Sputtered Aluminum Oxide and p⁺ Amorphous Silicon Back-Contact for Improved Hole Extraction in Polycrystalline CdSexTe1-x and CdTe Photovoltaics

A thin layer of Al ₂ O ₃ at the back of CdSe _x T _e1-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 (V _OC. ) Adding a p ⁺ amorphous silicon layer behind the Al ₂ O ₃ bends the conduction band upward, reducing the barrier to hole extraction and improving collection. Further optimization of the Al ₂ O ₃ , amorphous silicon (a-Si), and indium-doped tin oxide (ITO) layers, as well as their interaction with the CdCl ₂ passivation process, are necessary to translate these electro-optical improvements into gains in voltage.