The future of solar energy might not depend on rare metals at all.
Researchers at the Chinese Academy of Sciences have achieved a world-record power conversion efficiency of 15.45% with a kesterite solar cell — smashing the previous record of 14.2% that the same team set in 2024.
Why does this matter? Because kesterite is made from copper, zinc, tin, and sulfur — four of the most abundant, cheapest, and least toxic materials on Earth. No rare earth metals. No supply chain bottlenecks. No geopolitical drama.
Traditional high-efficiency thin-film solar cells rely on materials like CIGS (copper indium gallium selenide), which deliver impressive performance but face looming supply constraints. Kesterite has long been seen as the democratic alternative — a solar material that any country could source locally — but defects formed during manufacturing have kept its efficiency stubbornly low.
Until now.
The breakthrough came from solving what the team calls 'uncontrollable metal ion migration' — a core technical challenge where mobile ions swap positions within the crystal lattice, creating defects that tank efficiency and long-term stability.
The CAS team developed an ingenious solution: an interphase layer based on a lithium tin sulfide compound called Li₂SnS₃ (LTS). This layer modifies how copper and tin ions migrate through the cell, balancing their movement and stabilising the crucial junction where electricity is generated.
The result? Not just higher efficiency, but better stability — a cell that maintains its performance over time rather than gradually degrading.
The internationally certified third-party efficiency came in at 15.04%, confirming the breakthrough is real and reproducible.
'This paves the way for the industrialisation of next-generation solar cells,' the researchers stated. And they're not exaggerating — the jump from 14.2% to 15.45% represents a significant leap in a field where gains are typically measured in fractions of a percent.
While kesterite cells still lag behind silicon (which dominates at 26%+) and cutting-edge perovskites, they offer something no other technology can match: a completely sustainable supply chain using materials that will never run out.
Imagine a world where solar panels can be manufactured anywhere, from locally sourced materials, without depending on mining operations in politically unstable regions. That's the promise of kesterite — and this record-breaking result brings it meaningfully closer to reality. ☀️