New quantum states in 2D materials have important implications for condensed matter physics and the development of modern optoelectronic devices. However， terahertz photoelectric detection technology with broadband， room temperature， and fast response capabilities still faces great challenges due to the lack of an optimal balance between dark current and light absorption. In this study， a novel topological insulator material， GeBi₄Te₇， was synthesized， and its van der Waals heterojunction with Bi₂Te₃ was constructed to realize a highly sensitive terahertz photodetector. Direct generation of photocurrents at low-energy terahertz bands of room temperature has been realized in planar metal-material-metal structures. The results show that the Bi₂Te₃-GeBi₄Te₇-based terahertz photodetector can achieve wide spectral detection from 0.02 THz to 0.54 THz with high photosensitivity （592 V?W^-1 at 0.112 THz， 203 V?W^-1 at 0.27 THz， 40 V?W^-1 at 0.5 THz）， and a response time of less than 6 μs. Notably， it is already available for high-frequency terahertz imaging. These findings make it possible to use Bi₂Te₃-GeBi₄Te₇ topological insulator heterojunction materials for low-energy optoelectronic applications.