Organic solar cell

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.

An interpenetrating donor-acceptor morphology in a photovoltaic absorber. Small domains facilitate exciton access to interfaces, while continuous pathways in each phase allow separated charges to reach selective contacts.