New Solar Cell Technology Could Revolutionise the Industry

Scientists are constantly investigating ways of improving the efficiency of solar PV.

Recently there have been two major developments in solar cell technology that could greatly improve the way energy is harvested from the sun.

Scientists say that the two studies which have been published in Nature Energy and Nature Photonics, will transform the efficiency, and significantly reduce the cost of producing solar cells. Thanks to a new technology the amount of energy that can be harvested from ‘invisible light’ and used in solar cells has been given a serious boost.

Scientists at the RMIT University and UNSW University in Australia and the University of Kentucky in the United States have discovered a way to turn low energy light into heavy energy light that can be captured by solar cells using ‘oxygen’ as a key ingredient.

This first breakthrough by researchers from the ARC Centre of Excellence in Exciton Science and UNSW Sydney, involves ‘upconverting’ low energy, non-visible light into high energy light so that more electricity can be generated from the same amount of sunlight. This will allow solar power arrays to generate more electricity making them far more efficient.

Professor Tim Schmidt from UNSW Sydney, said:

“The energy from the sun is not just visible light. The spectrum is broad, including infrared light which gives us heat and ultraviolet light which can burn our skin. Most solar cells are made from silicon, which cannot respond to light less energetic than the near infrared. This means that some parts of the light spectrum are going unused by many of our current devices and technologies.”

This energy is referred to as “invisible energy’ because it is invisible to the solar cell. Photovoltaic cells or crystalline silicon cells only absorb light in the visible region.

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The technique used involves tiny semiconductors known as quantum dots which are nanoscale man-made crystals, absorbing the low energy light and molecular oxygen turning it into visible light to capture the energy.

Usually oxygen has an adverse effect on molecular excitons, but at such low energies its role changes and it can mediate energy transfer. This lets the organic molecules emit visible light above the silicon band gap.

Contributing author Professor Jared Cole of RMIT University, explained that more often than not things work well without oxygen and stop working when you do use it.

The Molecular Photonics Laboratories at UNSW Sydney Credit: UNSW Sydney/Exciton Science

He said:

‘It was the Achilles heel that ruined all our plans, but now, not only have we found a way around it, suddenly it helps us.’

The process of turning low energy light into more energetic, visible light can excite the silicon in many solar panels. Tim Schmidt explains that you can do this by capturing multiple smaller energy photons of light and gluing them together. This is achieved by interacting the excitons – the bound states of electrons and electron holes that transport energy without net charge – in organic molecules.  

Until now, this had never been achieved beyond the silicon band gap, which is the minimum energy that is required to excite an electron in silicon up to a state where it can participate in conduction. 

Tim Schmidt, said:

“Most solar cells, charge-coupled device (CCD) cameras and photodiodes (a semiconductor that converts light into electrical current) are made from silicon, which cannot respond to light less energetic than the near infrared. This means that some parts of the light spectrum are going unused by many of our current devices and technologies.”

However, according to Tim Schmidt, the new technology is still fairly inefficient so is not ready for commercial applications yet, but scientists have strategies to improve this in the near future.

Tim Schmidt, said:

“This is an early demonstration, and there’s quite a lot of development needed to make commercial solar cells, but this shows us it’s possible.”

Lead author Elham Gholizadeh, of UNSW Sydney, is still optimistic about the potential of the work to make a rapid positive impact on the research field.

She says:

“As this is the first time, we’ve been successful with this method, we will face some challenges. But I’m very hopeful and think that we can improve the efficiency quickly. I think it’s quite exciting for everyone. It’s a good method to use oxygen to transfer energy. Violanthrone doesn’t have the perfect photoluminescence quantum yield so the next step will be to look for an even better molecule.”

Scientists have created a next generation of solar modules that are more efficient and stable than the current commercial solar cells which are made of silicon in a second breakthrough for the industry using a type of material called perovskites.

As well as being flexible and lightweight, solar cells made from perovskites are also cheaper to produce. The main problem with the material until now is that it is difficult to scale up to create solar panels that are several metres in length.

Dr Luis Ono, a co-author of the study, said:

“Scaling up is very demanding. Any defects in the material become more pronounced so you need high-quality materials and better fabrication techniques.”

Scientists have found a new approach now by making use of multiple layers to prevent energy being lost or toxic chemicals from leaking as it degrades.

Testing on a small scale has shown that a module measuring 22.4cm can achieve an efficiency of 16.6% which is a very high efficiency for a module of that size, while maintaining a high level of performance even after 2,000 hours of constant use.

The plan now is for the researchers to test their techniques on larger solar modules with the hope that the technology can be commercialised in the future.

The sun is a powerful source of clean reusable energy to power our world. What’s more this energy is free and does not create pollution.

The future of solar PV continues to be one of intense research and development. It is foreseen that the role of PV in the generation of electricity will overtake other forms of renewable energy and that 50 % of all new buildings will incorporate PV in their design