Stable Materials Advisory Research Team (SMART) was established to develop a unified approach to address the stability problem in a‐Si:H based solar cells. The goal of the coordinated research effort by industrial laboratory and research institution members is to resolve whether a‐Si:H based materials are intrinsically unstable and if high efficiency cells can have a 20 year lifetime. This paper reviews ongoing research which addresses both material and device issues in the effort to improve the material properties and solar cell performance. Results are presented for materials and device structures obtained using several deposition techniques with hydrogen content varying from about 20% to 8%. Also several issues are discussed which arose from the wide range of measurements carried out on the same materials in different laboratories.