Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
Publication date: 22nd December 2022
Copper-based oxides (CuxBiyOz) suffer from the phenomenon of photocorrosion (leading to self-oxidation or self-reduction) and insufficient light absorption, which limits their usage and long-term durability for different applications. An alternative to overcome these limitations is copper-based chalcogenide, such as copper-bismuth chalcogenides (i.e., Cu-Bi-S), which has been explored as a promising material for solar energy conversion. Recently, devices based on wittichenite-type (Cu3BiS3) compound has spurred interest for photovoltaics and water splitting application[1,2], due to its favorable optoelectronic properties, such as p-type conductivity and direct band gap (Eg ≈ 1.10–1.86 eV) with high optical absorption coefficient (>105 cm) in the visible region[3]. The aforementioned properties imply that the CuxBiySz could be suitable for different applications, however, CBS is still largely unexplored as photo absorber in photovoltaic devices (maximum 1.281% PEC)[4] and as a semiconductor/photocatalyst. This is largely due to the lack of control over different Cu-Bi-S phases, such as Cu3BiS3 and CuBi3S5, for which the stability domains are quite narrow in the phase diagram. In this work, we obtain CBS phases by sulfurization of CuxBiyOz (CBO) precursor films, with varying Cu:Bi stoichiometry (1:3, 3:1) in the optimized temperature range (350-425oC). The films were characterized by SEM, RAMAN, XRD, optical absorption spectroscopy. XPS studies were performed in order to identify the stoichiometry and oxidation states of the 3:1 and 1:3 (Cu:Bi) precursor sulfurized at the best temperature condition. The results confirmed the total conversion of CBO to CBS. Although mixed phases were identified for both Cu:Bi ratio at different sulfurization temperature, 3:1 (Cu:Bi) precursor film sulfurized at 350oC yields Cu3BiS3 single phase, which is corroborated by Raman peaks at 279 and 470 cm-1 corresponding to Cu3BiS3 phase. Sulfurization of 1:3 (Cu:Bi) precursor film at 425oC leads to CuBi3S5 phase; while at 350oC both Cu3BiS3 and CuBi3S5 phases are observed, however, Cu3BiS3 is more evident, which is in agreement with Raman. Optical measurements showed that 1:3 and 3:1 (Cu:Bi) precursor sulfurized at 350oC presented similar Eg (1.61 and 1.54 eV, respectively); while 1:3 sulfurized at 425oC has low Eg (1.0 eV), indicating that the presence of CuBi3S5 phase decreases the band gap energy. Band-edges from XPS results confirmed that CBS is promising for different applications.
The authors are grateful to the Hasselt University, EnergyVille 2, the IMO-IMOMEC Institute and IMEC for the infrastructure. The authors also acknowledge the support of the Synergetic design of catalytic materials for integrated photo-and electrochemical CO2 conversion processes (SYN-CAT) project.
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