Study On CuInSe₂-Class Photovoltaic Powders

CuInSe₂-Class material is one of the most promising materials for absorberlayers for thin film solar cell, due to high absorption coefficient and stability.Mechanical alloying （MA） is expected to produce CuInSe₂-Class powders withlow cost, owing to its simplicity of operation and high yield.CuInSe₂-Class powder materials including CuInSe₂, CuIn(S_0.5Se_0.5)₂andCuIn_{（1-x）}AlxSe₂, are prepared by a planetary ball mill, using elemental aluminum,copper, indium, selenium, and sulfur powders as raw materials. The effectmilling parameters and the content of raw materials on synthesis ofCuInSe₂-Class powders are studied, and mechanical alloying process ofCu-In-S-Se and Cu-In-Al-Se systems are analyzed. The milled powders arecharacterized by X-ray diffraction （XRD）, scanning electron microscope （SEM）,transmission electron microscopy （TEM）, and energy dispersive spectroscopy（EDS） and laser particle size analyzer. The main conclusions as following:Rotating speed of the grinding ball and fill coefficients have an importanteffect on the incubation and the composition of products synthetized byMechanical alloying from Cu/1.2In/2.3Se powders. Along with the increase ofrotating speed, the incubation period shortens, and the deviation in chemicalcomposition of products decreases first and then increases; Along with theincrease of filling coefficient, the incubation period extends, and the deviation inchemical composition of products decreases first and then increases. When therotating speed of grinding is500rpm, the filling coefficient is20.25%, nearstoichiometric nanocrystalline CuInSe₂powders can be prepared, and theircomposition Cu/In/Se atom is25.24/25.16/49.60. That CuInSe₂powders aremilled for another2hours, the particle size distribution is concentrated in2.5¹0μm and the grain size is20.2nm.Mechanism of the CuIn(S_0.5Se_0.5)₂powders synthesized by Mechanicalalloying is mechanically induced self-propagating reaction. Beforeself-propagating reaction, the process corresponding to mechanical activation ofmixed powders, and composite particles forming with a finer layer structure, elements of critical powders are nanocrystalline or amorphous. When themilling ball in similar size, the difference of activities of critical powders mainlycome from powder surface energy. When induced self-propagating reactionfinishes, synthetic CuIn(S_0.5Se_0.5)2powders have already been nanocrystalline.With the increase of milling ball diameter, the residual of indium decreases.When x≤0.4, mechanism of CuIn（1-x）AlxSe₂powders synthesized byMechanical alloying is mechanically induced self-propagating reaction; Alongwith the increase of content of Al, incubation period extends, the grain size ofsynthetic Cu（In, Al） Se₂powders reducts. When x≥0.45, mechanically inducedself-propagating reaction of Cu-In-Al-Se systems can not happened.