Perovskite solar cells could capture more electricity

Thursday, 28 November, 2019

Perovskite solar cells could capture more electricity

Scientists from Nanyang Technological University, Singapore (NTU Singapore) and the University of Groningen (UG) in the Netherlands have developed a method to analyse which pairs of materials in next-generation perovskite solar cells will harvest the most energy. Their work has been published in the journal Science Advances.

Conventionally, a solar cell absorbs sunlight and converts it to electrical charge. During this process, the light particles have more energy than needed to generate the electrical charges in the solar cells. This excess energy gives rise to what are called ‘hot’ charges, which lose their excess energy very fast as heat (within one picosecond), leaving only ‘cold’ charges available for electrical power generation. This energy loss is why conventional solar cells have a theoretical limit of 33% for power conversion efficiency.

The best perovskite solar cells so far have exhibited 25% efficiency — almost on a par with the best-performing silicon solar cells. Scientists believe that if hot charges could be extracted fast enough, then together with the harvested cold charges, this could lead to a hot carrier solar cell with a theoretical efficiency of up to 66%.

The key to extracting these hot charges quickly enough lies in the selection of the correct ‘extraction’ material to bond with the perovskite. Physicists led by NTU’s Professor Sum Tze Chien and UG’s Professor Maxim Pshenichnikov have now devised a way to measure which are the best extraction materials.

“Our latest findings show how ‘hot’ these charges have to be, in order to cross over the energy barrier without being wasted as heat,” Prof Sum said. “This highlights the need for better pairing of ‘extraction’ materials with perovskites if we want to lower this energy barrier for more efficient solar cells.”

(From left) NTU physicists Professor Sum Tze Chien, Dr David Giovanni, Dr Lim Swee Sien and Lim Jia Wei Melvin worked with UG Professor Maxim Pshenichnikov to develop a method to analyse which pairs of materials in next-generation perovskite solar cells will harvest the most energy.

Perovskite solar cells’ primary advantage over silicon solar cells is that they are cheap and easy to manufacture using common chemistry laboratory supplies, and do not need silicon’s costly and energy-intensive manufacturing processes. Prof Sum and his collaborators previously discovered that hot charges in perovskites lose their excess energies more slowly than in other semiconductors, and subsequently slowed this energy loss further using nano-sized perovskites, making it easier to extract the hot charges as electricity.

In their latest experiments, the scientists ‘watched’ the solar cells at work using femtosecond pulsed lasers that can measure processes that occur roughly 100 billion times faster than a camera flash. The scientists studied the behaviour of the hot charges that are generated and how they moved through the perovskite into the extractor material without losing their excess energy as heat.

“Such high-efficiency solar cells could mean the possibility of increasing the energy supply from solar panels without the need for more surface area,” Prof Pshenichnikov said.

The team is now looking at discovering better and more efficient extractor materials, which could work to increase the performance of perovskite solar cells.

Top image: The researchers used extremely fast lasers to observe how an energy barrier forms when perovskite is joined with a material that extracts the electrical charges to make a solar cell.

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