Dr Jian-Yao Zheng
Peroskovites are a growing family of photovoltaic materials that have created a vast amount of research since their recent discovery. Due to their tunable electronic and optical properties, they are considered state-of-the art materials for solar cell and laser devices. Up to now most work has focused on polycrystalline thin films. A holy grail in this field is the development of ultrathin large-size single crystalline nanosheets which have low defect density and superior properties than their polycrystalline counterparts.
“Looking at silicon as the exemplar material, it is clear that the availability of large single crystals with low point defect and dislocation densities is the key enabler for most of our ICT technologies. For perovskites, we need to have a source of large-area ultrathin materials that are compatible with standard lithography for optoelectronic device production”, says Prof. John Donegan, School of Physics and AMBER principal investigator at the CRANN Institute, Trinity College Dublin, the leader of the semiconductor photonics group and this project.
In spite of prior reports on the fabrication of perovskite nanosheets, the synthetic control over this material is still quite limited compared with other semiconductors. Several methods have been explored to synthesize bulk perovskite single crystals but the thickness is also large, which need further processing for practical device applications. Ultrathin single crystals are also reported but the sizes are less than 1 mm. In this project we have tackled this challenge. The work was carried out under the AMBER industry research programme in the CRANN Institute in Trinity College Dublin in collaboration with the Thermal Management Research Group, of Nokia Bell Labs.
“In an attempt to make PbBr2 nanowires, we unintentionally obtained these shiny crystals in solution at room temperature. When we drop-cast these nanosheets and measured the thickness of them, to our surprise, they are only 100 nm or less in thickness, however, the lateral size can go up to millimeter in the first try”, says Jian-Yao Zheng, the first author of the paper and former postdoctoral researcher at AMBER and the CRANN Institute. “In order to get centimeter-size nanosheets, we carefully controlled the concentration and the temperature of the system, then you can see the growth of large colorful nanosheets. The growth occurred at very low temperature (about 40 ℃), the solution can be heated up in an oven or by an infrared lamp. Therefore, we can observe the in-situ growth of crystals in real time under an optical microscope”.
The growth of nanosheets is highly anisotropic, with an aspect ratio reaching 100,000. In collaborating with Prof. Stefano Sanvito, the director of CRANN as well as the expert in molecular dynamics theory, we find very different formation energy of different crystal facets can lead to the preferential two dimensional growth, resulting in the formation of nanosheets. It is noteworthy that (1) the preparation is low-cost, fast, with environment friendly with simple solvents (ethanol and acetone) and all the chemicals can be recycled, we don’t need bulky equipment such as chemical vapor deposition (CVD) system; (2) The as-prepared crystals are free-standing and are found floating in the solvent, you can scoop them up easily onto any substrate. These lead halide nanosheets are much more stable than perovskite materials which are sensitive to heat, moisture, and oxygen. Lead halide is immune to these environmental factors and can be stored for a long time without degradation. They can be converted to perovskite whenever necessary to incorporate into optoelectronic devices.
These PbBr2 nanosheets are single crystalline. However, following the conversion to perovskite, we cannot be sure about the crystalline nature of the converted material. We do not have convincing evidence that the materials remain as a single crystal. This still needs much more rigorous experimental work. X-ray diffraction (XRD) results show clear and sharp peaks with both lead halide and perovskite nanosheets. We did transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) characterization on these converted nanosheets. The perovskite nanosheets are not stable on exposure to the electron beam, they suffer from the degradation, therefore, we are still not quite sure if our nanosheets are single-crystalline before exposing them to the intense electron beam. Further effort can be made on either improving the conversion process or the extensive study of the crystal nature of these samples after conversion.
Once fabricated, we are very interested in the nanolasers and photodetectors made from these nanoscale perovskite materials. By utilizing focused ion beam (FIB) milling in our Advanced Microscopy Laboratory (AML), we are able to make nice patterns and arrays out from these large nanosheets. Dr. Hugh G. Manning and Prof. John J. Boland of AMBER and the CRANN Institute, assisted with the characterization of photoconducting behavior of these samples. All of these devices are working with 100% device yield, indicating the high quality of the perovskite materials.
