The incessant progress in thin layers technology, especially the graded index inhomogeneous dielectrics, allows the realization of antireflection coatings (ARCs). Graded refractive index silicon oxynitrides are deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) controlled in situ by monochromatic ellipsometry. While avoiding the complexity of the classical multilayer ARCs, graded coatings permit to obtain the same performances, or furthermore to improve solar cells efficiency. A theoretical model, validated by confrontation to ellipsometric spectra, and reflectance measurements were used to optimize different suggested profiles. Calculation predicts an enhancement of photogenerated current exceeding 45% and a weighted reflectance (between 300 and 1100 nm) around 5.6%. On texturized surfaces, these ARCs should enhance short-circuit current by 52.79%. (c) 2004 Elsevier B.V. All rights reserved.