Research in the Marder Group
The Marder Group seeks to advance fundamental knowledge and adapt new discoveries to practical applications through hypothesis-driven molecular design, effective synthesis, and close collaboration with theoreticians and device scientists.
The common thread of research in the Marder Group is the manipulation of electrons in organic and organometallic systems. We design molecules to control localization and delocalization in conjugated materials to probe the influence of molecular structure on bulk properties in nonlinear optical, organic electronic, and surface modifying materials. Further materials design often extends insights gained in the fundamental structure-property research to functional materials that are useful in optical devices, organic light emitting diodes (OLEDs), organic field effect transistors (OFETs), and organic solar cells.
A thorough understanding of our materials and processes is gained through collaboration with outstanding theoreticians, physicists, device scientists, and engineers throughout the world.
Materials such as (MeNH3)PbI3 adopt a 3D perovskite-type crystal structure and exhibit a unique combination of properties; their optical and electrical properties resemble those of traditional inorganic semiconductors, but are much less sensitive to the presence of impurities, while the materials themselves can be processed from organic solvents, rather than required high-temperature processing. In particular, these materials can serve as the active layers of highly efficient perovskite solar cells (PSCs) as emitters in light-emitting diodes. Hybrid organic lead-halide materials with larger organic cations form lower dimensional materials with a vast structural diversity and a variety of potential applications, including protective capping layers for 3D materials. The Marder group has developed organic transport materials to be used, with or without dopants, as carrier-selective extraction layers for use in PSCs, and has synthesized many new low-dimensional hybrid organic lead-halide materials, particularly focusing on understanding the relation between the chemical structure of the organic cation and the crystal structures of the resulting hybrid materials.
Organic Solar Cells
The Marder Group designs and synthesizes light-absorbing and/or charge-transporting materials for organic solar cells. We have worked in the area of dye-sensitized solar cells (DSSCs), where have developed dye sensitizers based on a highly absorbing core to increase utilization of solar energy Most of our efforts, however, have focused on bulk heterojunction (BHJ) solar cells, which typically consist of blends of light-absorbing and hole-transporting “donor” polymers and electron-transporting “acceptor” molecules. We have worked on both donor and acceptor components, but our current efforts are primarily focused on fused-ring non-fullerene acceptors, which have recently led to dramatic increases in solar-cell efficiency due in much more significantly contributing to light absorption than the traditional fullerenes. We are currently working to understand how the structures of these NFAs can be modified to tune their light-absorption, increase their stability, increase processability for environmentally benign solvent, and/or affect phase separation from donor polymers, which is critical for BHJ solar cells. We are also looking how changes in processing conditions affect the morphological evolution of the materials and its impact on device efficiency.
The Marder Group designs electrical dopants for organic semiconductors to increase the conductivity of organic semiconductors and to modify the energetic barriers for charge-carrier transport across interfacing; doping has applications in devices including organic light emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaics (OPVs, see above), and lead-halide perovskite solar cells (PSCs, see below). We have worked on developing both p- dopants (oxidants) for hole transport materials and n-dopants (reductants) for electron transport materials. While the simplest approach to dopants is to use one-electron oxidants or reductants, powerful n-dopants that follow this paradigm will necessarily be highly air-sensitive. Accordingly, we and other have developed “complex” n-dopants in which the electron-transfer is coupled to other chemistry, allowing for powerful dopants that are moderately air stable. In particular, we have developed dimeric dopants n-dopant based on dimers of highly reducing species, both 19-electron organometallic sandwich compounds and certain organic radicals. These molecules can be handled in air, yet in some cases are capable of doping challenging substrates including molecules used as electron-transport materials in OLEDs. We have performed detailed mechanistic studies on these dimers that provides insight into their scope of use of dopants and to help develop the next generation of air-stable, widely processable dopants. We have collaborated widely to demonstrate the benefits of these dopants in a wide range of organic and hybrid organic-inorganic electronic devices.
The Marder Group designs molecules that bind to both planar and nanoparticle inorganic surfaces to manipulate surface properties such as work function, wettability, stability, and processability. Classes of modifiers that w have worked with include phosphonic acids for oxides such as indium tin oxide (ITO), N-heterocyclic carbenes for gold, and redox-active dopants (see above) for use on metals, metal oxides, and low-dimensional materials such as few-layer metal chalcogenides and graphene. Applications include modification of the substrate work function to match a variety of organic electronic materials for OLEDs, OFETs, and OPVs\and compatibilization ofinorganic metal oxide nanoparticles with polymer matrices , allowing the preparation of composites with high electric permittivity and dielectric strength for high-density energy storage. Currently we are working on phosphonic acid surface modifiers including redox-active moieties for applications in organic and perovskite solar cells.
Covalent Organic Frameworks
Two-dimensional covalent organic frameworks (2D COFs) are a class of 2D polymer consisting of macromolecular sheets with periodic voids that are produced from topologically planar monomers. These monomers can be rationally modulated to: tune pore size, topology, and dimensionality; alter the framework’s linkage chemistry; or incorporate desired chemical functionality at precise locations within the network. The unique structural aspects and synthetic versatility of 2DPs have led to substantial interest in these materials for organic electronics, nanofiltration membranes, energy storage devices, and chemical sensors. The Marder group has synthesized new monomers for COFs, based on a variety of linkage chemistry for both polymerization as single-layer materials on surfaces and for bulk synthesis of COF powders and films. We have focused on the synthesis of materials with potentially interesting electronic or optical properties, in some cases as predicted by collaborating theoreticians. In particular, we have developed new monomers with redox activity and that can be linked to give in-plane conjugation that is strong compared to that in many COFs studied to date, and applied our dopants (see above) to modulation of the electronic properties of COFs.