Recent developments in amorphous silicon‐based solar cells

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 siliconbased absorber layers, while keeping its advantages of potentially low‐cost production.