Photovoltaic energy is a promising source of renewable and sustainable power, but developing efficient, stable, and low-cost solar cells remains a challenge. Chalcogenide materials, such as CuInS₂, are attractive candidates due to their high light absorption, suitable band gaps, and good stability. However, their development has stalled for nearly three decades since achieving 12.2% efficiency in high-temperature-processed devices in 1996.

In a study published in Joule, Prof. WANG Mingtai's team from Hefei Institutes of Physical Science of the Chinese Academy of Sciences developed a low-temperature solution-processing strategy for fabricating CuInS₂ thin-film solar cells, and achieved a CuInS₂ solar cell with an efficiency up to 12.28%.

Researchers developed a low-temperature solution-processing strategy. They designed an interdigitation architecture in an indium-rich CuInS₂ absorber layer at temperatures below 300 °C, overcoming the limitations of bilayer structures caused by short charge diffusion lengths, and enhancing both photon absorption and charge generation.

In addition, researchers introduced a sulfur anion-induced gradient phase transformation (S^2--GPT) process at 180 °C, effectively reducing shallow- and deep-level defects to reduce non-radiative recombination, and creating an internal electric field that improves the transport of photogenerated charges.

The CuInS₂ solar cell reached an efficiency of 12.28% and an open-circuit voltage of 0.83 V, indicating a strong power-generating capability. Even without encapsulation, the device retained 86.3% of its initial efficiency after 500 days under ambient conditions, demonstrating that low-temperature processing can produce both efficient and durable solar cells.

This study offers a promising way to chalcogenide solar cells and the application of CuInS₂ devices, providing a promising alternative to perovskite solar cells.

CuInS₂ thin-film solar cell fabricated by low-temperature solution-processing strategy delivers new records of efficiency and open-circuit voltage. (Image by ZHANG Chaofan)