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This makes CuGaSe₂ a promising candidate for next-generation, indium-free solar cell absorber layers.
Scientists at Japan’s National Institute of Advanced Industrial Science & Technology (AIST) have set a new efficiency record for copper gallium selenide (CuGaSe₂) solar cells, achieving a power conversion efficiency of 12.28%. 
CuGaSe₂ is a chalcogenide semiconductor in the chalcopyrite family, closely related to the more widely used copper indium gallium selenide (CIGS) materials. Its direct bandgap of roughly 1.68 eV allows it to efficiently absorb visible sunlight, enabling strong performance in solar energy conversion. 
This makes CuGaSe₂ a promising candidate for next-generation, indium-free solar cell absorber layers, while also underscoring the significant potential of wide-bandgap materials in high-performance, environmentally friendly photovoltaic applications worldwide.
The copper gallium selenide material used in the solar cell shows strong defect tolerance, helping to reduce charge carrier recombination and maintain high performance even when the crystal structure is not perfect, pv magazine reported.
According to the study’s lead author, Shogo Ishizuka, the achieved 12.28% efficiency represents the highest reported for wide-bandgap chalcogenide solar cells in the 1.65–1.75 eV range, particularly for indium-free chalcopyrite or CIGS-related solar cells. It surpasses previous records for CuGaSe₂-aluminum solar cells listed in the latest Efficiency Tables – Version 67, published by Progress in Photovoltaics.
The solar cell’s performance was independently verified by the Photovoltaic Calibration, Standards and Measurement Team at the Renewable Energy Advanced Research Center, AIST. Building on a previous design developed by AIST researchers in 2024, the device incorporates aluminum in the backside region of the CuGaSe₂ films. 
This modification enhances the cell’s open-circuit voltage, fill factor, and overall efficiency by creating a back-surface field (BSF) that improves minority carrier collection and reduces losses, enabling stronger overall performance.
The record-setting solar cell is based on a copper gallium selenide absorber grown through a precise three-stage process. Aluminum and rubidium fluoride are introduced during the first stage, with additional RbF added in the final stage to enhance the open-circuit voltage while maintaining high efficiency.
The cell is built on a soda-lime glass substrate with a molybdenum back contact. Above this sits the indium-free chalcopyrite absorber, followed by a 150-nm cadmium sulfide buffer layer, a zinc oxide window layer, and a metallic grid electrode. This carefully engineered layer structure helps maximize carrier collection and overall solar cell performance, pv magazine notes.
The scientists emphasized that their work focuses on fundamental research and development of wide-bandgap devices designed for top cells in tandem solar cells. Ishizuka explained that creating a full prototype would also require a compatible bottom cell and tandem technology, so the research is not yet ready for mass production. However, he added that a detailed cost assessment has not been carried out, as the project is still in the early stages of fundamental study.
Bojan Stojkovski is a freelance journalist based in Skopje, North Macedonia, covering foreign policy and technology for more than a decade. His work has appeared in Foreign Policy, ZDNet, and Nature.
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