An international research team led by the Martin Luther University Halle-Wittenberg (MLU), Germany, have developed a new method for constructing solar cells that could significantly increase their efficiency.
The cells are made up of thin layers that consist of specifically arranged nanoblocks. As described in the scientific journal Nano Letters, the research team is therefore studying the so-called anomalous photovoltaic effect which occurs in certain materials. The anomalous photovoltaic effect does not require a p-n junction which otherwise enables the flow of current in silicon solar cells. The direction of the current is determined at the atomic level by the asymmetric crystal structure of the corresponding materials. These materials are usually oxides, which are easier to manufacture and significantly more durable. However, they often do not absorb much sunlight and have a very high electrical resistance.
To solve this issue, the physicists introduced a novel cell architecture, named nanocomposite. In their experiment, the researchers stacked single layers of a typical material a few nanometres in thickness on top of one another and offset them with nickel oxide strips running perpendicularly.
Dr Akash Bhatnagar, a physicist from the Centre for Innovation Competence (ZIK) at Martin Luther University Halle-Wittenberg, said: “The strips act as a fast lane for the electrons that are generated when sunlight is converted into electricity and which are meant to reach the electrode in the solar cell.” This is precisely the transport that would otherwise be impeded by the electrons having to traverse each individual horizontal layer.
The new architecture, which is very easy to implement, increased the cell’s electrical output by a factor of five. Lutz Mühlenbein, lead author of the study, explained: “The material forms this desired structure on its own. No extreme external conditions are needed to force it into this state.” The idea, for which the researchers have now provided an initial feasibility study, could also be applied to materials other than nickel oxide. Follow-up studies now need to examine if and how such solar cells can be produced on an industrial scale.