The pursuit of increased efficiency of photoelectric energy conversion through optimized semiconductor structures remains highly competitive, with current results yet to align with broad expectations. In this study, we discover a significant enhancement in photocurrent performance of a p-3C-SiC nanothin film on p-Si/n-Si double junction (DJ) heterostructure that integrates p-3C-SiC/p-Si heterojunction and p-Si/n-Si homojunction. The vertical photocurrent (VPC) and vertical photoresponsivity exhibit a substantial enhancement in the DJ heterostructure, surpassing by a maximum of 43-fold compared to the p-3C-SiC/n-Si single junction (SJ) counterpart. The p-3C-SiC layer and n-Si substrate of the two heterostructures have similar material and geometrical properties. More importantly, the fabrication costs for the DJ and SJ heterostructure devices are comparable. Our results demonstrate a significant potential for using DJ devices in energy harvesters, micro/nano electromechanical systems, and sensing applications. This research may also lead to the creation of advanced optoelectronic devices using DJ structures, where employing various semiconductor materials to achieve exceptional performance through the application of the concept and theoretical model described in this work.