SITA featured on Solar RRL

SITA was featured on Solar RRL - a green energy journal covering all aspects of solar energy conversion, published by Wiley.

The work published evaluates In2O3:W as a transparent back contact material in wide-gap (Ag,Cu)(In,Ga)Se2 solar cells for potential application as a top cell in a tandem device.

Jan Keller, first author, explains that “Unlike the best perovskite materials, wide-gap chalcopyrite absorbers suffer from short minority carrier lifetimes, leading to low diffusion lengths. This makes carrier collection at rear illumination really challenging.

In this work we tuned the absorber composition in a way that its doping density is substantially decreased (almost intrinsic), leading to a spread of the space charge region across the entire (Ag,Cu)(In,Ga)Se2 layer. When carriers are moving in an electric field, we no longer talk about the diffusion, but about the drift length, which is (or can be) significantly higher than the diffusion length. This strategy allowed us to reach rather high Jsc values at rear illumination (~60-66% cf. front illumination), despite a very low diffusion length < 300 nm.”

Cross-section SEM images of the sample with a 400 nm- (top, run 1) and with a 1 μm-thick (bottom, run 4) ACIGS absorber. The scale bar refers to both images.

Depth profiles of the AAC and GGI ratios as determined by GDOES (quantified according to integral XRF-deduced compositions). The normalized sodium and oxygen profiles are shown, too. An adequate quantification of the absorber composition can only be provided for sputter depths, at which the GDOES signal does not contain elements from different layers/phases at the surface and back interface (white area).

a) STEM bright-field image of the complete device with a 400 nm-thick absorber (run 1) as well as higher magnified b) bright-field and as c) dark-field images of the corresponding back contact region.

Read publication: Bifacial Wide‐Gap (Ag,Cu)(In,Ga)Se2 Solar Cell with 13.6% Efficiency Using In2O3:W as a Back Contact Material (wiley.com)

The consortium is actively working towards developing chalcogenide solar cells with high performance and transparency for use as top cells in tandem solar cells.