Toward low-cost large-area CIGS thin film III: Effect of Se concentration on crystal growth and defect formation of sequentially electrodeposited CIGS thin films

• Se concentration affects the crystal growth and the defect formation of electrodeposited CIGS films.
• Pin holes and larger defect holes caused by grain growth and Cu2−ySe respectively are recognized.
• A growth model of In-rich whiskers grown in midair is suggested.

Nowadays, large area CuInxGa1−xSe2 (CIGS) thin film solar cells still face difficulties and challenges of the uniformity of composition and structure. This study illustrates how Se concentration affects the crystal growth and the defect formation of CIGS from low cost electrodeposited stacked Cu/In/Cu/Ga/Cu layers selenized in the rapid thermal process. Various crystal growth modes were observed in the film selenized with different Se concentrations. It was found that the crystal growth was strongly dependent on the Se concentration in the early stage of selenization between 250 and 350 °C, which can lead to variations of film composition and structure including a phase separation of CuGaSe2 from CuInSe2 and formation of defect holes in a CIGS film at a higher selenization temperature.

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