The role of oxygen defects engineering via passivation of the Al₂O₃ interfacial layer for the direct growth of a graphene-silicon Schottky junction solar cell

Over the past decade, graphene-based solar cells have received increasing exploration. In particular, the metal–insulator–semiconductor (MIS)-type solar cells have an inherent cost advantage compared to the p-n junction solar cells. However, the technological progress in graphene solar cells based on the MIS junction is currently facing a number of serious challenges, including long-term stability, surface recombination at the interface level, and surface defects. To overcome these barriers, a simple, cost-effective method is developed herein for the interfacial single-component passivation of Al₂O₃ with NH₃ or H₂O₂, and co-passivation with NH₃ and H₂O₂ together. The interfacial layer between the silicon and the directly-grown graphene operates as an effective electron blocking layer, thus leading to the minimization of surface recombination. Further, the NH₃-H₂O₂ co-passivated Al₂O₃ performs the dual role of providing a good platform for the growth of graphene and enhancing the performance of the fabricated solar cell. Moreover, in a proof of concept demonstration, the fabricated graphene-silicon (Gr/Si) Schottky junction with an NH₃-H₂O₂ co-passivated Al₂O₃ interfacial layer exhibits an efficiency of 9.49%, which is a major enhancement over that of the Gr/Si solar cell without an interfacial layer (i.e., 3.19%). These results demonstrate that the control of oxygen-related defects containing non-lattice oxygen in the Al₂O₃ interfacial layer remarkably impacts the charge transfer resistance and electron recombination processes. This work can be viewed as an elegant interface engineering approach to the co-passivation of Al₂O₃ for optoelectronic applications.