Walking past a special university building on his way to work fills Mohammad Khaja Nazeeruddin with an immense pleasure and pride. Because the ingenious and beautiful technology displayed outside and inside this building is a cornerstone of the professor’s work, representing more than 25 years of devotion to developing energy-generating and energy-saving materials.
There’s one word that keeps cropping up when Nazeeruddin talks about his work. Well, obviously there are many words specifically related to his research that recur, such as ‘solar cells’, ‘energy efficiency’, ‘materials’ and ‘metal complexes’. But when describing all of this, there’s one word he just can’t help using: ‘beauty’.
“The beauty of these solar cells is that they give you different colours, which you can integrate into buildings,” he says, referring to the 300 square metre installation gracing the west façade of the SwissTech Convention Center at École Polytechnique Fédérale de Lausanne (EPFL). A world first, this impressive glass surface showcases the potential of dye-sensitised solar cells, a type of thin film solar cells that reproduce the principles of photosynthesis in plants.
The solar cells contain a dye that absorbs sunlight, just like the chlorophyll in green leaves. But unlike plant leaves, these solar cells are transparent – letting the sunlight pass through.
“The dye absorbs different portions of the visible light – green, red, orange and so on. And because it’s translucent, it can capture the light from outside and inside. So you can recycle room light – that’s the beauty of our technology,” says Nazeeruddin – also called Nazeer among colleagues.
Originally from India, Nazeer has worked in Switzerland since 1987. After his first year as a postdoc in the lab of Michael Graetzel at EPFL, he was promoted to senior scientist and became instrumental in developing these low-cost, dye-sensitised solar cells, also known as Graetzel cells.
Around a dozen companies are now licensed to market Graetzel cells. The innovative SwissTech Center installation, funded by Romande Energie, is a first step towards large-scale production and use of the technology. And for Nazeer, that’s a major career highlight.
“The way we have designed these dye molecules with respect to colour and efficiency — it has been delivered. Seeing a company providing such long-term funding because of their satisfaction with materials we have developed — that’s an immense pleasure,” he says.
Designing functional materials by dictating metal behaviour
Engineering molecules and functional materials is what Nazeer is all about. Since his early days of studying inorganic chemistry at Osmania University in Hyderabad – where he earned his master’s and PhD degrees – he has been deeply fascinated by the way it’s possible to control the properties of molecules. This passion started with his realisation of how ‘clever’ certain metal complexes in our own bodies are – specifically, the iron complex that’s an essential part of our red blood cells.
“The beauty of this iron complex is the way it works – by binding the oxygen we breathe and releasing it at the right sites in our tissues. This fine balance of oxygen uptake is really dictated by the different ligands that bind to the central iron complex in the haemoglobin,” Nazeer explains.
And creating such fine balancing qualities in metal complexes is what he does – synthetically. “If a metal complex has six ligands, for example, I can replace them one by one. That way, I can dictate functionalities to the metal complex,” he says.
Using this approach to modify metal complexes that harness the properties of light, Nazeer specialises in designing materials for photovoltaic and light-emitting applications. “If I want a material to absorb light in the visible spectrum, I can fine-tune the different ligands in the metal complex so that the material scatters blue light with a wavelength of 450 nanometres, for example, or green light with a wavelength of 520 nanometres,” he explains.
Exploring a new, competitive material for solar cells
Nazeer’s research group – which now counts a total of 20 PhD students and postdocs – is currently focusing on a light-absorbing material that confers very high efficiency to solar cells. Originally discovered in Russia in 1839, the material – called perovskite – has recently attracted enormous interest because of its potential in photovoltaic systems.
Optimising the crystallinity and crystal size of perovskite films, which can be produced quickly and cheaply in the lab, Nazeer’s researchers have developed perovskite-based solar cells with an energy conversion efficiency of 20 per cent.
He is confident that – with continued optimisation – they will soon match the top efficiency of 25 per cent obtained with single crystal silicon solar cells, the most common type to date. It all comes down to fine-tuning the properties of the materials, making the electric charges travel as efficiently as possible through the perovskite film.
