47043-AC10
Side Chains with Incompatible Packing: A Strategy to Assemble Organic Semiconductors
In organic-based photovoltaic (OPV) cells, it is a challenge to assemble p-conjugated semiconductors, which act as electron- and hole-conductors, into nanoscale structures with a heterojunction between the charge-carrier conductors for efficient charge separation and continuous phases of the charge-carrier conductors for high charge mobility. Our approach involves appending side chains to electron-rich and electron-poor moieties such that side chains are immiscible. Based on chemical nature and packing propensities, we had identified various pairs of moieties that are immiscible. The archetypical example of such a pair is where one moiety is hydrophobic and another moiety is hydrophilic. Similarly, it well known that an aliphatic fluorocarbon will not form a co-crystal with an aliphatic hydrocarbon. Consequently, if a molecule has hydrocarbon and fluorocarbon sections, then in the solid state packing, these sections phase separate. Similar observations have been made in polymeric and dendritic systems. The mutual phobicity of the hydrocarbon-fluorocarbon interactions have also been used in the field of protein engineering and in biomedical applications.
The proposal had identified five research objectives. The current status for each these objectives is shown below
Specific Research Objectives (reproduced verbatim) | Current Status |
To synthesize molecular dyads with terthiophenes or quaterthiophenes as the p-type semiconductor and naphthalenediimide as the n-type semiconductor | Accomplished |
To synthesize semiconductor dyads with side chains that will have incompatible packing | Accomplished |
To crystallize the dyads and study the solid state packing using single crystal X-ray crystallography | In Progress |
For molecules that do not crystallize, characterize the morphology of the annealed thin films from these dyads using X-ray diffraction or scattering, electron microscopy and atomic force microscopy, and | In Progress |
To show that side chain pairs with incompatible packing can be used to create heterojunctions for photovoltaic cells | In Progress |
Plans for Year 2:
We are in the processing of characterizing dyads and polymers using thin film characterization techniques such as X-ray diffraction, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. We will also evaluate the utility of various side chains in obtaining segregated structures. We have also established collaboration with Prof. Jayant Kumar at the University of Massachusetts Lowell to measure mobilities and photovoltaic cell metrics of the polymeric systems. These studies will also be completed this year.
