Theoretical Maximum Efficiencies of Optimized Slab and Spherical Betavoltaic Systems Utilizing Sulfur-35, Strontium-90, and Yttrium-90

Monte Carlo simulations have been used for calculating the energy deposition of beta particles in the depletion region of a silicon carbide (SiC) betavoltaic cell along with the corresponding theoretical efficiencies. Three Monte Carlo codes were used in the study: GEANT4, PENELOPE, and MCNPX. These codes were used to examine the transportation of beta particles from ⁹⁰Y, ⁹⁰Sr, and ³⁵S. Both the average beta energy from each source and the entire spectrum were modeled for calculating maximum theoretical energy deposition in both a spherical and slab geometry. A simulated depletion region was added in postprocessing containing the maximum energy deposited per micrometer. The calculated maximum efficiencies with the slab configuration model are approximately 1.95%, 0.30%, and 0.025% using monoenergetic average energy and 1.54%, 0.25%, and 0.019% using an energy spectrum for ³⁵S, ⁹⁰Sr, and ⁹⁰Y, respectively. These efficiencies when using the spherical configuration model are 2.02%, 0.31%, and 0.023% using the monoenergetic average energy and 1.10%, 0.17%, and 0.013% using an energy spectrum for ³⁵S, ⁹⁰Sr, and ⁹⁰Y, respectively.