Organic Solar Cells: On the Efficiency of Charge Transfer State Splitting in Polymer:Fullerene Solar Cells (Adv. Mater. 16/2014)

A so called “energy river” originates in the active layer of a bulk-heterojunction solar cell as described in work by D. Neher, K. Vandewal, and co-workers on page 2533. This river contains polymer chains and cools down from its hot origin to a cold front. The riverbank is created by “fullerene walls” with different heights. Flashes create hot electrons in the energy river. These electrons need to decrease in temperature during their refrigerating evolution in the river. The cold electrons on the right side cannot escape the river, hidden by the big fullerene wall, and get lost. The cold electrons on the left side are the “good guys”. They are able to splash out of the river and generate electrical power.