In the race to push solar technology beyond the limits of silicon and the instability of perovskite, one such mineral has reentered the solar game. Kesterite is a compound of copper, zinc, tin, and sulfur (CZTS) that researchers are studying as a non-toxic, low-cost option for future solar cells, although it is still at laboratory stage.
UNSW reported a new kesterite record in January 2025
Researchers at the University of New South Wales (UNSW) in Australia, led by Scientia Professor Xiaojing Hao, say they have set a world record for high-bandgap kesterite solar cells, reaching 13.2% efficiency in a laboratory-scale cell, up from a plateau of around 11% since 2018. The secret to such performances is hydrogen. Two caveats apply. The peer-reviewed Nature Energy paper from the same project reports a certified 11.4%, and a Chinese Academy of Sciences team reported a certified efficiency of about 13.2% for pure-sulfide kesterite in the same journal in early 2025. Kesterite cells that also contain selenium have since reached 15.45% (15.04% certified) at the Chinese Academy of Sciences in February 2026.
The way in which researchers achieved the result was through hydrogen passivation, a fabrication technique that reduces the impact of the microscopic defects that typically plague CZTS cells. This is important as these defect cells have been decreasing the material’s efficiency making it problematic more than promising. Heat-treating the cell in a hydrogen-containing atmosphere helps it convert sunlight into electricity more efficiently than earlier cells of this type.
According to Professor Hao:“What we are trying to do is answer the question coming from the PV industry as to what the next generation of cells will be made of.”
Having said this, Kesterite has several advantages. Kesterite’s advantages tend to be as elemental as its composition, being made entirely from abundant, low-cost, and non-toxic materials, unlike perovskites, which often rely on lead-based compounds and suffer from stability issues. In contrast, UNSW describes CZTS as environmentally friendly, cost-effective to manufacture and known to maintain its performance over a long period.
Kesterite cells, with their higher bandgaps, are a candidate for stacking atop silicon cells in tandem panels that capture a broader spectrum of light, which is where researchers see its best use. UNSW describes it as a possible add-on or replacement for silicon-based panels.
Simulations in China and Malaysia suggest higher efficiency is possible
The joy about kesterite doesn’t stop in Sydney as a team of researchers in China and Malaysia also simulated an innovative CZTS solar cell design that incorporates a tungsten oxide (WO₃) buffer layer and a CZTSe back surface field (BSF). What resulted was a theoretical 29.3% efficiency, roughly double the best kesterite cells built so far. This comes from a computer-modeling study published in Energy Reports, not from a fabricated device, so it shows potential but does not prove that kesterite could outperform commercial silicon panels.
Part of the design replaces cadmium sulfide (CdS), a toxic and expensive material, with WO₃, which the authors describe as having a high bandgap and excellent electrical conductivity.
Kesterite: Not better, but smarter
What makes kesterite a truly compelling option is the fact that it shows a balance between sustainability and performance. Hao has said perovskite is “much less stable” and that its panels “might only last for one year”. CZTS, by contrast, is known to maintain its performance over a long period, according to UNSW. Its non-toxic composition is one reason researchers call it environmentally friendly.
Professor Hao further notes:
“Whereas with CZTS if we can get it to 20% efficiency then I think it will really take off because there are no other limitations since it meets all the criteria for the type of material we want to be using.”
The UNSW team expects CZTS to be commercialized by 2030, but that is the researchers’ own forecast, not a guarantee.
Kesterite is promising, but still in the lab
Albeit a dark horse, kesterite is still a laboratory material, not a commercial product. While kesterite may not be as flashy as perovskite, nor as big a solar statement as silicon, it combines low-cost, non-toxic ingredients and technical promise, which is why researchers keep working on it.
Kesterite has been studied for decades, with solar cells made from it reported since the late 1990s. The main obstacle has been defects created during manufacturing, which kept efficiency near 11% for six years until new methods reported in early 2025, including UNSW’s hydrogen treatment. As we questioned why we are still making flat solar panels, we should also ask why kesterite has taken so long to move from the laboratory to the market.
This article was first published on May 4, 2025, and was corrected on October 28, 2026, to remove inaccurate statements.
