Conference Presentation: CMD 2022

Two of the group gave oral presentations at CMD29 in Manchester.

Group PhD student Hoyeon Choi reported his work on the “Impact of Microstructure of Crystallinity driven singlet fission efficiency in diF-TES-ADT“, a collaboration between Jenny Clark (Sheffield) our our group.

Group PDRA Stephen Church reported his work on “Disentangling gain, distributed losses and end-facet losses in freestanding nanowires lasers using automated high-throughput micro-spectroscopy“, a collaboration between Huiyun Liu (UCL) and our group.

New Paper: Holistic Determination of Optoelectronic Properties using High-Throughput Spectroscopy of Surface-Guided CsPbBr3 Nanowires

Optoelectronic materials form the building blocks of crucial components of modern technology, including solar cells, CCDs, lasers and LEDs. The past decade has seen significant developments in materials science that enable the shrinking of these materials to the nano-scale. These advancements have also created entirely new technologies based around light manipulation. We can now create nano-scale light sources, nano-scale light detectors and nano-scale optics: so we can build a chip that performs processes using light instead of electrical signals.

An important component of these devices are nanowires: these can act as on-chip light sources and tiny optical fibers, essentially the power and wiring of a light based circuit. As materials are shrunk towards the nano-scale, their performance is affected strongly by their size, providing a handle to tune performance of these nanowires  to suit the application. However, herein lies one of the major challenges of this technology; it remains difficult to accurately and repeatedly control the size of these nano-materials when they are made leading to  an unwanted spread in their performance.

High-throughput experiments to study inhomogeneity

Stephen Church of the OMS Lab worked with colleagues in the Joselevich group at the Weizmann Institute in Israel to developed a methodology to optimize these nano-materials by harnessing the inherent variation using big data approaches. He has developed an automated microscope that can study the properties of more than 10,000 individual nano-wires with a suite of different optical experiments. This approach produces a vast dataset that, when considered together, describes the nano-material and can therefore be used to establish the best way to optimize their performance. Crucially, this approach requires very little prior knowledge of the sample and can be applied generally to new nano-materials.

Soft nanowires and the impact of strain

In their recent paper, we demonstrate this approach on wires made of halide perovskites, an emerging material touted for its superior light emission and detection. The material is also “soft”, deforming to fit on its substrate; this causes further spread in properties as the thickness of the wire changes. The big data approach shows the impact of this deformation on the color and the efficiency of light emission from the nano-wires, and shows how the degree of deformation varies across the population.

Open data

This publication is made up of more than just a journal report. The raw data has been made available via FigShare, and the analysis code via github. It is possible to explore and manipulate the raw data using the Google Colab platform.

Reference: Holistic Determination of Optoelectronic Properties using High-Throughput Spectroscopy of Surface-Guided CsPbBr3 Nanowires, Stephen A. Church, Hoyeon Choi, Nawal Al-Amairi, Ruqaiya Al-Abri, Ella Sanders, Eitan Oksenberg, Ernesto Joselevich and Patrick W. Parkinson, ACS Nano (2022) DOI: 10.1021/acsnano.2c01086

New Review : Measuring, controlling and exploiting heterogeneity in optoelectronic nanowires

Interwire and intrawire inhomogeneity

Group PhD students Ruqaiya Al-Abri and Hoyeon Choi have written an invited review article for JPhys Photonics, published today.

Lead author Ruqaiya Al-Abri describes this work:

Among the one-dimensional structures, semiconductor nanowires have attracted great attention; from the growth process to the production of functional devices they have been widely studied. The growth condition of the nanowires can lead to non-uniformity (disorder) in the crystal structure, morphology, and geometry of the nanowire. Consequently, this affects the functionality of individual and/or ensembles of nanowires. However, researchers have benefited from disorder; it has been shown that disorder can enhance the performance of ensemble of nanowires such as in photovoltaic devices. This review article attempts to understand the disorder in these structures, investigates the origin of the inhomogeneity within “interwire” and between “intrawire” nanowires, and outlines different approaches to correlate disorder to functional parameters and hence optimize the performance of the nanowires.

Reference: Measuring, controlling and exploiting heterogeneity in optoelectronic nanowires, Ruqaiya Al-Abri, Hoyeon Choi and Patrick Parkinson, JPhys Photonics, (2021) DOI:10.1088/2515-7647/abe282

New Paper: Visualizing the role of photoinduced ion migration on photoluminescence in halide perovskite grains​

Group student Hoyeon has had a paper accepted in the RSC Journal of Materials Chemistry C, studying the photo-brightening effect in perovskite grains using correlated optical and chemical mapping. In collaboration with the Flavell group and the NanoSIMS group at Manchester, this study linked luminescence lifetime and emission energies to local changes in oxygen and iodine density close to the surface of methyammonium lead iodide grains; a prototypical next-generation photovoltaic material.

This new study unambiguously links the emission efficiency improvement under illumination – the so-called photo-brightening effect – to light-induced migration of iodine into the bulk of the crystal and an increase in oxygen levels close to the surface of the grains. By mapping the emission efficiency and chemical levels on the sub-micron scale, we find that grain size has a decreasing role with light-soaking.

Reference: “Visualizing the role of photoinduced ion migration on photoluminescence in halide perovskite grains​“, J. Mater. Chem. C (2020), DOI:10.1039/d0tc01441a

Conference Proceedings: Spatially and temporally resolved degradation in antisolvent treated perovskite films

Group PhD student Hoyeon Choi has had a conference proceedings accepted for SPIE Europe 2020. As this conference has been cancelled, his talk is available throught the SPIE Digital Form.

In his work, Hoyeon describes the application of confocal and time-resolved spectral mapping to study and understand photobrightening and degradation processes in a prototypical perovskite material fabricated with and without use of anti-solvent treatment.

The presentation and paper are available online now.

Reference: Spatially and temporally resolved degradation in antisolvent treated perovskite films, Hoyeon Choi, Chun-Ren Ke, Stefan Skalsky, Wendy Flavell, and Patrick Parkinson, Proc. SPIE 11365, Organic Electronics and Photonics: Fundamentals and Devices II, 113650Q