Organic solar cells (OSCs), which use organic polymers to convert sunlight into electricity, have received much attention for their desirable properties as next-generation energy sources. These properties include its lightweight nature, flexibility, scalability and high power conversion efficiency (>19%). Currently, there are several strategies to improve the performance and stability of OSCs. However, a problem that remains is the difficulty of controlling the morphology of the active layer in OSCs when scaling to large areas. This makes it difficult to obtain high-quality active layer thin films and, in turn, to fine-tune device performance.
In a recent study, a team of researchers from Korea’s Gwangju Institute of Science and Technology set out to address this issue. In their work, published in Advanced Functional Materialsproposed a solution that seems rather counterintuitive at first glance: using water treatment to control the morphology of the active layer.
“Water is known to hinder the performance of organic electronic devices as it remains in the ‘trap states’ of the organic material, blocking charge flow and degrading device performance. However, we realized that using water instead of an organic solvent-based active solution as the treatment medium would allow the necessary physical changes without causing chemical reactions,” explains Professor Dong-Yu Kim, who led the study.
The researchers chose polymers PTB7-Th and PM6 as donor materials and PC61BM and EH-IDTBR and Y6 as acceptor materials for the active layer. They observed that inducing a vortex to mix the donor and acceptor materials in the active solution could lead to a well-mixed active solution, however it was not sufficient by itself.
The active solution was hydrophobic, and thus the researchers decided to use deionized (DI) water and vortexers to agitate the solution. They let the donor and acceptor materials sit in chlorobenzene (active host solution) overnight, then added DI water to the solution and stirred it, creating tiny eddies.
Due to the hydrophobic nature of the solution, the water pushed the donor and acceptor molecules, causing them to dissolve more finely in the solution. They then let the solution rest, which caused the water to separate from the solution. This water was then removed and the water-treated reactive solution was used to prepare thin films of PTB7-Th: PC61BM (F, fullerene), PTB7-Th: EH-IDTBR (NF, fullerene), and PM6: Y6 (H- NF , high yield non-fullerene).
The researchers then tested the photovoltaic performance of these thin films in an inverted slot-coated OSC configuration and compared them to those for OSCs without water treatment.
“We observed that the water-treated active solution resulted in a more uniform active layer of thin films, which exhibited higher power conversion efficiency compared to those not treated with water. In addition, we fabricated large-area OSC units with an active area of 10 cm2 , which showed a conversion efficiency of up to 11.92% for water-treated H-NF films,” says Professor Kim.
Over 14% efficiency for ternary organic solar cell with 300 nm active layer More information: Nara Han et al, Introduction of water treatment in slit-coating organic solar cells to improve device performance and stability, Advanced Functional Materials (2022). DOI: 10.1002/adfm.202204871
Provided by GIST (Gwangju Institute of Science and Technology)
Reference: Researchers pave the way for large-scale, efficient organic solar cells with water treatment (2022, September 15) Retrieved September 15, 2022 from
This document is subject to copyright. Except for any fair dealing for purposes of private study or research, no part may be reproduced without written permission. Content is provided for informational purposes only.
