title: Increased photovoltaic power output via diffractive spectrum separation.
abstract: In this Letter, we report the preliminary demonstration of a new paradigm for photovoltaic power generation that utilizes a broadband diffractive-optical element (BDOE) to efficiently separate sunlight into laterally spaced spectral bands. These bands are then absorbed by single-junction photovoltaic cells, whose band gaps correspond to the incident spectral bands. We designed such BDOEs by utilizing a modified version of the direct-binary-search algorithm. Gray scale lithography was used to fabricate these multilevel optics. They were experimentally characterized with an overall optical efficiency of 70% over a wavelength range of 350-1100 nm, which was in excellent agreement with simulation predictions. Finally, two prototype devices were assembled: one with a pair of copper indium gallium selenide based photovoltaic devices, and another with GaAs and c-Si photovoltaic devices. These devices demonstrated an increase in output peak electrical power of ∼ 42% and ∼ 22%, respectively, under white-light illumination. Because of the optical versatility and manufacturability of the proposed BDOEs, the reported spectrum-splitting approach provides a new approach toward low-cost solar power.
authors.affiliation: Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Ganghun
authors.initials: G
authors.lastname: Kim
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Jose A
authors.initials: JA
authors.lastname: Dominguez-Caballero
authors.affiliation: Stion Corporation, San Jose, California 95119 USA.
authors.forename: Howard
authors.initials: H
authors.lastname: Lee
authors.affiliation: National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Friedman
authors.affiliation: Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Menon