It is beneficial to investigate multifunctional self-powered sensors with high sensitivity and energy-scavenging capabilities, which are essential for the development of a smart infrastructure in the era of 5G and Internet of Things (IoT). This paper reports the photo-piezojunction coupling effect, i.e., the coupling of piezojunction effect with photovoltaic effect, in an n-type 3C-SiC/p-type Si heterojunction (n-3C-SiC/p-Si) and demonstrates it through a proof-of-concept self-powered strain-sensing device. The device exhibits superior photon energy-harvesting capability, generating 24.54 mV with a laser power of only 10 μW, approximately five times higher than that of reported devices utilizing the lateral photovoltaic effect, and an exceptionally high strain sensitivity, achieving |(ΔV/V)/ϵ| ratios of 43.14 and 21.34 for tensile and compressive strain, respectively, which are 4.3 times more than that of devices reported in previous studies. The findings of this study significantly advance the understanding of the photo-piezojunction coupling effect in n-3C-SiC/p-Si heterostructures, laying the foundation for the development of multifunctional sensor systems capable of harvesting photon energy.