Utilizing Quantum Dot Assemblies for Light Harvesting Applications

Semiconductor quantum dots are of significant interest as a versatile light harvesting material in solar cells. The research contained in this thesis investigates two aspects of quantum dot utilization for photovoltaics, incorporation of energy transfer processes and quantum dot annealing. In photovoltaics, energy transfer can be used as a complementary mechanism for charge separation. Energy transfer was investigated in quantum dot systems in two projects. First, energy transfer was studied between a squaraine dye used as a linker molecule in liquid junction solar cells and CdSe quantum dots as a function of quantum dot size. The mechanism of energy transfer changed from resonance energy transfer to Dexter energy transfer as quantum dot size decreased, representing a different strategy to incorporate energy transfer into liquid junction photovoltaics. Second, the impact of surface chemistry on resonance energy transfer was investigated in quantum dot films. Energy transfer efficiency varied drastically with quantum dot surface passivation. Solid state ligand exchange, a process used to make thick quantum dot films,was found to extinguish resonance energy transfer, highlighting the importance of quantum dot surface chemistry for effective resonance energy transfer. Lead halide perovskites are an exciting class of emerging materials for photovoltaics. Using cesium in place of organics in the perovskite structure improves material stability, but increases the difficulty of direct solution deposition. In this work, bulk CsPbBr3 perovskite films were formed through quantum dot annealing, a process used to make close packed quantum dot films. The mechanism of the annealing procedure was studied, and the photovoltaic performance of the resulting devices was investigated. CsPbI3 was formed from annealed CsPbBr3 quantum dot films through halide exchange. Halide exchange was also used to form mixed halide CsPbBrxI3-x films that featured a gradient composition as a function of film depth. The structure exhibited ultrafast hole transfer to the iodide rich film regions, showing a potential way to enhance charge separation in mixed halide perovskites.