Wednesday, 22 May 2019

NYU Tandon researchers build non-fullerene organic solar cells with improved efficiency

Using a squaraine molecule in a novel way - as a crystallizing agent - facilitates the orientation of the donor-acceptor polymer (PBDB-T) with the non-fullerene acceptor (ITIC) in a favourable arrangement

NYU Tandon - Non-fullerene organic photovoltaic

5 Mar 2018 | Editor

A team of researchers from NYU Tandon - led by Tandon Associate Professor André D. Taylor of the Chemical and Biomolecular Engineering Department - have found an innovative and promising way to improve organic solar cells and make their use in many applications more likely.

According to the researchers most organic solar cells use fullerenes, spherical molecules of carbon. Taylor said the problem is that fullerenes are expensive and don't absorb enough light.

Over the last 10 years Taylor has made significant progress in improving organic solar cells, and he has recently focused on using non-fullerenes, which until now have been inefficient. However, he says, "the non-fullerenes are improving enough to give fullerenes a run for their money."

Think of a solar cell as a sandwich, the active layer - made of electron donors and acceptors - is in the middle, absorbing sunlight and transforming it into electricity (electrons and holes), while the outside layers, consist of electrodes that transport that electricity.

Taylor and his team's goal was to have the cell absorb light across as large a spectrum as possible using a variety of materials, yet at the same time allow these materials to work together well.

The group works on key parts of the 'sandwich,' such as the electron and hole transporting layers, while other groups may work only on the interlayer materials. The question is: How do you get them to play together? The right blend of these disparate materials is extremely difficult to achieve."

Using a squaraine molecule in a new way - as a crystallizing agent - did the trick. Taylor added a small molecule that functions as an electron donor by itself and enhances the absorption of the active layer. By adding this small molecule, it facilitates the orientation of the donor-acceptor polymer (called PBDB-T) with the non-fullerene acceptor, ITIC, in a favourable arrangement.

This solar architecture also uses another design mechanism that the Taylor group pioneered known as a FRET-based solar cell. FRET, or Förster resonance energy transfer, is an energy transfer mechanism first observed in photosynthesis, by which plants use sunlight. Using a new polymer and non-fullerene blend with squaraine, the team converted more than 10 percent of solar energy into power. Just a few years ago this was considered too lofty a goal for single-junction polymer solar cells. There are now newer polymer non-fullerene systems that can perform above 13 percent, so the researcher's view is that their contribution is a viable strategy for improving these systems.

The organic solar cells developed by Taylor and his team are flexible and could one day be used in applications supporting electric vehicles, wearable electronics, or backpacks to charge cell phones. Eventually, they could contribute significantly to the supply of electric power. "We expect that this crystallizing-agent method will attract attention from chemists and materials scientists affiliated with organic electronics.

The researchers have recently started working on perovskite solar cells as well as continuing to improve non-fullerene organic solar cells.

The National Natural Science Foundation of China, the Project of Science and Technology of Sichuan Province, the U.S. National Science Foundation, and the Yale Institute for Nanoscience and Quantum Engineering supported the research.

A Highly Efficient Polymer Non-Fullerene Organic Solar Cell Enhanced by Introducing a Small Molecule as a Crystallizing-Agent

Yifan Zheng | Jiang Huang | Gang Wang | Jaemin Kong | Di Huang | Megan Mohadjer Beromi | Nilay Hazari | André D.Taylor | Junsheng Yu


Non-fullerene organic solar cells (OSCs) have attracted tremendous interest because of their potential to replace traditional expensive fullerene-based OSCs. To further increase the power conversion efficiency (PCE), it is necessary to offset the narrow absorption of the non-fullerene materials, which is often achieved by adding an additive (>10 wt%) to form a ternary blend. However, a high ratio of the third component can often be detrimental to the active layer morphology and can increase the complexity in understanding the device physics toward rationally designed improvements. In this work, we introduce 2,4-bis-[(N,N-diisobutylamino)-2,6-dihydroxyphenyl]-4-(4-diphenyliminio) squaraine (ASSQ) in the poly [(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) benzo [1,2-b:4,5-b′] dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl) benzo [1,2-c:4,5-c′] dithiophene-4,8-dione)] (PBDB-T): 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno [2,3-d:2′,3′-d′]-s-indaceno [1,2-b:5,6-b′] dithiophene (ITIC) as an active layer “crystallizing-agent”. Through detailed morphology characterization, we find that the addition of 4 wt% ASSQ assists ITIC organization order and promotes PDBD-T:ITIC aggregation in the preferential face-on orientation. In addition, we demonstrate that the ASSQ and PBDB-T show efficient exciton dissociation in the ternary blend over Förster resonance energy transfer (FRET). We reveal using surface potential and solubility measurements that a ASSQ-ITIC co-crystalline structure forms which facilitates a significant improvement in the device PCE, from 8.98% to 10.86%.


About NYU Tandon

The NYU Tandon School of Engineering dates to 1854, the founding date for both the New York University School of Civil Engineering and Architecture and the Brooklyn Collegiate and Polytechnic Institute (widely known as Brooklyn Poly). A January 2014 merger created a comprehensive school of education and research in engineering and applied sciences, rooted in a tradition of invention and entrepreneurship and dedicated to furthering technology in service to society. In addition to its main location in Brooklyn, NYU Tandon collaborates with other schools within NYU, the country's largest private research university, and is closely connected to engineering programs at NYU Abu Dhabi and NYU Shanghai. It operates Future Labs focused on start-up businesses in downtown Manhattan and Brooklyn and an award-winning online graduate program.

Source: NYU Tandon

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