Efficiency prediction of planar betavoltaic batteries basing on precise modeling of semiconductor units

Betavoltaic batteries are highly attractive for numerous application scenarios where power sources with super-long lifetime and high energy density are required. However, the reported betavoltaic batteries still suffer from low output power and low efficiency, which are much lower than theoretical predictions and bring uncertainty to the future of betavoltaics. In this work, we started from the fundamental hypothesis of betavoltaics and found that, in practice, betavoltaic batteries work under small injection conditions, where the device behavior deviates from the ideal p–n junction, resulting in the performance gap between theoretical and experimental results. We proposed a precise model on semiconductor units, taking into account the recombination current and realistic parameters, and systematically investigated the conversion efficiencies of common planar betavoltaic batteries. Modeling results suggested that semiconductors with low recombination current and a wide bandgap could be ideal candidates for planar betavoltaic batteries using 63Ni and 3H. The validity of this model is confirmed by the experimental results of a prototype battery consisting of a SiC p+–n junction and a 63Ni source. Our work provides a powerful tool for predicting the output performance and optimizing the device structure of betavoltaic batteries.