Last but not least, can we make even larger nanosheets? The answer is yes. Firstly, the precursors should be continuously supplied during the growth. Secondly, the solvent (acetone and ethanol) is volatile and suffer from the loss during the synthesis, resulting in the change of concentration of precursor, which is very important to control the growth equilibrium. An improved apparatus will facilitate the growth of nanosheets up to wafer-scale while the thickness remains at nanoscale, which should be extremely interesting both in fundamental and practical sense and offer a novel, facile and scalable strategy to make perovskite optoelectronic devices, this is our ambitious hypothesis and we hope it will be realized in the near future.
Figure: The PbBr2 nanosheets form easily in solution and grow over time to be 1 cm or more in diameter and less than 100 nm in thickness. Both photodiode and laser devices were fabricated once the PbBr2 was converted to perovskite materials.
Research presents a predictive model which can enable a material-by-design approach for nanowire networks
Researchers at AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research hosted at Trinity College Dublin, in collaboration with University of Calgary, have developed the first fully predictive model of both the electrical and optical performances of any metal nanowire network. The model, which has been experimentally verified, will enable researchers to quickly benchmark the performance of their materials facilitating a much sought after material-by-design approach. This important breakthrough pushes forward the potential for metallic nanowire networks to meet the needs of next-generation device technologies that require flexible transparent conductors – such as touch screen, display, lighting and solar cells.
The research presents a model which opens new avenues to develop materials for applications requiring transparent conductive (TC) properties beyond the current market leading material ITO (indium tin oxide). ITO, which is found in most touch screen devices, has drawbacks in terms of flexibility, being brittle, coupled with the scarcity of indium and the high cost of the ITO film deposition. In addition to smart phones and other touch screens, transparent conductors are used in modern photovoltaics, light-emitting devices and thin-film heaters. Nanowire networks are well suited as replacements for ITO in a wide variety of current and emerging flexible TC applications. Silver nanowire networks (Ag NWNs), for example, offer a promising alternative as it matches the electro-optical performance of ITO, and can also fulfil the demands for the emerging flexible electronics market, next-generation flexible solar cells, touch screens, displays, thin-film heaters, wearables and anti-static coatings that require flexible electro-optical components.
The development of a predictive model for NWNs is an important step towards a materials-by-design approach for TC applications. The results of this work show that simulation of NWNs can be used as a tool in benchmarking the effectiveness of post-deposition processing methods to be evaluated, potentially improving the efficacies of post-processing methods, and offers a strategic approach to exploring the potential applications of NWN materials guiding the synthesis of systems for specific needs.
The research, published in Scientific Reports*, was a collaboration between Professors John Boland and Mauro Ferreira, AMBER researchers in Trinity’s Schools of Chemistry and Physics, Dr Hugh Manning (lead author) and Dr Claudia Gomes da Rocha at University of Calgary, Canada. This research builds upon previously published work in ACS Nano Nanoscale and Physical Chemistry Chemical Physics.
Lead author of the paper, Dr. Hugh Manning, AMBER and Trinity’s School of Chemistry, said, “There is enormous interest in the development of high performing transparent conductors for a wide variety of applications. Nanowire networks are amongst the leading competitors to the currently used material ITO (indium tin oxide), and also meet the growing industry needs for mechanical flexibility. The key bottleneck in mainstreaming nanowire technologies lies in the need for high optical transparency in balance with low sheet resistance – or essentially maintaining the highly conductive and transparent nature of current transparent conductors, such as ITO, which is found in smart phones for example. The model we have developed can help researchers optimise nanowire networks for various applications by assessing the effectiveness of processing steps taken to improve network performance. Different technologies such as touch screens, lighting, or solar cells require different levels of performance, through material selection and carefully chosen processing steps you can tune the electrical performance of the nanowires to suit the application; this model can help guide that fine tuning.
