Diamond Annual Review 2023/24

39 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 3 / 2 4 Unlocking potential: 3D strainmapping for high-performance halide perovskite devices In the race to address energy and climate challenges, the goal is to capture and emit energy efficiently, while reducing reliance on fossil fuels. In recent years, halide perovskites have been used to make high performance solar cells which offer many advantages over conventional silicon-based cells. While the latter require high crystal purity, high temperature manufacturing, and greater thickness to absorb sufficient light, thin film halide perovskite solar cells are lighter, flexible, absorb light more strongly, and are easier to manufacture, opening doors for cheaper and less energy intensive applications. However, strain and defects in halide perovskite materials can influence their mechanical stability and energy-conversion properties, which in turn affect overall solar cell performance. Furthermore, dislocations (a specific kind of material defect uncovered in this study) formed during manufacture and operation can lead to delamination and cracking, and even mechanical failure of the solar cells, reducing their longevity. To gain a full understanding of strain and its impact on performance in halide perovskites, strain has to be characterised on a local scale and in three dimensions. Furthermore, experiments must be conducted under operational conditions to understand modes of device degradation and failure. In experiments to understand the structural changes that can occur during device operation, scientists used Synchrotron-based Bragg Coherent Diffraction Imaging (BCDI) - an X-ray-based imaging technique - to map nanoscale strain in halide perovskite microcrystals (MAPbBr 3 [MA = CH 3 NH 3 ]), including strain around defects. The experiments on Diamond’s high energy beamline I13-1 involved shooting an X-ray beam onto a halide perovskite sample and measuring the X-rays that are diffracted by the sample to learn about its internal structure. Because solar cells have to have light shone on them to produce electricity, these measurements were performed both in the dark and under illumination to understand what effect light has on halide perovskite structure. The experiments revealed the dynamic migration of nanoscale extended defects in halide perovskites under continuous light illumination. These insights demonstrate the highly dynamic nature of the structure of halide perovskite materials and how they evolve under operational conditions, highlighting the close links between nanoscale structure, dislocations, and device performance and stability. Orr, K.W.P. et al . DOI: 10.1021/ acsenergylett.4c00921 Figure: Tracking defect migration in halide perovskites. The grey volumes outline a particular halide perovskite crystal measured in the experiment with black lines indicating defects (specifically, dislocation defects in this case). Under continuous illumination the defects dramatically migrate and change shape indicating that the nanoscale structure of halide perovskites is fluxional under conditions of solar cell operation. Differences in bumblebee vision help different species share resources A central theme of ecology is understanding how species coexist in an environment. A traditional explanation is that species partition the available resources by space or time, a process called niche partitioning. Different bees, for example, specialise on foraging on specific flower species, and some are physically adapted to do so. However, this specialisation does not provide a complete explanation, as coexisting bee species often overlap in their choice of flowers. Suggestions of complementary or alternative partitioning mechanisms include the selection of microhabitats based on temperature, light and wind conditions. Without a more thorough explanation of the mechanisms that underpin local coexistence, we may struggle to understand the factors behind the ongoing loss of bee diversity. A team of researchers from Lund University, Stockholm University and Queen’s University Belfast investigated whether differences in vision allow bumblebee species to forage in different light conditions. On beamline I13- 2, they used X-ray micro-CT to scan sample bumblebee eyes, performing volumetric and computational analyses. By scanning at I13-2, the researchers were able to not only rapidly acquire data from many specimens but the images they obtained enabled them to reconstruct 3D volumes of the bee eyes in the high-resolution detail required for their analyses. The team showed that bumblebee species niche partition according to the light conditions. As light intensity increased, so did the abundance of bumblebee species with a low eye parameter (that is, eyes that are better adapted to bright light). In contrast, the abundance of bumblebee species with a high eye parameter (eyes that are well adapted to dim light vision) peaked at intermediate light levels or even decreased with light. The results of this study are the first to show that sensory traits are important in understanding how bees use their environment, and that microhabitat niche partitioning related to sensory trait expression may well be one of the mechanisms underpinning species coexistence. Bartholomée, O. et al. DOI: 10.1098/rspb.2022.2548 Figure: Role of light and temperature on bumblebee community composition.