Solvothermal Synthesis of Cu₃BiS₃ Enabled by Precursor Complexing

Abstract

Copper bismuth sulfide, Cu 3 BiS 3 , has been prepared by a solvothermal method that relies on precursor complexing to achieve the desired ternary chalcogenide preferentially over possible binary sulfides in the system. The complexing agent L-cystine also simultaneously donates sulfur to the compound when the complexes are dissociated at a single temperature. This low temperature and use of nitrate salts instead of the commonly employed but less "green" chloride salts provide a path toward cleaner methods. The reaction progression has been characterized by X-ray powder diffraction of sequential samples and shows complete reaction of reagents to form the Wittichenite phase. Spectroscopy analysis reveals confirmation of a direct bandgap at approximately 1.5 eV. Microscopy images reveal varying morphology dominated by nanorods and including particles with aspect ratios approaching 1:1. A low-temperature Cu 3 BiS 3 synthesis employing L-cystine as a sulfur source and complexing agent, nitrate salt precursors, and pure ethylene glycol has been demonstrated. ■ INTRODUCTIONIncreasing attention is being directed toward the development of alternative and earth-abundant semiconductors for photovoltaic and other optoelectronic applications. One promising class is the I−V−VI family that includes Cu 3 BiS 3 . Naturally occurring in the "Wittichenite" mineral form, 1 the compound is stable for a broad range of processing temperatures. 2,3 As such, various techniques have been employed to synthesize Cu 3 BiS 3 and other ternary sulfide films and nanostructures. Sputtering, 4−9 coevaporation, 10−12 and solid-state reactions 9,13,14 have been successful in producing stoichiometric compounds depending on the nature of the processes. Solution-based syntheses of both hydrothermal 15 and solvothermal 9,16−20 routes have been demonstrated with a range of precursors. While most rely on thermal heating to exceed the reaction threshold, microwave heating has also been demonstrated. 20 Solution-based synthesis of ternary chalcogenides also brings with it the risk of producing counterproductive binary compounds. Strong reducers are often employed to facilitate and expedite ternary syntheses, but their toxicity is a growing concern if any process is to be scaled for manufacturing. In a rising trend toward green synthesis, the employment of biological complexing agents has been successful. The use of L-cystine as a sulfur donator was demonstrated for Sb 2 S 3 , 17 and its use as a complexing agent for the ternary Cu 3 SbS 3 system followed quickly. 19 The Cu 3 BiS 3 morphologies produced in a similar fashion have resulted in varying morphologies, including dendrites, 14,20 rods, 21 and flower (or coral) like structures. 18,22 There remains until now a lack of Cu 3 BiS 3 synthesis employing a solvothermal system, L-cystine as a sulfur donator and a complexing agent, radiant heating, and nitrate salt precursors; this new and useful method is presented here. ■ EXPERIMENTAL SECTIONReagents. All chemicals in this work were used as obtained and in...

Copper—antimony and copper—bismuth chalcogenides—Research opportunities and review for solar photovoltaics

“…This is reported for CuSbS 2 (CuCl 2 -2H 2 O, potassium antimonyl tartratetrihydrate, elemental sulfur, and diethylenetriamine) 189 and Cu 3 BiS 3 (from nitrates and L-cystine). 190,191 This method is more often used for nanoparticles.…”

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Near-infrared photoactive Cu3BiS3 thin films by co-evaporation

“…Synthesis of Cu 3 BiS 3 involve the solution methods [5][6][7][8][9][10][11] and combining the chemical bath deposition 12 and sputtering process 13,14 besides Cu 3 BiS 3 thin films have a forbidden band gap of about 1.4 eV, an optimum for photo energy conversion. Co-evaporated thin films show good structural and optical properties.…”