Chemical linkage strategy yields 18.53% efficient solution-processed chalcopyrite solar cells

Solution-processed chalcopyrite solar cells have taken a step forward, with researchers reporting a precursor chemistry that produces high-purity copper indium gallium diselenide (Cu(In,Ga)Se2) thin films and devices reaching a champion power conversion efficiency of 18.53%, with a certified value of 17.53%.

The work, published in Nature Energy, addresses a long-standing problem in low-cost fabrication of chalcopyrite photovoltaics: controlling how the absorber layer crystallizes from solution while achieving the right elemental composition.

The team used simple metal salts and thiourea as precursors. The key innovation was introducing an acetate anion, which carries both hydrogen-bonding and coordination-bonding capabilities, into the precursor solution.

According to the study, this acetate-driven linkage builds a molecular network connecting copper–thiourea and indium or gallium complexes in the solution. That network facilitates controlled reactions and prevents the formation of undesired secondary phases during crystallization.

The coordination between gallium and the acetate anion also enables uniform and complete gallium alloying, yielding high-purity, single-phase Cu(In,Ga)Se2 films. Gallium distribution has historically been difficult to control in solution-processed chalcopyrites, making this a notable outcome.

The resulting solar cells achieved the reported 18.53% champion efficiency, certified at 17.53%, based on the absorbers produced with this chemical linkage strategy.

The authors argue that their findings show phase-pure multi-element chalcogenide materials can be achieved through rational and precise design of solution chemistry, rather than through more complex precursor systems.

Solution processing is attractive for chalcopyrite solar cells because of its potential to lower fabrication costs, but the field has struggled with controlling crystallization and achieving desirable composition. This study presents a molecular-level approach to both challenges using inexpensive starting materials.

Subject of Research: Solution chemistry for efficient chalcopyrite thin-film solar cells

Article Title: Chemical-linkage-regulated single-phase crystallization and uniform gallium alloying for efficient solution-processed chalcopyrite solar cells

Article References: Ma, C., Wu, K., Liu, X., Yan, W., Tao, W., Guo, H., Xiang, C., Li, X., Li, Y., Liu, Y., Cang, Y., Zhao, N., Wang, S., Huang, W., & Xin, H. (2026). Chemical-linkage-regulated single-phase crystallization and uniform gallium alloying for efficient solution-processed chalcopyrite solar cells. Nature Energy. https://doi.org/10.1038/s41560-026-02157-9

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02157-9

Keywords: chalcopyrite solar cells, Cu(In,Ga)Se2, solution processing, thin-film photovoltaics, gallium alloying, crystallization, precursor chemistry, thiourea, acetate anion, power conversion efficiency, Nature Energy, Chemical-linkage-regulated