Ultrathin crystalline-silicon solar cells with embedded photonic crystals

Photonic crystals (PCs) can be used to trap light in thin-film solar cells to increase optical absorption. We fabricated ultrathin c-Si solar cells whose active layer was patterned into a two-dimensional PC with a square lattice of 450 nm diameter holes spaced at a period of 750 nm. The PC couples incident light into quasiguided modes and can be engineered to increase coupling and thus optimize optical absorption. Both short-circuit current and external quantum efficiency measurements show an enhancement in optical absorption, especially at longer wavelengths. Scanning photocurrent maps confirm the improved optical absorption in the PC regions. (C) 2012 American Institute of Physics. [doi:10.1063/1.3680602]