Study of a-SiGe:H films and n–i–p devices used in high efficiency triple junction solar cells

We report our systematic studies on a-SiGe:H thin films and n–i–p solar cells for GeH4/Si2H6 ratio varying from 1.43 to 0. This results in a variation of band gap from 1.37 to 1.84 eV. The FTIR studies show that the total hydrogen content in these films decreases as Ge content increases. For Ge rich films, the hydrogen also goes in to Ge–H mode. I–V measurements on n–i–p solar cells with i-layer having different Ge content show that as Ge content increase, Short circuit current (Jsc) increases, whereas open circuit voltage (Voc), fill factor (FF) and conversion efficiency (η) decrease. For Ge rich films, Jsc does not significantly increase after GeH4/Si2H6 ratio increases beyond 0.72; however Voc, FF and η decrease drastically. The quantum efficiency (QE) measurements in the subgap absorption range show that band gap and Urbach slope of the i-layer can very well be estimated in the devices.