Numerical analysis of non-uniform Cu(In, Ga)Se2 growth in a selenization process on large-area substrates for mass production

Abstract

Growth of a Cu(In, Ga)Se2 (CIGS) layer during a selenization process is numerically studied to understand mechanisms for formation of stains on large-area substrates batched. CIGS layers need to be uniformly deposited onto the substrates to obtain even conversion efficiency. However, it is difficult to control growth of large-area CIGS layers due to turbulent thermal-fluid flow leaving stains on the substrates. In the present research, the selenization process for an industrial-scale substrates of which sizes are order of square-meters is considered with integrated simulations of detailed key physical processes such turbulent convection, convective-radiative-conductive heat transfer, and chemical reactions. Ascending or descending gas generated by heaters is identified by the time-averaged velocity fields. Descending flow in the passages between substrates produces uneven flow rates across the substrates leading to inhomogeneous supply of heat energy and gas species to the surface chemical reactions. The uneven temperature distribution is the major cause for the stain formation on the substrates. Gross shapes of the stains are found to be well matched with the predicted velocity contour of gas flow above the substrate. The stains are expected to be alleviated by rectifying gas flow such that flow rates become uniform across substrates before entering the passages.