Designed Copper Selenide Nanotubes as Counter Electrodes of Quantum-Dot-Sensitized Solar Cells

Description

1st Paragraph:  Copper chalcogenide nanostructures have been the focus of interest because of their unique properties and great potential in various applications. Among them, copper chalcogenide nanotubes (NTs) have been the subject of extensive studies not only because their electronic structures and properties can be engineered over a broad range for diverse applications such as photodetectors,[1, 2] photovoltaics,[3] and electronics,[4] but also because their unique morphology consists of internal tubes and external nanostructures to form a large surface area, which enables them to be good electron transporters and show better performance than that of solid analogues.[5] For example, counter electrodes (CEs) made from Cu_2-xSe NTs and Cu_2-xS NTs boost the conversion efficiency of quantum-dot-sensitized solar cells (QDSSCs), due to their unique structures and properties. More specifically, the nanotube structure provides larger surface area for adsorption of polysulfide electrolyte (i.e., providing more catalytic sites) than bulk metal electrode.[6] Compared with the binary copper selenide, ternary cooper silver selenide (CuAgSe) has high mobility from both Cu⁺ and Ag⁺ ions, and displays better performance than binary Ag₂Se or Cu₂Se in electrochemical devices.[7-9] This material was initially reported in the 1950s,[10, 11] and has been rarely studied owing to relatively difficulties in synthesis, especially for the preparation of nanostructures. Ternary CuAgSe is conventionally synthesized by heating a mixture of Ag, Cu, and Se powder to over 1000 K with several heating and cooling steps.[12, 13] Thin CuAgSe films can be prepared by the electrodeposition method.[14] The crystal size of the products generated by these methods is quite large and uncontrollable, and recent advances in nanofabrication have led to new insights into the preparation and application of ternary CuAgSe nanostructures. For example, surfactant-free CuAgSe nanoparticles were prepared on a large scale to show the temperature-dependent reversible transition of metallic n–p conductivity, and great potential in converting heat into electricity through the Seebeck effect.[15] Both dendritic and tubular CuAgSe were prepared from Ag₂Se/Ag or Ag₂Se/Se templates,[7, 16] but it was time consuming and difficult to avoid Ag or Se in the final products. Thus, a facile and efficient method for the synthesis of ternary CuAgSe nanomaterials with well-defined composition and architecture is desirable.

Authors: Xinqi Chen, Jianping Yang, Ming Xiao, and Wei Dai

Keywords: Copper Selenide, Nanotubes, Semiconductors, Room-Temperature Synthesis, Counter Electrodes