Prof John Boland, AMBER and Trinity’s School of Chemistry, said, “Nanowire networks offer promising architectures for next generation flexible, transparent devices due to their electrical and optical properties. The model our team has developed has the potential to reduce the lag time from bench to finalised device for specific applications utilising nanowire networks. We envisage the next phase of our research is to expand the model to work with different type of metal nanowires, providing opportunities to further refine the model and its effectiveness, and enhance our understanding of these networks
This publication has emanated from research supported by Science Foundation Ireland (SFI) AMBER Centre under Grant Number SFI/12/RC/2278 and PI grant 16/IA/4462 and the European Research Council under Advanced Grant 321160.
Professor Wolfgang Schmitt from Trinity’s School of Chemistry, and AMBER, the SFI Research Centre for Advanced Materials and BioEngineering Research, at Trinity, has today been announced as a recipient of the European Research Council’s (ERC) Proof of Concept (POC) grant, worth €150,000
This is a top-up for his ERC Consolidator grant of €2 million awarded in 2015 and brings his total research funding awarded in the last 6 years to over €4.5 million.
The award will be used to explore the commercial applications of a new advanced technology that facilitates efficient CO2 capture from air. The POC grant will enable the development of a commercial, stand-alone prototype that will demonstrate the economic and ecological viability of this emerging approach to atmospheric CO2capture.
Proof of Concept grants are awarded to ERC grant holders as top-up funding to explore the commercial or innovation potential of the results of their ERC-funded research. Professor Schmitt at Trinity’s School of Chemistry, was awarded an ERC grant in 2015.
Through his ERC SUPRAMOL and Science Foundation Ireland-funded projects in particular, Professor Schmitt and his research team have examined metal-organic materials (MOFs) and other porous inorganic compounds. These materials can be functionalised and reveal unique, intrinsic micro- and macro-molecular structures that allow efficient capture of CO2.
The technology that will be explored through the POC grant should have exceptionally low operational CO2 capture costs, be modular and not be restricted to fixed locations or CO2 point sources. As a result, it could conceptually lead to negative or net zero CO2 emissions.
Professor Wolfgang Schmitt said:
We are delighted to be awarded this ERC Proof of Concept grant, which allows us to take our technology to prototype level and commercialise it. It is highly satisfying to work on research projects of global impact tackling CO2 emissions which are creating unprecedented threats to the world’s ecosystems and human activities.
Importantly, the award allows us to collaborate with the commercial team of the spin-out company, Trinity Green Energies and our friend & co-inventor – Professor Don MacElroy Emeritus Professor, University College Dublin – who is an expert in experimental gas adsorption measurements, gas diffusion and process simulations.
Dr Sebastien Vaesen, the lead chemical engineer within the ERC projects and co-developer of the CO2 capture technology said:
“We are delighted that the potential of our research results in the area of CO2capture are recognised by this award. The technology has the potential to facilitate the reduction of Ireland’s greenhouse gas emissions thus highlighting the potential impact and scalability of the proposed technology at European and global levels.”
Professor Michael Morris, Director of AMBER, added:
“The award of this Proof of Concept grant to Professor Schmitt is particularly pleasing and an excellent acknowledgement of the world-leading research work being carried out by himself and the team of researchers he has assembled. His studies are being undertaken to solve complex problems around the mitigation of climate change by absorption of CO2.”
“It provides a route to develop practical solutions to ameliorate global warming and bring national and international environmental and societal benefits as well as economic development to Ireland. It is a central component of AMBER’s programme looking at making breakthrough advances in creating materials and technologies that can foster a sustainable future for us all.”
Source: Trinity College Dublin - 25 July 2019
Athlone Institute of Technology has become the first institute of technology and the eight higher education institute to accede to the prestigious Advanced Materials and BioEngineering Research (AMBER) SFI Research Centre headquartered at Trinity College Dublin. This new partnership will foster research and education initiatives between the institute and existing AMBER members (TCD, RSCI, UCC, DCU, NUIG, UL and Tyndall Institute) promoting academic exchange and the development of research and innovation, particularly in the field of bio-materials for health and the circular economy, an economic system aimed at minimizing waste.
