In conventional solid-state solar cells, charge carriers – electrons and holes - are created by light absorption in a semiconductor. Subsequent transport and separation of the charge carriers, together with collection of the current, is carried out within the semiconductor itself. To accomplish all this at once, the semiconductor needs to be free of impurities, which increases manufacturing costs.

To overcome this problem, McFarland and Jing have developed a multi-layer device that separates the light-absorption and charge-carrier transport processes. Photons are collected using “photoreceptor” dye molecules placed on the surface of a thin gold film, which rests on a layer of semiconducting titanium dioxide. The photoexcited electrons from the dye molecules are first transferred to the gold layer and then to the conduction band in the titanium dioxide layer, thus producing a current.

The main advantage of the method is that an unusually large number of the photons absorbed by the dye layer – about 10% - generate electric current. In addition, the device is based on electrons only, which makes it less sensitive to impurities and imperfections.

The team now hopes to increase the internal quantum efficiency of their device. “This requires investigations of improved absorbers such as other dyes and quantum dots, improved coupling of the absorber to the metal film, and decreasing film thickness,” McFarland told PhysicsWeb.