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Extremely thin solar absorbers

Martijn de Sterke

IPOS Institute of Photonics and Optical Science

› Current photovoltaics based on silicon, but

- Silicon is expensive to extract and to process

- Poor absorption (indirect bandgap); excellent electronic properties

› Possible alternative: “earth-abundant materials” eg FeS2, CuO2

- Good absorbers; poor electronic properties (short diffusion length)

- Get around this by Extremely Thin Absorbers (10’s of nanometers), which yet need to absorb strongly

› Standard solution: highly convoluted surface, but large surface area and associated recombination

ETAs

ETAs (cont’d)

› Our approach (Catchpole & de Sterke + White, McP, Botten)- Evanescent field enhancement—evanescent fields not subject to

energy conservation- Plasmonic enhancement in metals (been rarely used in solar cells)- Dielectric enhancement via evanescent grating orders

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Possible geometries

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Scale bars are 1 μm

Tools

› Electron beam lithography› Nanoimprinting› Nanoparticle fabrication› Deposition and etching › PL› High-resolution microscopy

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all in unusual materials

Outlook

› Growing area with strong societal demand› Two very strong groups already in this area (UNSW and ANU)

+ much other work elsewhere › But on the other hand

- Solutions seem to require excellent theory/modeling expertise- Funding from multiple sources available (cf Mary O’Kane’s

comments at 2011 IPOS workshop)

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