Transparent Conductive Oxide-Less Dye-Sensitized Solar Cells Consisting of Dye-Cocktail and Cobalt Based Redox Electrolyte

Abstract

Thin Ti-metal protected stainless steel metal mesh coated with mesoporous TiO2 as flexible photoanode has been used to fabricate back contact transparent conductive oxide-less dye-sensitized solar cells. TiO2 nanoparticle having a particle size of 15–20 nm sensitized with dye cocktail of two indoline dyes D-205 and D-131 were first utilized owing to their complementary light harvesting properties. Short-circuit photocurrent density (Jsc) for the dye cocktail combination of D-205 and D-131 (1:1) was found to be increased due to the increased photon harvesting in the 400–500 nm mainly associated with the contribution from D-131 dye. In addition, the electron recombination was suppressed when dye cocktail was employed as confirmed by the dark current measurement leading to higher open-circuit voltage (Voc). The enhanced Jsc accompanied with increased Voc resulted in to an improved efficiency of 3.59% for this cocktail combination. To enhance the efficiency even further, we have utilized TiO2 nanoparticle having a larger particle size of 30 nm facilitating the mass transport of the bulky [Co(bpy)3]3+/2+ redox species. In order to enhance the photon harvesting window TiO2 nanoparticles were sensitized with porphyrin dye (YD2-o-C8) along with different dye cocktail combinations with another complementary dye (Y123). Utilization of a dye cocktail of YD2-o-C8 and Y123 (4:1) led to improved photoconversion efficiency of 5.25% under simulated solar irradiation.