We report a study on a-Si:H materials and p(a-SiC:H)/i(a-Si:H)/n(mu c-Si) solar cells prepared without and with hydrogen dilution (10 : 1) at substrate temperatures between 240 degrees C and 130 degrees C. In contrast to previously reported studies, the cell characteristics in the annealed state of these similar to 4000 Angstrom thick cells could be directly correlated with the properties of their corresponding i-layer materials. Also, despite the importance of the p/i interface regions, very similar kinetics of light-induced changes are observed in the cells and the corresponding films. In particular, both cells and films fabricated with hydrogen dilution reach a degraded steady state in less than 100 h of AM1 illumination, which offers a well-defined ＇＇marker＇＇ for the direct correlation of their respective light-induced changes. Advantage is also taken of the differences in degradation kinetics between diluted and undiluted materials in fabricating custom-designed cells in which these well-characterized intrinsic materials are incorporated into either the bulk or the p/i interface regions.