Athlone Institute of Technology’s engagement will grow AMBER’s world leading academic and industry-orientated materials science research in critical and emerging sectors of the economy related to polymers for applications in the life sciences, sustainable materials and industrial manufacturing. The institute’s accession to AMBER and its established research clusters will enable the centre to address current gaps in knowledge, drive advances in materials science and engineering, and translate research excellence into new products and technologies for society and solutions for industry.
Alongside researchers from Athlone Institute of Technology, AMBER partners in UCC and TCD will help develop new sustainable polymer strategies, such as polymer recycling and emerging biopolymers, as alternatives to the reliance on the traditional fossil fuel-driven polymer sector. This will allow the centre to work with companies across multiple sectors in the area of waste reduction and efficient resource utilization. Crucially, Athlone Institute of Technology will enhance AMBER through its extensive polymer processing expertise so that the span of materials discovery through to application can be studied.
Athlone Institute of Technology joins AMBER at a critical time as the centre drives expansion of its activities. AMBER currently partners with 40 companies across the fields of ICT, medical technologies and devices, as well as those in sustainability and manufacturing. AMBER will continue to significantly scale its industry investment during the centre’s second phase, aligning its vision with Enterprise 2025, Ireland’s national policy document by the Department of Business, Enterprise and Innovation. AMBER will play a crucial role for both multi-nationals and SMEs in driving innovation and will demonstrate economic impacts through retaining Irish-based multinationals, driving their research and development agendas as well as helping catalyse and grow new industry engagements. It will also attract new foreign direct investment to Ireland and investment from foreign-owned businesses within Ireland, strengthen SME investment in research and develop and create new spin out businesses.
Welcoming the announcement, Professor Mark Ferguson, Director General of Science Foundation Ireland and Chief Scientific Adviser to the Government of Ireland, said: “This partnership marks a significant opportunity for research collaboration, bringing diverse talents together to forge economic and social progress and the translation of research to industry. Science Foundation Ireland looks forward to continuing to support the world leading AMBER SFI Research Centre, increasing Ireland’s ability to positively impact both society and the economy through excellent scientific research.”
Professor Mick Morris, Director of AMBER, added: “As part of AMBER’s second phase, the centre will demonstrate significant impacts which will benefit individuals, communities, organisations and society both in Ireland and around the world. We are delighted to welcome Athlone Institute of Technology into the centre to deliver world-class materials science research and form strategic alliances with industry. The quality of our scientific research is critical for AMBER in attracting and sustaining long term engagements with industry, providing a skilled workforce competing for non-exchequer funding and tackling global challenges. Athlone Institute of Technology will play a significant role in delivering these ambitious goals as part of the centre.”
Dr Declan Devine, Director of the Materials Research Institute at Athlone Institute of Technology, said “We have a long established reputation for excellent science with translational potential. Partnering with the AMBER SFI Research Centre will further enable us to grow research in our areas of expertise, through the Applied Polymer Technologies (APT) Gateway, Ireland’s National Centre for Polymer Materials and Processing Research, which is hosted in our Materials Research Institute, and our development of materials for biomedical applications, such as bone regeneration and biodegradable polymer stents, and structural thermoplastic composites.”
AMBER (Advanced Materials and BioEngineering Research) is a world-leading SFI Research Centre funded by Science Foundation Ireland, hosted by Trinity College Dublin which provides a partnership between leading researchers in materials science and industry to develop new materials and devices for a range of sectors, particularly the ICT, medical devices and industrial technology sectors. AMBER is a national centre working in collaboration with CRANN (Trinity’s Centre for Research on Adaptive Nanostructures and Nanodevices) and the Trinity Centre for Biomedical Engineering, Trinity College Dublin, RCSI (The Royal College of Surgeons in Ireland), University College Cork, Dublin City University, NUIG, Tyndall National Institute, University of Limerick and Athlone Institute of Technology.
Source: Athlone Institute of Technology