Enhanced performance of dye co-sensitized solar cells by panchromatic light harvesting

Abstract

The Photovoltaic properties of dye co-sensitized solar cells fabricated by using a one-bath mixed dye solution were compared with those of mono-sensitized devices. Co-sensitized TiO2 photo-electrodes were prepared from a mixed dye solution of M-Red [2-cyano-3(10-hexthyl-phenothiazin)acrylic acid] or D-Red [3,3′-hexyl-bis(phenothiazine-2-cyanoacrylic acid)] and S-Blue [(5-carboxy-3,3-dimethyl-1-nonyl-indolium)methylene-2-(E)-(5-carboxy-3,3-dimethyl-1-octylindolin-2-ylidene)-3-oxocyclobut-1-enolate)] to improve the short-circuit current (Jsc) of dyesensitized solar cells (DSSCs). When the photo-electrode was co-sensitized from the mixed solution of M-Red (75%) and S-Blue (25%), the power conversion efficiency (PCE) of the resulting DSSCs exhibited an 11.2% increase, compared to that of M-Red dye (100%). Use of the mixed dye solution of M-red and S-Blue is thought to have ability to reduce the aggregation of S-Blue dye adsorbed on TiO2 surface, leading to an enhancement in Jsc of the co-sensitized solar cells. In the case of D-Red dye, the co-sensitized device prepared from the mixed solution of D-Red (50%) and S-Blue (50%) dye showed a 31.7% enhancement in the PCE, compared to that of the solar cell with a mono (D-Red)-sensitized photo-electrode. Unlike the co-sensitization system using the mixed solution of M-Red and S-Blue, the optimum photovoltaic performance was found from the mixed solution with a 1:1 ratio (D-Red:S-Blue). This could be attributed to the adsorption rate of D-Red (dimeric red) being faster than that of M-Red (monomeric red) dye, there inducing similar adsorption rates for the D-Red and the S-blue dye in the one-bath adsorption process for co-sensitization.