Part of the Physical Seminar Series Abstract To understand the electronic physics of organic semiconductors (i.e. pi-conjugated molecules in the solid-state), I use a range of spectroscopic techniques. In this talk, I will concentrate on describing our current understanding of a process known as ‘singlet exciton fission’ that occurs in some organic semiconductor materials. In singlet exciton fission, the photoexcited singlet (spin-0) exciton spontaneously splits into two triplet (spin-1) excitons. This two-for-one process offers the possibility of beating the Shockley Quiesser limit in solar cells, overcoming thermalisation. Singlet fission can be very rapid (100fs-100ps) and is generally described as proceeding through an intermediate triplet-pair state. The nature of this intermediate state has been the subject of much debate. In this talk, I will discuss our recent work on singlet fission materials with particular emphasis on the nature of the intermediate triplet-pair state. I will conclude by describing some very recent work demonstrating how photon-exciton interactions in organic exciton microcavities can be used to squeeze light out of the triplet pair states by coupling them to the cavity's photon mode.