The group is collaborating with several industrial partners, and the work is also funded by the European Union – currently under the Seventh Framework Programme through a project called MESO. The MESO partners believe perovskite-based solar cell technology has “tremendous scope to compete with the very best crystalline semiconductor and thin film technologies on efficiency, while offering the very lowest potential cost for materials and solution processed manufacturing”.
Tackling toxicity and instability
“From an efficiency and processing point of view, the technology should be easy to commercialise. The only potential problem that we foresee is the toxicity of the lead,” Nazeer says.
The perovskite materials contain lead, a heavy metal that has a bad name owing to its well-documented toxicity. However, Nazeer believes the tiny amounts of lead used to produce perovskite will be insignificant in terms of human and environmental toxicity. “Whether these low levels will be deemed acceptable depends on pending toxicity tests and future legislation,” he says.
He has a backup plan, though: replacing lead with other compounds. “This could be other inorganic pigments, or organic pigments. Over the next five to six years, part of our effort will go into finding alternative pigments. If lead is accepted, it’s fine; if not, then we have something else in the pipeline,” Nazeer says.
“So these studies have two benefits. One, the material can go directly to the market. Two, we learn from all of perovskite’s good properties and implement them into new materials.”
One of the special properties of perovskite solar cells is their ability to generate a voltage that’s almost double that of silicon solar cells. Researchers in the Nazeer/Graetzel lab are exploiting this high electric potential to develop an artificial photosynthesis system that can convert sunlight and water directly into hydrogen gas – a process known as solar water splitting. Perovskite-based solar water splitting is a strong contender in the race to enable efficient storage of solar power. “On the lab scale, the efficiency is the highest in the literature,” Nazeer says.
There is a major drawback, though: long-term instability of the perovskite. But Nazeer is optimistic that his team will be able to solve this challenge with the help of ‘hard-core chemistry’. “This comes back to molecular engineering of functionality to create new materials,” he says.
Branching out: from energy-generation to energy-saving
Another of Nazeer’s major focus areas is organic light-emitting diodes (OLEDs), which are typically used to create digital displays in devices such as televisions, computers and mobile phones. Researchers around the world put a lot of effort into developing white OLEDs as a next-generation light source.
Along with international partners, Nazeer has secured major funding from the EU Horizon 2020 programme for a new project called SOLEDLIGHT. “What we want to do in this project is develop materials that give the highest possible luminescence. Then we will develop three types of materials in blue, green and red. Eventually we can combine these colours to get white OLEDs,” he says.
“This way you can save a lot of energy. Using as little as five volts, you can get the same luminosity as with existing technologies – that’s the beauty of these materials.”
The urgent need to develop energy-saving technologies is a strong motivation for Nazeer. Having lived or travelled extensively in such severely polluted cities as Hyderabad, Shanghai and Delhi, he feels passionately about the world’s long-term energy issues and pollution. “This cannot continue, because one day the oil will exhaust,” he says.
“No option but solar energy”
Nazeer is not in favour of nuclear energy because he worries about storage of radioactive waste.
“I’m not sure we understand the properties of this radioactive material and the stability of it, on a scale of thousands and millions of years. What happens if we release all this material into the earth?” he muses.
“Right now, we are losing, as some countries are strongly in favour of nuclear energy. But in the long run, some way or another, humankind has to solve this problem. And then the obvious technology is solar power – or other forms of sustainable energy, such as wind power. Whether it happens in the next 10 or 100 years, there’s no option but solar energy.”
An eternal optimist, Nazeer is positive about the prospects, even in the short term. “If you had asked three years ago what the efficiency of our solar cell technology would be today, I would have said 13 per cent. Now we have 20 per cent. How do I know what other beautiful materials we may discover in the next three years? They may give the highest energy efficiency at the theoretical limit of 33 per cent,” he says.
“Reaching this limit – and developing solar batteries to store the power – will reduce our dependence on other power-generating technologies. Every house and every community can produce their own electricity, and store the surplus – or feed it back into the grid for someone else to use. The consumer will become the producer.”
Such future scenarios inspire Nazeer to persist in his work – alongside his equally motivated postdocs and students – to pioneer new materials and revolutionary renewable energy technologies.
By Lillian Sando