Functional Scanning Probe Imaging of Nanostructured Solar Energy Materials

Giridharagopal, Rajiv; Cox, Phillip A.; Ginger, David S.

doi:10.1021/acs.accounts.6b00255

Cited by 43 publications

(43 citation statements)

References 67 publications

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“…The surface morphology information (as shown in Figure 2 ), such as surface phase separation, surface roughness, surface potential, surface composition, and so on, is usually obtained via optical microscopy, AFM or functional modified AFM, and X‐ray photoelectron spectroscopy (XPS), or near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy.…”

Section: Morphology Characterizationsmentioning

confidence: 99%

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Morphology Control in Organic Solar Cells

Zhao

Wang

Zhan

2018

Advanced Energy Materials

470

394

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the working mechanism includes four key steps (as shown in Figure 1): (1) light absorption and Frenkel exciton generation; (2) exciton diffusion to the D/A interface; (3) exciton dissociation into free charge carrier; (4) charge transport and collection. Each step is very important and could become a bottleneck leading to an inferior performance of OSCs. The second and forth steps are dominated by the morphology of the active layer. Since the Frenkel excitons are tightly bounded by Coulombic force, the lifetime of exciton is limited and its diffusion length is only 5-14 nm. [8][9][10] As a result, the domain size should be confined in 5-30 nm to ensure excitons reach D/A interfacial zone and then dissociate into free charge carriers efficiently. On the other hand, high domain purity and fine bicontinuous interpenetrating network nanostructure are also necessary to enable the charge carriers transfer to the electrodes quickly and reduce the bimolecular recombination.The PCE is the overall parameter to evaluate the performance of OSCs, which is the product of open-circuit voltage (V OC ), short-circuit current density (J SC ), and fill factor (FF). Since V OC is proportional to the difference of the highest occupied molecular orbital energy level of the donor and the lowest unoccupied molecular orbital energy level of the acceptor, [11][12][13] the V OC is mainly determined by the donor and acceptor materials. However, V OC is also related to the morphology of the active layer, such as D/A interface area, microstructure, crystallinity and so on. [14] The J SC is dominated by the whole photoelectric conversion process, namely exciton generation, diffusion and dissociation, and charge transport and collection. Among them, efficient exciton diffusion and dissociation, and charge transport strongly depend on the fine morphology of the active layer. [15] FF represents the diode characteristic of the device and is bound up with the charge transport and recombination in the active layer. The fast charge transport and low charge recombination also mainly depend on the morphology, such as crystallinity, molecular orientation, domain purity, vertical phase separation, etc. [15] Therefore, the ideal morphology of the active layer is the crucial factor to achieve high-performance OSCs.The nanomorphology of the active layer is affected by various factors, such as the D/A properties (solubility, crystallinity, miscibility, etc.), film processing, device configuration, and so on. There are only several successful as-cast films affording satisfactory morphology and performance [16][17][18] since it is very hard to obtain ideal morphology and good performance just depending energy and present some advantages, such as low cost, light weight, flexibility, semitransparency, and roll-to-roll large-area fabrication. Due to the short diffusion length of exciton (≈10 nm) in organic semiconductor materials, the ideal nanoscale phase separation in the active layer is one of the crucial factors for achieving efficient exciton dissociation an...

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Section: Morphology Characterizationsmentioning

confidence: 99%

“…Alexeev et al first used C‐AFM to characterize a blend of two semiconducting polymers . C‐AFM was used in OSCs to investigate the dark charge transport in the blend and to distinguish different component domains based on transport properties . pcAFM is one variation of C‐AFM.…”

Section: Morphology Characterizationsmentioning

confidence: 99%

Morphology Control in Organic Solar Cells

Zhao

Wang

Zhan

2018

Advanced Energy Materials

470

394

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“…Based on recent reports, the photocurrent direction and intensity in perovskite can be switched by applying an external field, which shows giant potentials in optical communication and innovative solar cell designs. [44][45][46] To study the transport properties of photocurrent, we calculate the current density along the x-axis direction, written as:…”

Section: Optical Propertiesmentioning

confidence: 99%

A time‐dependent density functional study on optical response in all‐inorganic lead‐halide perovskite nanostructures

