Researchers Integrate Recyclable Materials into Design of Semiconductors
Current recycling methods often involve harsh chemical treatments that destroy valuable components of organic semiconductors. The UNC team sought to address this by incorporating ester linkers—chemical bonds that can be selectively broken—into the backbone of organic polymers.
January 23, 2025 I By Dave DeFusco
In the quest to make organic electronics more environmentally friendly, researchers in the Department of Chemistry at UNC-Chapel Hill have developed a promising strategy for recycling organic semiconductors.
In the study, “Achieving Closed-Loop Recycling of a Semi-Conjugated Polymer Through the Incorporation of Ester Linkers Along the Backbone,” published in ChemSusChem, Anthony Megret-Bonilla, lead author of the paper and Ph.D. student, and Dr. Wei You, senior author of the paper and professor of chemistry, focus on creating polymers that not only perform well in electronic devices but can also be broken down and reused, addressing the growing issue of electronic waste, or E-waste.
Organic electronics, such as solar cells, transistors and light-emitting diodes used in TV and smartphone screens, have gained popularity due to their flexibility, lightweight design and tunable properties; however, as their use becomes widespread, the challenge of dealing with discarded devices looms large.
“Unlike traditional electronics, which often end up in landfills, the goal is to design organic semiconductors that can be fully recycled, minimizing environmental harm,” said Megret-Bonilla.
Traditional organic semiconductors are made from materials that are difficult to break down and reuse. Current recycling methods often involve harsh chemical treatments that destroy valuable components or require expensive waste management. The UNC team sought to address this by incorporating ester linkers—chemical bonds that can be selectively broken—into the backbone of organic polymers.
The researchers synthesized three types of ester-based monomers, or building blocks: Thiophene-Ester-Ethylene-Thiophene (TEET); Thiophene-Ester-Methylene-Thiophene (TEMT); and Thiophene-Ester-Thiophene (TET).
These monomers were combined with a commonly used unit, benzodithiophene (BnDT), to create three new polymers: PBnDT-TEET; PBnDT-TEMT; and PBnDT-TET. The goal was to study how the ester linkers affected the polymers’ performance in devices and their ability to be recycled. The study’s key Findings are:
- Recyclability
All three polymers could be broken down using a mild chemical process called methanolysis, which uses methanol to target the ester linkers. Among the three, PBnDT-TEET showed the highest potential for recycling. When broken down, it produced a single, reusable product with a 92% yield, which could then be repolymerized into the original polymer. - Performance in Devices
The polymers were tested in organic solar cells to evaluate their efficiency. PBnDT-TET performed the best among the ester-based materials, achieving an efficiency of 0.37%; however, this was still significantly lower than the 1.83% efficiency of a fully conjugated polymer (PBnDT-T2) without ester linkers. - Trade-Offs
The incorporation of ester linkers disrupted the flow of electrical charge along the polymer chain, reducing the polymers’ overall performance. PBnDT-TEET, while the most recyclable, had the lowest efficiency (0.03%) due to its disrupted molecular structure.
This research highlights the delicate balance between designing materials that are both high-performing and sustainable. While PBnDT-TEET excels in recyclability, its low efficiency underscores the challenge of creating polymers that meet both goals. The study provides a roadmap for future work, emphasizing the need to optimize polymer structures to maintain performance while enabling closed-loop recycling.
“The findings represent a significant step toward reducing E-waste from organic electronics,” said Dr. You. “By integrating recyclable materials into the design of semiconductors, we’re paving the way for a more sustainable future. The team’s work demonstrates that with innovative chemistry, it is possible to rethink the lifecycle of electronic materials, ensuring they can be reused rather than discarded.”