Ultrafast Transient Absorption and Terahertz Spectroscopy as Tools to Probe Photoexcited States and Dynamics in Colloidal 2D Nanostructures

Lauth, Jannika; Kinge, Sachin; Siebbeles, Laurens D. A.

doi:10.1515/zpch-2016-0911

Cited by 16 publications

(15 citation statements)

References 24 publications

(29 reference statements)

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“…Despite the simplicity of this approach, it often provides very valuable information. [158] CdSe-quantumdot-sensitized ZnO nanowires were investigated by a combination of transient optical absorption and time-resolved THz spectroscopy by Žídek et al: [159] an efficient electron injection from the quantum dot to the semiconductor nanowire was observed on a picosecond timescale; this supports the hypothesis that the charge transfer state mediates the electron injection. [154] Despite the lack of spectral information, the bare THz signal kinetics is a powerful source of information particularly in combination with ultrafast optical spectroscopies.…”

Section: Wwwadvopticalmatdementioning

confidence: 89%

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

Kužel

Němec

2019

Advanced Optical Materials

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Transport of charges is a fundamental process in many high-tech applications including photovoltaic or optoelectronic devices, but also in more ordinary components such as unsophisticated wires and other circuitry. The development of nanotechnologies resulted in the fabrication of highly complex materials consisting of a large variety of nanosized elements, which inevitably involve a multitude of charge transport processes occurring on various time-and length-scales. Figure 1 summarizes the most common nanoelements with high application potential.For example, the electrodes employed in Grätzel solar cells [1] are composed of percolated networks of a huge number of metal oxide nanoparticles (top-left panel in Figure 1). Colloidal nanocrystals form the basis for thin film electronics and flexible electronic devices. [2] The synthetic approaches control their composition, size and electronic structure (energy levels, density of states within the bands and in the bandgap) and the charge-carrier transport. [2,3] Nanowires and nanotubes made of conventional semiconductors are quasi 1D systems combining Terahertz spectroscopy has been used for almost two decades for investigations of nanomaterials, including nanocrystals, nanoparticles, nanowires, nanotubes or 2D crystals. Its great importance stems from the fact that it is a noncontact method and, owing to its high frequency and broadband character, it is capable of characterizing charge transport properties within individual nano-objects but also among them. In addition, probing of photoinitiated ultrafast charge dynamics is possible thanks to the sub-picosecond time resolution. Despite this unprecedented potential, the interpretation of the measured terahertz conductivity spectra in many materials is still intensively debated. Herein is presented a review of the experiments performed on nanostructures of conventional semiconductors and on carbon nanomaterials (graphene and carbon nanotubes) during the past decade. The state of the art of the theoretical formalism is provided and discussed, including the intrinsic response, as well as the role of inherent heterogeneity and of the experimental conditions.

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Section: Wwwadvopticalmatdementioning

confidence: 89%

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

Kužel

Němec

2019

Advanced Optical Materials

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“…Reproduced with permission. [149] Copyright 2019, de Gruyter. b-d) Psuedocolor (−ΔT/T 0 ) TA spectra of probe wavelength versus pump-probe delay (Δt) for the layered perovskite thin film (C 4 H 9 NH 3 I) 2 (CH 3 NH 3 I) n−1 (PbI 2 ) n : b) n = 1; c) n = 2; d) n = 3.…”

Section: Terahertz Spectroscopymentioning

confidence: 99%

“…Figure 7. a) Schematic image of the transient absorption set up with the pump exciting the sample and the probe monitoring the sample's response at different times (top)and schematic of the contributions to the ΔA spectrum with a negative ΔA signal from the ground-state bleach and stimulated emission and a positive ΔA signal originating from excited-state absorption. Reproduced with permission [149]. Copyright 2019, de Gruyter.…”

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confidence: 99%

Layered Perovskites in Solar Cells: Structure, Optoelectronic Properties, and Device Design

