Manipulating Light with Molecular Excitons

There are many applications that demand that the properties of light be controlled by molecular excitons. This includes upconversion applications, where shorter wavelengths are generated from longer wavelengths, and multiple exciton generation and photon multiplication, where a high energy photon is split into smaller energy packets.
 
Over the past decade, we have applied triplet-triplet annihilation upconversion to photovoltaics. Recently, we achieved photochemical upconversion from beyond the silicon bandgap for the first time.
 
Singlet fission is a process where a photon-generated singlet state splits into two spin-correlated triplets. In solar cells it is hoped that this will give rise to two excitons per absorbed photon above a certain energy, increasing the efficiency limit to nearly 46%. Here I will discuss the role of the excimer state in singlet fission.