Chemical fluctuations in polycrystalline thin-films for photovoltaic devices

Chemical fluctuations in polycrystalline thin-films for photovoltaic devices

Within this project we investigate chemical fluctuations at the nanometre scale in polycrystalline Cu(In,Ga)Se2 and CuInS2 thin-flims used as absorber material in solar cells.

Secondary phase formation as well as chemical fluctuations such as impurity segregation at structural defects like grain boundaries can significantly affect the optoelectronical properties of photovoltaic materials. Within this project we investigate such chemical fluctuations at the nanometre scale in polycrystalline Cu(In,Ga)Se2 and CuInS2 thin-flims used as absorber material in solar cells. We apply combined scanning transmission electron microscopy (STEM) with energy dispersive X-ray spectroscopy (EDX) as well as correlated transmission Kikuchi diffraction (TKD) and atom probe tomography (APT).

Accumulation and diffusion of Na (green) along Cu depleted structural defects (blue) in epitaxial grown CuInSe2 films on GaAs substrate
Mechanistic description of In/Ga interdiffusion. STEM-BF image of a cross section from a Na2Se treated CuInSe2 film grown on GaAs substrate and corresponding Ga, In and Cu elemental maps.

Image quality maps from a TKD measurement of an APT needle and  corresponding unique color map showing a RHAGB (blue) and ∑3 TB (red). Na & C co-segregation as well as Cu enrichment (blue iso-concentration surface) at the RHAGB. Concentration profile across the RHAGB revealing an atomic redistribution.

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