New material could spark solar energy revolution
The fight against climate change might be gaining pace, but green energy silicon solar cells are reaching the limits of what they can do.
“It took people forty years to double the efficiency of silicon,” says Professor Ho-Baillie. “Perovskite caught up with silicon in just ten years.”
The good news? Ground-breaking work is underway at the University of Sydney to perfect a new substance that might be cheaper, easier to handle and even more efficient for next-generation solar cells.
Silicon solar panels reaching their ‘best before’ date
There is an enormous fission reactor in our planet’s sky. In just one hour, this reactor bathes the Earth’s surface in enough energy to supply all humanity’s electricity needs for a whole year. The problem is, the Sun’s energy arrives as solar radiation but we need to turn it into electricity.
The most direct way to make the conversion right now is with solar panels, but there are other reasons why they’re the great hope of renewable energy.
Their key component, silicon, is the second most abundant substance on Earth after oxygen; since panels can be put where the power is needed – on homes, factories, commercial buildings, ships, road vehicles, there’s less need to transmit power across landscapes; and mass production means solar panels are now so cheap the economics of using them are becoming inarguable.
According to the International Energy Agency’s 2020 energy outlook report, solar panels in some locations are producing the cheapest commercial electricity in history.
Even that traditional bug-bear “what about when it’s dark or cloudy?” is becoming less problematic thanks to transformative advances in storage technology.
If you’re expecting a but, here it is: but silicon solar panels are reaching the practical limits of their efficiency because of some quite inconvenient laws of physics. Commercial silicon solar cells are now only about 20% efficient (though up to 28% in lab environments. Their practical limit being 30%).
The University of Sydney’s Professor Anita Ho-Baillie is a world-leader in developing next-generation solar cells
The University of Sydney’s Professor Anita Ho-Baillie is a world-leader in developing next-generation solar cells
Academics at the University of Sydney Nano Institute are discovering and harnessing new science at the nanoscale.
Academics at the University of Sydney Nano Institute are discovering and harnessing new science at the nanoscale.
Perovskite: the new solar wonder material?
This means that solar panel technology must soon evolve. A world-leader in helping that evolution take place is Professor Anita Ho-Baillie, from the University of Sydney Nano Institute.
The substance that has become the focus of her research, and research around the world, is part of a class of crystalline compounds called perovskite; specifically, metal halide perovskite.
Like silicon, this crystalline substance is photoactive, meaning that when it’s hit by light, electrons in its structure become excited enough to break away from their atoms (this freeing of electrons is the basis of all electricity generation, from batteries to nuclear power plants). Allowing that electricity is in effect, a conga line of electrons, when the loose electrons from silicon or perovskite are channeled into a wire, electricity is the result.
“It used to take me four weeks to make a silicon cell in the lab. With perovskite, it takes only two days."
That’s because perovskite is a simple mixture of salt solutions that is heated to 100-200C to establish its photoactive properties.
Like ink, it can be printed onto surfaces, and it’s bendable in a way that rigid silicon isn’t. Being used at a thickness of up to 500 times less than silicon, it’s also super-light and can be semi-transparent. This means it can be applied to all sorts of surfaces like on phones and windows. The real excitement though, is around perovskite’s energy production potential.
The first perovskite devices in 2009, converted just 3.8% of sunlight into electricity. By 2020, efficiency was 25.5%, close to silicon’s lab record of 27.6%. There is a sense that its efficiency could soon reach 30%. “It took people forty years to double the efficiency of silicon,” says Professor Ho-Baillie. “Perovskite caught up with silicon in just ten years.”
Overcoming perovskite’s challenges
If you’re expecting a ‘but’ about perovskite, well, there are a couple. A component of the perovskite crystalline lattice is lead. The quantity is tiny, but the potential toxicity of lead means it is a consideration. The real problem is that unprotected perovskite easily degrades through heat, moisture and humidity, unlike silicon panels which are routinely sold with 25-year guarantees.
“That’s the biggest challenge,” says Professor Ho-Baillie. “You really want it to be long lasting if you’re going to put it on buildings or in solar farms.”
It’s the work Professor Ho-Baillie and her team are doing in this area that has recently captured international attention. The goal was for a perovskite cell to pass the industry-critical heat and humidity test set for solar panels by the International Electrotechnical Commission. The Ho-Baillie device was the first to pass, and it passed comfortably.
The innovation that made it possible was to laminate the perovskite cell with glass and the sort of polymers used in double-glazing windows. It was cheap and easy to do and, as it turned out, effective.
“This worked because as perovskite breaks down it starts to release gas – we actually call it outgassing,” says Professor Ho-Baillie. “We found, if you laminate the cell onto a piece of glass with polymer so the cell is sealed off, the gas has nowhere to go. This prevents the outgassing, and so the breakdown, from happening at all.”
This has given a huge boost to the prospects of perovskite and seen Professor Ho-Baillie become highly cited by researchers internationally. The timing is good too because the last few years have offered something that could produce the best solar cell efficiency ever seen.
The gloved hand of Professor Anita Ho-Baillie holding experimental perovskite solar cells.
The gloved hand of Professor Anita Ho-Baillie holding experimental perovskite solar cells.
The Sydney Nanoscience Hub is purpose-built to explore the nature of matter, design new technologies and engineer them in some of the best cleanroom and nanofabrication facilities in the world.
The Sydney Nanoscience Hub is purpose-built to explore the nature of matter, design new technologies and engineer them in some of the best cleanroom and nanofabrication facilities in the world.
Pairing old with new to revolutionize renewable energy
It’s called silicon perovskite tandeming, where the two substances are layered into the same cell to give a higher voltage than either could give on its own.
This works because silicon is better at dealing low energy light waves, and perovskite works well with higher energy visible light. Perovskite can also be tuned to absorb different wavelengths of light – red, green, blue. With careful aligning of silicon and perovskite, this means each cell will turn more of the light spectrum into energy.
The numbers are impressive: a single layer could give 33% efficiency; stack two cells, it’s 45%; three layers would give 51% efficiency. These sorts of figures, if they can be realized commercially, would revolutionize renewable energy.
Fast facts about the University of Sydney
- Australia's first university, established in 1850
- Ranked 1st in Australia and 2nd in the world for impact
- Ranked 1st in Australia and 4th globally for graduate employability
- 100% of our research is rated as 'above' or 'well above' world standard.
This content was paid for and created by The University of Sydney. The editorial staff of The Chronicle had no role in its preparation. Find out more about paid content.
Built with Shorthand