Centre for Sustainable Chemical Technologies

Our Solar Cell Research Featured in International Research Highlights

Thu May 19 12:26:00 BST 2016

Research published by CSCT PhD student Oliver Weber in the Weller group of Department of Chemistry, is featured as one of the scientific highlights from 2015 in the annual report of the Institut Laue-Langevin (ILL), an international neutron source in Grenoble, France.

Solar cells convert sunlight directly into electricity; understanding the materials they are made from is crucial for the development of a sustainable energy supply in future. Crystalline materials are often studied using diffraction techniques – by firing a beam of X-rays, neutrons or electrons at the material and recording the interference patterns that result, which can then be used to find the atomic structure.

Neutron diffraction can be a powerful technique for probing the structure of materials, but a nuclear reactor or spallation source is required to generate the neutrons, so these experiments take place at international facilities such as the Institut Laue-Langevin, rather than in the laboratory. Researchers from the Weller group went to Grenoble to investigate a new class of materials known as hybrid perovskites. The featured article, published in Chemical Communications last year, was the first study to provide high quality experimental evidence for the complete structure of methylammonium lead iodide over a wide temperature range.

20160519-solar-cellRelated neutron experiments, carried out at ISIS in Oxfordshire, were published in the Journal of Physical Chemistry Letters. From these data, researchers found the room temperature structure of formamidinium lead iodide to be cubic, overturning previously held assumptions and underlining the advantages of using neutrons to study these hybrid materials. These findings are now being applied by theorists and experimentalists to gain a better understanding of the behaviour of these materials.

Picture on the right shows the atomic structure of methylammonium lead iodide just above room temperature (the operating temperature for solar cells).

Few solar cell developments have ever sparked such an intense wave of research activity around the world as for hybrid perovskites. The first high efficiency devices were reported in 2012, since then the efficiency of solar cells made in the lab has climbed precipitously to over 22%, in the same bracket as already commercial silicon and thin film technologies.

In a research field where gains in solar cell efficiency are typically incredibly hard-won, this swift progress is previously unheard of and stems from the ease with which these materials can be deposited as thin films from solution, which in turn promises extremely cheap means of manufacture. Combined with low cost starting materials, the overall price of solar electricity could be much lower than for current technologies.

20160519-solar-cell3 Picture on the right shows hybrid perovskite solar cells Oliver Weber made during a visit to SPECIFIC in Swansea. Most of the thickness of the cell is the glass substrate – the solar cell itself is just a few thin film layers sitting on top of the glass.

However, hybrid perovskites come equipped with an Achilles heel behind each foot. The films that are so readily formed are equally easy to decompose if left unprotected. Most of the compounds also contain lead, a toxic element which combined with their instability means that any ruptured cells could leach lead into the environment. The race is on to identify less toxic and more stable compounds that can maintain high efficiencies and cheap routes to manufacture. To this end, CSCT PhD student, Oliver Weber has discovered several new hybrid compounds, the results of which are published in Acta. Cryst. B.

At the Centre for Sustainable Chemical Technologies, we’re extremely fortunate to have scientists attacking these problems from multiple angles at once, from making  devices to computational simulations and to work closely in collaboration with other groups around the world, such as SPECIFIC, industrial partners to Oliver Weber's PhD project in the CSCT.

Picture above shows part of the neutron powder diffraction patterns of methylammonium lead iodide collected on the D20 instrument at ILL.

For more information, please contact:

Rubina Kalra
Digital Communications Co-ordinator
Centre for Sustainable Chemical Technologies

e-mail: R.Kalra@bath.ac.uk
Tel: 01225 385827

About CSCT:
Established in 2008, the Centre for Sustainable Chemical Technologies brings together academic expertise from the University of Bath with international industrial, academic and stakeholder partners to carry out research, training and outreach in sustainable chemical technologies.