Abstract: Understanding and controlling the ultrafast charge carrier and exciton dynamics at the interface of semiconductor nanocrystals (NCs) offer an excellent opportunity to improve the charge collection and the overall performance of many optoelectronic and energy-based devices. In this dissertation, we study how interfacial engineering of these materials can have a direct influence on controlling the charge transfer and the nonradiative losses in different donor-acceptor systems. The first introductory chapter provides an overview of all the fundamental photophysical processes controlling the interfacial phenomena. Then, the second chapter highlights all the chemicals and synthesis methods employed during this thesis. The subsequent two chapters discuss the detailed experimental studies and observations related to different materials and interfaces. First, it describes how we can dramatically tune the intersystem crossing (ISC) rate, the triplet state lifetime, turn on/off the electron injection at the CdTe-Prophyrin interface via tuning either the quantum dot size or the porphyrin molecular structure. Also, how the intermolecular distances, electronic coupling, and subsequently, the photoinduced charge transfer can be controlled by the interfacial electrostatic interactions at CdTe-Fullerene interfaces. Second, due to the promise that of perovskite NCs holds for improving many solar cell and optoelectronic applications, chapter 3 highlights the tremendous effect that the shape of perovskite nanocrystals has on the rate and the mechanism of charge transfer at the MAPbBr3- TCNE interface. Besides, it demonstrates how the confinement effect brought by changing the dimensionality influence the charge transfer dynamics at the MAPbBr3-BQ interface. Finally, it explains how the effective passivation of the surface defects and the subsequent suppression of the formation of surface nonradiative recombination centers in CsPbCl3 NCs controls the photoluminescence quantum yield and the photodetector performance.