Effect of Al content on the performance of Cu(In,Al)Se2 powders prepared by mechanochemical process

Cu(In,Al)Se2 (CIAS) powders with varying Al/(In+Al) ratios x (x=0, 0.15, 0.23, 0.38, 0.57) were synthesized by mechanochemical process (MCP). Composition, morphology of CIAS powders was investigated by energy dispersive analysis and scanning electron microscopy, respectively. Influence of Al content on structural and optical properties of CIAS was detected by X-ray diffraction and UV–Vis spectroscopy, respectively. The results show molecularity and stoichiometry deviation of composition were small. Particle aggregation and inhomogeneous distribution of Cu, In, Al and Se element is observed at early milling stage. Field emission transmission electron microscopy image confirms that the particles can be milled to several hundred nanometers. Chalcopyrite characteristic peaks of CuInSe2 are clearly observed. CIAS crystalline size decreases as Al2O3 increases in the products. CIAS (1 1 2) peaks shifts to high value and lattice constants for CIAS samples decrease with the Al additions. The band gap enlarged from 1.01 eV to 1.29 eV by adding Al. Al2O3 impurities impact CIAS powder grain size and the band gap seriously. All CIAS samples detected by hot probe method show the p-type conductivity.