Band-engineering in lead-free double perovskites

Article written by Dr Gregor Kieslich

Hybrid double perovskites have recently gained a vast amount of attention in the research area of photovoltaics as lead-free alternatives to the ground-breaking parent material [CH3NH3]PbI3.1 In double perovskites with the general formula A2B’B’’X6, two Pb2+ cations are effectively replaced with a monovalent B’ and a trivalent B’’ cation. Among the many fascinating properties of hybrid inorganic-organic perovskites, it is arguably the combination of strong light absorbance and long carrier lifetimes that make them so interesting for photovoltaic applications and light-emission devices. Recent experimental and theoretical studies on [CH3NH3]PbI3 revealed a direct-indirect character of the bandgap, i.e. [CH3NH3]PbI3 exhibits a direct band gap which is only approximately 47-60 meV higher in energy than the indirect band gap. Presumably, this is the origin of the paradox of strong absorption and long charge carrier lifetimes. When now turning our attention to lead free double perovskites, examples such as [CH3NH3]2KBiCl6 and [CH3NH3]2AgBiBr6 exhibit an indirect band gap,1 hence unfavourable light absorption properties. The symmetry mismatch that leads to the indirect band gap in such materials was recently studied by D. O. Scanlon and A. Zunger theoretically.2,3 Consequently, it is important to ask the question: is it possible to experimentally design a direct band gap in double perovskites?

In the recent article in Materials Horizons, ‘Designing Indirect-Direct Bandgap Transitions in Double Perovskites’,4 T. M. McQueen and co-workers have tackled this important question, studying the solid solution Cs2AgIn1-xSbxCl6 as a prototypical example. By wisely choosing B’ and B’’, a direct band gap in Cs2AgInCl6 has been achieved. The beauty lies in the simplicity of the concept – the understanding of band theory, i.e. symmetry and formation of bands with s-type and p-type character, see Figure 1. Going along the solid solution Cs2AgIn1-xSbxCl6, the valence band remains basically unchanged, whilst the character of the conduction band is continuously altered from s-type to p-type character. Clearly, the use of a chloride and in turn the ionic character of the solid with a band-gap larger than 3.5 eV limits the application of Cs2AgInCl6 in optoelectronics. However, the results depict a textbook example of how to manipulate properties in crystalline materials and open exciting opportunities for going forward in the field. For instance, one can easily envision a computational screening study of potential A2B’B’’X6 perovskites by using symmetry-based descriptors. Furthermore, it is important to note, that band engineering is a common concept in related areas of materials science, such as thermoelectrics and magnetic materials, and is a common tool for solid state chemists in general. Therefore, it is refreshing to see that band engineering now enters arguably one of the most fascinating developments of materials science within the last decade.

 

Figure 1. Schematic presentation of the orbital overlap (a) and the energy as a function of k for bands of s and p-σ orbitals (b) in a linear chain.

 

[1] F. Wei, Z. Deng, S. Sun, F. Xie, G. Kieslich, D. M. Evans, M. A. Carpenter, P. D. Bristowe, A. K. Cheetham ‘The synthesis, structure and electronic properties of a lead-free hybrid inorganic-organic double perovskites (MA)2KBiCl6 (MA = methylammonium)Mater. Horiz. 2016, 3, 328.

[2] C. N. Savory, A. Walsh and D. O. Scanlon ‘Can Pb-Free Halide Double Perovskites Support High-Efficiency Solar Cells?’ ACS Energy Lett. 2016, 1, 949.

[3] X.-G. Zhao, D. Yang, Y. Sun, T. Li, L. Zhang, L. Yu, A. Zunger ‘Cu-In Halide Perovskite Solar Absorbers’ J. Am. Chem. Soc. 2017, 139, 6718.

[4] T. Thao Tran, J. R. Panella, J. R. Chamorro, J. R. Morey, T. M. McQueen ‘Designing Indirect-Direct Bandgap Transitions in Double PerovskitesMater. Horiz. 2017, DOI: 10.1039/C7MH00239D.

