Polycrystalline CuInSe2 thin films were deposited by a novel solution-based continuous flow microreactor (CFM) method at low temperature. In order to investigate the effect of the Cu to In mole ratio on the film formation, the concentrations of indium reagent were varied in the preparation of precursor solutions. The estimated optical band gaps were similar to 1.54 eV and similar to 1.25 eV for the as-deposited and the annealed CuInSe2 thin films which could be a result of quantum size effect. A tetragonal chalcopyrite structure of CuInSe2 was identified in XRD analysis. From the XRD analysis, it was found that the crystal growth of the as-deposited and the annealed films are affected by the molar concentration of indium reagents. The film deposited from a solution with 0.025 M of InCl3 shows the best crystallinity. The film thickness reaches around 2.5 mu m after only a 7 min of deposition time which will provide good throughput for thin film PV manufacturing. (C) 2010 Elsevier B. V. All rights reserved.