Background Betavoltaic isotope batteries have long service life, high energy density, and good environmental adaptability, making them promising power sources for deep-space exploration, deep-sea observation, and implantable medical devices.

Purpose This study investigates the effects of self-absorption in finite-volume β sources, energy distribution in Schottky metal layers, and non-uniform carrier collection in Si on device output performance.

Methods A radioactive source–metal–Si model was established using Geant4. A depth-dependent carrier collection model and a non-ideal single-diode model were further introduced to calculate the electrical output. Two published ⁶³Ni/Au/Si devices were used for model benchmarking.

Results The reference thicknesses of the ³H, ⁶³Ni and ¹⁴⁷Pm sources were 1, 2 and 28 μm, respectively. As the metal layer thickness increased, the backscattered escaping energy quickly approached a stable value, the energy deposited in the metal increased, and the energy deposited in Si decreased. For the device reported by Liu et al., the absolute relative deviations of the four output parameters ranged from 1.26% to 8.02%. For the device reported by Wang et al., the deviations of short-circuit current density and fill factor were 10.38% and 4.23%, respectively, while the other two parameters showed larger deviations. Considering energy transport and metal properties, Au was selected as the Schottky metal. For the ¹⁴⁷Pm/Au/Si structure with an Si thickness of 80 μm, the short-circuit current, open-circuit voltage, fill factor, maximum output power, and maximum volume power density were 118.441 μA, 0.359 V, 0.692, 29.433 μW and 3.679 mW·cm⁻³, respectively.

Conclusions The results can provide a reference for the structural design of Si/metal Schottky junction betavoltaic batteries.