We investigate the unique structural and optical properties of an alternately H-2-diluted protocrystalline silicon multilayers (pc-Si:H) compared to a hydrogenated amorphous silicon (a-Si:H) layer. Strong evidence for the isolated nano-sized silicon (nc-Si) grains embedded in the a-Si:H matrix is provided. The vertically regular distribution of the nc-Si grains is concluded as the main reason for the fast light-induced metastability with the low degradation for the fabricated pc-Si:H multilayer solar cell by localizing the photocreation of dangling bonds near the defective grain-boundary layers. (C) 2013 Elsevier B.V. All rights reserved.