Organic photovoltaic (OPV) technology is a potentially widespread approach for sustainable and economical solar-electric conversion owing to its promise of roll-to-roll fabrication on flexible substrates, using a solution-phase process. In an OPV device, a thin film (active-layer) is coated on a flat substrate from a biphasic solution consisting of two organic materials (electron donors and acceptor). However, optical losses in such a device are high and efficiencies are low. This project introduces a new processing paradigm for light-trapping and higher efficiencies ? coating conformal layers of polymeric OPV blends on sub-micron scale textured topographies. (1) Active-layers of OPVs will be spin-coated on textured topographies and processing-structure-property correlations will be established. (2) A theoretical framework to model fluid-flow and evaporation while coating on textured topographies will be developed to inform the experimental task of best topographical dimensions and appropriate processing conditions. Knowledge discovery emerging will then be used to fabricate textured OPV cells using doctor-blading technique (a prototype for roll-to-roll manufacturing). Overall objective of this project is to establish a library of topographies and processing conditions that are amenable to achieving conformal polymer films on such surfaces, so that effective light trapping and higher solar-electric conversion efficiencies are realized.
The proposed research takes the thin-film paradigm into the third dimension (textured approach), thus promising to overcome the classic OPV trade-off pertaining to dissimilar photonic and charge-transport scales. Intellectual merit and transformative nature of proposed research lies in the attempt to answer the following fundamental question ? What should be the dimensions of underlying topographies and processing conditions, such that not only effective optical absorption is achieved in ultra-thin polymer layers, but it is also possible to coat such films, conformally on these topographies? Fabrication and characterization, including optical and device modeling will be coupled with fluid-flow modeling to achieve this overall objective. Other than the field of OPVs, the proposed research will also have implications on a more general problem of thin film coating over functional substrates containing topographical features. This problem is of enormous significance for various engineering, industrial and physical applications.
The proposed work is highly interdisciplinary combining elements from experimental work on photovoltaic devices, and computational work on fluid-mechanics and phase-transformation. The multidisciplinary components of the project will be integrated into a larger educational effort to offer students a solid foundation in scientific computing and renewable energy. Our education and outreach plans further include (1) modules for existing course on organic electronics and a new course in multiscale mdoelling, (2) developing a mentoring program, linking graduate with undergraduate students, with special emphasis on underrepresented groups ? with an objective of increasing recruitment and retention, and (3) outreach activities that demonstrate to the K-12 community the crucial role of computing in science and technology. To this end, the PIs will create educational modules involving immersive simulations of OPV processes which will be demonstrated to Ames high school students, (4) preparing modules for the lesson and hands-on components based Toying With Technology program, in place at Iowa State for the current and future K-12 teachers, (5) continuing to work with ?Women in Mechanical Engineering? in engaging women and minority undergraduate students.
