Surface Energy Relay Between Cosensitized Molecules in Solid-State Dye-Sensitized Solar Cells

We employ cosensitization of a visible absorbing organic sensitizer and a near IR absorbing Zn-phthalocyanine complex to significantly enhance the optical bandwidth in spiro-OMeTAD based solid-state DSCs. The cosensitized cells exhibit greatly enhanced performance, with full sun AM1.5 power conversion efficiencies of 4.7%, as compared to 3.9% for the best monosensitized device. Unexpectedly, further to broadening the spectral response, the addition of the near IR sensitizer greatly enhances the spectral response in the visible region. Through both electronic and spectroscopic investigations, we demonstrate that resonant energy transfer occurs from the visible to the near IR sensitizer. This unforeseen charge generation route works in conjunction with direct electron transfer from the visible sensitizer, improving the overall charge generation efficiency and explaining the panchromatic enhancements with the cosensitized system. This previously unobserved mechanism for charge generation relaxes the design criteria for visible absorbing sensitizers, providing a second, and possibly primary, channel for efficient charge generation.