Study On CuInSe₂ And Similar Photovoltaic Powders Prepared By Mechanical Alloying

Solar energy is the most important one in kinds of renewable energy, and it is also the clear energy for human being's application. In recent years, solar photovoltaic power generation is the most promising area of solar energy applications.CuInSe2 thin film solar cells gets more attention than traditional silicon solar cells due to their high photoelectric conversion efficiencies, excellent stability under solar radiation and long operational lifetime.It can reduce the costs of solar cells by adding some Al or S in CuInSe2 material to replace valuable In or toxic Se partly. Moreover, it can adjust the band gap of CuInSe2 materials to enable them to use solar radiation effectively.Currently, most of the CuInSe2 and similar photovoltaic materials are prepared in high temperature under high vacuum conditions, which usually take a long time and cost a lot. In this paper, chalcopyrite CuInSe2,Cu(In,Al)Se2,CuIn(S,Se)2 and Cu(In,Al)(S,Se)2 compounds have been prepared from cupper, indium, aluminium, sulfur and selenium by mechanical alloying (MA). The structure, morphology and composition of obtained photovoltaic powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The paper studied on the following aspects:Cupper, indium and selenium mixture powders were grinding or milling by three different MA methods, which were grinding, rotary ball milling and planetary ball milling, respectively. It was found that chalcopyrite CuInSe2 can be synthesized by grinding and planetary ball milling. The MA process of Cu-In-Se system has been researched. It shows that mechanically induced self-sustaining reactions (MSR) occurred in MA. HRTEM analysis indicates that the red smog collected during MSR was volatile selenium particle. A series ball milling parameters such as rotational speed, ball-to-powder weight ratio, milling periods have been studied systematically on the Cu-In-Se systems. Near stoichiometric chalcopyrite CuInSe2 powder can be synthesized by MA. The particle size of the products was in the range of 100 nm-3μm.Cu(In,Al)Se2 and CuIn(S,Se)2 powders with different amounts of Al and S have also been synthesized by MA. The relationship between lattice constants of Cu(In,Al)Se2 and Al content, CuIn(S,Se)2 and S content were studied by XRD. It shows that the lattice constants of Cu(In,Al)Se2 and CuIn(S,Se)2 decrease as Al and S increase, respectively. The powders have also been compressed into small tablets to detect their electrical properties. The resistivity of Cu(In,Al)Se2 and CuIn(S,Se)2 has been detected by four probes equipment. It shows that the resistivity of Cu(In,Al)Se2 and CuIn(S,Se)2 increasing as the Al and S content increasing. All the samples were p-type conductors.The reaction mechanism about MSR which occurred during preparing CuInSe2 photovoltaic materials was discussed. Thermodynamics calculations and MSR criterion: (?)analysis of Cu-In-Se and Cu-In-S systems has shown that the reactions of Cu-In-Se and Cu-In-S system satisfy the thermodynamic criterion of MSR, which can explain the experimental phenomena occurred in these systems well.At last, CuInSe2 powders were applied in vacuum evaporation and the particle deposition process. The CuInSe2 thin films deposited by vacuum evaporation were near stoichiometric with high optical absorption coefficiencies, nearly about 105 cm-1.