SUSTAINABLE INORGANIC NANOCRYSTALS FOR SOLAR ENERGY CONVERSION AND STORAGE APPLICATIONS

摘要

The ever-growing need for energy generation and storage applications demands development of materials with high performance and long term stability. Solar-based technologies are one of the major contributors towards meeting the energy needs. As compared to conventional silicon-based solar cells, thin film solar panels are light weight and flexible and are thus preferable for a variety of applications. In recent years, different phases of the copper-antimony-sulfide system, composed of sustainable and non- toxic elements, have been proposed as alternatives for CIGS in thin film solar cells. These materials have large absorption coefficient of over 10~5 cm~(-1) at visible wavelengths, which is comparable or higher than those for the CZTS and CIGS systems. Four major phases are known to exist in the Cu-Sb-S system, namely CuSbS2 (Chalcostibite), Cu12Sb4S13 (Tetrahedrite), Cu3SbS3 (Skinnerite) and Cu3SbS4 (Femitinite). All four phases are p-type semiconductors with band gap values between 0.5 and 2 eV. Of these phases, CuSbS2 has been investigated in some detail in view of its potential as a solar energy absorber for thin film solar cells because of its optimal band gap and large absorption coefficient. In conventional solid state synthesis these phases usually co-exist because of very narrow thermodynamic stability windows. Thus the selective synthesis of phase-pure nanocrystals of all four phases of Cu-Sb-S is challenging. By careful selection of metal and sulfide precursors and the experimental conditions, herein, we report on solution-based hot- injection methods for phase-pure synthesis of nanocrystals of all four phases - CuSbS2, Cu12Sb4S13, Cu3SbS3, and Cu3SbS4 along with detailed electronic structure calculations of these phases to assess their suitability for solar energy applications. In addition, investigations on 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.