Zhang

Lin

et al. 2020

Int J of Quantum Chemistry

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Recently, all-inorganic perovskite nanostructures have become a hot research topic due to their unique optical response and novel properties. Here, we theoretically study the optical response in Cs 2 PbX 4 and CsPb 2 X 5 (X = Cl, Br, and I) nanostructures.First, to study the ground state, we calculate the band structures of the periodic system using the HSE06 method, which shows that all those periodic perovskites possess the direct band gaps, with distribution from 2.225 to 3.536 eV. Their valence band maximum are mainly contributed from both halogen and lead atoms, while the conduction band minimum are mainly contributed from lead atoms. Then, we study the excited state using the time-dependent density functional theory method and find that, with the increase of halogen atom radius, the photogenerated carrier concentrations in perovskite nanostructures become larger, while the surface plasmon resonance becomes localized rather than long-range. Moreover, through the analysis of photocurrent and local field enhancement, Cs 2 PbX 4 and CsPb 2 X 5 nanostructures exhibit nearly 40 μA photocurrent along the direction of optical polarization. Besides, by regulating the different anions, we predict that field enhancement in Cs 2 PbI 4 and CsPb 2 I 5 share a much stronger distribution at both the center and border parts of Pb-I planes due to localized plasmon resonance, while other perovskites are distributed at the edge parts of Pb-I planes, caused by long-range plasmon resonance. Our research shows that all-inorganic perovskite nanostructures are great candidate materials for developing optoelectronic devices working in high-frequency and high-energy regions and improving their application in sensitive detection and sensors.

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“…[1,2] Among the various types of approaches developed in recent years, dye-sensitized solar cells (DSSCs) are among those receiving the largest amount of attention because of their simple preparation, low cost, clean, and relative high-energy-conversion efficiency. [1,2] Among the various types of approaches developed in recent years, dye-sensitized solar cells (DSSCs) are among those receiving the largest amount of attention because of their simple preparation, low cost, clean, and relative high-energy-conversion efficiency.…”

Section: Introductionmentioning

confidence: 99%

van der Waals Epitaxial Growth of 2D Metal–Porphyrin Framework Derived Thin Films for Dye‐Sensitized Solar Cells

Wang

Chen

Haldar

et al. 2018

Adv Materials Inter

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nature, which cannot meet the increasing demand for its broad applications in DSSCs. Thus, there is a huge interest in Pt-free materials for CE fabrication, such as inorganic semiconductors, [5] carbon materials, [6] conductive organic polymers, [7] and so on. [8,9] Metal-organic frameworks (MOFs) represent a class of porous coordination polymers that consist of organic ligands linker by metal ions to form crystalline assemblies, [10,11] which have been widely investigated for their attractive physical and chemical properties. [12,13] Recently, the tunable functionality of MOFs has allowed these porous materials as precursors or sacrificial templates for the preparation of electrode materials in DSSCs. [14,15] In particular, porphyrin-based MOFs (also called metal-porphyrin frameworks) [16] have been demonstrated to exhibit tunable optical, electrical, and photophysical properties, [17][18][19] which in particular suggest applications in DSSCs. However, up to now, employing metal-porphyrin frameworks for CE materials in DSSCs has not been reported.When aiming to use the potential of MOFs for electrical, electrochemical, and electronic applications, MOF thin films [20][21][22] prepared by a layer-by-layer (lbl) liquid-phase epitaxial (LPE) procedure have attracted huge interest. These surfacemounted MOFs or SURMOFs are assembled by a sequence of simple immersion processes, subsequently into solution of the metal source and the organic ligand. They exhibit a number of interesting properties, including controllable thickness, crystallinity, high degree of orientation, and homogeneous surface. So far, the lbl-approach has been successfully used to realize several types of SURMOFs, [23] e.g., HKUST-1 (Cu 3 (BTC) 2 , BTC = benzene-1,3,5-tri-carboxylate), SURMOF-2, Zn(2-methylimidazolate) 2 (ZIF-8), etc. [23][24][25] These SUR-MOFs are epitaxially grown on appropriately functionalized substrates by coordination bonding between metal ions and organic ligands. The growth of SURMOFs based on lbl protocols involving noncovalent interactions (such as van der Waals, hydrogen bonding, and other weak interactions, etc.) has not yet been studied. When using porphyrinic ligands, such SUR-MOFs are expected to have interesting applications in catalysis, electronic devices, and in photovoltaics. [26][27][28][29][30][31][32][33][34] Herein, we report a layer-by-layer epitaxial growth strategy for preparing SURMOFs with a layered structure. 2D sheets consisting of paddle-wheel (PW) units linked by porphyrin linkers are stacked by the interaction between layers being of van der Waals type. X-ray diffraction (XRD) data reveal that layer-by-layer deposition on appropriately functionalized substrates yields In this work, monolithic, crystalline, porous, and oriented porphyrin thin films are grown using a novel van der Waals layer-by-layer (lbl) epitaxial growth protocol, yielding an unusual AB-stacking motif of these interesting macrocycles units. Subsequently, these surface-mounted metal-organic frameworks (SURMOFs) are transformed by th...

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Functional Scanning Probe Imaging of Nanostructured Solar Energy Materials

Cited by 43 publications

References 67 publications

Morphology Control in Organic Solar Cells

Morphology Control in Organic Solar Cells

A time‐dependent density functional study on optical response in all‐inorganic lead‐halide perovskite nanostructures

van der Waals Epitaxial Growth of 2D Metal–Porphyrin Framework Derived Thin Films for Dye‐Sensitized Solar Cells

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