Understanding the element/impurity redistribution and defects formation at the CIGS p-n junctions

The CdS/CIGS interface was investigated in the literature by several techniques such as energy dispersive x-ray spectroscopy (EDX) [5-7], x-ray photoelectron spectroscopy (XPS) [8], Auger electron spectroscopy (AES) [8], secondary ion mass spectrometry (SIMS) [8], and scanning Kelvin probe microscopy (SKPM) [9]. These studies showed that the buffer/absorber layer interface is in general intermixed.

3D APT elemental map highlighting the presence of the CdS/Cu(In,Ga)Se2 heterointerface and of a grain boundary in Cu(In,Ga)Se2 layer decorated by the Na impurity.

The CdS/CIGS interface was investigated in the literature by several techniques such as energy dispersive x-ray spectroscopy (EDX) [5-7], x-ray photoelectron spectroscopy (XPS) [8], Auger electron spectroscopy (AES) [8], secondary ion mass spectrometry (SIMS) [8], and scanning Kelvin probe microscopy (SKPM) [9]. These studies showed that the buffer/absorber layer interface is in general intermixed. Recently, we could clearly resolve a Cd-enriched/Cu,Ga-depleted zone of ~ 1 nm in thickness at the CIGS surface by using the laser-assisted atom probe tomography (APT) [11]. However, the conclusion of the previous study was that the APT results for this particular CIGS solar cell cannot be generally transferred to other CIGS solar cells, as different heat treatments of the CdS buffer layer might result in different compositional gradients at the CdS/CIGS interface.

Moreover, the recent studies performed by density functional theory (DFT) calculation [12, 13] took into account that the CIGS surface is depleted in Cu (Cu vacancies-VCu), but no study spoke about the Ga and Cu depleted CIGS surface. Therefore, the current project elucidates the element/impurity redistribution at the p-n junction and the interaction between these element/impurity and defects in this region. For a complete understanding of point defects in CIGS, first-principles calculation will be performed in this project.

References:

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