 This research has developed a new method for creating epitaxially grown Janus colloidal lead halide perovskite nanocrystal, NC, hetero structures with ultra-fast charge separation across the electronically coupled interface. By varying reaction parameters, the size of each domain can be precisely controlled, allowing for modulation of the optical properties of Janus NCs. Transient absorption measurements and modeling results show that photo-excited electrons rapidly transfer within 9 picoseconds from the CSPBBR3 to the CD's domains. This greatly improves the responsivity and detectivity of the device, making it promising for ultra-sensitive photo-detection. This article was authored by Hung Wei Cho, Foo Lee, Sean Hee and others.