CdS Q-Dot-Impregnated TiO2-B Nanowire-Based Photoanodes for Efficient Photovoltaic Conversion in 'Q-Dot Co-sensitized DSSC'

Cadmium sulfide (CdS) as a narrow-band-gap semiconductor has been coupled in 0-15 wt % to hydrothermally grown titanium dioxide bronze-phase (TiO2-B) nanowires (TNWs), reducing the optical band gap from 2.96 to 2.71 eV. In CdS Q-dot-impregnated TNW/CdS composite nanowires, absorption of light extends toward the visible range of the solar spectrum and effective light-harvesting improves via increased specific surface area; furthermore, the properly aligned band edges between CdS and TiO2-B ascertain efficient separation of the photogenerated charge carriers. Overall, an optimum photoanode material characteristic has been demonstrated in TNW/CdS-10 nanocomposite that achieves a typical photovoltaic (PV) conversion efficiency, eta similar to 1.63%, in Q-dot-sensitized solar cells (QDSSCs), compared to the eta similar to 0.86% of the simple electrochemical cell with a pristine TNW photoanode. N3 dye sensitization of the pristine TNW photoanode leads to a conversion efficiency of eta similar to 3.88% in dye-sensitized solar cells (DSSCs). When the CdS Q-dot-sensitized TNW/CdS-10 photoanode is further co-sensitized by the N3 dye, an enhanced PV conversion efficiency of eta similar to 8.04% is attained in the "Q-dot co-sensitized DSSC" device by virtue of the optimum light absorption facilitated by the maximum dye-loading capacity retained by the widest available surface area on the composite photoanode, contributing to a superior incident-photon-to-current conversion efficiency (IPCE) of similar to 69.60% at 520 nm. Interfacial electron injection and the recombination dynamics of the cells studied using impedance spectroscopy demonstrate that the DSSC performance increases due to minimization of the electron-hole recombination rate and the increase of the conduction of charge carriers via reduced charge-transfer resistance of the photoanode(Q-dots/dye)/electrolyte interface at an optimum 10 wt % CdS loading. Sequential sensitization of TiO2-B nanowire photoanodes via CdS Q-dot impregnation and further by N3 dye molecule adsorption improves light-harvesting, facilitates efficient photocarrier generation, and prevents interfacial charge recombination, and their cumulative electron injection results in a better photovoltaic performance via novel "CdS Q-dots and N3 dye co-sensitization of TiO2-B NWs" in Q-dot co-sensitized DSSCs.