Energy Transfer from Metal Halide Perovskites: Insights for Solar Energy Harvesting

Harvesting solar energy is essential for meeting the increasing global energy demand driven by population growth. Inspired by natural photosynthesis, solar energy is harnessed for both electricity production (photovoltaics) and fuel generation (photocatalysis). Semiconductor nanomaterials have emerged as key light absorbers for photovoltaic and photocatalytic applications. The semiconductor nanomaterials are coupled with chromophores and other cocatalysts to facilitate charge/energy transfer for efficient light harvesting. Of particular interest is the energy transfer process, wherein semiconductor nanocrystals can populate the singlet and triplet states of the acceptor, each with its own distinct utility. Moreover, this energy transfer process can initiate nonlinear processes, further enhancing energy utilization. This dissertation elucidates the mechanisms underlying the energy transfer processes in a semiconductor-molecule hybrid assembly. As a model system, cesium lead halide perovskite as the sensitizer and rubrene and DBP (a perylene derivative) as acceptor chromophores are selected. Lead halide perovskites are particularly appealing as sensitizers due to their strong light absorption and tunable optical properties. Understanding the spectral characteristics of transient excited states in acceptor molecules is crucial for distinguishing between singlet/triplet energy transfer and charge transfer processes. We elucidated the spectroscopic signatures of singlet, triplet, radical anion, and radical cation of rubrene and DBP through a combination of spectroscopic and electrochemical techniques. The ambiguity surrounding the interactions between rubrene and DBP posed challenges for the application of these systems. However, we have demonstrated that DBP efficiently extracts singlet energy from rubrene. A semiconductor-chromophore assembly was crafted utilizing cesium lead halide nanocrystals along with rubrene and DBP. In the cesium lead bromide-multichromophore assembly, sequential energy transfer was observed. Initially, singlet energy transfers from cesium lead bromide to rubrene, followed by a subsequent transfer from rubrene to DBP. This cascade of energy transfer showcases a down-conversion of energy, exemplifying the potential of semiconductor-multichromophore assemblies in energy manipulation. Conversely, in cesium lead iodide-rubrene assembly, triplet energy transfer was observed. Finally, the triplet-triplet annihilation process in rubrene-DBP system was demonstrated. Through the cesium lead iodide-rubrene-DBP assembly, the energy can be upconverted. Taken together the projects detailed in this dissertation provide important insights into understanding the mechanism of interactions in semiconductor-chromophore assembly. Additionally, the experimental techniques and methodologies outlined herein can serve as versatile tools for identifying and comprehending interactions within semiconductor-chromophore assemblies more broadly.