Investigating performance metrics in high volumetric utilization betavoltaic convertors: A Monte Carlo and analytical approach

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Due to their low active volume, betavoltaic cells, especially those with low-energy beta sources, are often inefficient in applications that require high power density. Incorporating auxiliary side sources into high volumetric utilization structures can improve open-circuit voltage, short-circuit current, fill factor, and power density, at the expense of a reduced energy conversion efficiency. Monte Carlo simulations combined with analytical relationships were employed to investigate high-volumetric-utilization betavoltaic structures, and the accuracy of the simulation framework was verified using a laboratory-scale reference cell. The simulations integrated tritium and strontium auxiliary sources with single-stage and ten-stage SiC semiconductor converters. Key battery parameters for each structure were derived and compared. In single-stage cells, the most significant increase in short-circuit current density was observed in a cell with a primary tritium source supplemented by four planar strontium auxiliary sources. These structures increased the short-circuit current density from 72.16nA/cm 2 to 144.50nA/cm 2 . Furthermore, the open-circuit voltage, maximum output power, power density, and Fill Factor improved from 2.093 V, 26.80 nW, 21.185 µW/g, and 0.9340 to 2.111 V, 54.16 nW, 38.419 µW/g, and 0.9345, respectively, while the efficiency decreased from 13.88% to 0.80%. In ten-stage cells, the same setup yielded a short-circuit current density of 5.73 µA/cm 2 , an open-circuit voltage of 2.206 V, a maximum output power of 2.250 µW, a power density of 163.433 µW/g, and a Fill Factor of 0.9368, with an efficiency of 3.43%. While high-volumetric-utilization structures significantly increase all battery output parameters except efficiency, changing to a ten-stage arrangement increases the contribution of auxiliary sources to the desired outputs and reduces efficiency losses. The study also found that annular auxiliary sources yielded lower outputs than planar sources due to specific loss mechanisms in the source-converter design.