Shedding light on polymer solar cells: Illuminating how solvent
additives improve efficiency

Date:
January 28, 2022
Source:
Nara Institute of Science and Technology
Summary:
Researchers imaged nanoscale photocurrents in an all-polymer blend
solar cell using photoconductive atomic force microscopy. Trace
solvent additives were found to enhance polymer ordering and
crystallization without undesirable changes in the scale of
phase separation necessary for device performance. The findings
explain the basis of the performance enhancement attributed to
solvent additives and will accelerate research efforts aimed
at establishing all-polymer blend solar cells as a viable
environmentally sustainable choice.



FULL STORY ========================================================================== All-polymer blend solar cells are expected to play an important role in
the transition to clean energy technologies because they can be easily
produced in large-scale flexible sheets. However, their performance has
lagged behind that of more traditional silicon alternatives, as well as
other organic solar cells.


========================================================================== All-polymer blend solar cells are formed by combining two polymer
solutions that solidify into a film on an electrode with in the form of interpenetrating networks, a kind of "phase-separation." The introduction
of solvent additives to the polymer solution has been shown to increase
the efficiency of all- polymer blend solar cells. However, the exact
process underlying this improvement has not been fully understood. Now, in
a study recently published in ACS Applied Polymer Materials, researchers
from Nara Institute of Science and Technology have investigated the
performance enhancement mechanism using photoconductive atomic force
microscopy (PC-AFM). Their findings are expected to help accelerate the widespread application of polymer-based solar cells.

"The empirical nature of solvent additive-mediated efficiency enhancement
has hindered the optimization of all-polymer blend solar cell performance,
so there has been an urgent need for a greater understanding of the
process," explains senior author Hiroaki Benten. "To that end, we used
PC-AFM to interrogate the nanoarchitecture that underpins the performance enhancement." PC-AFM is an advanced microscopy technique that allows photocurrents to be visualized with nanometer-scale resolution. The
researchers found that trace solvent additives improved the power
conversion and photocurrent density of an all-polymer blend solar cell
by a factor of up to ~3 by enhancing the ordering and crystallization
of the polymer microstructure in the solar cell without damaging the phase-separated structure.

Absorption spectroscopy measurements further confirmed that the trace
additives improved the ordering in the polymer microstructures. By forming
a network that efficiently transports the photogenerated charges to the external electrode, the flow of photocurrent is increased.

"We found that local photocurrents were enhanced, somewhat like forming a
new charge current highway, while the scale of phase separation that is critical to device functionality was retained," says coauthor Masakazu Nakamura. "We believe that this insight will be broadly applicable
to all-polymer blend solar cells, not just those based on our choice
of polymers." The results of the study are expected to be important
for optimizing the performance of all-polymer blend solar cells. By
using the findings to minimize laboratory trial-and-error, it is hoped researchers can speed up ongoing bench- to-market efforts, taking us
a step closer to high-performance solar cells that are environmentally sustainable and easy to produce on a large scale.

========================================================================== Story Source: Materials provided by
Nara_Institute_of_Science_and_Technology. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Yuji Yamagata, Hiroaki Benten, Toshiki Kawanishi, Masakazu Nakamura.

Nanoscale Observation of the Influence of Solvent Additives on
All- Polymer Blend Solar Cells by Photoconductive Atomic Force
Microscopy. ACS Applied Polymer Materials, 2021; 4 (1): 169 DOI:
10.1021/acsapm.1c01173 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220128100753.htm

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