Functional Atomic Membranes for High-Performance Organic Photovoltaic Materials

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

1033346 Arnold Intellectual Merit Organic photovoltaic (OPV) devices based on organic semiconductors are attractive for next-generation solar cells because of their strong optical absorptivity, economical fabrication, and tunable optoelectronic properties. However, despite these advantages, OPVs have not found widespread use. One limitation on OPV device performance is the susceptibility of OPVs to photo-oxidation effects, which limits their practical lifetime. Another limitation is that the power conversion efficiency of OPVs is still several times lower than that of single-junction inorganic photovoltaic devices. The relatively poor performance of OPVs is due to the inefficient charge and energy transport mechanisms in organic semiconducting materials. In this research, the incorporation of atomically-thin graphene membranes at the active interfaces of OPV devices is proposed to increase the stability of OPV devices and improve their performance by simultaneously adding multiple functionalities. Specifically, it is hypothesized that these two-dimensional, crystalline, graphene membranes will impart four unique functionalities to OPV devices. First, they will act as impermeable diffusion barriers, excluding oxygen, water vapor, and migrating ions from the active layers of OPVs, thereby enhancing organic semiconductor stability and lifetime. Second, the grapheme membranes will template the quasi-epitaxial crystalline growth of organic semiconductors, thereby improving charge and energy transport and device performance. Third, the grapheme membrane has the potential to modulate charge injection and extraction at the organic/organic and organic/electrode interfaces, to enable an additional device performance tuning capability. Finally, it is proposed that the grapheme membranes will Increase the durability of OPVs on flexible substrates. Specifically, graphene monolayer/indium tin oxide (ITO) hybrid transparent conductors are proposed in which cracks in ITO are ?healed? by grapheme monolayer bridges. The research plan has two major objectives. The first objective is to develop an understanding of how to best integrate, grow, and deposit atomically-thin, crystalline graphene or boron-nitride membranes at the active interfaces of OPVs. The second objective is to evaluate the properties of these membranes at interfaces ? specifically for their behavior as diffusion barriers, their effect on molecular templating, their modulation of charge and energy transport, and their applicability as hybrid transparent conductors. Successful completion of the proposed work may result in higher efficiency OPV devices with extended lifetime; an improved understanding of diffusion through atomic membranes; new strategies for templating organic crystalline growth; and new understanding of charge and energy transport mechanisms across ideal interfaces. Broader Impacts The proposed education and outreach plan includes student training, course development, and public outreach centered on the proposed research and solar photovoltaics. The education plan will train one graduate student and involve three undergraduate students in the proposed research. Research on transport in atomic membranes will be incorporated into graduate level electronic materials course, and an undergraduate transport phenomena course. To engage the public, the PI will work with the UW-Madison Energy Institute to develop web-based educational modules on solar photovoltaics. Furthermore, a public lecture developed by the PI titled "Why doesn't my electricity come from the sun? Future materials for solar photovoltaic solar cells" will be enhanced and then aired on a local Public Broadcasting System (PBS) program.