Organic-Based ('Excitonic') Solar Cells

The existing types of organic-based solar cells, including dye-sensitized solar cells (DSSCs), can be categorized by their photoconversion mechanism as excitonic solar cells, XSCs. Their distinguishing characteristic is that charge generation and separation are simultaneous and this occurs via exciton dissociation at a heterointerface. Electrons are photogenerated on one side of the interface andholes on the other. This results in fundamental differences between XSCs and conventional PV cells. For example, the open circuit photovoltage, Voc, in conventional cells is limited to less than the magnitude of the band bending, ?bi; however, Voc in XSCs is commonly greater than ?bi. A general theoretical description is employed to quantify the differences between conventional and excitoniccells. The key difference is the dominant importance, in XSCs, of the photoinduced chemical potential energy gradient, ..delta..?hn, whereas ..delta..?hn is unimportant, and therefore neglected, in theoretical descriptions of conventional PV cells. Several examples are provided.