Effect of Orientation of Porphyrin Single-Crystal Slices on Optoelectronic Properties

Liu, Chong Yang; Tang, Huajun; Bard, Allen J.

doi:10.1021/jp9516093

Cited by 25 publications

(39 citation statements)

References 19 publications

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“…The orientation of these bulky groups insulates the core and prevent aggregation of the dye thereby improving the V oc . Also it is known that the surface orientation of the dye strongly impacts the optoelectronic properties by altering the effective barrier width for through space charge tunneling and the μ orientation which influences the electron injection . It is also observed in our study that, all the dyes bearing alkoxy chains at ortho ‐positions of their meso ‐phenyl rings have R2 and R4 groups oriented perpendicular to the plane of porphyrin ring.…”

Section: Resultssupporting

confidence: 64%

Molecular design of porphyrin dyes for dye sensitized solar cells: A quantitative structure property relationship study

Madugula

Soujanya

2017

Int J Quantum Chem

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Porphyrins dyes are known as promising sensitizers for dye sensitized solar cell (DSC) devices because of their intrinsic features with maximum reported light-to-electricity conversion efficiency of about 12%. Our objective in this study is to rationally design new porphyin sensitizers with enhanced photovoltaic (PV) properties, V oc (open-circuit voltage), or J sc (short-circuit current density) for DSC applications. We have used quantitative structure-property relationship technique following a heuristic approach to build a structure-property (PV) relationship on a dataset of 45 experimentally reported push-pull Zn-porphyrin based sensitizers. The model is further used to predict PV properties; V oc and J sc of 71 new structures. The model includes a unique combination of constitutional, topological, and electrostatic descriptors along with the widely used quantum chemical descriptors to establish a structure-property relationship. The results furnished guide-in principles in identifying 8 structures as potential candidates based on their frontier molecular orbital energies, absorption in visible-near IR region (extending up to 900 nm), reorganization energies, in addition to favorable PV properties. In conclusion, the study has demonstrated how a subtle variation in porphyrin structure particularly of the auxiliary groups can be used to modulate their PV properties. K E Y W O R D S descriptors, dye sensitized solar cell, Porphyrin sensitizers, quantitative structure-property relationship, Voc and Jsc Int J Quantum Chem. 2017;117:e25385.

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Section: Resultssupporting

confidence: 64%

Molecular design of porphyrin dyes for dye sensitized solar cells: A quantitative structure property relationship study

Madugula

Soujanya

2017

Int J Quantum Chem

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“…[9,16±21] In a number of previous works it has been shown that a clear relationship exists between the mobility of charge carriers and the thermotropic phase of the liquid-crystalline porphyrin layer. [15,19,22] Also, the quasi-one-dimensional character of the charge transport within these stacks has been demonstrated. [19] However, so far only a few studies concerning the relationship between the molecular arrangement within a porphyrin antenna layer and the exciton diffusion length have been reported.…”

Section: Introductionmentioning

confidence: 94%

“…[15,19,22] Also, the quasi-one-dimensional character of the charge transport within these stacks has been demonstrated. [19] However, so far only a few studies concerning the relationship between the molecular arrangement within a porphyrin antenna layer and the exciton diffusion length have been reported. [15] Recently, we have shown that the flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) provides a powerful method for measuring the dynamics of photoinduced CS in photoactive systems.…”

Section: Introductionmentioning

confidence: 99%

Singlet and Triplet Exciton Diffusion in a Self‐Organizing Porphyrin Antenna Layer

Kroeze

Koehorst

Savenije³

2004

Adv Funct Materials

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We have studied the photoinduced charge separation in a double layer consisting of a 50 nm thick, discotic antenna layer, i.e., free‐base tetra‐para‐octylphenyl porphyrin (H2TOPP), spin‐coated onto a smooth layer of anatase TiO2 using the electrodeless “flash‐photolysis time‐resolved microwave conductivity” technique (FP‐TRMC). This method enables the investigation of the relationship between the morphology of the antenna layer and the exciton diffusion dynamics. Photons absorbed by the porphyrin result in the formation of free mobile electrons in the conduction band of the TiO2. The freshly spin‐coated double layer shows an incident‐photon‐to‐charge‐separation efficiency (IPCSE) of 10 % on excitation at 430 nm. From the amplitude and the temporal shape of the photoconductivity transients we conclude that for the freshly spin‐coated double layer, electron injection occurs both from the singlet and the long‐lived triplet excited state. These triplet states can travel by (Dexter) energy transfer over distances of at least 9.6 nm. After heating the sample above the crystalline–discotic‐lamellar (C–DL) phase‐transition temperature of H2TOPP and subsequent cooling, changes in the optical absorption spectrum are observed, while the IPCSE drops to ca. 1 %. These results are explained in terms of a transition of the morphology of the antenna layer from a predominantly random distribution of the porphyrin molecules just after spin‐coating to a lamellar arrangement upon annealing, consisting of domains of ordered porphyrin stacks. Since the porphyrin macrocycles are perpendicularly oriented with respect to the plane of the lamellae, the center‐to‐center distance between neighboring lamellae disables efficient triplet energy transfer, leaving only the lamella directly adjacent to the TiO2 layer photoactive.

