Understanding the impact of strain (structural deformation) is crucial to the success of halide perovskite materials used in optoelectronic devices such as solar cells, X-ray detectors, and LEDs. While halide perovskites demonstrate the potential for enhanced efficiency in these devices, research is ongoing to investigate strain and defects that still hinder device performance and stability.
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 (MAPbBr3 [MA = CH3NH3]), including strain around defects. Published in Advanced Materials, the experiments were part of a recent study from Diamond’s I13-1 beamline (Figure 1), which reveals 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.
With primary funding from the Engineering and Physical Sciences Research Council (EPSRC) and the European Research Council (ERC), the experiments took place from October 2019 – September 2023 at the University of Cambridge (UK) and Diamond Light Source (UK), and included scientists from the University of Cambridge, University College London (UK), King Abdullah University of Science and Technology Catalysis Center (KAUST) (Saudi Arabia), Brookhaven National Laboratory (USA), and Diamond Light Source.
Shaping the future of solar cells, LEDS and X-ray detectors using advanced imaging techniques
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.
Darren Batey, Principal Beamline Scientist on Diamond’s Beamline I13-1, said:
The world is in need of efficient solar cells and batteries to capture and store sustainable energy but these devices rely on electronic structures that degrade over time. If we can track how strain is affecting performance and stability, we can begin to explore how to engineer these materials and optimise their performance, robustness, and reliability.
Kieran Orr, who conducted the research as a PhD student at the University of Cambridge and is now a Research Fellow at Stanford University in the USA, explained:
Another exciting use of halide perovskites is in X-ray detection. X-rays are a part of the electromagnetic spectrum just like visible light, but with a different wavelength. Therefore, Halide perovskites can also absorb X-rays to produce electricity and be used in X-ray detector technologies. There are promising results which suggest that X-ray detectors based on halide perovskites could be more sensitive than current versions, meaning they can detect lower intensities. This is particularly useful for medical imaging applications (like mammography and radiography) where it is important to limit the body’s exposure to X-rays.
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Image: 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.
Credit: Orr, K. W. P. et al., Adv. Mater. 35, 2305549 (2023)