One way to make solar cells more efficient is to find a material that will capture energy from a large portion of the spectrum of sunlight — from infrared to visible light to ultraviolet.
Energy transfers from photons to a photovoltaic material when the material absorbs lightwaves that contain the same amount of energy as its bandgap. A bandgap is the energy required to push an electron from a material’s valence band to the conduction band where electrons are free to flow.
Most photovoltaic materials absorb a relatively narrow range of light energy, however. The most efficient silicon solar cells capture only about 25 percent. Multijunction solar cells made from several different materials boost efficiency as high as 36 percent, but are relatively difficult to make and therefore expensive.