can improve the performance of DSSCs fabricated using CM501 and CM502, with the V_oc value greatly improved but the J_sc value slightly decreased. However, with the addition of TBP in the electrolyte, the efficiency of the cells sensitized by CM503 dropped significantly (from 4.9% to 1.0% when 0.1 M TBP was added).