Professor Trisha L. Andrew and her students at the University of Massachusetts Amherst were supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to develop a novel approach to fabricate textile electronic devices. The team?s ultimate aim was to transform familiar fabrics and threads into electronic circuit components by coating the fabric surface with conjugated organic polymers. The project investigated the chemical processes involved in the vapor deposition of conjugated polymers on fabrics and the reaction conditions that could enable the growth of an organic solar cell or light-emitting diode directly on commodity or prewoven fabrics, thus establishing the fundamental chemistries needed to create solar harvesting textiles.

The project explored the range of electronic polymer films that can be created by reactive vapor coating. The focus was on chemical processes involved in the vapor deposition of Type II donor-acceptor heterojunctions, which is the basis of most organic solar cells (OSCs). Professor Andrew and her students gained a significant amount of learning and understanding through the project period in the form of both successes, and key reaction and process failures that educated the team on the scope and limitations of reactive vapor coating as a tool for the synthesis of conjugated materials.

Notably, Professor Andrew and her students demonstrated and optimized vapor coating recipes for two different Type II heterojunctions, both of which contained a novel ambipolar polycyclic aromatic hydrocarbon (PAH) oligomer as an unconventional, fullerene-free electron-accepting layer. The team also developed a vapor coating recipe to polymerize a bioderived dye, guaiazulene, and access a visible-NIR-absorbing, hole-conducting film that forms Type II heterojunctions with many electron acceptors, including the PAH oligomer described earlier. In sum, these chemical processes successfully created green-processed optoelectronic coatings for solar harvesting textiles.

Two key insights were gained during the fruitful journey of developing recipes for these two heterojunctions. First, extended pi-conjugated aromatic systems, such as acenaphthene, phenanthrene, benzofuran and benzothiophene, and derivatives thereof, were discovered to be unreliable monomers for reactive vapor coating because their ?sticking coefficient? was observed to be close to unity. Such near-unity sticking coefficients meant that these molecules were pinned at any surface close to the vapor source and, therefore, could not diffuse to collide with another reactant to initiate a bimolecular reaction, even with applied heat and vacuum. Due to this ?sticking? effect, coatings resulting from these extended pi-conjugated monomers were unpolymerized, nonuniform and easily dissolved.

The second key insight gained during this project was a solution to this ?sticking? problem. The team demonstrated that non-planar and/or strategically hydrogenated versions of a desired pi-conjugated repeat unit were ideal monomers for reactive vapor coating because the saturation points provided geometric nonplanarity that afforded the molecules greater rotational/translational energy and surface mobility and, therefore, the chance to collide with monomers/oxidants/initiators and participate in chain extension interactions. A unique feature of the oxidative vapor coating process used by the team was that the hydrogenated moieties were quantitatively re-oxidized in situ, providing access to electronic polymer films and coatings at the end. Most interestingly, the team showed that robust and conformal PAH textile coatings could be created via this pre-hydrogenation strategy and that the PAH films thus created were uniquely ambipolar and could serve as fullerene-free electron acceptors in OSCs.

Unexpected discoveries were also made during the project period, as a result of research endeavors meant to tackle the proposed project aims. A new vapor polymerization process was demonstrated by Professor Andrew and her students?photoinitiated chemical vapor deposition (piCVD)?that introduced light and a ketone-containing photoinitiator as reagents for creating robust textile coatings via a vapor-phase Norrish Type I reaction. The team used this piCVD process to create robust, ultrathin protective coatings for various textile electronics and, most usefully, enzyme-based biosensors that are susceptible to degradation in storage. The team also discovered that living plants survived the vapor coating process and successfully decorated selected seedlings with patterns of conducting polymer coatings. The conducting polymer ?tattoos? on the seedlings were then used as connection points to electronically reveal UV damage and ozone damage in the growing plants and, by proxy, monitor the UV and ground ozone levels in orchards. Professor Andrew and her students also discovered that vapor-coated textiles smartly incorporated into garments at strategic locations were unusually-efficient wearable thermoelectric generators, whose on-body thermopower generation abilities were improved upon exposure to sweat and moisture.

Ten peer-reviewed Journal publications were produced by the project. Professor Andrew was named a ?Highly Cited Researcher? by the Royal Society of Chemistry during the project period.

The project provided education and training to a diverse population of researchers, including three graduate students engaged in Ph.D. research, two undergraduates gaining their first research experiences, and two community college students participating in an internship program that increased opportunities for minority, underprivileged and first-generation researchers.

Last Modified: 10/24/2022
Modified by: Trisha L Andrew