 

Dr Gregor Kieslich is a Liebig-Fellow at Department of Chemistry, Technical University of Munich and is a member of the Community Board for Materials Horizons. He is an inorganic chemist focusing on crystal chemistry and structure–property relations in functional solids and hybrid frameworks: https://kieslichresearch.wordpress.com/

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1st European Conference on Chemistry of Two-Dimensional Materials (Chem2DMat)

Materials Horizons will be supporting the 1st European Conference on Chemistry of Two-Dimensional Materials (Chem2DMat), which will take place in Strasbourg on 22-26 August 2017. This conference aims at providing a forum to the rapidly growing community of scientists mastering the chemical approaches to 2D materials in order to fabricate systems and devices exhibiting tunable performance.

 

The conference will cover all areas related to 2D materials’ chemistry spanning their synthesis as well as their functionalization, using covalent and non-covalent approaches, for composites, foams and coatings, membranes, (bio-)sensing, (electro- and photo-)catalysis, energy conversion, harvesting and storage, electronics, nanomedicine, biomaterials, with sessions on the following themes:

  • Synthesis, processing and multiscale characterization
  • Bottom-up growth
  • Covalent and non-covalent functionalization
  • Synthetic two-dimensional materials
  • Design of 3D functional materials from layered systems

 

Some important deadlines:

  • Abstract submission (poster & talks) on 15 June
  • Early-bird registration ends 15 May

Visit the website for a full list of the speakers and to register your interest: http://bit.ly/chem2Dmat_reg

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A coating inspired by fish scales could highlight structural weakness in buildings and vehicles

Article written by Simon Neil

Inspired by natural iridescence in fish skin, scientists in Germany have developed a graphene-based coating that changes colour when deformed. It could provide a simple way to warn of hidden damage in buildings, bridges and other structures.

Many materials are coloured by chemical pigments, which absorb light at particular wavelengths and reflect the remaining light, which we see as colour. Other materials, however, are given colour by periodically arranged microscopic surface structures. These cause interference between reflected light waves, amplifying them at specific visible frequencies. This strategy is used in some of nature’s most vibrant materials, from fish scales to peacock feathers, butterfly wings and cephalopod skins.

To read the full article visit Chemistry World.

Variable structural colouration of composite interphases
Yinhu Deng, Shanglin Gao, Jianwen Liu, Uwe Gohs, Edith Mäder and Gert Heinrich
Journal Article Mater. Horiz., 2017, Advance Article
DOI: 10.1039/C6MH00559D, Communication

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#RSCPoster Twitter Poster Conference 2017

Congratulations to Paolo Actis from the University of Leeds on winning Second prize in the #RSCMat category of the #RSCPoster Twitter Poster Conference 2017.

Paolo’s poster was titled was Creative use of electrowetting to perform biopsies from living cells

We are delighted to award Paolo the prize of a £50 RSC book voucher on behalf of Materials Horizons.

Thank you for participating in the Twitter conference and congratulations again on your achievement!

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Outstanding Reviewers for Materials Horizons in 2016

Following the success of Peer Review Week in September 2016 (dedicated to reviewer recognition) during which we published a list of our top reviewers, we are delighted to announce that we will continue to recognise the contribution that our reviewers make to the journal by announcing our Outstanding Reviewers each year.

We would like to highlight the Outstanding Reviewers for Materials Horizons in 2016, as selected by the editorial team, for their significant contribution to the journal. The reviewers have been chosen based on the number, timeliness and quality of the reports completed over the last 12 months.

We would like to say a big thank you to those individuals listed here as well as to all of the reviewers that have supported the journal. Each Outstanding Reviewer will receive a certificate to give recognition for their significant contribution.

Professor Fei Huang, South China University of Technology
Dr Susan Kelleher, University College Dublin
Professor Christine Luscombe, University of Washington
Professor Markus Niederberger, ETH Zurich
Dr Genqiang Zhang, University of Science and Technology of China

We would also like to thank the Materials Horizons board and the materials community for their continued support of the journal, as authors, reviewers and readers.

If you would like to become a reviewer for our journal, just email us with details of your research interests and an up-to-date CV or résumé. You can find more details in our author and reviewer resource centre

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Spider silk strength is in the loop

Article written by Simon Neil

Discovery of hidden thread in silk of deadly spider inspires material-toughening strategy

Scientists have discovered microscopic metastructures in the web of the recluse spider that offer a blueprint for tough new materials.

