Solar energy has the potential for being a top renewable source of power, but the goal of inexpensive and abundant solar power has not yet been achieved because current solar cells are expensive to manufacture. Photovoltaic cells utilize semiconductors to change light energy into electrical energy, and silicon, the material used in the cells, does so fairly efficiently. Silicon cells are costly, however, and while other thin-film semiconductors are reaching the market, their lower cost does not sufficiently offset their inefficiency. Arthur Nozik, senior research fellow at the National Renewable Energy Laboratory, theorized in the 1990s that quantum dots of specific semiconductor materials could release two or more electrons when they were hit with high-energy photons. Victor Klimov at Los Alamos National Laboratory proved Nozik right in 2004, and in 2006, showed that quantum dots made of lead selenide could provide up to seven electrons per photon when exposed to high-energy ultraviolet light. The effect was also shown in quantum dots made of lead sulfide and lead telluride. While these experiments have yet to produce a material that is appropriate for the commercial market, they indicate that quantum dots may increase the efficiency of using solar energy to provide electricity in the future. Since quantum dots can be made with simple chemical reactions, they could make the manufacture of solar cells much cheaper as well.