̽��ֱ�� of Cambridge - Diamond Light Source

Mystery of high-performing solar cell materials revealed in stunning clarity

erh68 — Mon, 22 Nov 2021 15:38:18 +0000

̽��ֱ��most commonly used material for producing solar panels is crystalline silicon, but achieving efficient energy conversion requires an energy-intensive and time-consuming production process to create a highly ordered wafer structure.

In the last decade, perovskite materials have emerged as promising alternatives to silicon.

̽��ֱ��lead salts used to make perovskites are much more abundant and cheaper to produce than crystalline silicon, and they can be prepared in liquid ink that is simply printed to produce a film of the material. They also show great potential for other applications, such as energy-efficient light-emitting diodes (LEDs) and X-ray detectors.

̽��ֱ��performance of perovskites is surprising. ̽��ֱ��typical model for an excellent semiconductor is a highly ordered structure, but the array of different chemical elements in perovskites creates a much ‘messier’ landscape.

This messiness causes defects in the material that lead to tiny ‘traps’, which typically reduce performance. But despite the presence of these defects, perovskite materials still show efficiency levels comparable to their silicon alternatives.

In fact, earlier research by the same team behind the current work showed the disordered structure can actually increase the performance of perovskite optoelectronics, and their latest work seeks to explain why.

Combining a series of new microscopy techniques, the group present a complete picture of the nanoscale chemical, structural and optoelectronic landscape of these materials, that reveals the complex interactions between these competing factors and ultimately, shows which comes out on top.

“What we see is that we have two forms of disorder happening in parallel,” said first author Kyle Frohna from Cambridge’s Department of Chemical Engineering and Biotechnology (CEB). “ ̽��ֱ��electronic disorder associated with the defects that reduce performance, and then the spatial chemical disorder that seems to improve it.

“And what we’ve found is that the chemical disorder – the ‘good’ disorder in this case – mitigates the ‘bad’ disorder from the defects by funnelling the charge carriers away from these traps that they might otherwise get caught in.”

In collaboration with researchers from the Cavendish Laboratory, the Diamond Light Source synchrotron facility in Didcot, and the Okinawa Institute of Science and Technology in Japan, the researchers used several different microscopic techniques to look at the same regions in the perovskite film. They could then compare the results from all these methods to present the full picture of what’s happening at a nanoscale level in these materials.

̽��ֱ��findings will allow researchers to further refine how perovskite solar cells are made in order to maximise efficiency.

“We have visualised and given reasons why we can call these materials defect tolerant,” said co-author Miguel Anaya, also from CEB. “This methodology enables new routes to optimise them at the nanoscale to perform better for a targeted application. Now, we can look at other types of perovskites that are not only good for solar cells but also for LEDs or detectors and understand their working principles.”

“Through these visualisations, we now much better understand the nanoscale landscape in these fascinating semiconductors – the good, the bad and the ugly,” said Dr Sam Stranks from CEB, who led the research. “These results explain how the empirical optimisation of these materials by the field has driven these mixed composition perovskites to such high performances. But it has also revealed blueprints for design of new semiconductors that may have similar attributes – where disorder can be exploited to tailor performance.”

Reference:
Kyle Frohna et al ‘Nanoscale chemical heterogeneity dominates the optoelectronic response of alloyed perovskite solar cells.’ Nature Nanotechnology (2021) DOI: 10.1038/s41565-021-01019-7

Researchers have visualised, for the first time, why perovskites – materials which could replace silicon in next-generation solar cells - are seemingly so tolerant of defects in their structure. ̽��ֱ��findings, led by researchers from the ̽��ֱ�� of Cambridge, are published in the journal Nature Nanotechnology.

We now much better understand the nanoscale landscape in these fascinating semiconductors – the good, the bad and the ugly

Sam Stranks

Alex T at Ella Maru Studios

Artistic representation of electrons funneling into high quality areas of perovskite material

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New glass manufacturing technique could enable design of hybrid glasses and revolutionise gas storage

cjb250 — Fri, 28 Aug 2015 09:00:00 +0000

̽��ֱ��work revolves around a family of compounds called metal-organic frameworks (MOFs), which are cage-like structures consisting of metal ions, linked by organic bonds. Their porous properties have led to proposed application in carbon capture, hydrogen storage and toxic gas separations, due to their ability to selectively adsorb and store pre-selected target molecules, much like a building a sieve which discriminates not only on size, but also chemical identity.

However, since their discovery a quarter of a century ago, their potential for large-scale industrial use has been limited due to difficulties in producing linings, thin films, fibrous or other 'shaped' structures from the powders produced by chemical synthesis. Such limitations arise from the relatively poor thermal and mechanical properties of MOFs compared to materials such as ceramics or metals, and have in the past resulted in structural collapse during post-processing techniques such as sintering or melt-casting.

Now, a team of researchers from Europe, China and Japan has discovered that careful MOF selection and heating under argon appears to raise their decomposition temperature just enough to allow melting, rather than the powders breaking down. ̽��ֱ��liquids formed have the potential to be shaped, cast and recrystallised, to enable solid structures with uses in gas separation and storage.

Dr Thomas Bennett from the Department of Materials Science and Metallurgy at the ̽��ֱ�� of Cambridge says: “Traditional methods used in melt-casting of metals or sintering of ceramics cause the structural collapse of MOFs due to the structures thermally degrading at low temperatures. Through exploring the interface between melting, recrystallisation and thermal decomposition, we now should be able to manufacture a variety of shapes and structures that were previously impossible, making applications for MOFs more industrially relevant”.

Equally importantly, say the researchers, the glasses that can be produced by cooling the liquids quickly are themselves a new category of materials. Further tailoring of the chemical functionalities may be possible by utilising the ease with which different elements can be incorporated into MOFs before melting and cooling.

Professor Yuanzheng Yue from Aalborg ̽��ֱ�� adds: “A second facet to the work is in the glasses themselves, which appear distinct from existing categories. ̽��ֱ��formation of glasses that contain highly interchangeable metal and organic components, in is highly unusual, as they are normally either purely organic, for example in solar cell conducting polymers, or entirely inorganic, such as oxide or metallic glasses. Understanding the mechanism of hybrid glass formation will also greatly contribute to our knowledge of glass formers in general.”

Using the advanced capabilities at the UK’s synchrotron, Diamond Light Source, the team were able to scrutinise the metal organic frameworks in atomic detail. Professor Trevor Rayment, Physical Science Director at Diamond, comments: "This work is an exciting example of how work with synchrotron radiation which deepens our fundamental understanding of the properties of glasses also produces tantalising prospects of practical applications of new materials. This work could have a lasting impact on both frontiers of knowledge.”

̽��ֱ��researchers believe the new technique could open up the possibility of the production of 'chemically designed' glasses whereby different metals or organics are swapped into, or out of, the MOFs before melting.

Reference
Bennett, TD et al. Hybrid glasses from strong and fragile metal-organic framework liquids. Nature Communications; 28 August 2015

A new method of manufacturing glass could lead to the production of ‘designer glasses’ with applications in advanced photonics, whilst also facilitating industrial scale carbon capture and storage. An international team of researchers, writing today in the journal Nature Communications, report how they have managed to use a relatively new family of sponge-like porous materials to develop new hybrid glasses.

We now should be able to manufacture a variety of shapes and structures that were previously impossible

Thomas Bennett

Rosmarie Voegtli

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