TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: The absorber layers are deposited sequentially or simultaneously. The deposition of the first and second absorber layers is by high-temperature vacuum deposition. It comprises heating the substrate to a first high temperature to deposit the first absorber layer and heating the substrate to a second high temperature that is higher than the first high temperature to deposit the second absorber layer. The first and second windows are deposited in a chemical bath. The first absorber is deposited at a first temperature, the second absorber is deposited at a second temperature, the first window is deposited at a third temperature and the second window is deposited at a fourth temperature in which the fourth temperature is lower than or equal to the third temperature, which is lower than or equal to the second temperature, which is lower than or equal to the first temperature.The method further comprises depositing first and second transparent conductor layers onto the opposing sides of the substrate prior to depositing the first and second absorber layers, and then depositing the first absorber layer onto the first transparent conductor layer and the second absorber onto the second transparent conductor layer. The first and second transparent conductor layers are deposited by chemical vapor deposition. The method further includes depositing a third transparent conductor layer onto the first window layer and a fourth transparent conductor layer onto the second window layer. The third and fourth transparent conductors are deposited by radio frequency magnetron sputtering. A metal grid (30) is deposited onto the third transparent conductor and a metal layer onto the fourth transparent conductor. The metal grid and the metal layer are deposited sequentially or simultaneously. The first bandgap and second bandgap absorber layers are p-type semiconductor materials. The solar cell further comprises a metal grid applied onto the third transparent conductor layer and a metal layer applied onto the fourth transparent conductor layer.Preferred Parameters: The high temperature is 350-700 (preferably 500-700)degreesC. The low temperature is at most 200 degreesC. Each of the first and second absorber layers has a bandgap of 1.7 eV. The first bandgap is 1.7 eV, and the second bandgap is 1.1 eV.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The first absorber layer comprises copper-gallium selenide (CuGaSe2). The second absorber layer comprises copper (indium, gallium) selenide (Cu(In,Ga)Se2) with a bandgap less than 1.7 eV. The first and second window layers comprise cadmium sulfide. The transparent substrate comprises glass, or quartz. Each transparent conductor comprises a transparent conductive oxide comprising tin oxide or zinc oxide. The first and second transparent conductors comprise tin oxide and the third and fourth transparent conductors comprise zinc oxide. The first and second window layers are n-type semiconductor material. The first and second window layers comprise cadmium sulfide. The homojunction is formed from materials such as Cu(In,Ga)Se2, CuGaSe2, copper gallium sulfide, cadmium zinc tellurium, cadmium manganese tellurium, cadmium manganese telluride, cadmium magnesium telluride, cadmium telluride, or copper indium selenide. The metal layer and metal grid comprise molybdenum, aluminum, or silver.