PySTH: A Python program for calculating and analyzing theoretical solar-to-hydrogen efficiency

Solar-to-hydrogen (STH) efficiency is a key metric for evaluating the economic feasibility of hydrogen production via solar-driven water splitting. However, accurately calculating theoretical STH efficiency remains challenging due to the complexity of the underlying integrals and the presence of multiple interdependent material parameters, which hampers computational efficiency and reproducibility. In this work, we introduce PySTH, a Python-based command-line program designed to enable rapid and reliable computation and intuitive visualization of theoretical STH efficiencies for two-dimensional photocatalysts under various sets of material property parameters. All required parameters are derived from first-principles calculations. The program supports four distinct photocatalytic systems: conventional photocatalysts, Janus materials, Z-scheme heterojunctions, and Janus Z-scheme systems. PySTH also generates high-resolution efficiency maps that reveal how the interplay among different material parameters affects STH efficiency, thereby offering valuable insights into synergistic optimization strategies. A series of benchmark examples demonstrate the accuracy, versatility, and practical utility of the program in theoretical photocatalysis research.