Multi-spectral detection had significant applications in many fields of industry. High-performance broadband photodetectors integrating multi-band responses became one of the important research directions of optical imaging technology. Current research progress of broadband photodetectors was briefly introduced. The prospects of 2-D/3-D mix-dimensional van der Waals (VDW) heterojunctions in the development of broadband photodetectors were elaborated. Some progress of broadband phototransistors based on 2-D transition metal dichalcogenides/3-D group Ⅳ materials VDW heterojunctions by the research group, including traditional NPN-type, PNP-type phototransistors and emerging phototransistors with Schottky junction collectors were reviewed. Ultimately, the applications of these phototransistors were prospected.