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Singlet Sensitization-Enhanced Upconversion Solar Cells via Self-Assembled Trilayers

Photon upconversion via triplet–triplet annihilation (TTA-UC) is a promising strategy for increasing maximum theoretical solar cell efficiencies by a factor of 1.3. However, one factor limiting integrated TTA-UC solar cell performance is the transmission window between sensitizer and acceptor molecule absorption. Here we demonstrate that the incorporation of a singlet sensitizer (SS) into a self-assembled trilayer is an effective means of harnessing that previously transmitted light. A record TTA-UC photocurrent density of 0.315 mA cm–2 under 1 sun irradiation was achieved and is attributed to directional SS-to-sensitizer singlet energy transfer and sensitizer-to-acceptor triplet energy transfer, followed by TTA, excited-state electron transfer into TiO2, and regeneration by a redox mediator in solution. These results demonstrate that singlet sensitization-enhanced self-assembled trilayers are a promising strategy for enhancing broad-band light absorption and improving the performance of TTA-UC solar cells.