Bilayer Graphene Insertion to Regulate the Optoelectronic Properties of the ZnO/Si Heterojunction

We investigate the modulation mechanism of inserting bilayer graphene (BLG) on the optoelectronic properties of a two-dimensional ZnO/Si heterojunction by combining density functional theory with experimental validation. The results demonstrate that BLG transforms the interfacial Si–O bonds from covalent to van der Waals interactions, suppressing vacancy defects and reconstructing the PN junction into the Schottky junction, which is supported by band structure, differential charge density, and Bader charge analysis. Although optical absorption decreases by ∼3%, carrier recombination probability is significantly reduced, and mobility rises 4-fold. Experiments further reveal that with highly lattice-integrous graphene, ZnO epitaxially grown on BLG exhibits optimal crystallinity, leading to unexpected enhancements in conductivity (2.97 × 105 /(Ω·cm)) and carrier concentration (2.57 × 1021 /cm3), highlighting the dominant role of improved material quality in device performance. The research provides new insights for high-efficiency photovoltaic design.