Semiconductor Junctions for Photon Up and Downconversion: From Nanocrystals to Bulk Solids

Materials that repackage the energy of incoherent light, by either summing its photons together or dividing them into lower energy pairs, offer potential for new technologies for solar energy conversion, photon detection, catalysis, and quantum information science. Organic dimers, polymers, and extended solids that undergo singlet fission offer a potential means for achieving this goal as this process converts high-energy single spin-triplet excitons into pairs of low-energy spin-triplet exciton pairs. Likewise, singlet fission’s inverse, triplet fusion, can be used to combine low-energy exciton pairs into high-energy states. However, designing applications based on these materials necessitates design of both highly stable singlet fission/triplet fusion materials as well as hybrid organic:inorganic junctions that allow triplet excitons to interface with commercial semiconductor technologies. In this presentation, I will review our group’s efforts to produce covalently tethered structures for this purpose. The presentation’s first half will focus on the design of photostable single fission-capable solids based on perylenediimide dyes while its second half will focus on model semiconductor junctions that interface these and related materials with semiconductor quantum dots. Lessons learned from these studies will be used as a basis for designing silicon:organic structures that allow for spin-triplet exciton transfer across their junction.