Long-range hot-carrier transport in hybrid perovskites visualized by ultrafast microscopy

Guo, Zhi; Wan, Yan; Yang, Mengjin; Snaider, Jordan; Zhu, Kai; Huang, Libai

doi:10.1126/science.aam7744

Cited by 459 publications

(524 citation statements)

References 45 publications

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“…Although it is still limited by optical diffraction, TAM has been used to study photocarrier diffusion in space and time by measuring the temporal change of the spatial size of the photocarrier distribution, the resolution of which is only limited by SNR and can reach tens of nanometers [54].…”

Section: Recent Resultsmentioning

confidence: 99%

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Scanning ultrafast electron microscopy: A novel technique to probe photocarrier dynamics with high spatial and temporal resolutions

Liao

Najafi

2017

Materials Today Physics

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The dynamics of photo-excited charge carriers, particularly their transport and interactions with defects and interfaces, play an essential role in determining the performance of a wide range of solar and optoelectronic devices. A thorough understanding of these processes requires tracking the motion of photocarriers in both space and time simultaneously with extremely high resolutions, which poses a significant challenge for previously developed techniques, mostly based on ultrafast optical spectroscopy. Scanning ultrafast electron microscopy (SUEM) is a recently developed photon-pump-electron-probe technique that combines the spatial resolution of scanning electron microscopes (SEM) and the temporal resolution of femtosecond ultrafast lasers. Despite many recent excellent reviews for the ultrafast electron microscopy, we dedicate this article specifically to SUEM, where we review the working principle and contrast mechanisms of SUEM in the secondary-electron-detection mode from a users' perspective and discuss the applications of SUEM to directly image photocarrier dynamics in various materials. Furthermore, we propose future theoretical and experimental directions for better understanding and fully utilizing the SUEM measurements to obtain detailed information about the dynamics of photocarriers. To conclude, we envision the potential of expanding SUEM into a versatile platform for probing photophysical processes beyond photocarrier dynamics.

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Section: Recent Resultsmentioning

confidence: 99%

“…One exception is the transient absorption microscopy (TAM), an optical pump-probe technique that acquires spatial resolution by scanning one or both of the pump and the probe beams across the sample surface [51][52][53][54].…”

Section: Recent Resultsmentioning

confidence: 99%

Scanning ultrafast electron microscopy: A novel technique to probe photocarrier dynamics with high spatial and temporal resolutions

Liao

Najafi

2017

Materials Today Physics

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“…[69] Thus, the actual initial HC temperature should be ≈580 K. The scattering of charge carriers with LO-phonons, charge defects, and even with one another can be reduced by the dynamic screening in polar semiconductors. [10,70] They suggested that the large polaron formation rate competes favorably with the initial LO-phonon cooling time to greatly slow down the HC cooling in MAPbBr 3 . [69,[72][73][74] Zhu et al proposed that the dynamical screening from the reorientational motions of the dipolar molecular cations and the large polaron formation give rise to the long-lived HCs in organic-inorganic hybrid perovskites.…”

Section: Large Polaron Formation At Low Carrier Densitymentioning

confidence: 99%

“…

rapidly (within hundreds of femtoseconds), making HCs extraction extremely challenging. [9] Long HC transport lengths (≈600 nm) in MAPbI 3 thin films were visualized by Huang et al [10] These exciting findings forebode the potential of perovskite HCSCs that could dramatically boost perovskite solar cell efficiencies beyond their SQ limits. Since the first reports of slow HC cooling (≈0.4 ps) in MAPbI 3 polycrystalline thin films, [7,8] there have been growing interests about this novel phenomenon.

…”

mentioning

confidence: 93%

Slow Hot‐Carrier Cooling in Halide Perovskites: Prospects for Hot‐Carrier Solar Cells

