Employing first-principles theory and nonadiabatic molecular dynamics simulations, we have systematically reported stability, electronic, optical, photocatalytic, and charge transfer characteristics of Janus PtSSe/BeP heterostructures for water splitting. SePtS/BeP and SPtSe/BeP heterostructures have semiconducting properties ($E_g\sim 0.23–1.18\mathrm{eV}$), low excitonic binding energy ($E_{\mathrm{exb}}\sim 0.31–0.41\mathrm{eV}$), high charge carrier mobility of the order of ${\mu }_e\approx {10}^4\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ and ${\mu }_h\approx {10}^5\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$, and suitable alignment of bands engulfing water redox potentials. The calculated electron-hole recombination time of 0.09 ps (1.67 ps), which is faster (slower) than the electron transfer time 0.14 ps (0.71 ps) and hole transfer time 0.19 ps (1.01 ps) suggests a $Z$-scheme (type-II) charge transfer mechanism for the SePtS/BeP (SPtSe/BeP) heterostructure. Our study also demonstrates that the heterostructures have enough potential to carry out spontaneous hydrogen evolution reaction and oxygen evolution reaction mechanisms occurring on both surfaces, as it owns zero overpotential (${\eta }_{\mathrm{HER}/\mathrm{OER}}=0$), making it desirable to be a photocatalyst candidate for water splitting. Furthermore, in order to improve the solar-to-hydrogen (STH) efficiency of respective heterostructures, we incorporated a twisting strategy by interlayer rotation at angles of 13.2°, 21.8°, and 27.8°. Having the considerable deviation in band alignments and maintaining the charge transfer mechanism of the pristine heterostructure, the STH efficiency of the PtSSe/BeP heterostructure was enhanced to ∼16%, which suggests the potential use of the respective heterostructure to produce hydrogen. Our results not only offer a strategy for the performance of photocatalytic material to be improved by incorporating twisting layers of heterostructure but also provide a solid photocatalytic mechanism for improved activity.

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• Charge dynamics
• Electronic structure
• Optoelectronics
• Twistronics
• First-principles calculations