Molecular photon upconversion, by way of triplet–triplet annihilation (TTA-UC), is an intriguing strategy to increase solar cell efficiencies beyond the Shockley–Queisser limit. Here we introduce self-assembled bilayers of acceptor and sensitizer molecules on high surface area electrodes as a means of generating an integrated TTA-UC dye-sensitized solar cell. Intensity dependence and IPCE measurements indicate that bilayer films effectively generate photocurrent by two different mechanisms: (1) direct excitation and electron injection from the acceptor molecule and (2) low-energy light absorption by the sensitizer molecule followed by TTA-UC and electron injection from the upconverted state. The power conversion efficiency from the upconverted photons is the highest yet reported for an integrated TTA-UC solar cell. Energy transfer and photocurrent generation efficiency of the bilayer device is also directly compared to the previously reported heterogeneous UC scheme.
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Hill et al. (2016) studied this question.