Improved light-harvesting and suppressed charge recombination by introduction of a nanograss-like SnO₂ interlayer for efficient CdS quantum dot sensitized solar cells

Quantum dot sensitized solar cell (QDSSC) performance is primarily limited by the recombination of charges at the interfaces of TiO₂/quantum dot (QD) sensitizer/electrolyte. Hence, blocking or suppressing the charge recombination is an essential requirement to elevate the QDSSC performance to the next level. To retard the charge recombination, herein, we propose the introduction of a SnO₂ nanograss (NG) interlayer on the surface of TiO₂ using the facile chemical bath deposition method. The SnO₂ NG interlayer not only inhibits the interfacial recombination processes in QDSSCs but also enhances the light-harvesting capability in generating more excitons. Hence, the TiO₂/SnO₂ NG/CdS QDSSCs can achieve the power conversion efficiency of 3.15%, which is superior to that of a TiO₂/CdS device (2.16%). Electrochemical impedance spectroscopy, open-circuit voltage decay and dark current analyses confirm that the recombination of charges at the photoanode/electrolyte interface is suppressed and the life time is improved by introducing the SnO₂ NG interlayer between the TiO₂ and CdS QD sensitizer.