Photon-induced molecular charge separation studied by nanosecond time-resolved microwave conductivity
01 Dec 1982-Vol. 73, Iss: 3, pp 35-53
TL;DR: In this paper, the application of the time-resolved microwave conductivity (TRMC) technique to the quantitative measurement of charge separation in flash-photolysed molecular systems is desecribed.
Abstract: The application of the time-resolved microwave conductivity (TRMC) technique to the quantitative measurement of charge separation in flash-photolysed molecular systems is desecribed. The apparatus required, background theory and problems involved in deriving absolute values related to the charge-separation process are fully discussed. The use of the technique is illustrated by experiments carried out on the flash photolysis of 4-dimethylamino-4′-nitrostilbene (DMANS) in several solvents. Values of the dipole moments of the T 1 and S 1 states have been estimated and for S 1 are in good agreement with literature values derived in other ways. Other parameters important to the understanding of the photophysics of DMANS are also derived.
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TL;DR: The Rehybridization of the Acceptor (RICT) and Planarization ofThe Molecule (PICT) III is presented, with a comparison of the effects on yield and radiationless deactivation processes.
Abstract: 6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916
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TL;DR: PBB3 showed a long-lived excitonic state and the slowest electron transfer dynamics of the series of polymers, as well as the fastest recombination rate of the charge-separated (CS) species, indicating that electrons and holes are more tightly bound in these species.
Abstract: A new low band gap copolymer PBB3 containing [6,6′]bi[thieno[3,4-b]thiophenyl]-2,2′-dicarboxylic acid bis-(2-butyloctyl) ester (BTT) and 4,8-bis(2-butyloctyl)benzo[1,2-b:4,5-b′]dithiophene (BDT) units was synthesized and tested for solar cell efficiency. PBB3 showed a broad absorbance in the near-IR region with a substantially red-shifted (by more than 100 nm) λmax at 790 nm as compared to the PTB series of polymers, which have been previously reported. The PBB3 polymer also showed both a favorable energy level match with PCBM (with a LUMO energy level of −3.29 eV) and a favorable film domain morphology as evidenced by TEM images. Despite these seemingly optimal parameters, a bulk heterojunction (BHJ) photovoltaic device fabricated from a blend of PBB3 and PC71BM showed an overall power conversion efficiency (PCE) of only 2.04% under AM 1.5G/100 mW cm–2. The transient absorption spectra of PBB3 showed the absence of cationic and pseudo charge transfer states that were observed previously in the PTB series...
390 citations
TL;DR: In this paper, the flash photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study photoinduced charge separation in bilayers consisting of a smooth, transparent, 80 nm thick layer of anatase TiO2 onto which poly(3hexylthiophene) (P3HT) sensitizer layers have been spin-coated.
Abstract: The flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study photoinduced charge separation in bilayers consisting of a smooth, transparent, 80 nm thick layer of anatase TiO2 onto which poly(3-hexylthiophene) (P3HT) sensitizer layers have been spin-coated. Interfacial charge separation, resulting from excitation of the polymer in the visible, is found to persist well into the millisecond time domain. Photoconductivity action spectra have been measured between 420 and 700 nm for P3HT layer thicknesses, L, from ∼2 to 200 nm. Using this electrodeless technique, the bilayers could be irradiated from either the polymer (“front”) or semiconductor (“back”) side. On front-side irradiation at 540 nm (close to the absorption maximum of the polymer), the efficiency of charge separation per incident photon (IPCSE) initially increased to a maximum value of 0.8% for L ≈ 10 nm. For thicker layers the IPCSE gradually decreased, eventually to 0.1% for L ≈ 170 nm. On back-side irradi...
360 citations
TL;DR: In this article, the authors investigated the reliability and the possibilities of microwave conductivity measurements, and derived the quantitative relationship between the reflected microwave signal and the change in conductivity for a wafer of singlecrystalline Si.
Abstract: The study of the excess conductivity induced in a material by pulsed optical excitation yields information on the optoelectronic properties of the material and is receiving increasing attention. As conventional conductivity techniques are hampered by the need to apply electrical contacts, we have investigated the reliability and the possibilities of microwave conductivity measurements. This paper first presents the general background for excess conductivity measurements in the microwave range, and then derives the quantitative relationship between the reflected microwave signal and the change in conductivity for a wafer of single‐crystalline Si. For this sample, the theory of excess charge carrier kinetics is also developed. After a short description of our apparatus, kinetic measurements on a nano‐ and microsecond timescale are compared to theory.
336 citations
References
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TL;DR: The thermally stable photochemically fatigue resistant title compound and its coloured form provide a photochromic system well suited for chemical actinometry in the near u.v. and visible spectral regions.
Abstract: The thermally stable photochemically fatigue resistant title compound and its coloured form provide a photochromic system well suited for chemical actinometry in the near-u.v. and visible spectral regions. A solution of the photochromic compound in many common organic solvents can be used repeatedly and, provided the stirred solution absorbs all the incident radiation, the radiant flux can be determined simply by measuring an absorbance change.
270 citations
TL;DR: In this paper, the authors applied microwave techniques to the study of the diffusion of electrons and positive ions in helium, and measured the measured value of the ambipolar diffusion coefficient, which is a measure of the flow of charged particles of both signs is equalized by the space charge field which they set up.
Abstract: Microwave techniques are applied to the study of the diffusion of electrons and positive ions in helium. For the electron and ion densities realized experimentally, the diffusion takes place ambipolarly; that is, the flow of charged particles of both signs is equalized by the space charge field which they set up. At 1 mm Hg pressure and 0.039-ev average energy, the measured value of the ambipolar diffusion coefficient, ${D}_{a}$, is 540 ${\mathrm{cm}}^{2}$/sec. The measured variation of ${D}_{a}$ with gas density, energy of the particles, and diffusion container size and shape agrees closely with theory.
156 citations
TL;DR: In this article, a method of measuring conductivity changes in pulse irradiated liquids, on a ns timescale, by microwave absorption is described, and quantitative relationships between the measured absorption signal and the change in conductivity are derived for several cell designs.
Abstract: The method of measuring conductivity changes in pulse irradiated liquids, on a ns timescale, by microwave absorption is described. Quantitative relationships between the measured absorption signal and the change in conductivity are derived for several cell designs. The method is compared with optical absorption and DC conductivity techniques for the detection of ion formation. The value of the product of the free ion yield and the electron mobility in 2.2.4 trimethylpentane (iso-octane) is found to be 1.62 × 10 -4 m 2 V -1 s -1 (100 eV) -1 . Electron-positive ion recombination in iso-octane is found to obey the Debye relation.
136 citations
116 citations