Perovskite photovoltaics fine-tuned with new approach to material design

The performance of perovskite solar cells could be improved with a new approach to designing materials from UK universities.

perovskite solar cells
Perovskites responding to light (Credit Greg Stewart/SLAC National Accelerator Laboratory)

Perovskite solar cells are a photovoltaic technology with a power conversion efficiency over 20 per cent, but their performance is hindered by ion defects that can move around and affect the internal electric environment within the cell.

The Perovskite material absorbs light to create an electronic charge and helps to extract the charge into an external circuit before it is lost to recombination. The majority of detrimental recombination can occur in different locations within the solar cell. In some designs it occurs predominantly within the perovskite, while in others it happens at the edges of the perovskite where it contacts adjacent materials called transport layers.

Researchers from the Universities of Portsmouth, Southampton and Bath have now developed a way to adjust the properties of the transport layers to encourage the ionic defects within the perovskite to suppress recombination and encourage more efficient charge extraction.

In a statement, Dr Jamie Foster, a study participant from Portsmouth University, said: “Careful cell design can manipulate the ionic defects to move to regions where they enhance the extraction of electronic charge, thereby increasing the useful power that a cell can deliver.”

The study, published in Energy and Environmental Science, showed that the performance of PSCs is strongly dependent on the permittivity, which is the measure of a material’s ability to store an electric field, and the effective doping density of the transport layers.

Dr Foster said: “Understanding how and which transport layer properties affect cell performance is vital for informing the design of cell architectures in order to obtain the most power while minimising degradation.

“We found that ion movement plays a significant role in the steady-state device performance, through the resulting accumulation of ionic charge and band bending in narrow layers adjacent to the interfaces between the perovskite and the transport layers. The distribution of the electric potential is key in determining the transient and steady-state behaviour of a cell.

“Further to this, we suggest that the doping density and/or permittivities of each transport layer may be tuned to reduce losses due to interfacial recombination. Once this and the rate-limiting charge carrier has been identified, our work provides a systematic tool to tune transport layer properties to enhance performance.”

The researchers also suggest that PSCs made using transport layers with low permittivity and doping are more stable than those with high permittivity and doping. These cells reportedly show reduced ion vacancy accumulation within the perovskite layers, which has been linked to chemical degradation at the edges of the perovskite layer.