et al. 2019

Advanced Materials

211

312

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rapidly (within hundreds of femtoseconds), making HCs extraction extremely challenging. A reduced HC cooling rate in solar absorbers is therefore a key material criterion for realizing HCSC.Halide perovskites possess novel slow HC cooling properties favorable for development as HCSC. Since the first reports of slow HC cooling (≈0.4 ps) in MAPbI 3 polycrystalline thin films, [7,8] there have been growing interests about this novel phenomenon. Li et al. reported a drastic slowdown of HC cooling by a further two orders in MAPbBr 3 colloidal nanocrystals (≈30 ps) at high pump fluence and demonstrated efficient (≈83%) extraction of HCs with an energy-selective organic layer. [9] Long HC transport lengths (≈600 nm) in MAPbI 3 thin films were visualized by Huang et al. [10] These exciting findings forebode the potential of perovskite HCSCs that could dramatically boost perovskite solar cell efficiencies beyond their SQ limits. Presently, the origins and mechanisms of slow HC cooling in halide perovskites remain fragmented and confusing with disparate models being proposed. A clear understanding of the intrinsic photophysics of HC cooling is essential for further technological developments.In this review, we examine the milestones and advancements of slow HC cooling in halide perovskites and distill their photophysical mechanisms. We begin with a brief introduction of the operation principles of HCSCs and carrier relaxation processes, followed by highlighting the seminal experimental and theoretical works on slow HC cooling in halide perovskites, before explicating their origins and mechanisms. A developmental toolbox for engineering slow HC cooling in halide perovskites and developing new perovskite materials with slower HC cooling will also be discussed. Lastly, we highlight the challenges and opportunities for perovskite HCSCs. How Hot Carriers Can Be Used?We begin with a quick overview of the several concepts for highefficiency solar cells. Figure 1a illustrates the energy band diagram of a typical single junction solar cell with its major energy loss processes following light illumination. [11,12] In all solar cells, photons possessing energies greater than the semiconductor bandgap can create free carriers or excitons with excess energies above the bandgap. These carriers or excitons with a temperature higher than the lattice temperature are termed "hot Rapid hot-carrier cooling is a major loss channel in solar cells. Thermodynamic calculations reveal a 66% solar conversion efficiency for single junction cells (under 1 sun illumination) if these hot carriers are harvested before cooling to the lattice temperature. A reduced hot-carrier cooling rate for efficient extraction is a key enabler to this disruptive technology. Recently, halide perovskites emerge as promising candidates with favorable hot-carrier properties: slow hot-carrier cooling lifetimes several orders of magnitude longer than conventional solar cell absorbers, longrange hot-carrier transport (up to ≈600 nm), and highly efficient hot-carrier extractio...

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“…16 By spatially resolving interfaces and domains, microscopy could obtain domain specific knowledge and mitigate ensemble averaging. [17][18][19][20][21] Yet, in traditional optical microscopy, signals of non-centrosymmetric molecular interfaces and domains are often overwhelmed by those of isotropic bulk materials. Even-order nonlinear optical microscopy, such as second harmonic generation (SHG) microscopy, 22 has been a popular technique to image non-centrosymmetric systems and is widely implemented in biophysics.…”

mentioning

confidence: 99%

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

2017

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Vibrational sum frequency generation (VSFG) spectroscopy has been a powerful technique to probe molecular structures at non-centrosymmetric media. Recent developed heterodyne (HD) detection can further reveal spectral phase and molecular orientations. Adding imaging capability to an HD VSFG signal can bring spatial visualization capability into this non-linear optical technique. However, it has been a challenge to build an HD VSFG microscope that is both easy to align and has good spectral phase stability -two necessary criterions for the broad application of this technique into various areas of science. Here, we report a fully-collinear HD VSFG microscope, which meets both phase stability and optical alignment requirements that can spatially resolve images of molecular interfaces and domains, with chemical and structural sensitivities. The phase stability is more than nine times better than a Michelson Interferometric HD VSFG microscope. Using this HD VSFG microscope, we study the structures of molecular selfassembly films. Because of the superior phase sensitivity, we successfully identify two molecular domains with different molecular orientations, which we show is not possible to extract from an ensemble-averaged VSFG spectrum or homodyne-detected VSFG image.

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Long-range hot-carrier transport in hybrid perovskites visualized by ultrafast microscopy

Cited by 459 publications

References 45 publications

Scanning ultrafast electron microscopy: A novel technique to probe photocarrier dynamics with high spatial and temporal resolutions

Scanning ultrafast electron microscopy: A novel technique to probe photocarrier dynamics with high spatial and temporal resolutions

Slow Hot‐Carrier Cooling in Halide Perovskites: Prospects for Hot‐Carrier Solar Cells

Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

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