Selecting ions for better solar cells

Trapping sunlight’s abundant energy to power our enormous demand for energy offers a way to enjoy the advantages of technology while avoiding the environmental cost of fossil fuel burning.  

Mohammad Alotaibi of the National Center for Petrochemicals Technology at KACST works on this challenge with a world-leading research group led by Michael Gratzel at the Swiss Federal Institute of Technology in Lausanne. Alotaibi has participated in research revealing how changes in the structure of perovskites can affect their performance in solar cells. The results should help the march toward ever more efficient and cost-effective conversion of sunlight into electricity. 

Perovskites are materials that share the same basic crystal structure as the natural perovskite calcium titanium oxide (CaTiO₃). A wide variety of ions can be used to replace one or more ions of the natural perovskite structure. Adjusting the ions alters the photochemical and electrical properties, creating materials for solar cells and many other applications, including catalysis and the separation of gases. 

Alotaibi and his colleagues looked at the differences between perovskites containing formamidinium (CH(NH₂)₂⁺) or caesium (Cs⁺) ions together with lead and bromide ions. They analysed the effects of the changed structures on current densities and voltages in response to varied illumination conditions. 

“We have successfully unravelled the fundamental electronic processes occurring in the lead/bromide-based perovskite solar cells,” the researchers say, summarising the detailed results of their complex electronic analysis in the journal Advanced Functional Materials. They confirmed that the light capture and electric charge transfer activity of the perovskite is strongly influenced by the nature of the positively charged ions. This “will pave a way to further improve the performance of perovskite solar cells,” they write. 

A major challenge in creating materials for solar cells is to reduce the amount of light energy lost as heat, instead of being converted into an electric current. This research is helping to reveal the aspects of perovskite structure that will reduce these energy losses.

The researchers believe their findings will be more widely applicable to understanding the performance of light-harvesting materials besides perovskite solar cells. As well as helping convert light into electricity, this could assist the creation of materials that use solar energy to split water into hydrogen and oxygen. This water-splitting process could form the basis of a clean and sustainable power supply system. The hydrogen and oxygen eventually recombine to form water as a clean and reusable end-product

1. Yadav, P., Alotaibi, M. H., Arora, N., Dar, M. I., Zakeeruddin, S. M. & Gratzel, M. Influence of the nature of A cation on dynamics of charge transfer processes in perovskite solar cells. Advanced Functional Materials 28, 1706073 (2018). | article