Upping the solar efficiency

Solar cells are inefficient because they are picky! If an incoming photon has too little energy, the cell won’t absorb it. If a photon has too much, the excess is wasted as heat. No matter what, a silicon solar cell can never generate more than one electron from a single photon. Now, researchers at the Massachusetts Institute of Technology’s Center for Excitonics have published a compelling case that the key to greater solar efficiency might be an organic dye called pentacene.

A photovoltaic cell based on pentacene can generate two electrons from a single photon—more electricity from the same amount of sun. Previous research had accomplished similar tricks using quantum dots (tiny pieces of matter that behave like atoms) and deep-ultraviolet light. In addition to using visible light, the present work has shown that [this process] works very, very effectively in organic materials.

Yes, for now, the pentacene cell works only with an extremely narrow band of visible light. But the team hopes it should be possible to create a pentacene coating for silicon solar cells that boosts the total conversion efficiency from today’s 25 percent to a shade over 30 percent—a significant jump. Of course, it is all theory now. But science debvelops from theory to experiment and we can hope!