Electrodeposition of selenium from 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate

Electrodeposition of Se films from air and water stable 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate ionic liquid was studied in open air conditions. The electrochemical behavior of H2SeO3 on gold and copper substrates was investigated in ionic liquid–water mixtures, and the influence of the deposition parameters such as time and bath temperature on the crystallinity of the film was examined. For the gold substrate, a reddish deposit containing amorphous, hexagonal and rhombohedral Se phases was identified at room temperature, while a grayish film of hexagonal and rhombohedral phases was formed at higher temperatures. The reddish Se film was found to exhibit a smoother surface with lower reflectivity in comparison to the grayish one. The band gap of the reddish film was close to that of pure amorphous red Se reported in literature, while the band gap of the grayish film was close to the pure hexagonal film. Photoelectron spectroscopy and energy dispersive X-ray spectroscopy show that both films consist of pure Se with only slight surface contaminations by remnants from the electrodeposition. In the case of a copper substrate, the electrodeposition of Se was accompanied by the formation of copper–selenide due to the reactivity of copper in H2SeO3.

► Using ionic liquid enables Se deposition under moderate conditions.
► The reddish Se film of amorphous, rhombohedral and hexagonal phases is deposited at 25 °C
► The grayish Se film of rhombohedral and hexagonal phases is deposited at a temperatures of ≥70 °C.
► The smooth reddish Se film showed lower absorption than the rough grayish one.
► Copper–selenides films are formed for the Se deposition on copper substrates.