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Uncovering the secret of ternary polymer solar cell success

April 21, 2022
University of Tsukuba
A research team has used electron spin resonance spectroscopy to investigate a polymer solar cell while in operation. Molecular level comparison of the PTzBT/PC61BM system with and without added ITIC allowed them to establish the mechanism for the improvements in stability and power conversion efficiency observed when ITIC is added. It is hoped that this insight will contribute to the commercial realization of cost-effective flexible polymer solar cells.

Solar cells will doubtless play a significant part in a sustainable energy future. Polymer solar cells (PSCs) specifically provide an excellent option because they are cheap to produce and can be both flexible and semitransparent. Ternary polymer solar cells are showing encouraging power conversion efficiencies, but it isn't always clear why. Now, researchers from the University of Tsukuba and Hiroshima University have taken a closer look at PSCs in operation. Their findings are published in npj Flexible Electronics.

PSCs generally contain a material that is the p-type semiconductor mixed with one that is the n-type semiconductor. This blend gives the right combination of charge carriers -- holes and electrons -- for a current to flow when sunlight shines on the cell.

Blends with these two components are known as binary PSCs. However, it has recently been found that adding an extra ingredient to the mix -- giving what is known as a ternary PSC -- can improve the power conversion efficiency (PCE) and stability of the solar cell. The trouble is that up until now nobody has thoroughly investigated why.

The researchers therefore conducted electron spin resonance (ESR) spectroscopy while the PSC was operating. This gave them the chance to observe the behavior of the electrons and holes when the cell was irradiated with sunlight and to get answers on a molecular level.

"It has been reported that the accumulation of charge over time contributes to the performance of cells deteriorating," explain study author Professor Itaru Osaka and study corresponding author Professor Kazuhiro Marumoto. "We therefore used ESR to look at a system made up of the polymer PTzBT and large molecule PC61BM. It has been found that adding an acceptor molecule, known as ITIC, to this system improves the PCE and the stability of the cell, so we looked closely at cells with and without ITIC to determine why."

The ESR spectroscopy experiment showed that the short-circuit current decreased as a result of the accumulation of electrons in the PC61BM and holes in PTzBT. Adding ITIC was found to reduce this accumulation by enhancing the orientation of the chainlike PTzBT polymer molecules in the active layer.

"Being able to understand why something works is important for ensuring that effects are optimized to their full potential," says study corresponding author Professor Kazuhiro Marumoto. "By getting a molecular level picture of the effects of ITIC on a very promising PSC system, we believe we have taken a step closer to the commercial reality of polymer solar cells as part of a greener future."

This work was partially supported by JSPS KAKENHI Grant Number JP19K21955, by JST PRESTO, by The MIKIYA Science And Technology Foundation, by Iketani Science and Technology Foundation, by The Iwatani Naoji Foundation, by JST SPRING Grant Number JPMJSP2124, by JST ALCA Grant Number JPMJAL1603, and by JST MIRAI Grant Number JPMJMI20C5, Japan.

Story Source:

Materials provided by University of Tsukuba. Note: Content may be edited for style and length.

Journal Reference:

  1. Dong Xue, Masahiko Saito, Itaru Osaka, Kazuhiro Marumoto. Stability improvement mechanism due to less charge accumulation in ternary polymer solar cells. npj Flexible Electronics, 2022; 6 (1) DOI: 10.1038/s41528-022-00153-z

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University of Tsukuba. "Uncovering the secret of ternary polymer solar cell success." ScienceDaily. ScienceDaily, 21 April 2022. <>.
University of Tsukuba. (2022, April 21). Uncovering the secret of ternary polymer solar cell success. ScienceDaily. Retrieved July 12, 2024 from
University of Tsukuba. "Uncovering the secret of ternary polymer solar cell success." ScienceDaily. (accessed July 12, 2024).

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