Backwall superstrate configuration for ultrathin Cu(In,Ga)Se₂ solar cells

A backwall superstrate device structure that outperforms conventional substrate Cu(In,Ga)Se₂ devices for thin absorbers is demonstrated. The backwall structure (glass/In₂O₃-SnO₂/MoO_3-x/Cu(In,Ga)Se₂/CdS/i-ZnO/Ag) utilizes a MoO_3−x transparent back contact to allow illumination of the device from the back. In combination with a silver front reflector this cell structure is tailored to enhance performance of devices with submicron thick absorbers. It was found that devices with the backwall configuration outperform substrate devices in the absorber thickness range d_CIGS = 0.1-0.5 μm. The advantage of the backwall configuration is mainly through superior J_SC, achieved by application of a front reflector and elimination of parasitic absorption in CdS.