Aggregation and Morphology Control Enables Multiple Cases of Polymer Solar Cells with Efficiencies near 11 percent

He Yan^a, Harald Ade^b

^aHong Kong University of Science and Technology, Department of Chemistry, Hong Kong

^bNorth Carolina State University, Partners Way, 911, Raleigh, United States

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Invited Speaker Session, He Yan, presentation 203
Publication date: 5th February 2015

Polymer solar cell (PSC) technology has attracted much attention due to its promise as low-cost conversion of solar energy. Despite recent progress, several limitations are holding back PSC development. For instance, current high-efficiency (>9.0%) PSCs{Liao, 2013 #103}are restricted to materials combinations that are based on limited donor polymers and only one specific fullerene acceptor, PC₇₁BM. Furthermore, best-efficiency PSCs are mostly based on relatively thin (100 nm) active layers. Thick-film PSCs generally exhibit lower fill factors and efficiencies compared to the best thin-film PSCs.Here we reportmultiple cases of high-performance thick-film(300 nm) PSCs (efficiencies up to 10.8%, fill factors up to 77%) based on conventional PCBM and many non-PCBM fullerenes. Our simple aggregation control and materials design rules allowed us to develop, within a short time, three new donor polymer, six fullerenes (including C60-based fullerenes), and over ten polymer:fullerene combinations, all of which yielded higher efficiency than previous state of art devices(~9.5%). The commonstructural featureof the three new donor polymers, the 2-octyldodecyl (2OD)alkyl chains sitting on quaterthiophene, causes a temperature-dependent aggregation behavior that allows for the processing of the polymer solutions at moderately elevated temperature, and more importantly, controlled aggregation and strong crystallization of the polymer during the film cooling and drying process.This results in a well-controlled and near-ideal polymer:fullerene morphology(containinghighly crystalline, preferentially orientated, yet small polymer domains) that is controlled by polymer aggregation during warm casting and thus insensitive to the choice of fullerenes. With further interface and optical engineering, polymer solar cells with 11.5% PCE have been achieved. The second part of this presentation will describe highly efficient non-fullerene PSCs with power conversion efficiencies up to 7.0%. There are several attractive features of our non-fullerene PSCs. 1) An exceptionally high Voc of nearly 1V can be achieved for a PSC with an optical bandgap of 1.6 eV. 2) A new small molecule acceptor with a unique 3D structure was developed that exhibits similar morphological and electronic properties to those of PCBMs. 3) Efficient all-polymer solar cells can be achieved using a pair of crystalline polymers that can maintain their crystallinity in the polymer/polymer blend.
Polymer structures and device performance of multiple cases highly efficient thick-film polymer:fullerene solar cells.
1. Liu, Y., Zhao, J., Li, Z., Mu, C., Ma, W., Hu, H., Jiang, K., Lin, H., Ade, H. and Yan, H., Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells. Nat. Commun., 5, 5293, (2014). 2. Liu, Y., Jiang, K., Zhao, J., Li, Y., Zhang, L., Mu, C., Li, Z., Lai, Joshua., Hu, R., Huang, X., Tang, B. and Yan, H.,  tetraphenylethylene core-based 3D-structure small molecule acceptor enabling efficient non-fullerene organic solar cells. Adv. Mater., (2014), DOI: 10.1002/adma.201404152, in press. 3. Zhao, J., Li, Y., Lin, H., Liu, Y., Jiang, K., Mu, C., Ma, T., Lai, Joshua. and Yan, H., High-Efficiency Non-Fullerene Organic Solar Cells Enabled by a Difluorobenzothiadizole-Based Donor Polymer Combined with a Properly Matched Small Molecule Acceptor. Energy & Environmental Science, (2014), DOI:10.1039/C4EE02990A, in press. 4. Mu, C., Liu, P., Ma, W., Jiang, K., Zhao, J., Zhang, K., Chen, Z., Wei, Z., Yi, Y., Wang, J., Yang, S., Huang, F., Facchetti, A., Ade, H. and Yan, H., igh-Efficiency All-Polymer Solar Cells Based on a Pair of Crystalline Low-Bandgap Polymers. Adv. Mater., (2014), DOI: 10.1002/adma.201402473. 5. Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J.; Dotz, F.; Kastler, M.; Facchetti, A.  high-mobility electron-transporting polymer for printed transistors. Nature，(2009), 457(7230), 679-686.

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