Fabrication of Wide Bandgap Chalcopyrite Photovoltaics at Low Temperatures for Prospective Tandem Solar Cells

Adapting photovoltaics as a reliable renewable energy source, advanced technological solutions must be brought at the cell level.

The power conversion efficiency targets must be higher than the currently available commercial single-junction solar cells of silicon (Si) or low-bandgap copper indium gallium selenide (CIGSe).

The efficiency of photovoltaics can be increased by joining two cells in a single stack (top/bottom) called a tandem solar cell.

Such a configuration needs a wide bandgap solar cell to be joined atop the commercial low bandgap Si or CIGSe photovoltaics. This project aims to develop such a wide-bandgap thin-film solar cell.

By careful compositional engineering, silver (Ag) will be substituted for a fraction of copper (Cu) in sulfur-rich CIGS to yield wide bandgap (1.65-1.7 eV) ACIGS absorbers.

Ag substitution is expected to reduce the melting point of the resulting absorber (ACIGS), thus allowing its deposition at relatively low temperatures. This provision eliminates the bottom cell damage while adapting ACIGS as a top cell in a tandem configuration. The project also investigates defects in ACIGS and their mitigation by implementing adequate passivation strategies.

The solar cell device architecture will be tailored to yield high open-circuit voltages reducing the non-radiative losses across the absorber/buffer layer interface.

Drift-diffusion simulations will be carried out connecting the materials properties, defects, and recombination mechanisms with the observed experimental results.

The small-scale ACIGS devices fabricated in the laboratory will be scaled up at the industry partner fabricating mini-modules.

The expected project results have the potential to be a major milestone in the development of tandem PV and to be readily exploited in industry.