<p dir="ltr">In response to the ongoing global energy crisis, significant efforts have been made to enhance the efficiency of energy conversion devices that utilize renewable resources. This has spurred the development of multi-component semiconductors, which combine the strengths of both organic and inorganic materials to offset their individual limitations. This dissertation investigates advanced band engineering strategies to manipulate photophysical phenomena in these hybrid systems for specific applications. By focusing on two-dimensional perovskites and heterostructures formed from transition metal dichalcogenides and organic molecules, we explore how the inorganic components can sensitize their organic counterparts, examining the charge and energy transfer processes occurring at their interfaces and giving rise to unique excited states with diverse optical properties which hold significant potential for energy harvesting technologies.</p><p dir="ltr"><b>CHAPTER 1</b> furnishes readers with extensive insights into the semiconducting materials discussed in this dissertation, along with essential knowledge of fundamental concepts (such as excitons, charge and energy transfer, singlet fission, Marcus Theory, etc.) crucial for a deeper understanding of subsequent chapters. It also highlights the unresolved questions addressed later in this dissertation.</p><p dir="ltr"><b>CHAPTER 2 </b>provides a comprehensive overview of the spectroscopic and other characterization techniques used to study these materials.</p><p dir="ltr"><b>CHAPTER 3 </b>illustrates how the relative band alignment and coupling between the organic and inorganic layers of 2D perovskites impact the rates and dynamics of the transfer of triplet excitons across the hybrid interface. It also demonstrates how one can utilize extremely fast triplet transfer times to induce rapid photon upconversion in the perovskite, facilitated by doping of the organic layer. Triplet energy transfer driven photon upconversion is a promising method for enhancing the efficiencies of solar cells; therefore, this chapter makes a stride towards contributing newer insights for optimizing solar energy conversion.</p><p dir="ltr"><b>CHAPTER 4</b> focuses on how tuning the dimensionalities of 2D perovskites can modify their energy landscapes and further impact the interfacial photophysics, leading to the creation of long lived and mobile ‘interfacial’ excitons with enhanced electro-optic properties, promising for potential applications in solar cells and quantum computing.</p><p dir="ltr">In <b>Chapter 5</b>, the focus shifts to organic molecules that can undergo singlet fission, which are sensitized by highly absorbing monolayer transition metal dichalcogenides (TMDCs). This chapter explores how to induce intense emission from triplet pairs of the organic molecules — the critical yet elusive intermediate species in singlet fission, by engineering direct energy transfer into them from the TMDCs. Singlet fission-based technologies hold the potential to significantly enhance solar cell efficiencies, driving extensive research into optimizing the behavior of multi-excitonic triplet pairs. These triplet pairs offer the exciting possibility of multiphoton emission and/or the donation of multiple electrons (or excitons) in a single step. Our work aims to advance the understanding of these prospects and contribute to their practical application.</p><p dir="ltr"><b>CHAPTER 6 </b>summarizes the key findings from the previous chapters and explores potential future research directions. This dissertation, as a whole, contributes to and paves the way for further investigation into optimizing band engineering-based functionalities in 2D organic-inorganic semiconductors. These efforts aim to advance photophysical applications focused on improving energy conversion for a cleaner, more sustainable future.</p>