MATERIALS | PHOTOVOLTAICS
because conductivity and efficiency depend on it. A common challenge is that the slow charge carriers must be extracted from the organic solar cell before recombination can take place. This is the only way the solar electricity can be used. “One of the key findings of our study is that
transport resistance is a performance-limiting mechanism in modern organic solar cells that needs to be addressed,” said Carsten Deibel, who led the research.
Above: Heliatek has installed organ- ic solar cells at the Port of Barcelona in Spain
– though they are typically less efficient than conventional solar cells. “Optimising the efficiency of these solar cells is
like creating a new cake recipe — it needs a knowledgeable cook who knows how to tweak the ingredients, plus a bit of trial and error,” he said. Vandenberghe, and colleague Julia Hsu, have been investigating how dilute-donor organic solar cells work – and how to advance the technology. Hsu has conducted extensive research into solar energy, including on solar cells made from another material called halide perovskite. “We need to have a portfolio of different types
of renewable energy,” said Hsu. Hsu’s experiments found differences in the
efficiency of organic solar cells made with two types of donor molecules, but it was not clear why one performed better. Using computer simulations, the team found that they could make organic solar cells more efficient if they changed the shape of the donor material. While more research is needed to make organic solar cells viable, the team’s findings help to advance a property of organic solar cell technology that could one day help to boost output current.
Right:
University of Michigan Researchers have found a way to scale up their semi- transparent solar cells
Slow electrons Research by Chemnitz University of Technology and partner universities has shown that slow electrons reduce the efficiency of plastic-based organic solar cells. Organic solar cells offer a more affordable
alternative than conventional solar cells – which are typically based on silicon. However, organic solar cells usually have a lower potential for energy conversion efficiency. The results of the study have been published in
Nature Communications. Although organic semiconductors capture sunlight well, the low mobility of the charge carriers is still a drawback, say the researchers. This is
24 FILM & SHEET EXTRUSION | April 2023
www.filmandsheet.com
Stopping degradation Researchers from South Korea have discovered what causes degradation in large-area organic solar cells – and developed a new polymer additive to prevent it. The team, from the Advanced Photovoltaics
Research Centre at the Korea Institute of Science and Technology (KIST) focused on the photoactive layer’s compositional form in and the solution process – which is a part of the organic solar cell manufacturing process. The spin-coating method, which is mainly used in the laboratory, creates a uniform photoactive layer mixture as the solvent evaporates rapidly while the substrate rotates at a high speed. However, the large-area, continuous solution process designed for industrial use caused solar cell performance deterioration because the so evaporation rate was too slow. This led to unwant- ed aggregation between the photoactive materials. The researchers developed a polymer additive to
prevent this – by interacting with materials prone to aggregation. In addition, owing to possible nano- level structure control, solar cell performance improvements and stability security are acquired against light-induced temperature increases during solar cell operation. A 14.7% module efficiency was achieved, resulting in a 23.5% performance increase compared to that of the conventional binary system.
IMAGE: HELIATEK
SILVIA CARDARELLI, UNIVERSITY OF MICHIGAN
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