Solar cells made of novel organic semiconductors, which can be manufactured using established printing or thermal evaporation methods, are currently the focus of collaboration between researchers from Chemnitz University of Technology’s Professorship of Optics and Photonics of Condensed Matter, which is led by Prof. Dr. Carsten Deibel. Other partner institutions are also participating in the project.
As part of the research unit “Printed and Stable Organic Photovoltaics from Non-fullerene Acceptors—POPULAR,” the researchers are pursuing a strongly interdisciplinary approach in order to fundamentally comprehend and further develop this class of photovoltaic materials. Here, mastery of science and materials science, as well as physical science and arithmetic, is joined with printing innovation.
According to Deibel, who is also the head of the POPULAR research group, “research on organic photovoltaics is extremely relevant in regard to the development of resource-efficient renewable energies because they can be processed at high throughput at room temperature.”
“Because organic semiconductors are excellent light absorbers, the light-absorbing layer in solar cells is 1,000 times thinner than in crystalline silicon solar cells.”
Prof. Dr. Carsten Deibel, of Chemnitz University of Technology
“Natural semiconductors are generally excellent light safeguards, so the light-retaining layer in sun-powered cells is multiple times more slender than in translucent silicon sun-oriented cells,” says the Chemnitz material science teacher. Organic solar cells, in contrast to the latter, are disordered rather than highly ordered. Deibel explains, “This means that for the transportation of the electrons and holes generated by sunlight in organic semiconductors, they move not on a highway but on a bumpy road with many traps that catch electrons or holes and lead to a slower, but not lower, current flow.” One method for portraying this vivacious scene is the thickness of states.
Unexpected insight: Power regulation depicts the thickness of the conditions of natural sun-oriented cells.
To more likely comprehend charge transport in natural sun-oriented cells, Deibel and his exploration collaborator Maria Saladina, along with partners from the College of Nuremberg-Erlangen, the Helmholtz Organization Erlangen-Nuremberg for Environmentally Friendly Power, and Heliatek GmbH in Dresden, produced various kinds of natural sun-based cells, examined them, and interestingly revealed the electronic imperfection scene. This is the result of precise measurements of the organic solar cells’ open-circuit voltage, which is a measure of how much energy photogenerated electrons and holes have when no current is flowing.
A wide range of temperatures and light intensities were used for the measurements. The analysis of the data revealed that instead of being described by a Gaussian or exponential distribution, the organic solar cell density of states has a shape that cannot be explained by either. ” This indicates that, in contrast to earlier models, solar cells have smaller open-circuit voltages in an energetic range where there are more traps. “Fortunately, the open-circuit voltage is higher and the density of states contains fewer traps under working conditions of organic solar cells at room temperature under sunlight irradiation,” says Saladina.
The exploration results were distributed in actual audit letters, and the original copy was chosen as an editor’s idea. The authors of the technical article estimate that there is no fundamental obstacle to the production of highly efficient organic solar cells using printing or evaporation technologies, despite the fact that these new insights necessitate rethinking the theoretical description of organic solar cells.
“We are persuaded that the scattered idea of natural semiconductors for sunlight-based cells is straightforwardly connected to the large-scale manufacturing and viable assembly prospects,” says Deibel.
“We have realized that the density of states, which determines the processes of charge transport and recombination in organic solar cells, is more complex than previously assumed,” Saladina states in addition. The difficulties related to this will likewise be looked at by the DFG research unit Famous and the Marie Skodowska-Curie Ph.D. network EIFFEL.
More information: Maria Saladina et al, Power-Law Density of States in Organic Solar Cells Revealed by the Open-Circuit Voltage Dependence of the Ideality Factor, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.236403
