Recent progress in techniques to prepare stable silicon thin films for solar cells application is reviewed with the aim of controlling chemical reaction at growing surface. For preparing either a-Si:H or solar cells, (1) hydrogen dilution, (2) hot-wire CVD and (3) chemical annealing are discussed with regard to the control of medium-range order structure of Si network related to the stability for light soaking. The issues involved in the individual novel techniques for preparing solar cells are also addressed. Polycrystalline silicon thin films grown at low temperatures as well as the solar cells are introduced by controlling surface chemical reactions. (C) 2001 Elsevier Science B.V. All rights reserved.