Solving the efficiency challenge in kesterite and other emerging earth-abundant solar cells

For more than two decades, kesterite solar cells (made from copper, zinc, tin and sulfur/selenium) have promised a sustainable alternative to other emerging thin-film photovoltaics. They’re non-toxic, earth-abundant, and compatible with low-cost manufacturing. Yet despite their strong theoretical potential, kesterite devices remained stalled below 13% efficiency for many years.

Kesterite’s complex chemical structure, Cu₂ZnSn(S,Se)₄ (CZTSSe), makes it versatile but also prone to defect formation during material fabrication. Overcoming this efficiency bottleneck has been one of the most persistent challenges in emerging photovoltaic research.

A major breakthrough is now reported in Nature Energy (2026) in the Review article “Formation pathway of high-efficiency kesterite solar cells fabricated through molecular ink chemistry”, authored by an international team including Scientia Professor Xiaojing Hao (UNSW) (corresponding author) and Dr Kaiwen Sun, alongside collaborators from leading research institutes in Europe and Asia. The work synthesises more than a decade of experimental insight and establishes a unifying framework that directly links precursor chemistry, reaction pathways and defect formation to device performance.

At the heart of this advance is precise control of the kesterite formation pathway using molecular ink chemistry, instead of relying on traditional vacuum-based fabrication methods. The review demonstrates that managing oxidation states, molecular coordination and phase evolution during synthesis prevents kinetically trapped defects that previously limited performance.

By engineering these pathways, kesterite solar cells have now surpassed 15% power conversion efficiency, a milestone that repositions the technology as a credible, scalable alternative to less sustainable thin-film options.

Professor Hao and her team at UNSW have played a leading role in this progress, building sustained expertise in kesterite materials, defect physics and solution-processed photovoltaics. This leadership has been strongly supported by the Australian Centre for Advanced Photovoltaics (ACAP) and its collaborative model that enables close integration between materials science, device engineering and advanced characterisation. ACAP-supported research has helped translate fundamental chemistry insights into reproducible, high-performance devices, while fostering international collaboration across academia and industry.

Published in Nature Energy, the work shows how carefully controlling the chemistry during fabrication — using solution-based “molecular ink” methods — prevents defects and improves kesterite solar cell performance.

Beyond kesterites, the framework outlined in this Nature Energy publication provides a roadmap for other complex semiconductors, reinforcing Australia’s role in shaping the future of sustainable solar technologies.

Reference: 

Jimenez-Arguijo, A., Gong, Y., Caño, I. et al. Formation pathway of high-efficiency kesterite solar cells fabricated through molecular ink chemistry. Nat Energy (2026). https://doi.org/10.1038/s41560-025-01900-y