Ion-assisted plasma enhanced deposition of diamond-like carbon (DLC) films on the surface of photovoltaic solar cells is accomplished with a method and apparatus for controlling ion energy. The quality of DLC layers is fine-tuned by a properly biased system of special electrodes and by exact control of the feed gas mixture compositions. Uniform (with degree of non-uniformity of optical parameters less than 5%) large area (more than 110 cm.sup.2) DLC films with optical parameters varied within the given range and with stability against harmful effects of the environment are achieved.
CONTRACTUAL ORIGIN OF INVENTION
 The United States Government has rights in this invention pursuant to Contract No. DEAC36-99GO10337 between the U.S. Department of Energy and the National Renewable Energy Laboratory, a Division of Midwest Research Institute.