Copper incorporation in Mn2+-doped Sn2S3 nanocrystals and the resultant structural, optical, and electrochemical characteristics

Sn2S3 nanocrystals (NCs) with both Mn2+ doping and Cu2+ incorporation were synthesized using a chemical bath deposition method. The Cu2+ ions formed an anorthic Mn2+-doped Cu2SnS3 structure with Eg = 1.44 eV, which altered the material's optical and photo/electrochemical properties. After coating the bare Nb2O5 electrode with Mn2+-doped Sn2S3 or Mn2+-doped Cu2SnS3 NCs, the photoluminescence spectrum was blue-shifted to 411.13 nm from 411.69 nm. Compared to the sample without Cu2+, the Cu2+-incorporated sample showed a slightly stronger emission at the same position, possibly due to disorder in the crystalline structure based on variations at the interface of Mn2+-doped Cu2SnS3 NCs. Electrochemical analysis showed a lower charge transfer resistance in the Mn2+-doped Cu2SnS3, which is related to its larger electroactive surface area. The larger electroactive surface area is attributed to the Faradaic redox processes at the electrode surface, which suppresses the carrier recombination. The coexistence of Cu2+ and Mn2+ ions shortened the electron transport pathway at the interface and improved the carrier diffusion coefficient and diffusion length, leading to a higher specific capacitance that implies higher energy storage performance. Finally, the I-V characteristics of the Mn2+-doped Cu2SnS3-coated Nb2O5 electrode under various light illumination conditions indicated its better efficiency in photoresponse, electron generation, and charge collection, owing to a superior charge transport mechanism. Detailed results were obtained about the charge dynamics in the as-prepared photo/electrochemical devices with Cu2+ incorporation in the Mn2+-doped SnS3 electrode.