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International Year of Light - Yue Hu

Yue Hu

Tell us about your PhD project

Photovoltaics are devices that convert solar energy into electrical energy. The dye-sensitized solar cell (DSSC), which our group is doing research on, is unique because it is the only solar cell that mimics natural photosynthesis. Like green plants and algae it uses a molecular absorber - the dye - to harvest sunlight and generate electric charges, achieving for the first time the separation of the two functions of light harvesting and charge-carrier transport. 

Different aspects of DSSCs have been investigated in our group to improve their efficiency and long-term stability, such as semiconductor films, sensitizing dyes and hole-transport materials.  I am focusing on the study of dyes, both pure-organic dyes and Ru-based complexes.

Dye molecules are used in our daily life to color our fabrics, hair and food. However, in order to use them as sensitizers in DSSC, we need to design carefully to give the dyes the right color, right bonding groups to attach the dyes to the surfaces and the right properties for helping electrons to move around a solar cell.

I love this research very much not only because it involves a lot of colour and looks very cool, but also because it's so close to real life application. I do feel that our research can help make the world better.

Why is light important to your research?

This question suits my research so well. How can a solar cell work without light? Especially for my research, the dyes are made to absorb light.

When light shines on the solar cell, a particle of light called a photon hits the dye molecule, and gives an electron enough energy to escape the molecule and move to the attached semiconductor film then to the out circuit. When this happens, a hole is left behind. A mediator in the hole-transport material then fills the hole with one of its own electrons and regenerates the dye.

The optimal dye for the DSSC should be panchromatic, i.e. absorb visible light of all colours. Ideally, all photons below a threshold wavelength of about 920 nm should be harvested and converted into electric current. For commercial use, all different colours of dyes are made as everybody wants colourful buildings instead of just black.

A variety of differently coloured cells

Describe your average day of PhD work here in the School of Chemistry

Sometimes, people will ask me ???What chemistry are you doing???? And I really don???t know how to answer that question, because my PhD includes organic chemistry, inorganic chemistry, physical chemistry, analytical chemistry and even physics.

To make a typical Ru-based dye-sensitised solar cell, I first design a molecule and use computational chemistry to calculate its frontier molecular orbitals. Then I need to synthesize the ligand, usually an organic molecule. Next, I will introduce the organic molecule as one ligand of a tetrahedral Ru complex. The properties of these dyes will be characterised through electrochemical, spectroscopic and computational techniques. Finally, DSSCs devices will be fabricated and lots of tests can be done.

So, as an average day of my PhD, you may find me doing column in the synthetic lab, or testing electrochemical and spectroscopic properties in the testing room, or fabricating solar cells in the solar cell room, or doing computational chemistry in the office.

Besides my PhD, I am also the coordinator of a public engagement project called ???The Solar Spark???. The project has been running very successfully for several years including workshops at science festivals and school, training for school teachers, podcasts, animations, facebook, twitter, press articles and more. As well as activities within Scotland, we work to help organise and support outreach activities of other partner research groups in Universities across the UK.

This year, we will be at the Dunbar Science Festival and Edinburgh Science Festival with our most popular workshops and Dr. Neil Robertson???s talk.

A flexible solar cell

What's your favourite chemical reaction?

2KNO3(s) + S(s) + 3C(s) ??? 3CO2(g) + K2S(s) + N2(g)

The reaction of black powder is my favourite chemical reaction not only because it???s the basic chemistry behind fireworks, but also it???s one of four great inventions from ancient China. This reaction is an almost ridiculously simple recipe. By blending three commonly used chemicals in a simple way, huge power and wonderful results can be produced. This is just magic.