Bidirectional Triplet Exciton Transfer Between Silicon Nanocrystals and Perylene

Inorganic solar cells on the market today fall short of absorbing all of the energy available in sunlight. Inorganic quantum dots functionalized with triplet exciton accepting surface ligands are a promising platform for the upconversion to improve the efficiency of these photovoltaic (PV) cells and overcome the Shockley–Queisser limit. Here, we functionalize silicon quantum dots (Si QDs) with triplet exciton-accepting perylene ligands which capture photons with wavelengths as long as 730 nm to deliver spin-triplet excitons to their surrounding environment that drive upconversion via triplet fusion. Using transient absorption spectroscopy, we have characterized the efficiency of key steps in this energy transfer chain. We find spin-triplet excitons produced in perylene-functionalized Si QDs establish an equilibrium wherein they readily move between the Si QD core and surface-bound perylene molecules. Adjusting the electronic structure of the surface-bound exciton acceptor can shift this equilibrium, making nearly all excitons available for extraction. Importantly, our work not only identifies ways to improve the function of Si QD-based photon upconversion systems, but also decisively demonstrates molecule-to-silicon spin-triplet exciton transfer is possible. This finding can enable the design of light-harvesting systems and quantum information devices that make use of singlet fission, triplet fusion’s inverse process, to achieve unique functionality.