Singlet fission and triplet fusion have emerged as attractive processes for reshaping the frequency spectrum of incoherent light for applications in solar energy conversion, catalysis, light detection, and fluorescence imaging. However, realizing such applications requires creating hybrid organic:inorganic interfaces that readily exchange energy in the form of spin-triplet excitons. As triplet exciton exchange proceeds via the direct transfer of electrons between an energy donor and acceptor, careful control of the interfacial structure of these junctions is needed to ensure sufficient electronic coupling of the organic and inorganic components. In this presentation, I will describe efforts to design hybrid interfaces that allow for efficient triplet exciton transfer with a particular emphasis placed on interfaces involving chemically functionalized silicon. First, I will describe work to develop silicon nanocrystals featuring triplet-accepting acene and rylene molecules anchored to their surface for light upconversion systems. These materials exhibit forward and reverse exciton transfer rates that are highly dependent on both the chemical nature of their connecting tether as well as the degree of exciton energy matching between silicon and the organic triplet acceptor. Subtle changes in these parameters can cause energy transfer rates to vary from a few tens of nanoseconds to several microseconds. Next, I will discuss how we are applying lessons learned from nanocrystal systems to create planar Si(111):organic junctions that readily transmit triplet excitons. Using electronic sum frequency generation spectroscopy, we have assessed how subtle changes in molecular packing at silicon surfaces impacts the energetic landscape relevant for triplet energy transfer. In particular, we find that the application of strain to organic films at an inorganic interface can shift their exciton energies by 100 meV, which can aid exciton extraction by creating an energy sink that can attract excitons to these interfacial regions.

Designing nanoscale Interfaces for summing & splitting photons

ACS Fall 2021

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