Terahertz Spectroscopic Probe of Hot Electron and Hole Transfer from Colloidal CsPbBr<sub>3</sub> Perovskite Nanocrystals

Sarkar, Sohini; Ravi, Vikash Kumar; Banerjee, Sneha; Yettapu, Gurivi Reddy; Markad, Ganesh B.; Nag, Angshuman; Mandal, Pankaj

doi:10.1021/acs.nanolett.7b02003

Cited by 74 publications

(82 citation statements)

References 48 publications

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“…[117] TRTS is a very useful noncontact photoconductivity probe to investigate the HC transfer kinetics in NCs system. [117] TRTS is a very useful noncontact photoconductivity probe to investigate the HC transfer kinetics in NCs system.…”

Section: Efficient Hc Extractionmentioning

confidence: 99%

“…[118][119][120] [9] Copyright 2017, Nature Publishing Group. [117] Copyright 2017, American Chemical Society. Inset: extracted HC temperature versus delay time for a CsPbI 3 film with and without P3HT at excitation condition).…”

Section: Efficient Hc Extractionmentioning

confidence: 99%

“…www.advmat.de www.advancedsciencenews.com the two phonon-resonance modes at ≈1.8 and ≈3 THz in conductivity spectra (i.e., due to HC-phonon interactions present in neat NCs [117,121,122] ) for NCs/acceptor complex (for example for NC/PTZ system) (Figure 10f) suggests that HC transfer is faster than HC relaxation to the band edges. Do note that in their experiments, the energy levels of the extraction layers lie in between CsPbBr 3 bandgap.…”

Section: Efficient Hc Extractionmentioning

confidence: 99%

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

et al. 2019

Advanced Materials

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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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Section: Efficient Hc Extractionmentioning

confidence: 99%

Section: Efficient Hc Extractionmentioning

confidence: 99%

Section: Efficient Hc Extractionmentioning

confidence: 99%

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

et al. 2019

Advanced Materials

217

326

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“…Metal halide perovskite materials are now widely studied for their rediscovered, highly tunable, and desirable optoelectronic properties . Lead halide perovskites in particular have emerged as a material system of high interest for photovoltaics, lighting/display/lasing, detectors, and other applications due to a bandgap energy that is tunable throughout the visible and near infrared spectrum and the material's ability to be processed via many variable, low‐cost methods. In general, bright emission and long‐lived carriers are observed in these semiconductors despite the films often containing a large degree of structural disorder .…”

Section: Fp‐trmc Yield‐mobility Products (φσμ) For the Samples Displamentioning

confidence: 99%

Conductivity Tuning via Doping with Electron Donating and Withdrawing Molecules in Perovskite CsPbI₃ Nanocrystal Films

et al. 2019

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Doping of semiconductors enables fine control over the excess charge carriers, and thus the overall electronic properties, crucial to many technologies. Controlled doping in lead-halide perovskite semiconductors has thus far proven to be difficult. However, lower dimensional perovskites such as nanocrystals, with their high surface-area-to-volume ratio, are particularly well-suited for doping via ground-state molecular charge transfer. Here, the tunability of the electronic properties of perovskite nanocrystal arrays is detailed using physically adsorbed molecular dopants. Incorporation of the dopant molecules into electronically coupled CsPbI 3 nanocrystal arrays is confirmed via infrared and photoelectron spectroscopies. Untreated CsPbI 3 nanocrystal films are found to be slightly p-type with increasing conductivity achieved by incorporating the electron-accepting dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) and decreasing conductivity for the electron-donating dopant benzyl viologen. Time-resolved spectroscopic measurements reveal the time scales of Auger-mediated recombination in the presence of excess electrons or holes. Microwave conductance and field-effect transistor measurements demonstrate that both the local and long-range hole mobility are improved by F 4 TCNQ doping of the nanocrystal arrays. The improved hole mobility in photoexcited p-type arrays leads to a pronounced enhancement in phototransistors.

