Improving Energy Relay Dyes for Dye Sensitized Solar Cells by Increasing Donor Homotransfer

The use of energy relay dyes in dye sensitized solar cells presents an opportunity to improve efficiency by increasing the range of absorption of the solar spectrum. In experiments, relay dyes have achieved high efficiency of energy transfer to the sensitizing dye, but the overall power conversion efficiencies of the solar cells is not yet competitive with single-dye dye sensitized solar cells. Using kinetic Monte Carlo simulations, we explored how energy transfer among relay dyes affects the energy transfer to sensitizing dyes and found that high concentrations of energy relay dyes with high rates of homotransfer (a large donor-to-donor Förster radius) can be used to improve the efficiency of excitation transfer to the sensitizing dyes. We examined the effect of Förster radii, quenching, pore size, and dye concentration on the excitation transfer efficiency. The improved understanding of the interplay between the donor–donor and donor–acceptor Förster transfer radii effectively relaxes requirements and expands the spectrum of molecules that can be used as energy relay dyes in dye sensitized solar cells, opening up the possibility of solar cells with relay dyes surpassing single-dye cells in efficiency.