One way to lower the cost of solar power is to dramatically reduce the thickness of light-absorbing layers in solar cells. This project first demonstrated record light absorption per unit volume in material virtually one atom in thickness. Now, the researchers seek to demonstrate proof of concept for ultrathin light absorbers for solar cells.
An important task during the first year of the project was to identify a semiconductor material that is highly damping, which will channel the light absorption to the semiconductor rather than the metal component, but also could be deposited evenly on metal nanostructures. The researchers investigated the application of tin sulfide by atomic layer deposition. Tin monosulfide has an ideal bandgap for photovoltaics, but it is not a very good conductor. However, the extremely thin thicknesses the researchers are targeting may alleviate this limitation.
The researchers are attempting to distinguish electron-hole pair generation in the semiconductor layer from absorption in the metal part of the array, so that the feasibility of these nanocomposite layers can be evaluated with respect to photovoltaic applications.
The researchers have also demonstrated that light absorption in thin semiconductor layers can be enhanced significantly by placement directly on top of a metal substrate. A mere 12 nanometers of germanium placed on an optically thick silver film can enable close to 100 percent light absorption, of which 98 percent is in the desirable germanium layer. The researchers are currently working on an experimental realization of this structure.
“Omnidirectional Near-Unity Absorption in an Ultrathin Planar Semiconductor Layer on a Metal Substrate” ACS Photonics, 2014, 1 (9), 812–821