Source: © Schniepp Lab The recluse spider spins its ribbon-like silk into loops

At first glance, the venomous yet timid Chilean recluse spider (Loxosceles laeta) seems to be highly disorganised in constructing its web. Traversing its lair, it deposits clumpy bales of silk in a messy, tangled cobweb. Look closer. Work led by Hannes Schniepp at the College of William and Mary, in Virginia, US, in collaboration with Fritz Vollrath at the University of Oxford, UK, has shown that the spider carefully choreographs its spinnerets to sew silk in thousands of micrometre-sized loops. When strained, the loops sequentially open to reveal hidden length in the thread, dissipating energy and staving off breakage.

To read the full article visit Chemistry World.

Toughness-enhancing metastructure in the recluse spider’s looped ribbon silk
S. R. Koebley, F. Vollrath and H. C. Schniepp
Journal Article Mater. Horiz., 2017, Advance Article
DOI: 10.1039/C6MH00473C, Communication

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Hydrogel wound sealant simplifies trauma treatment

Article written by Simon Neil

Spray-on bandage dissolves on demand

Scientists in the US have developed a hydrogel-based wound sealant that can be easily applied to stem severe bleeding then gently and precisely removed to allow surgery.

On the 3 October 1993, Corporal James Smith, a 21-year-old US army ranger on operations in Mogadishu, bled to death from a gunshot wound to his thigh and pelvis. You might already know the story of that night, recounted in Mark Bowden’s book Black hawk down. The harrowing story of Smith’s death highlights how difficult it can be for a medic to control internal bleeding before it’s too late – especially if they are pinned down at night by enemy fire, hours from surgical help. Even far from the battlefield, haemorrhage is a serious threat to anyone with a severe wound. Each year, it kills more Americans than those who died in the entire Vietnam war.

To read the full article visit Chemistry World.

A hydrogel sealant for the treatment of severe hepatic and aortic trauma with a dissolution feature for post-emergent care
Marlena D. Konieczynska, Juan C. Villa-Camacho, Cynthia Ghobril, Miguel Perez-Viloria, William A. Blessing, Ara Nazarian, Edward K. Rodriguez and Mark W. Grinstaff
Journal Article Mater. Horiz., 2017, Advance Article
DOI: 10.1039/C6MH00378H, Communication

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The new and expanded Materials Horizons Community Board

Our early career researcher Advisory Board

Last year, we launched the first early career researcher Board for Materials Horizons, the Community Board. Since then, these Board members have provided invaluable feedback regarding journal activities, as well as being ambassadors for the journal. Based on this success, we have expanded the Community Board, through requesting nominations from our Board members, as well as the wider academic community.

We are now delighted to announce the new and expanded Materials Horizons Community Board. Many of our original Board members from last year are continuing to serve for a second term, and now the Board consists of an international set of 33 researchers at different stages of their early careers, ranging from PhD candidates to Associate Professors.

Read more about our Board members below. We have also introduced the Nanoscale Horizons Community Board, find out more here.

Sarit Agasti
Sarit received his Bachelor’s degree in Chemistry from the University of Calcutta, in 2003 and then his Master’s degree from the Indian Institute of Technology, Kanpur in 2005. Sarit went on to receive his PhD from the University of Massachusetts at Amherst under the supervision of Professor Vincent M. Rotello. Since his PhD, he has been a Postdoctoral Fellow at both the Massachusetts General hospital-Harvard Medical School and the Wyss Institute at Harvard University working with Professor Ralph Weissleder and Professor Peng Yin, respectively. Sarit has now returned to India and is working as a Faculty fellow at the Jawaharlal Nehru Centre for Advanced Scientific Research. His lab is interested in engineering small molecules and programmable molecular materials to address challenges in bioimaging, specifically in super-resolution microscopy.
Athina Anastasaki
Athina received her Bachelor’s degree in Chemistry from the National and Kapodistrian University of Athens. She then undertook a PhD in Polymer Chemistry at the University of Warwick under the supervision of Professor David Haddleton. She then undertook the position of a Monash-Warwick Alliance Research Fellow in the research groups of Professor David Haddleton and Professor Thomas Davis, focusing on controlled living radical polymerization methods, mechanistic studies, photochemistry and sequence-controlled polymers. Currently, she is an Elings Fellow working alongside Professor Hawker at the University of California, Santa Barbara (UCSB).
Maartje Bastings
Maartje Bastings studied Biomedical Engineering at the Eindhoven University of Technology (TU/e) and graduated Cum Laude in the group of Prof. E. W. (Bert) Meijer, where she continued her Ph.D. program funded by a Toptalent Fellowship from the Dutch Science Foundation (NWO). Her research focused on the understanding of multivalent binding mechanisms for directed targeting and the development of supramolecular biomaterials. She was awarded the University Academic Award in 2013 for best Ph.D. thesis at the TU/e. She moved to the Wyss Institute of Harvard University in Boston as a NWO Rubicon and Human Frontier Science Program postdoctoral fellow in the lab of Prof. William M. Shih. She studies DNA as a programmable biomaterial to design immune responses and assemble into multimodal nanoparticles. In January 2017 she will start as tenure track Assistant Professor in the Materials Science and Engineering Department at EPFL, Switzerland.
Read more »
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AsiaNANO poster prize winners

