High-Performance and Lithography-Free Au/WS₂/Ag Vertical Schottky Junction Solar Cells

Due to their extraordinarily large optical absorption coefficients, transition metal dichalcogenides (TMDs) are gaining more and more attention for photovoltaic applications. Improving the device performance of a TMD solar cell requires an optimal device architecture and reliable fabrication processes. Metal/WS₂-multilayer/metal heterojunctions are fabricated using lithography-free processes. 20 nm thick WS₂ flakes are exfoliated on template-stripped Ag bottom electrodes, and then 10 nm thick Au top electrodes with a diameter of 2 µm are evaporated on the WS₂ surface using holey carbon films as shadow masks. Current-sensing atomic force microscope measurements reveal that the Au/WS₂/Ag devices exhibit prominent rectifying characteristics, indicating the formation of Schottky diodes. The power conversion efficiency of the Schottky junction is as high as 5.0%, when illuminated by a light-emitting diode with a peak wavelength of 625 nm and a power density of 2.5 mW cm⁻². These devices also possess broadband and incident-angle-insensitive absorption capability due to the very large refractive indices and extremely small thickness of the WS₂ flakes. The simple fabrication procedures proposed in this work demonstrate high-performance and high-yield TMD photovoltaic devices.