Conjugated polyelectrolytes are described by a polymer backbone with a polarizable pi-delocalized electronic structure and pendant groups bearing ionic functionalities. These materials thus incorporate the useful optical and electronic attributes of semiconducting and light harvesting polymers with the properties of polyelectrolytes, which are modulated by complex electrostatic interactions. Such a combination of properties opens unique opportunities for designing materials that can be integrated into optoelectronic devices. One attractive target involves the creation of stable p-n junctions, which constitute a cornerstone in the fabrication of inorganic solid state devices. Such a fundamental module in organic counterparts has been difficult to attain due to difficulties in depositing thin films with independent p-doped and n-doped layers. The approach will take advantage of ion migration across polymer bilayers and concomitant formation of covalent bonds for permanently fixing the junction. Specific polymers will be designed and synthesized that have anion receptor groups and solubility properties for multilayer device fabrication. Another opportunity lies in the design, synthesis and applications of conjugated polyzwitterions. These materials are generated by attaching Lewis acids to lone pairs of electrons present along the polymer chain. When this approach is used on a conjugated polymer with a donor/acceptor motif, it is possible to attain large red shifts in the absorption profiles due to the stabilization of charge transfer excited states. Such polymers are essentially unexplored and offer new opportunities in the design of new materials for solar cell fabrication.

NON-TECHNICAL SUMMARY

Emerging organic optoelectronic technologies require materials with suitable electronic properties that can enable mass fabrication by solution methods, for example similar to those used in the production of photographic film. Conjugated polyelectrolytes are a new class of semiconducting polymers that open opportunities to create modules similar to those widely used with silicon-based technologies. One of the principal goals of this proposal is to integrate these conjugated polyelectrolytes and related materials into diodes and plastic solar cells. The work will include molecular design, materials preparation, examination of physical properties and device fabrication and testing. Students will benefit from a broad scientific perspective, which will serve them well in their future careers. Additionally, international links are in place for raising their awareness to global collaborations. Programs are also in place for educational programs with undergraduate and minority-serving institutions.

Project Report

The completion of this project has provided the scientific and engineering communities with new types of smart materials with properties relevant for advancing a new generation of electronic and optoelectronic devices. Specifically, new polymers with molecular and semiconducting properties have been developed that allow integration into devices such as transistors, solar cells and light emitting diodes. Unlike inorganic semiconductors, these polymeric materials can be deposited from solution and therefore have the promise to be more economically viable. The types of polymeric structures studied in this program are named conjugated polyelectrolytes and are described by a long chain of repeat units that are strongly bound to each other while at the same time contain delocalized electron density. The latter is important for the semiconducting properties. Also, the long molecules contain ionic functionalities, which render them soluble in polar media, such as alcohols and water. One can therefore cast electronically active layers from environmentally friendly solvents such as water and alcohol. It was also shown in this program that the choice of electrostatic charge near the polymer backbone also determines whether one can add or subtract electrons easily thereby greatly changing the electronic behavior of the films. This ability to chose positive or negatively charged charge carriers is important for designing electronic function. A relevant illustration of function was demonstrated using light emitting field effect transistors, in which a very thin layer of the conjugated polyelectrolyte was used as an interlayer between metal electrodes and a neutral organic semiconductor. Only when the conjugated polyelectrolyte was present was it possible for the transistor to emit light. These observations, together with related mechanistic work, indicates that while only a nanoscale-thick layer of the conjugated polyelectrolyte is present in the device, it can greatly control how charges are injected and whether the management of these charges can lead to the creation of photons. From a practical perspective, such smart-material enabled devices can form the basis of future more power efficient display technologies.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Type
Standard Grant (Standard)
Application #
1005546
Program Officer
Andrew Lovinger
Project Start
Project End
Budget Start
2010-05-01
Budget End
2013-04-30
Support Year
Fiscal Year
2010
Total Cost
$405,000
Indirect Cost
Name
University of California Santa Barbara
Department
Type
DUNS #
City
Santa Barbara
State
CA
Country
United States
Zip Code
93106