Fill me: Improved efficiency of all polymer solar cells

High FFs (~70%) in all-polymer blend solar cells are achieved due to longer charge-carrier lifetimes due to lower bimolecular charge recombination coefficients. The preferred blend morphology for suppressing bimolecular charge recombination is characterized by a well-ordered local structure due to the chain integration of the polymer donor (D) and acceptor (A). Credit: Hiroaki Benten

Solar cells are an important contributor to a renewable energy supply, but solar panel waste can quickly become a major problem. Now, in a study that was recently published in Journal of Materials Chemistry Aresearchers from the Nara Institute of Science and Technology (NAIST) are investigating science that may help improve the utility of easily mass-producible, all-polymer-based solar cells.

Worldwide, approximately one-third of electricity currently comes from renewable sources. Silicon-based solar cells are the main contributor, but there is a growing problem: what to do with the panels after their 30-year lifespan. A May 2022 article on Chemical and Engineering News poses the problem: even if the facilities recycle the frames and covers of the panels, the most valuable or even the toxic elements are simply thrown away. With an estimated 80 million metric tons of solar panel waste generated by 2050, this is a huge waste problem.

Polymer-based solar cells are a possible, less wasteful solution. Such panels are thin and flexible, and thus in principle there are many. However, they have some problems; eg, a lower power conversion efficiency than silicon. “This efficiency is severely limited by fill factors: typically below 60%, even in advanced devices,” said corresponding author Hiroaki Benten of the Nara Institute of Science and Technology. “The science behind the limited efficiency of all-polymer composite solar cells remains insufficiently explored.”

A ground-breaking result of this research is the high filling factor: 70%, which remains 60% even for polymer films that are several hundred nanometers thick. Competing polymer technology shows a 40% filling factor at this thickness. This is because the bimolecular recombination of free electrons with free holes largely inhibited the fill factor in earlier work, but was suppressed in the current study.

What prevents bimolecular recombination within polymer blends? “There is considerable charge delocalization in the donor and acceptor domains,” explained Masakazu Nakamura, senior author. “The appropriate combination of polymer donors and acceptors led to a highly ordered local structure of the polymer, which helped to retain the separation of electrons from holes.”

Although the researchers have completely solved the problem of the efficiency of all-polymer solar cells, they still need to improve the 10-year service life of the most advanced research prototypes. Additional research efforts include optimizing film morphology, and even developing hybrid polymer/silicon solar cells, to optimize energy collection and efficiency. In the coming years, solar cells may look and work completely different from—and better than—modern technology.


Illuminating how solvent additives improve the efficiency of polymer solar cells


More information:
Ren Hagio et al, Chain aggregation dictates bimolecular charge recombination and fill factor in all-polymer blend solar cells, Journal of Materials Chemistry A (2022). DOI: 10.1039/D2TA04705E

Provided by Nara Institute of Science and Technology

Citation: Better efficiency of all-polymer solar cells (2022, October 3) retrieved 3 October 2022 from https://techxplore.com/news/2022-10-efficiency-all-polymer-solar-cells.html

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