Physical Properties and Photovoltaic Application of Semiconducting Pd₂Se₃ Monolayer.

Palladium selenides have attracted considerable attention because of their intriguing properties and wide applications. Motivated by the successful synthesis of Pd₂Se₃ monolayer (Lin et al., Phys. Rev. Lett., 2017, 119, 016101), here we systematically study its physical properties and device applications using state-of-the-art first principles calculations. We demonstrate that the Pd₂Se₃ monolayer has a desirable quasi-direct band gap (1.39 eV) for light absorption, a high electron mobility (140.4 cm²V-1s-1) and strong optical absorption (~10⁵ cm-1) in the visible solar spectrum, showing a great potential for absorber material in ultrathin photovoltaic devices. Furthermore, its bandgap can be tuned by applying biaxial strain, changing from indirect to direct. Equally important, replacing Se with S results in a stable Pd₂S₃ monolayer that can form a type-II heterostructure with the Pd₂Se₃ monolayer by vertically stacking them together. The power conversion efficiency (PCE) of the heterostructure-based solar cell reaches 20%, higher than that of MoS₂/MoSe₂ solar cell. Our study would motivate experimental efforts in achieving Pd₂Se₃ monolayer-based heterostructures for new efficient photovoltaic devices.