The Chinese Academy of Sciences (CAS) has fabricated a kesterite (CZTSSe) solar cell that achieved a world record power conversion efficiency of 15.45% and a certified efficiency of 15.04%.
Kesterite is one of the most promising light absorber material candidates for potential use in lower-cost thin-film solar cells. Kesterites include common elements such as copper, tin, zinc, and selenium. Unlike CIGS compounds, there are no supply bottlenecks expected in the future. However, kesterite is still less efficient than CIGS in mass production.
Before this latest result, the world record for kesterite cells stood at 14.2%, achieved for lab-scale devices by the same CAS in June 2024.
The researchers addressed a persistent challenge in CZTSSe devices – uncontrollable metal ion migration. This occurs when mobile ions, including copper, tin, and zinc, swap positions within the lattice, creating defects that act as recombination centers and reduce efficiency. Under an electric field, these ions can migrate to interfaces or grain boundaries, causing hysteresis in the current–voltage behavior and gradual performance degradation. Migrating ions may also react with other layers, forming secondary phases that compromise stability and long-term reliability.
To tackle this, the scientists proposed a new strategy based on interfacial phase equilibrium. They developed a interphase based on a lithium tin sulfide compound known as Li₂SnS₃ (LTS), which modifies cation migration paths and controls the movement of mobile ions. This interphase balances differences in copper and tin migration, reduces antisite defects, and stabilizes the cell junction, improving both efficiency and long-term device reliability.
“The LTS interphase selectively encapsulates CTSSe intermediate grains, thereby becoming the rate-determining layer for ion migration,” the academics explained. “The difference in migration barriers between zinc and tin is reduced from 0.41 eV in CTSSe to 0.21 eV in the LTS interphase. By slowing down reaction kinetics, the LTS interphase enables more controlled grain growth, thus promoting the formation of larger and more uniform grains. This significantly reduces deep-level defects and improves overall crystalline quality.”
Tested under standard illumination condition, the cell achieved an efficiency of 15.45% and an open-circuit voltage exceeding 600 mV at a bandgap of 1.10 eV, which is described as an exceptionally high voltage for kesterite. An undisclosed third party certified an efficiency of 15.04%.
“This breakthrough has led to the creation of an intellectual property portfolio covering the entire LTS process, thereby providing theoretical and technical support for the industrialization of CZTSSe solar cells,” the research team stated.
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