An isotope capacitor may include a plurality of isotope capacitor sheets that are stacked in a first direction, a first external electrode, and a second external electrode. Each isotope capacitor sheet of the plurality of isotope capacitor sheets includes a substrate including a first material and a second material and a radiation source. The second material may have an electrical conductivity higher than the electrical conductivity of the first material. The second material may be between the first material and the radiation source. The first external electrode and the second external electrode may be configured to transfer electrical energy generated by the plurality of stacked capacitor sheets to an external load.