Structure-Function Relations Underlying Charge Transfer In Organic Photovoltaic Systems
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Abstract
Organic photovoltaics (OPV) is an emerging solar cell technology with great potential advantages such as low-cost manufacturing, transparency, and solution processability. However, the performance of OPV devices is still prohibitively low, requiring a better understanding of the impact of molecular-level morphology on OPV function. This is challenging as OPV systems can have complex electronic structures and molecular morphologies. Here I show how a combination of scientific methods, for which I led the development, accurately measured CT at these different levels. In Chapter 1, I provide background information on organic solar cells as well as on some of the methods used to study them. Next, in Chapter 2, I detail the results of applying these methods to the SubPC/C60 system. The explicit treatment of solvent molecules identified a new type of molecular geometry and improves on the rate estimates given in past literature. Chapter 3 features the new open-source software CTRAMER which is a modular combination of state-of-the-art computational methods from molecular dynamics, electronic structure, and transition-rate theory. Finally, Chapter 4 covers how applying CTRAMER and physics-guided machine learning to the DBP/C70 system showed that the condensed phase stabilizes a wide variety of geometries, each with unique charge transfer characteristics. These results show the importance of accounting for explicit environmental effects when studying charge transfer in organic solar cells. Furthermore, in both systems studied, simulations showed that the interface is dominated by sub-optimal geometries as well as the clear link between molecular morphology and charge transfer performance. These findings should guide the future design and manufacture of organic solar cells.