Tritium-powered betavoltaic cells based on amorphous silicon

Betavoltaic cells based on hydrogenated amorphous silicon nip drift junctions with ultrathin (5 nm) metal contact layers were developed for tritium-powered batteries. A large variety of amorphous silicon cells has been exposed to a tritium gas atmosphere for 46 days, and their performance has been studied in several time intervals. Initially, a short circuit current density of 637 nA/cm/sup 2/, an open-circuit voltage of 457 mV, and an output power per unit area to a matched load of 136 nW/cm/sup 2/ have been achieved with a 450 nm thick amorphous silicon nip drift junction. Rather large degradation of junction performance has been observed due to diffusion of a significant amount of tritium into the amorphous silicon film. Similar results have been obtained with an np AlGaAs junction, which yielded initially a short circuit current density of 937 nA/cm/sup 2/, an open-circuit voltage of 467 mV, and an output power per unit area to a matched load of 259 nW/cm/sup 2/. An indirect conversion battery based on tritium, a cathodoluminescent phosphor, and amorphous silicon, has also been constructed for comparison.