Harnessing Hydrogen: Breaking Efficiency Barriers in Kesterite Solar Cells

In the quest for sustainable and cost-effective solar technologies, the advancement of photovoltaics (PVs) has been essential in harnessing sunlight to generate electricity. Engineers and researchers worldwide are tirelessly working to discover new materials and methods to enhance the power conversion efficiencies (PCEs) of solar cells while simultaneously cutting costs. A recent breakthrough using a hydrogen annealing approach has set a new efficiency record for kesterite solar cells, marking a significant stride forward in renewable energy technology.

Kesterite Cu₂ZnSnS₄ (CZTS) stands out as a promising material for solar technology due to its wide bandgap, environmentally benign nature, and the abundance of its components in the Earth’s crust. Unlike silicon, which currently dominates the PV market, CZTS offers a more sustainable and potentially more affordable alternative. However, the widespread adoption of CZTS has been historically limited by lower efficiency rates, previously capped at around 11%, due primarily to carrier recombination—an undesirable process where paired photo-generated electrons and holes recombine before contributing to the electrical output.

Researchers from the University of New South Wales, Sydney, have investigated a solution through hydrogen annealing—a process that involves heating the material in a hydrogen-rich environment. Their study, published in Nature Energy, reveals that this technique significantly enhances carrier collection in CZTS solar cells by redistributing sodium and promoting the passivation of defects near the absorber surface.

Employing this method, the researchers successfully built a cadmium-free CZTS solar cell that achieved a record efficiency of 11.4%. This technique not only improves the efficiency of CZTS cells but is also scalable, with the potential to enhance performance in other thin-film solar materials, such as Copper Indium Gallium Selenide (CIGS). The study highlights the strategic use of hydrogen to alter material properties, making CZTS more suitable as the top cell in tandem solar cell architectures, which pairs CZTS with silicon to utilize a broader spectrum of sunlight.

Senior author, Kaiwen Sun, emphasized the enormous potential of hydrogen annealing in expanding the utility of CZTS in solar energy solutions by improving the material’s optoelectronic properties. The team remains optimistic about further increasing the efficiency, with a target benchmark of 15%, while maintaining the environmental and economic advantages.

Key Takeaways:

• Hydrogen annealing raises kesterite Cu₂ZnSnS₄ (CZTS) solar cell efficiency to a record 11.4%.
• This technique enhances sodium distribution and reduces defects, leading to improved carrier collection.
• CZTS, with its earth-abundant and non-toxic elements, serves as a sustainable alternative to silicon in tandem solar cell designs.
• The scalable method has potential applications in other thin-film solar technologies, enabling a broader commercial deployment of efficient, sustainable solar energy solutions.

This advancement marks a significant leap in the journey toward more sustainable and accessible renewable energy technologies, positioning CZTS as a crucial component in future solar power systems.