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“…Several studies have already shown that perovskite NCs possess great potential for solution‐processable photovoltaic devices under ambient atmosphere due to their high environmental and thermodynamic stabilities . Other studies demonstrate the charge transfer dynamics for perovskite NCs in heterojunctions showing great potential for charge extraction in further applications . Most reported perovskite photovoltaic devices are generally fabricated in a layer‐by‐layer configuration in which the exciton dissociation occurs at the interface of the perovskite NC layer and the respective electron or hole‐transport layer.…”

Section: Responsivity (R) and Detectivity (D*) Of Photodetectors Undementioning

confidence: 99%

Exciton Diffusion Lengths and Dissociation Rates in CsPbBr₃ Nanocrystal–Fullerene Composites: Layer‐by‐Layer versus Blend Structures

Yao

Bohn

Huang

et al. 2019

Advanced Optical Materials

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These properties have led to an enormous progress in various optoelectronic applications, especially to the impressive advances in the efficiency of photovoltaics that surged from 3.8% to 22% during the past few years. [5][6][7][8][9] Although most early research studies were focused on bulk thin film perovskites, very recently there has been a growing interest in exploring perovskite nanocrystals (NCs) for various applications due to their enhanced stability in the presence of ligands. [10][11][12][13] Several studies have already shown that perovskite NCs possess great potential for solution-processable photovoltaic devices under ambient atmosphere due to their high environmental and thermodynamic stabilities. [14][15][16] Other studies demonstrate the charge transfer dynamics for perovskite NCs in heterojunctions showing great potential for charge extraction in further applications. [17][18][19][20] Most reported perovskite photovoltaic devices are generally fabricated in a layer-by-layer configuration in which the exciton dissociation occurs at the interface of the perovskite NC layer and the respective electron or hole-transport layer. Therefore, the device performance relies on the diffusion of excitons or free carriers in the perovskite NC layer, which is reported as a fatal issue for ligand-capped colloidal NCs. [21][22][23][24] It is worth mentioning that organic semiconductor-based photovoltaic devices also suffer from similar problems. In order to enrich the donor-acceptor interfaces as well as to shrink the exciton diffusion path length, blend structures (donor and acceptor materials are mixed in one layer) have often been employed for achieving highly efficient organic photovoltaic devices. [25][26][27][28] However, it is difficult to fabricate such blend structures based on bulk thin film perovskites which are grown using precursors dissolved in polar solvents such as dimethylformamide and dimethyl sulfoxide. [5][6][7][8][9] In contrast, perovskite NCs fortunately are commonly dispersed in organic solvents in which organic electron-acceptor materials such as the fullerene derivative phenyl-C 61 -butyric acid methyl ester (PCBM) can be dissolved as well. This enables the fabrication of perovskite NC/PCBM blend structures similar to bulk heterojunction configurations in organic photovoltaic devices. Recently, Shen et al. have shown the fabrication of Solution-processable perovskite nanocrystals (NCs) are gaining increasing interest in the field of photovoltaics because of their enhanced stability compared to their thin-film counterparts. However, the charge transfer dynamics in perovskite NC based light-harvesting systems are not well understood. By applying femtosecond differential transmission (DT) spectroscopy the photoinduced charge transfer from inorganic perovskite CsPbBr 3 NCs to the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) is investigated for two fundamentally different architectures, namely layer-by-layer heterostructures and blend structures. By varying the thickness ...

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Terahertz Spectroscopic Probe of Hot Electron and Hole Transfer from Colloidal CsPbBr₃ Perovskite Nanocrystals

Cited by 74 publications

References 48 publications

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

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

Conductivity Tuning via Doping with Electron Donating and Withdrawing Molecules in Perovskite CsPbI₃ Nanocrystal Films

Exciton Diffusion Lengths and Dissociation Rates in CsPbBr₃ Nanocrystal–Fullerene Composites: Layer‐by‐Layer versus Blend Structures

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Terahertz Spectroscopic Probe of Hot Electron and Hole Transfer from Colloidal CsPbBr3 Perovskite Nanocrystals

Cited by 74 publications

References 48 publications

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

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

Conductivity Tuning via Doping with Electron Donating and Withdrawing Molecules in Perovskite CsPbI3 Nanocrystal Films

Exciton Diffusion Lengths and Dissociation Rates in CsPbBr3 Nanocrystal–Fullerene Composites: Layer‐by‐Layer versus Blend Structures

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Terahertz Spectroscopic Probe of Hot Electron and Hole Transfer from Colloidal CsPbBr₃ Perovskite Nanocrystals

Conductivity Tuning via Doping with Electron Donating and Withdrawing Molecules in Perovskite CsPbI₃ Nanocrystal Films

Exciton Diffusion Lengths and Dissociation Rates in CsPbBr₃ Nanocrystal–Fullerene Composites: Layer‐by‐Layer versus Blend Structures