Sputtered aluminum oxide and p+ amorphous silicon back-contact for improved hole extraction in polycrystalline CdSexTe1-x and CdTe photovoltaics

A thin layer of Al2O3 at the back of CdSexTe1-x/CdTe devices is shown to passivate the back interface and drastically improve surface recombination lifetimes and photoluminescent response. Despite this, such devices do not show an improvement in open-circuit voltage (VOC.) Adding a p + amorphous silicon layer behind the Al2O3 bends the conduction band upward, reducing the barrier to hole extraction and improving collection. Further optimization of the Al2O3, amorphous silicon (a-Si), and indiumdoped tin oxide (ITO) layers, as well as their interaction with the CdCl2 passivation process, are necessary to translate these electrooptical improvements into gains in voltage