Ever growing need for energy generation and storage applications demands development of materials with high performance and long term stability. A wide variety of copper-based semiconducting chalcogenides have been investigated in recent years to address the need for sustainable solar cell materials. An attractive class of materials consisting of non-toxic and earth abundant elements is the copper-antimony-sulfides. The copper-antimony-sulfide system consists of four major phases, namely CuSbS2 (Chalcostibite), Cu12Sb4S13 (Tetrahedrite), Cu3SbS3 (Skinnerite) and Cu3SbS4 (Femitinite). All four phases are p-type semiconductors having energy band gap between 0.5 and 2 eV, with large absorption coefficient values over 105 cm-1. We have for the first time developed facile colloidal hot-injection methods for the phase-pure synthesis of nanocrystals of all four phases. Cu12Sb4S13 and Cu3SbS3 are found to have direct band gaps (1.6 eV and 1.4 eV, respectively), while the other two phases display indirect band gaps (1.1 eV and 1.2 eV for CuSbS2 and Cu3SbS4, respectively). The synthesis methods yield nanocrystals with distinct morphology for the different phases. In order to understand the optical and electrical properties, we have calculated the electronic structures of all four phases using the hybrid functional method (HSE 06) and PBE generalized gradient approximation to density functional theory. Consistent with experimental results, the calculations indicate that CuSbS2 and Cu3SbS4 are indirect band gap materials, but with somewhat higher band gap values of 1.6 and 2.5 eV, respectively. On the other hand, Cu3SbS3 is determined to be a direct band gap material with a gap of 1.5 eV. The absorption coefficient values at visible wavelengths for all the phases are estimated to range between 104 and 105 cm-1, confirming their potential for solar energy conversion applications. Exploring the use of these materials for supercapacitors have shown promising specific capacitance values with excellent cyclic stability. The unique properties of Cu-Sb-S nanocrystals make them attractive both for solar energy conversion and energy storage applications. The details of the synthesis methods, structural and optical characterizations, electrochemical measurements and band structure calculation will be presented and discussed.

Sustainable inorganic nanocrystals for solar energy conversion and storage applications

249th National Meeting (2015)

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