Sirbu

Balogun

Milot

et al. 2021

Advanced Energy Materials

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optoelectronic properties akin to industrial juggernauts gallium arsenide and silicon. [1,2] Yet, the materials are compatible with solution-processing techniques such as inkjet printing and spray coating. [3] This unprecedented combination has led to the development of solar cells which already show power conversion efficiencies of over 25%, similar to state-of-the-art poly-Si and other thin-film technologies, in just over 10 years of development. [4] Hybrid perovskites are particularly interesting for indoor applications, with impressive efficiencies of over 35% demonstrated under indoor illumination which may prove a viable option to power the ever expanding Internet of Things. [5] Rather than competing with the current technology giants, perovskites can work together with other solar cell technologies in a tandem configuration. Record efficiencies of over 29% for silicon-perovskite tandem solar cells have already been reported and further progress is expected in the near future. [6] Although perovskite solar cells (PSCs) are on the verge of mass production, two main challenges remain: stability [7] and toxicity. [8] Multiple reviews already address the toxicity concern, and it will not be discussed here. [9][10][11] Layered hybrid perovskites (LPKs) have emerged as an answer to battle stability concerns. Although known for decades, LPKs have only recently been incorporated in photovoltaic (PV) applications, resulting in modest device power conversion efficiencies due to poorer optoelectronic properties. [12][13][14] However, their key advantage is the stabilizing effects of the organic interlayers, which prevents perovskite degradation. [15,16] The organic spacer inhibits ion migration which prevents the formation of irreversible degradation products. [17] Alternatively, LPKs can be deposited over the state-of-the-art perovskite materials to combine the high performance of 3D perovskites with the stabilizing properties of LPKs. [15] Here, the limiting factor is inefficient charge transport across the organic interlayer, currently preventing the full exploitation of the layered structure in PSCs.This can be approached in two ways, either by keeping the LPK layer very thin, currently the most popular approach, or by increasing the electrical conductivity of the material. [18,19] The conductivity can be enhanced through increasing the number of inorganic layers n, but this comes at the price of reduced stability. [20][21][22] The better approach is to enhance the charge transport in LPKs through the molecular engineering of the organic Layered hybrid perovskites (LPKs) have emerged as a viable solution to address perovskite stability concerns and enable their implementation in wide-scale energy harvesting. Yet, although more stable, the performance of devices incorporating LPKs still lags behind that of state-of-the-art, multication perovskite materials. This is typically assigned to their poor charge transport, currently caused by the choice of cations used within the organic layer. On balance, a compromise bet...

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“…THz spectroscopy has been utilized for studying optical and optoelectronic properties of a wide area of 2D materials, including characterizing the charge carrier mobility of 2D InSe, GaAs, and InP nanosheets under photoexcitation, evaluating the factors that affect the optoelectronic properties of 2D perovskites such as charge transport properties, thickness, and excitonic effects, and also probing the conductivity and carrier dynamics of other types of layered 2D materials . The spatial resolution of THz spectroscopic imaging, however, is limited by the diffraction of THz wave, which means more solutions of improving the spatial resolution are of importance when adopting THz imaging.…”

Section: Spectroscopic Imagingmentioning

confidence: 99%

Microscale Spectroscopic Mapping of 2D Optical Materials

Dong

Yetisen

Köhler

et al. 2019

Advanced Optical Materials

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be used for flexible touch screens and displays, printable electronics, and thinfilm photovoltaics, [4] while FETs made of graphene can be used for highly sensitive biosensors. [5] Another 2D material MoS 2 , a direct-bandgap semiconductor, has applications in ultrasensitive photodetectors, transistors, and gas-sensing devices. [6][7][8][9] Other 2D materials have also shown potential in photovoltaic devices, memory, and light-emitting diodes (LEDs). [10,11] Broad application potential of 2D materials in optoelectronic devices, photonic devices, and optical sensors is mainly based on their unique optical performances. [12] 2D materials can be fabricated based on their layered structure. In the molecular structures of these materials, the atoms are bonded hard in the same plane, but the bond effect between two lateral layers is weak due to van der Waals forces. [13] 2D materials can be roughly categorized as semimetal like graphene, semiconductor like transition metal dichalcogenides (TMDs), and insulator like hexagonal boron nitride (hBN) from the aspect of bandgap differences. [14] Due to the experimentally practical manipulation of monolayer and multilayer 2D materials, remarkable optical performances can be realized for a wide range of optical applications. For example, the number of layers of 2D materials can strongly influence the photoluminescence performance. [15] The unconventional optical performances including adsorption and emission, light sensitivity, as well as plasmonic effects of 2D materials are closely related to their inner physical properties such as carrier mobility, density of states, and band structure based on the interaction of atoms, structural symmetry, and stacking patterns. [16,17] Through the control of layer number which could influence the bandgap value, 2D materials could react to different spectrum ranging from ultraviolet to infrared light. [18] Doping strategies are also effective to modify intrinsic 2D semiconductors and improve the response with respect to an extended range of spectrum. [19,20] The assessment of the optical properties of 2D materials is indispensable for device and sensor development. [21] Based on detailed surface mapping and spectral information, the suitability of 2D materials for optical devices or sensor applications can be thoroughly studied. [22,23] Microscopy, direct 2D mapping of materials, can provide basic spatial information, [24] while spectroscopy can offer one more dimensional spectral information which is 2D materials have unique optical properties due to their ultrathin layered structures, and are emerging as promising materials for optoelectronic devices. To characterize and evaluate these properties, diffraction-limited spectroscopic mapping, also known as microscale spectroscopic imaging, has been developed to provide abundant spatial and spectral information. The usefulness of microscale spectroscopic mapping for unique property study of 2D optical materials is addressed. Advances in both mature and growing microscale spectroscopic mapping...

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Ultrafast Transient Absorption and Terahertz Spectroscopy as Tools to Probe Photoexcited States and Dynamics in Colloidal 2D Nanostructures

Cited by 16 publications

References 24 publications

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

Terahertz Spectroscopy of Nanomaterials: a Close Look at Charge‐Carrier Transport

Layered Perovskites in Solar Cells: Structure, Optoelectronic Properties, and Device Design

Microscale Spectroscopic Mapping of 2D Optical Materials

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