Two examples of recent advances in the field of thin-film, amorphous hydrogenated silicon (a-Si : H) pin solar cells are described: the improved understanding and control of the p/i interface, and the improvement of wide-bandgap a-Si : H material deposited at low substrate temperature as absorber layer for cells with high stabilized open-circuit voltage. Stacked a-Si : H/a-Si : H cells incorporating these concepts exhibit less than 10% (relative) efficiency degradation and show stabilized efficiencies as high as 9 to 10% (modules 8 to 9%). The use of low-gap a-Si : H and its alloys like a-SiGe : H as bottom cell absorber materials in multi-bandgap stacked cells offers additional possibilities. The combination of a-Si : H based top cells with thin-film crystalline silicon-based bottom cells appears as a promising new trend. It offers the perspective to pass significantly beyond the present landmark of 10% module efficiency reached by the technology utilizing exclusively amorphous silicon-based absorber layers, while keeping its advantages of potentially low-cost production.