Uncovering the secret of ternary polymer solar cell success

Date:
April 21, 2022
Source:
University of Tsukuba
Summary:
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.



FULL STORY ========================================================================== 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.


========================================================================== Related Multimedia:
* Thin,_flexible_solar_cell ========================================================================== 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 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220421141613.htm

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