A microstructural and compositional analysis of CuInSe2 ingots grown by the vertical Bridgman technique

An in-depth microstructural study of CuInSe2 ingots grown by the vertical Bridgman technique has been carried out. Electron probe microanalysis (EPMA) has been used to analyse the matrix composition and second phase distribution as a function of distance along the Bridgman boule, By systematically varying the composition of the initial charge, we identified the optimum conditions for producing large regions of nearly stoichiometric single crystal CuInSe2, free from second phase inclusions. We found that additions of small amounts of excess copper aided the formation of the ''ideal'' crystal. Compositional variations along the length of the Bridgman boules have been identified and qualitatively explained in terms of the ternary composition field for the Cu, In, Se system. Furthermore, a number of characteristic second phases have been identified and their presence correlated with whether or not the initial charge was nominally stoichiometric, Cu-rich or In-rich. The effects of these second phases in terms of the microstructural defects they induce in the neighbouring CuInSe2 matrix has also been critically assessed.