A new method for building special solar cells could significantly increase their efficiency. The cells not only consist of thin layers, but also consist of specially arranged nanoblocks. This was shown in a new study by an international research team led by Martin Luther University Halle-Wittenberg (MLU), which was published in the journal Nano Letters.
Commercially available solar cells are usually made of silicon. “Because of the properties of silicon, it cannot be said that its efficiency can be increased indefinitely,” says Dr. Akash Bhatnagar, physicist at the Center for Innovation Competence (ZIK) “SiLi-nano” at the MLU. His research team is therefore investigating the so-called anomalous photovoltaic effect that occurs with certain materials. The anomalous photovoltaic effect does not require a pn junction, which would otherwise allow the flow of current in silicon solar cells. The direction of the current is determined at the atomic level by the asymmetrical crystal structure of the corresponding materials. These materials are usually oxides, which have several key advantages: They are easier to manufacture and much more durable. However, they often don’t absorb much sunlight and have very high electrical resistance. “In order to be able to use these materials and their effect, creative cell architectures are required that reinforce the advantages and compensate for the disadvantages,” explains Lutz Mühlenbein, lead author of the study.
In their new study, the physicists presented a new type of cell architecture, a so-called nanocomposite. They were supported by teams from the Bergakademie Freiberg, the Leibniz Institute for Surface Modification in Leipzig and the Banaras Hindu University in India. In their experiment, the researchers stacked individual layers of a typical material with a thickness of just a few nanometers on top of one another and offset them with perpendicular strips of nickel oxide. “The strips act as a fast lane for the electrons that are created when sunlight is converted into electricity and that are supposed to reach the electrode in the solar cell,” explains Bhatnagar. This is precisely the type of transport that would otherwise be hindered by the electrons having to cross each individual horizontal layer.
The new architecture increased the electrical output of the cell by a factor of five. Another advantage of the new method is that it is very easy to implement. “The material forms this desired structure independently. No extreme external conditions are required to force it into this state,” says Mühlenbein. The idea, for which the researchers have now presented an initial feasibility study, could also be applied to materials other than nickel oxide. Follow-up studies must now investigate whether and how such solar cells can be manufactured on an industrial scale.
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