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“…In this case, electrons from the excited state of ZnODEP molecules are injected into the irradiated ITO contact ͑termed an anodic current͒ while positive charges move to the opposite electrode. 1,5,[7][8][9][10][11][12][13] The relation between I sc as a function of time without bias ͑the short-circuit photocurrent͒ from pixel 4D is shown in Fig. 2b.…”

mentioning

confidence: 99%

Addressing of Optoelectronic Memory of Thin Film Zinc Porphyrin with Crossed 5 μm Indium Tin Oxide Arrays

Liu

Bard²

2001

Electrochem. Solid-State Lett.

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We report here the preparation and characterization of an optoelectronic memory device based on a single layer of organic thin film ͑ϳ0.9 m thick͒ of zinc octakis͑␤-decoxyethyl͒porphyrin, sandwiched between two crossed indium tin oxide ͑ITO͒ arrays. The ITO lines in the array were 5 m wide and were separated from each other by a 5 m gap. Data ͑in the form of an electric charge͒ could be independently stored at and retrieved from an intersection of the crossed ITO lines with irradiation. Each intersection defined one memory pixel (5 ϫ 5 m) and there was no cross talk with nearby pixels under the test conditions, clearly demonstrating its potential application as an information storage device using a molecular thin film.Zinc octakis͑␤-decoxyethyl͒porphyrin ͑ZnODEP͒ is a flat molecule with eight long hydrocarbon chains. 1 In the crystal, molecules are regularly stacked to form individual columns and the nonionic alkyl tails serve as an insulating coating, leading to a bundle of electrically insulated one-dimensional molecular ''wires.'' 1 Even within the same molecular column, the intermolecule separation is ϳ4 Å, 1 significantly larger than those in inorganic substances. This produces an intrinsic characteristic of a crystal structure consisting of discrete molecules that can be considered an ''orientated molecular gas.'' 2,3 This structure has an inherent advantage over inorganic materials as a medium for high-density charge trapping and, therefore, information storage, because charge carriers are localized on individual molecules and can be trapped for long times on structural defects or impurity sites. [2][3][4] In principle, the theoretical size of one memory element could be as small as a single molecular column representing the ultimate density in data storage. 5, 6 We have demonstrated previously that an individual pixel could be as small as a few tens of nanometers with a configuration of a sharp scanning tunneling microscopy ͑STM͒ tip/organic film/indium tin oxide ͑ITO͒. 5,7 While this tip-type movable structure is simple and convenient for testing the possibility of ultrahigh density data storage, it is not useful for most memory applications where a fixed rigid device is more desirable. Nor is it useful in examining cross talk among different pixels. This led us to the present study of an alternative configuration as shown in Fig. 1, in which each 5 m wide ITO line served as an independent electrode and was individually externally addressable.When a bias voltage was applied to two of the crossed ITO fingers ͑such as column 3 and row D͒, the organic film was subjected to the electric field at only that particular intersection ͑desig-nated as pixel 3D͒. Thus, Fig. 1 illustrates a total of 25 memory elements. Figure 2a shows the current as a function of bias voltage from pixel 3D with and without irradiation. The dark current is negligible over the potential range of Ϫ1 to ϩ1 V. Essentially the same result was seen with the other pixels. Note that in this and other measurements discussed below, the whole fi...

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Effect of Orientation of Porphyrin Single-Crystal Slices on Optoelectronic Properties

Cited by 25 publications

References 19 publications

Molecular design of porphyrin dyes for dye sensitized solar cells: A quantitative structure property relationship study

Molecular design of porphyrin dyes for dye sensitized solar cells: A quantitative structure property relationship study

Singlet and Triplet Exciton Diffusion in a Self‐Organizing Porphyrin Antenna Layer

Addressing of Optoelectronic Memory of Thin Film Zinc Porphyrin with Crossed 5 μm Indium Tin Oxide Arrays

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