Performance improvements for anomalous photovoltaic effect

Researchers at Martin Luther University Halle-Wittenberg (MLU) in Germany have used self-assembled, three-dimensional nanocomposite thin films to develop a new solar cell architecture based on the so-called anomalous photovoltaic effect.

This effect only relates to some types of semiconductor materials and occurs when a PV device provides an open-circuit voltage that is higher than the bandgap of the corresponding semiconductor, while exhibiting a very poor short-circuit current.

The materials that produce this effect usually have low power-conversion efficiencies. For this reason, they have never been applied in commercial PV production. However, the German researchers claim to have made some progress in overcoming this challenge with their novel “nanocomposite” cell architecture.

The academics used nickel(II) oxide (NiO) nanocolumns in Aurivillius, a type of layered perovskite. The structures were grown on single-crystal substrates made of strontium titanate (SrTiO3) via pulsed laser deposition (PLD) with single ceramic targets. In this configuration, the nickel oxide strips, which run perpendicularly to the cell layers, act as a fast lane for electron transport.

“This is precisely the transport that would otherwise be impeded by the electrons having to traverse each individual horizontal layer,” said researcher Akash Bhatnagar. “The new architecture actually increased the cell’s electrical output by a factor of five.”

They said the material used in the experiment can form the desired structure on its own, without external intervention.

“The nanocomposite thin films exhibit improved photovoltaic performance compared to both pure PbTiO₃ and homogeneous Aurivillius phase thin films,” the scientists explained.

The research group will now start evaluating materials other than nickel oxide and assess the potential of the solar cells for industrial-scale production. They described their research in “Nanocomposites with Three-Dimensional Architecture and Impact on Photovoltaic Effect,” which was recently published in Nano Letters.