Surface functionalization of CuInSe₂ and CsPbI₃ nanocrystals : conversion yields, exciton kinetics, and thermal stability

Solar power is a viable solution to the reduction of global dependence on non-renewable resources. Currently, silicon photovoltaic (PV) devices dominate the market. These devices are not only expensive to manufacture but also have a lengthy production process and they emit significant amounts of CO₂ into the atmosphere. Nanocrystal PVs have the potential to significantly lower manufacturing cost while maintaining high efficiencies. However, challenges with nanocrystal’s surface chemistry have impacted their performance. This dissertation examines the surface functionalization effects for copper indium diselenide (CIS) and cesium lead iodide (CsPbI₃) nanocrystals. Specifically, the effects of surface ligands on conversion yields, exciton kinetics, superlattice formation and thermal stability were explored. Using the hot injection synthetic method, nanocrystals were functionalized with organic ligands. The nanocrystals were characterized using various techniques, such as transmission electron microscopy, transient absorption spectroscopy, and small and wide-angle X-ray scattering. It was found that nanocrystals with less surface vacancies demonstrated the highest PV device performances. Additionally, longer lifetimes were discovered for nanocrystals with phosphinic acid ligands. These results are important prerequisites to the fabrication of low cost nanocrystal PV devices. By determining how the ligands affect the optical and electronic properties, the desired characteristics can be engineered and formed into nanoinks that can be deposited onto substrates under ambient conditions; opposed to the traditionally high energy processing.