Cu(InGa)Se2solar cells on a flexible polymer web

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Abstract
Deposition of CuInGaSe2films on 6‐inch wide Mo coated polyimide web substrate in a roll‐to‐roll vapor deposition system from elemental sources is described. Material transport from the sources to the moving web substrate has been modeled by combining an evaporative effusion model and the gas flow kinetics and by experimentally determining the flux intensity profile. The model gives a reasonably good approximation of the Ga profile in the films. Poor adhesion of the selenide film to molybdenum has been resolved by depositing a thin layer of β‐(Ga0.8In0.2)2Se3precursor layer. Two‐dimensional compositional mapping by energy dispersive spectroscopy of 5‐feet‐long web gave 0.88 ± 1.9% and 0.28 ± 2.5% respectively for Cu/(Ga+In) and Ga/(Ga+In) ratios, indicating highly uniform film composition. This compositional uniformity translated to the uniformity in the devices fabricated on the web. The open‐circuit voltages of the devices from the centerline of the 5‐feet web were measured to be 0.529 ± 0.86%. A two‐dimensional device efficiency survey gave 9.2 ± 1%. The process was able to produce high‐quality material, as defined by the best device efficiency, for a wide range of Cu/(Ga+In) ratios. The best efficiency achieved so far was 12.1% with MgF2anti‐reflection coating. Copyright © 2005 John Wiley & Sons, Ltd.

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