Impact of Al₂O₃ Passivation on the Photovoltaic Performance of Vertical WSe₂ Schottky Junction Solar Cells

Transition metal dichalcogenide (TMD) materials have emerged as promising candidates for thin-film solar cells due to their wide bandgap range across the visible wavelengths, high absorption coefficient, and ease of integration with both arbitrary substrates and conventional semiconductor technologies. However, reported TMD-based solar cells suffer from relatively low external quantum efficiencies (EQE) and low open circuit voltage due to unoptimized design and device fabrication. This paper studies Pt/WSe₂ vertical Schottky junction solar cells with various WSe₂ thicknesses in order to find the optimum absorber thickness. Also, we show that the devices' photovoltaic performance can be improved via Al₂O₃ passivation, which increases the EQE up to 29.5% at 410 nm wavelength incident light. The overall resulting short circuit current improves through antireflection coating, surface doping, and surface trap passivation effects. Thanks to the Al₂O₃ coating, this work demonstrates a device with an open circuit voltage (V_OC) of 380 mV and a short circuit current density (J_SC) of 10.7 mA/cm². Finally, the impact of Schottky barrier height inhomogeneity at the Pt/WSe₂ contact is investigated as a source of open circuit voltage lowering in these devices.