Enhancing the efficiency of solid-state dye-sensitized solar cells with plasmonic back reflectors

Solid-state dye-sensitized solar cells (ss-DSCs) are a type of solar cell that replaces the liquid electrolyte in a conventional DSC with a solid-state hole-transport material. SS-DSCs have already achieved power conversion efficiency over 6%, and they do not have problems with potential leakage and corrosion encountered by liquid electrolyte DSCs. However, current ss-DSCs are limited by both pore filling and electron-hole recombination such that the optimal thickness is around 2 μm, which is far too thin to absorb enough light. We show that the efficiency of ss-DSCs can be greatly enhanced by incorporation of plasmonic back reflectors, which consist of two-dimensional (2D) array of silver nanodomes. The plasmonic back reflectors can be fabricated by nanoimprint lithography. They enhance absorption through excitation of plasmonic modes and increased light scattering. SS-DSCs with plasmonic back reflectors show increased external quantum efficiency, particularly in the long wavelength region of the dye's absorption band. This approach is effective in increasing the efficiencies of ss-DSCs with normal thickness (2 μm) made with both ruthenium-complex sensitizers and strong-absorbing organic sensitizers, and the short-circuit photocurrents increased by 16% and 12%, respectively. They achieve power conversion efficiencies of 3.9% and 5.9%, on par with the world record for the devices with the same dyes. In addition to the device data, results on the theoretical modeling of plasmonic and photonic effects will also be presented.