Abstract
In a single-bandgap absorber, photons having energy less than the bandgap are not absorbed, while those having energy larger than the bandgap lose the excess energy via thermalization. We present outdoor measurements of a photovoltaic system that overcomes these losses via spectrum splitting and concentration using a planar diffractive optic. The system was comprised of the diffractive optic coupled with GaInP and CIGS solar cells. The optic provides a geometric concentration of 3X for each solar cell. It is easily fabricated by single-step grayscale lithography and it is ultra-thin with a maximum thickness of only 2.5μm. Electrical measurements under direct sunlight demonstrated an increase of ∼25% in total output power compared to the reference case without spectrum splitting and concentration. Since different bandgaps are in the same plane, the proposed photovoltaic system successfully circumvents the lattice-matching and current-matching issues in conventional tandem multi-junction solar cells. This system is also tolerant to solar spectrum variation and fill-factor degradation of constitutive solar cells.
Highlights
Despite the wide spectral content of sunlight, efficiency of single-junction solar cells is limited due to thermalization and nonabsorption losses.[1,2] Photons that have energy below the bandgap of the absorber are not absorbed
We show that one can increase the output power from a photovoltaic device by spectrally separating sunlight into two bands and concentrating these bands onto two single-junction solar cells positioned in the same plane via a broadband, planar diffractive optic
Such configuration successfully circumvents the issues of current- and lattice-matching present in traditional multijunction photovoltaics
Summary
Despite the wide spectral content of sunlight (with most of the power in the range of ∼350 nm to ∼2000 nm), efficiency of single-junction solar cells is limited due to thermalization and nonabsorption losses.[1,2] Photons that have energy below the bandgap of the absorber are not absorbed. This is termed as the non-absorption loss. As far as we are aware, this is the first demonstration of efficient diffractive spectrum-splitting and concentration under ambient sunlight resulting in an increase in the overall PV power output
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