This article reviews the results obtained in Kaiserslautern for research and development on amorphous (a-Si:H) and microcrystal line (mu c-Si:H) silicon based thin film solar cells as well as heterojunction solar cells applying entirely or mainly the HWCVD. The activities of the group cover the development of appropriate intrinsic and doped a-Si:H and mu c-Si:H films for the different solar cell structures, the realization of many types of such structures with different deposition sequences and the detailed study of their stability behavior. Also the preparation of an HW solar cell on medium size area is demonstrated. Initial and stabilized conversion efficiencies are presented and discussed for the different cell structures realized within about ten years of activity. Main focus will be on the recent activities dealing with the integration of mu c-Si:H films into solar cell structures and the extensive study of their stability behavior. In addition the degradation of the applied Ta catalyzer was intensively investigated. Finally advantages and disadvantages will be discussed concerning the commercial use of the HWCVD for solar cell fabrication. (c) 2007 Elsevier B.V All rights reserved.