Imaging photoinduced surface potentials on hybrid perovskites by real-time Scanning Electron Microscopy

Irde, Gabriele; Pietralunga, Silvia Maria; Sala, V.; Zani, Maurizio; Ball, James M.; Barker, Alex J.; Petrozza, Annamaria; Lanzani, Guglielmo; Tagliaferri, Alberto

doi:10.1016/j.micron.2019.03.002

Cited by 9 publications

(28 citation statements)

References 57 publications

(77 reference statements)

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“… 38 The magnitude and sign of this surface potential depend on the density and energy levels of the trap states, which are different for different surface terminations and/or bulk crystal orientations. The surface potential in turn influences the trajectories of the low-energy secondary electrons, 48 leading to a surface potential-dependent LISE collection efficiency. To examine this in more detail, we show in Figure 3 a diagonal cross sections for the intensity observed on the A and B surface lock-in USEM images at τ ≈ 8 ns.…”

mentioning

confidence: 99%

“… 49 − 53 On perovskites, surface photovoltages of ∼5 V arising from continuous laser illumination have been recently reported to influence SE trajectories to such an extent that a position-dependent collection efficiency can be observed. 48 We exclude the occurrence of localized surface potentials of this magnitude using a home-built retarding field analyzer (see section S4 of the Supporting Information ). Here, a retarding field between sample and ETD prevents SEs with an energy smaller than the field magnitude from reaching the detector.…”

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confidence: 99%

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Lock-in Ultrafast Electron Microscopy Simultaneously Visualizes Carrier Recombination and Interface-Mediated Trapping

Garming

Bolhuis

Conesa-Boj

et al. 2020

J. Phys. Chem. Lett.

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Visualizing charge carrier flow over interfaces or near surfaces meets great challenges concerning resolution and vastly different time scales of bulk and surface dynamics. Ultrafast or four-dimensional scanning electron microscopy (USEM) using a laser pump electron probe scheme circumvents the optical diffraction limit, but disentangling surface-mediated trapping and ultrafast carrier dynamics in a single measurement scheme has not yet been demonstrated. Here, we present lock-in USEM, which simultaneously visualizes fast bulk recombination and slow trapping. As a proof of concept, we show that the surface termination on GaAs, i.e., Ga or As, profoundly influences ultrafast movies. We demonstrate the differences can be attributed to trapping-induced surface voltages of approximately 100–200 mV, which is further supported by secondary electron particle tracing calculations. The simultaneous visualization of both competing processes opens new perspectives for studying carrier transport in layered, nanostructured, and two-dimensional semiconductors, where carrier trapping constitutes a major bottleneck for device efficiency.

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confidence: 99%

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confidence: 99%

Lock-in Ultrafast Electron Microscopy Simultaneously Visualizes Carrier Recombination and Interface-Mediated Trapping

Garming

Bolhuis

Conesa-Boj

et al. 2020

J. Phys. Chem. Lett.

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“…The TR‐SEM measures surface potential differences between the region under illumination and some reference point of the sample surface outside the illuminated region, being the sample and its surface grounded with respect to the SEM chamber, and its working principle was recently introduced. [ 27 ] A customized commercial SEM (Mod. Tescan MIRA III) is provided with optical viewports to focus light into the chamber and to illuminate the surface of the sample being tested.…”

Section: Experiments and Resultsmentioning

confidence: 99%

“…[ 41 ] Care was also taken to minimize electron‐beam damaging of the MAPbI 3 films. [ 27 ] Under SEM operating conditions the perturbation induced in the material by the primary electron (PE) beam is negligible with respect to optically induced effects, in terms of energy deposited over the excitation volume and of excited excess charge carrier density.…”

Section: Experiments and Resultsmentioning

confidence: 99%

“…TR‐SEM was recently introduced as a new and fast way to visualize photoinduced polarization at high irradiances. [ 27 ] It is based on the assumption that spatial modulations in work function can be depicted as secondary electron (SE) contrast patterns. [ 28 ] These can be originated by photoexciting excess charge carrier distributions in the subsurface volume, [ 29,30 ] as well as by changing the configuration of surface dipoles or by optically activating redox reactions at a local level.…”

Section: Introductionmentioning

confidence: 99%

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Dynamical Imaging of Surface Photopotentials in Hybrid Lead Iodide Perovskite Films under High Optical Irradiance and the Role of Selective Contacts

Pietralunga

Irde

Barker

et al. 2020

Adv Materials Inter

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To leverage the outstanding photonic qualities of lead halide hybrid perovskites under high optical irradiance, their reliability and temporal stability must be assessed. Time‐resolved scanning electron microscopy unveils that when illuminating the free surface of methylammonium lead iodide (MAPbI3) films at 500 Sun in vacuum, a giant photopotential locally develops in tens of seconds, differently evolving depending on charge‐selective substrates. It is reversible on timescales of minutes in the case of hole‐transporting poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate, while more persistent effects occurs, on the timescale of hours, in the case of electron‐transporting TiO2. In addition, films grown on TiO2 show irreversible decay of photoluminescence measured in situ and photoinduced alteration of the work function at some grain boundaries. Different responses at high irradiance are ascribable to contact‐dependent and light‐induced spatial redistribution of charged defects, either ions or localized dipoles. It is also clear that photoexcited charges play different roles in the photochemistry of systems, depending on selective contacts and they are likely to mediate diverse photoassisted redox reaction paths. The TiO2 layer may act as a photocatalyst, leading to MAPbI3 degradation and to irreversible polarization, which will hinder high‐irradiance applications.

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Nanoscale Surface Photovoltage Spectroscopy

Yalcinkaya,

Rohrbeck,

Schütz

et al. 2023

Advanced Optical Materials

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Understanding electron and ion dynamics is an important task for improving modern energy materials, such as photovoltaic perovskites. These materials usually have delicate nano‐ and microstructures that influence the device parameters. To resolve detailed structure–function relationships on the relevant micro‐ and nanometer length scales, the current macroscopic and microscopic measurement techniques are often not sufficient. Here, nanoscale surface photovoltage spectroscopy (nano‐SPV) and nanoscale ideality factor mapping (nano‐IFM) via time‐resolved Kelvin probe force microscopy are introduced. These methods can map nanoscale variations in charge carrier recombination, ion migration, and defects. To show the potential of nano‐SPV and nano‐IFM, these methods are applied to perovskite samples with different morphologies. The results clearly show an improved uniformity of the SPV and SPV decay distribution within the perovskite films upon passivation and increasing the grain size. Nevertheless, nano‐SPV and nano‐IFM can still detect local variations in the defect density on these optimized samples, guiding the way for further optimization.

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Imaging photoinduced surface potentials on hybrid perovskites by real-time Scanning Electron Microscopy

Cited by 9 publications

References 57 publications

Lock-in Ultrafast Electron Microscopy Simultaneously Visualizes Carrier Recombination and Interface-Mediated Trapping

Lock-in Ultrafast Electron Microscopy Simultaneously Visualizes Carrier Recombination and Interface-Mediated Trapping

Dynamical Imaging of Surface Photopotentials in Hybrid Lead Iodide Perovskite Films under High Optical Irradiance and the Role of Selective Contacts

Nanoscale Surface Photovoltage Spectroscopy

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