title: Symmetry-breaking nanostructures on crystalline silicon for enhanced light trapping in thin film solar cells.
abstract: We introduce a new approach to systematically break the symmetry in periodic nanostructures on a crystalline silicon surface. Our focus is inverted nanopyramid arrays with a prescribed symmetry. The arrangement and symmetry of nanopyramids are determined by etch mask design and its rotation with respect to the [110] orientation of the Si(001) substrate. This approach eliminates the need for using expensive off-cut silicon wafers. We also make use of low-cost, manufacturable, wet etching steps to fabricate the nanopyramids. Our experiment and computational modeling demonstrate that the symmetry breaking can increase the photovoltaic efficiency in thin-film silicon solar cells. For a 10-micron-thick active layer, the efficiency improves from 27.0 to 27.9% by enhanced light trapping over the broad sunlight spectrum. Our computation further reveals that this improvement would increase from 28.1 to 30.0% in the case of a 20-micron-thick active layer, when the unetched area between nanopyramids is minimized with over-etching. In addition to the immediate benefit to solar photovoltaics, our method of symmetry breaking provides a useful experimental platform to broadly study the effect of symmetry breaking on spectrally tuned light absorption and emission.
authors.forename: Seok Jun
authors.initials: SJ
authors.lastname: Han
authors.forename: Swapnadip
authors.initials: S
authors.lastname: Ghosh
authors.forename: Omar K
authors.initials: OK
authors.lastname: Abudayyeh
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Hoard
authors.forename: Ethan C
authors.initials: EC
authors.lastname: Culler
authors.forename: Jose E
authors.initials: JE
authors.lastname: Bonilla
authors.forename: Sang M
authors.initials: SM
authors.lastname: Han
authors.forename: Sang Eon
authors.initials: SE
authors.lastname: Han