We report on the formation of large voids in hydrogenated polymorphous silicon (pm-Si:H) PIN solar cells upon light-soaking. We could monitor in situ, the formation of macroscopic bubbles and holes during current-induced degradation of the same devices using optical microscopy. Forward bias, leading to a current-injection of 300 mA/cm(2), was applied to hydrogenated amorphous silicon (a-Si:H) and pm-Si:H PIN solar cells and series of optical images were taken on the same spot at various steps of current injection. During the current-injection, the pm-Si:H PIN solar cells experience significant topological changes, which we could not detect in a-Si:H PIN solar cells. These effects were further characterized by complementary ex-situ techniques such as SEM, AFM and spectroscopic ellipsometry. (C) 2017 Elsevier Ltd. All rights reserved.