Thin-film solar cells

Made from colloidal semiconductor nanocrystals. In recent years, much effort has been put into lowering the manufacturing cost of photovoltaic (PV) cells, used to convert sunlight into electricity. One route has been the development of thin plastic films of PV material. Although relatively easy to produce, the organic components of such films respond well only in a narrow range of the Sun’s spectrum, have poor carrier mobility, and degrade quickly when exposed to air. Conventional semiconductor PV cells are more efficient and durable but also much more expensive to make. A group led by Paul Alivisatos (Lawrence Berkeley National Laboratory and University of California, Berkeley) has now begun to combine the best of both worlds. Using rod-shaped particles of cadmium telluride, the team made a colloidal solution that they spin-cast into a thin film on a suitable substrate. A second film, of similarly prepared rod-shaped cadmium selenide colloidal particles, was overlaid. The resulting bilayer was an electrical insulator in the dark, but when it was exposed to sunlight, its conductivity rose by a factor of a thousand. The new inorganic films already match the 3% efficiency of organic PV films, have a broad spectral response to sunlight, and are stable in air. (I. Gur et al., Science 310, 462, 2005.)