Light Trapping in Solar Cells: Theory and Practical Implementation

Light trapping is a mechanism for creating enhanced absorption in a material, beyond that of a parallel polished wafer of the same material and the same thickness. Light trapping is an important feature of all solar cells, because it allows the use of thinner cells that perform equally or better than thick cells. A thinner cell leads to lower-volume recombination of photogenerated carriers,leading to higher cell performance. Thinner wafers can also help minimize the use of semiconducting material, therefore lowering the energy cost further. Light trapping in a wafer or a solar cell requires rough or textured surface(s); hence the detailed optics of light trapping is somewhat difficult to carry out. We have developed a software package, PV Optics, which performs light-trappingcalculations for solar cell applications. It determines optical absorption for a given structure and calculates photocurrent available from a given solar cell structure for many cases, such as when the cell is placed directly in the sun or encapsulated in a module. The cell can have a single- or multiple-junction configuration. This paper will review the principles of light trapping andpractical approaches to incorporate effective light trapping in silicon solar cells. We will demonstrate typical use of PV Optics for the design of crystalline and amorphous silicon solar cells.