Efficiency enhancement in dye-sensitized solar cells with co-sensitized, triple layered photoanode by enhanced light scattering and spectral responses

A method for impressive efficiency enhancement in TiO2-based nanoparticle (NP) dye-sensitized solar cells (DSSCs) is demonstrated by using a co-sensitized triple layered photoanode, comprising a nanofibre (NF) layer of TiO2 sandwiched between two TiO2 P25 NP layers. Rose Bengal (RB) and Eosin-Y (EY) dyes are used for the co-sensitization. DSSCs with conventional TiO2 (P25) NP bi-layer photoanode (NP/NP), sensitized with EY, showed an overall power conversion efficiency (η) of 0.89% under the illumination of 100 mW cm–2 (AM 1.5) with iodide-based liquid electrolyte. Whereas DSSCs fabricated with triple layered photoanode (NP/NF/NP) with the same total thickness and sensitized with EY yielded 1.77% efficiency under the same illumination conditions, showing an impressive ~99% enhancement in the overall power conversion efficiency. The DSSCs fabricated with RB-sensitized NP/NP and NP/NF/NP photoanodes showed 0.25 and 0.73% efficiencies, respectively. Upon optimization, DSSCs fabricated with co-sensitized NP/NP bi-layer and NP/NF/NP triple layer photoanodes showed 1.04 and 2.09% efficiencies, respectively, showing again an impressive ~100% enhancement in η due to the co-sensitized triple layer photoanode structure. Increase in the short circuit photocurrent density, UV–visible absorptions measurements, incident photon to current efficiency and electrochemical impedance spectroscopic measurements confirmed that this enhancement is very likely due to the enhanced light harvesting and reduction of recombination of photoelectrons combined with the enhanced spectral responses of the co-sensitized triple layered photoanode.