Strong competition between electromagnetic enhancement and surface-energy-transfer induced quenching in plasmonic dye-sensitized solar cells: A generic yet controllable effect

Light harvesting strategy using plasmonic metal nanostructures as subwavelength light concentrators provides a highly attractive solution to enhancing the performance of dye-sensitized solar cells (DSSCs). Through comprehensive optical spectroscopy and electrical characterizations together with a theoretical analysis, we demonstrate a strong competition between the surface energy transfer induced non-radiative quenching and the plasmonic electromagnetic enhancement effect in metal-dielectric-semiconductor core-shell-shell nanoparticle doped DSSCs, a generic yet unavoidable phenomenon in all types of plasmonic solar cells. The competition of the two effects results in a non-monotonic relationship between the device efficiency and the thickness of the dielectric shell covering the metal nanoparticles, and leads to an optimal thickness for the highest power conversion efficiency. This observation is further corroborated by photoluminescence spectroscopic measurements. Our experimental results are in good agreement with the Persson model that predicts a strong energy quenching effect when the distance between the photogenerated charge carrier and the metal core is short enough. Both experiment and theory show that the localized surface plasmon resonance enhanced light harvesting efficiency is suppressed by the surface energy transfer to the metal cores for the dielectric shell thickness shorter than a characteristic value (~7 nm in our study). Our work sheds new insights into the fundamental understanding of the photophysics mechanisms of plasmonic DSSCs and could push forward the study of plasmonic solar cells in terms of device design and fabrication.