Metal sulfides with moderate band gaps are desired for efficient generation of electricity or fuels from sunlight via photovoltaic or photoelectrochemical energy conversion. Bi2S3, with a direct optical band gap of 1.3 eV, has been commonly synthesized by successive ion layer adsorption and reaction (SILAR) to produce quantum dots or nanocrystalline films. Annealing of the solution-processed Bi2S3 nanocrystals has been attempted at temperatures lower than 300 °C or in air. The low-temperature processing may not lead to highly crystalline Bi2S3, and air annealing is likely to cause oxidation of Bi2S3. Here, we report a bulk crystalline Bi2S3 photoelectrode synthesized by high-temperature annealing of the solution-processed nanocrystalline films in a sulfur vapor environment, which simultaneously improves the crystallinity of Bi2S3 and prevents the material from oxidation. The bulk crystalline Bi2S3 film exhibits greatly enhanced light absorption (ηabs) and charge separation (ηsep) efficiencies compared to the nanocrystalline film. Furthermore, photoelectrochemical measurements show that Bi2S3 demonstrates significantly larger photocurrent by either pre-treating the material with aqueous Na2S solution or by directly measuring the material in an electrolyte containing Na2S. X-ray photoelectron spectroscopy analysis shows that the sulfide ions displace anionic surface impurities and passivate defect states of Bi2S3 that form during the synthesis and the photoelectrochemical measurement. These results indicate that sulfur vapor annealing and sulfide surface treatment can improve the optoelectronic performance of Bi2S3 for solar-electricity or solar-chemical energy conversion processes.

Tailored annealing and surface treatment of Bi2S3 thin film to enhance optoelectronic performance

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.