State-of-the art polymer solar cells are based on blends of semiconductive polymer and C60 fullerene derivatives. The advantage of these materials is that they can be co-dissolved in a common solvent and cheaply printed on a surface, potentially giving access to lightweight and low-cost solar energy. However, the performance of these materials lacks significantly behind those of inorganic solar cells (such as silicon-based solar cells).
See a recent presentation on this topic, given by Prof. Verduzco at the March 2015 APS meeting here.
The Verduzco laboratory is exploring the use of block copolymers (shown schematically above) for better performance in organic solar cells. While the idea of all-polymer solar cells is not new, the best all-polymer solar cells perform poorly even in comparison to polymer-fullerene blends. By designing new materials and exploring all-conjugated block copolymers, the Verduzco laboratory aims to improve performance and gain a better understanding of the limitations of organic solar cells.
In recent work, we have developed new synthetic strategies for the preparation of all-conjugated block copolymers; block copolymers which contain two pi-conjugated (semiconductive) polymer blocks. While some reports on these materials have been reported, approaches for preparing donor-acceptor block copolymers are limited. Using a “click” chemistry appraoch, we investigated crystallization of a series of P3HT-block-PF diblock conjugated copolymers. As shown below, these materials exhibit competitive crystallinity, with one block or the other dominating the crystalline morphology. The crystallites observed are determined by the ratio of block sizes.
In current work, we exploring all-conjugated block copolymers with both p- and n-type polymer blocks that can be used directly in the active layer of an organic solar cell. In exploring new all-conjugated block copolymers, we need to take into account the molecular structure of the copolymer as well as the film microstructure and processing conditions used.
1. Smith, Stewart, Yager, Strzalka, and Verduzco. “Control of all-conjugated block copolymer crystallization via thermal and solvent annealing,” J. Polym. Sci. B: Polym. Phys. 2014 52, 900-906.
2. Lin, Stewart, Yager, and Verduzco. “Lamellar and Liquid Crystal Ordering in Solvent-Annealed All-Conjugated Block Copolymer Thin Films,” Soft Matter 2014 10, 3817-3825. (OPEN ACCESS)
3. Lin, Verduzco. “Synthesis and Process-Dependent Film Structure of All-Conjugated Copolymers for Organic Photovoltaics,” in Polymer Composites for Energy Harvesting, Conversion, and Storage, 2014, Chapter 3, 49-70.
4. Smith, Yager, Pickel, Kissinger and Verduzco, “Conjugated Block Copolymers via Functionalized Initiators and Click Chemistry,” Journal of Polymer Science A: Polymer Chemistry 2013 52, 154-163.
5. Guo, Lin, Witma, Smith, Wang, Hexemer, Strzalka, Gomez, and Verduzco, “Conjugated Block Copolymer Photovoltaics with near 3% efficiencies through microphase separation,” Nano Letters, 2013 13, 2957-2963. pdf (featured in Materials Today, Solar Novus, AIChE’s CEP Magazine, and Futurity.org)
6. Kempf, Smith, Pesek, Li, Verduzco. “Amphiphilic poly(alkylthiophene) block copolymers prepared via externally initiated GRIM and click coupling,”Polym. Chem., 2013, 4, 2158-2163. pdf
7. Lin, Smith, Kempf, Verduzco. “Synthesis and Crystallinity of All-Conjugated Poly(3-hexyl thiophene) Block Copolymers,” Polym. Chem., 2013, 4, 229-232. pdf
9. Smith, Lin, Dement, Strzalka, Darling, Verduzco. “Synthesis and Crystallinity of All-Conjugated Block Copoly-mers prepared by Click Chemistry,” Macromolecules, 2013 46, 2636-2645. DOI: 10.1021/ma3026223 pdf
10. Botiz, Schaller, Verduzco, Darling. “Optoelectronic Properties and Charge Transfer in Donor–Acceptor All-Conjugated Diblock Copolymers,“ J. Phys. Chem. C., 2011, 115, 9260-9266. pdf
11. Verduzco, Botiz, Pickel, Kilbey, Hong, Dimasi, Darling. “Polythiophene-block-Polyfluorene and Polythiophene-block-Poly(fluorene-co-benzothiadiazole): insights into the self-assembly of all-conjugated block copolymers” Macromolecules, 2011, 44, 530-539.