Highly Efficient Copper–Zinc–Tin–Selenide (CZTSe) Solar Cells by Electrodeposition

Highly efficient copper–zinc–tin–selenide (Cu 2 ZnSnSe 4 ; CZTSe) thin‐film solar cells are prepared via the electrodepostion technique. A metallic alloy precursor (CZT) film with a Cu‐poor, Zn‐rich composition is directly deposited from a single aqueous bath under a constant current, and the precursor film is converted to CZTSe by annealing under a Se atmosphere at temperatures ranging from 400 °C to 600 °C. The crystallization of CZTSe starts at 400 °C and is completed at 500 °C, while crystal growth continues at higher temperatures. Owing to compromises between enhanced crystallinity and poor physical properties, CZTSe thin films annealed at 550 °C exhibit the best and most‐stable device performances, reaching up to 8.0 % active efficiency; among the highest efficiencies for CZTSe thin‐film solar cells prepared by electrodeposition. Further analysis of the electronic properties and a comparison with another state‐of‐the‐art device prepared from a hydrazine‐based solution, suggests that the conversion efficiency can be further improved by optimizing parameters such as film thickness, antireflection coating, MoSe 2 formation, and p–n junction properties.