Congratulations to the poster prize winners at the Asian Conferene on Nanoscience & Nanotechnology which took place from the 10th – 13th October in Sapporo, Japan. The conference was attended by 330 participants from over 10 different countries. There were 79 oral (31 invited) and 182 poster presentations. Materials Horizons and Nanoscale Horizons provided sponsorship in the form of poster prizes which were handed to the following winners:

Chee Leng Lay (University of Singapore) for her poster titled: Transformative Two-Dimensional Array Configurations by Geometrical Shape-shifting Protein Microstructures, Ryo Iida (Hokkaido University): Thermoresponsive assembly of gold nanospheres and nanorods, Satoshi Nakamura (Hokkaido University): Immobilization of AuNRs by assistance of a DNA brush and Zhepeng Zhang (Peking University): Direct Chemical Vapor Deposition Growth of MoS2/h-BN van der Waals Heterostructures on Au Foils.

The conference included recent hot topics on chemical and physical aspects of nanostructures as well as their fabrication and characterization technologies with its main focus on revolutionary approaches and results developed newly in nanochemistry and nanomaterials for the last two years. Further information can be found on the website.

Poster prize winners

Poster prize winners with Professor Masahiko Hara of Tokyo Institute of Technology/RIKEN (far left).

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A laser “writing” method for easily adjustable and complex 3D structures – a new HOT article

Different 3D structures created

Photographs of different 3D shapes generated from the same stretched Nafion/PDA films treated with a NIR laser with different facular region shapes.

A new and highly adaptable way to make 3D structures in a wide range of different shapes has been reported in a new HOT article, published in Materials Horizons. The technique allows adjustment of both the shape transition process and the final shape at the same time.

The strategy, which Jian Ji’s group at Zhejiang University describe as a “writing” process, uses polymer nanosheets as blank “paper”. These are guided into making specific shape changes with a near infra-red laser beam “pen”. By controlling which shape changes happen at which time, several sheets can be woven together into a complex interlocking structure. Unlike previous techniques, the order of these changes can be easily altered to change the interlocking pattern.

Ji’s group used pre-stretched composite sheets of Nafion, a shape memory polymer, and polydopamine. When a NIR laser was applied to specific parts of the nanosheet, the polydopamine converted the light energy into heat. This caused internal stress between the heated and non-heated parts, triggering a shape transition of the sheet to relieve the stress. Changing the shape or intensity of the laser beam or where it was applied modulated the shape change, giving rise to a huge number of possible shapes.

Because the nanosheets don’t require special pretreatment before forming each particular shape, a variety of shapes can be made from the same starting material in quick succession. The technique could in future be used to make “personalised” components for the healthcare industry.

Read the full article here:
A ‘‘writing’’ strategy for shape transition with infinitely adjustable shaping sequences and in situ tunable 3D structures
Tingting Chen, Huan Li, Zuhong Li, Qiao Jin and Jian Ji
Mater. Horiz., 2016, DOI: 10.1039/C6MH00295A

Susannah May is a guest web writer for the RSC Journal blogs. She currently works in the Publishing Department of the Royal Society of Chemistry, and has a keen interest in biology and biomedicine, and the frontiers of their intersection with chemistry. She can be found on Twitter using @SusannahCIMay.

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