Abstract—This paper proposes covalent-semiconductor-based lateral p-n junction film solar devices based on a theoretical model, and examines their power generation performance under illumination. The proposed theoretical model is implemented and tested in simulations. The results demonstrate that while Ge film devices have much lower performance at room temperature than Si film devices, this order is significantly reversed at temperatures below 250 K, which is very interesting. The obtained simulation results also reveal that the carrier generation characteristic of Ge film devices is very stable in terms of temperature variation in comparison to Si film devices. The simulation results suggest that thin-Si-film lateral p-n junction solar devices – implemented as multi-stacked solar devices formed on a transparent panel – are applicable to field sensor devices on the ground at temperatures lower than 300 K. However, thin-Ge-film lateral p-n junction solar devices are applicable to field sensor devices on satellites in space because the ambient temperature is lower than 250 K; again as a multistacked solar device formed on a transparent panel.