Theoretical investigations of novel Janus PbSSe monolayer as a potential multifunctional material for piezoelectric, photovoltaic, and thermoelectric applications.

Two-dimensional Janus nanomaterials, due to their unique electronic, optical, and piezoelectric characteristics resulting from the antisymmetric structures, exhibit great prospects in multifunctional energy application to alleviate the energy crisis. Monolayer Janus PbSSe, with a black phosphorus-like structure and an indirect band gap of 1.59 eV as well as high carrier mobility (526-2105 cm V s), displays outstanding potentials in the energy conversion between nanomechanical energy, solar energy, waste heat, and electricity, which has been comprehensively studied utilizing DFT-based simulations. The research results reveal that monolayer PbSSe not only possesses giant in-plane piezoelectricity of = 75.1 pm V but also superhigh out-of-plane piezoelectric coefficients ( = 0.5 pm V and = 15.7 pm V). Meanwhile, by constructing PbSSe bilayers, the out-of-plane piezoelectric coefficients can be significantly enhanced ( = 19.2 pm V and = 194.7 pm V). In addition, owing to the small conduction band offset, suitable donor band gap and excellent light absorption capability in the PbSSe/SnSe (PbSSe/GeSe) heterostructure, the power conversion efficiencies were calculated to be up to 20.02% (PbSSe/SnSe) and 19.28% (PbSSe/GeSe), making it a promising candidate for solar energy collection. Furthermore, from the thermoelectric electron and phonon transport calculations, it can be found that the PbSSe monolayer is an n-type thermoelectric material with ultrahigh = 2.19 (1.52) at room temperature, which can be traced back to its ultralow = 0.78 (0.99) W m K, and superhigh PF = 10.18 (8.25) mW m K along the () direction at the optimal doping concentration at 300 K. The abovementioned versatile characteristics in the Janus PbSSe monolayer, along with its comprehensive stabilities (energy, dynamic, thermal, and mechanical stabilities), highlight its potential in clean energy harvesting.