title: Graded-index structures for high-efficiency solar thermophotovoltaic emitting surfaces.
abstract: This Letter presents a highly efficient emitter structure for solar thermophotovoltaic systems. The structure consists of a graded index on tungsten, shows a spectral efficiency of 59%, or 70% with the use of a back reflector, and is compared to other state-of-the-art emitter structures. The effects of different structures and periodicities on the efficiency of the emitter are explored, as well as the effect of a protective oxide coating. The causes of the antireflection properties of these structures are also explored.
authors.forename: Craig
authors.initials: C
authors.lastname: Ungaro
authors.forename: Stephen K
authors.initials: SK
authors.lastname: Gray
authors.forename: Mool C
authors.initials: MC
authors.lastname: Gupta