Plasmon-Enhanced Triplet–Triplet Annihilation Using Silver Nanoplates

Photon upconversion processes have attracted substantial interest as a means of circumventing the Shockley–Queisser limit for single-junction photovoltaic devices. Despite this promise, the quantum yield of most upconversion processes is very low at the light intensities typical of solar radiation (∼100 mW/cm<sup>2</sup>). Additionally, bimolecular upconversion processes that rely on molecular diffusion (e.g., triplet–triplet annihilation) typically see further reductions in quantum yield when the upconverting chromophores are confined to a solid state or thin film matrix. Here we report a plasmon-based enhancement of the triplet–triplet annihilation process when silver nanoplates are embedded in poly­(methyl methacrylate) thin films containing the upconverting materials palladium­(II) octaethylporphyrin and 9,10-diphenylanthracene. The silver nanoplates are synthesized with localized surface plasmon resonance bands tailored to overlap strongly with the Q-band of the porphyrin, leading to enhanced light absorption within the film and higher overall triplet concentrations. Optimization of the silver nanoplate loading leads to a nearly 10-fold increase in the upconverted light intensity compared with control samples containing no silver.