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An organic solar cell converts light into electrical output using organic semiconductors, such as conjugated molecular or polymeric absorbers. Light absorption commonly produces a bound exciton, so useful charge generation requires more than simply creating an excited molecule.

In a donor–acceptor design, an exciton reaches an interface where charge transfer can separate its electron and electron hole. Selective contacts collect the separated charge carriers before they undergo recombination. A bulk heterojunction distributes donor–acceptor interfaces throughout the absorber, shortening the distance an exciton must travel. Its morphology must also supply connected transport pathways to the contacts. Absorption, exciton diffusion length, separation and charge collection therefore constrain performance together.

A researcher who coauthored a method for increasing the exciton diffusion length in organic solar cells. Diluting the absorbing donor molecules in a material with a wider band gap changed their interactions and increased the distance an exciton could travel. This helps excitations reach the charge-separating interface before they decay, improving useful collection of absorbed light.^[ref]