A Uniform Residence Time Flow Cell for the Microreactor-Assisted Solution Deposition of CdS on an FTO-Glass Substrate

Photovoltaic cells have long been a desirable alternative to the consumption of fossil fuels, but current manufacturing practices suffer from poor energy efficiency, large carbon footprints, low material utilization, and high processing temperatures. A critical step in production of thin film CdTe and CuInSe 2 solar cells is the chemical bath deposition of a CdS thin film to serve as a “buffer layer” between the optically absorbent layer and the transparent conducting oxide. In prior work, functional CdS films were demonstrated at low temperature using a continuous flow, microreactor-assisted deposition process showing good selectivity of heterogeneous surface reactions over homogeneous bulk precipitation. In this paper, we develop a flow cell for implementing a uniform CdS film over a 152 mm substrate. Analytical models are coupled with computational fluid dynamic simulations to design a flow cell with more uniform flow fields. Experimental results demonstrate a 12% coefficient of variance for a 21.5 nm thick film.