Solar energy supply is renewable, abundant, and environmentally benign. It is relatively free of problems associated with fossil fuels or nuclear energy, such as increasing fuel costs, waste disposal, heat dissipation, safety concerns, and the release of greenhouse gases. The solar cell is the key component of photovoltaic systems, which can directly convert the solar energy into electricity. While solar electricity generation technologies of today are dominated by silicon based materials, organic solar cells (OSCs) have attracted growing attention due to their low cost in fabrication, and their potential to be deployed in flexible structures. However, the energy efficiency of OSCs has thus far been impeded due to limited understanding of charge transport behaviors across length scales of OSCs; yet, such transport is crucial for device efficiency. The current try-and-error approach for optimization of OSC often fails due to nearly-infinite number of material combinations and processing conditions. The objective of this collaborative research is thus to develop a multiscale simulation and optimization methodology for OSCs that directly links the basic materials properties(electronic and optical), nanoscale morphology and their dependency on processing conditions (e.g. temperature and time), bulk material properties (e.g. bulk mobility), and device designs, to device efficiency. Successful completion of this research will pave a viable pathway for commercializing organic electronics in energy conversion, which can generate both green electricity and jobs throughout the United States.
The proposed research aims to merge simulation tools across multiple time and length scales using successive integration steps. The resulting tools would enable a holistic design approach where the design space will be systematically explored to dramatically improve the performance of OSC devices. Such a holistic approach integrates experimental validations to refine the simulations at each scale (micro, meso, and macro) and ultimately to verify the optimization results. More specifically, the research will verify the multiscale simulation by characterizing nanoscale morphology, measuring bulk mobility, and testing the devices. The PIs will then optimize the designs and fabrication processes of OSCs for high efficiency through surrogate modeling and sensitivity analysis of the multiscale models. Successful completion of this research will fill a critical knowledge gap in organic electronics research and will form a new simulation paradigm for organic electronics by accounting for multiscale coupling in charge transport and material properties and by experimental validation at each scale. The scheme to bridge the micro and macro scales in this project will set an example for multiscale simulation and optimization of other type of solar cells and energy devices such as super-capacitors and batteries. The results of these models and simulations will lead to more rational designs and greater potential for significant technological advances in OSCs.
