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Researcher Profile: Charlotte Platzer Björkman

Charlotte Platzer Björkman and her group can make the entire solar cell from beginning to end in the clean room. PHOTO: MIKAEL WALLERSTEDT

Every part is important in solar cells

If solar energy is to become available to more people, smart material choices need to be made. Charlotte Platzer Björkman is researching solar cells made from materials which are cheaper and more readily available than those used for today’s solar cells.

In the laboratory at the Department of Solid State Electronics there are strong lamps which imitate the sun. When they shine on a solar cell, you can see straight away how much solar energy is converted to electricity.

“One of the most satisfying things about this job is that we can see directly whether it is good or not. Then all we have to do is understand why”, says Charlotte Platzer Björkman.

The subject of her 2006 doctoral thesis was CIGS solar cells. These are thin-film solar cells made of copper, indium, gallium and selenium and they are produced industrially. She then went on to research silicon solar cells in Norway. Since 2010, however, she has focussed upon thin-film solar cells of the CZTS type. These resemble CIGS solar cells but the indium and gallium, which are rare and thus expensive metals, have been replaced by zinc and tin.

The solar cells are produced in the clean room at the Ångström Laboratory. The work involves very small components since the thin films are less than 3 micrometres thick. This is equivalent to a hundredth of the thickness of a hair.

“One of the advantages we have at the Ångström Laboratory is that we can make the entire solar cell from beginning to end in the clean room. We have equipment for dealing with all of the various layers. Another advantage is that there are chemists and materials physicists at close hand when materials need to be analysed.”

Last but not least, the electrical properties of the solar cells are tested in the laboratory. Under one of the ‘sun lamps’, the effectiveness of the cells are tested. How well they perform might depend upon something in one of the layers or in the interfaces between the various layers. And even when the combination of materials is right, defects may appear where atoms have changed places or where an atom is missing.

“At the first level, we can carry out a materials analysis and look at the major variations. But the electrical defects at atomic level very much affect the properties. Some of these defects we can only reach by measuring the completed solar cell.”

So far, they have achieved a level of effectiveness around half of that seen in solar cells on the market today. Their aim is to make them at least as good.

“In the long run, we want to go even further by, for example, developing tandem solar cells or multi solar cells. With a greater number of solar cells which each capture their own part of the sun’s spectrum, solar energy can be used in a more efficient manner. That would be a great leap forward.”

Charlotte Platzer Björkman did her degree project at ABB before she started her doctoral studies in 2001. She is interested in basic physics and in understanding the properties of materials. Just as important to her, however, is that there are suitable applications.

“I am an engineer after all. I don’t just want to understand how electrons move, I want to be able to apply such understanding and make things work over and over again."

If the researchers succeed with the new materials combination, it will be possible to make cheaper solar cells – which will make it possible to produce solar power on a large scale. This would not only benefit the environment but also contribute to a fairer world, according to Charlotte Platzer Björkman.

“The use of widespread energy sources instead of large centralised power plants would be a major change. It would make it possible to put a light in a hut for the poorest people. There are still plenty of problems which need to be solved but cheap technology which works is an important part of the puzzle.”

The research has recently begun to attract attention and has received support both from the Swedish Foundation for Strategic Research and the Wallenberg Foundations. This has enabled Charlotte Platzer Björkman not only to invest in new equipment but to also recruit people.

“This is a giant leap forward. There are currently ten of us in the group and we have a brand new sputtering system, especially designed for our project. This means that we can vary many factors and the combination of materials and see what the effects are."

Our experimental work has speeded up and we now make an average of 5-10 solar cells a week which can then be tested in the laboratory.

“The aim is to achieve a sufficiently high degree of effectiveness and then understand why it works as well as it does. This will then, hopefully, attract interest from industry."

Annica Hulth

Facts – Charlotte Platzer Björkman

Name: Charlotte Platzer Björkman.
Age: 39.
Title: University lecturer in solid state electronics.
Right now: I have been voted a Future Research Leader by SFS – the Swedish Foundation for Strategic Research –  and a Wallenberg Academy Fellow by the Wallenberg Foundations.
Spare time: I have three children so that a lot of my time is spent with my family. We have a holiday home which we are renovating and where we grow things and go boating. I was recently out on the water fishing for herring.
Makes me happy: Thoughtfulness.
Makes me angry: Egoism.
Hidden talent: I play tuba.
Last book read: Denna dagen, ett liv (‘On this Day, a Life’) a biography of Astrid Lindgren.
Driving force: I want to understand how electrons move and then I want to put this to good use. I am an engineer, after all, and I don’t want to just understand things but I also want to make use of them and make them work over and over again.