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In this letter, we employ a three-dimensional master equation calculation to investigate the mobility dependence of bulk heterojunction (BHJ) solar cell performance. By taking energetic disorder and morphology into consideration, we show mobility-enhanced device efficiency with a remarkable charge transport loss induced by molecular disorder and an open circuit voltage loss in high mobility region due to morphological defect-assisted bimolecular recombination. The result suggests that the description of interfacial processes is crucial in the modeling of BHJ photovoltaic devices. [ABSTRACT FROM AUTHOR]

The authors investigated the energy transfer between the chromophors of a white emitting polyspirobifluorene copolymer containing a blue emitting backbone, a green, and a red emitting dye. They demonstrate that the green dye is mainly excited by blue→green Förster resonant energy transfer (FRET), with a Förster radius R0bg=35 Å. The red dye is instead excited by direct blue→red FRET (R0br=21 Å) and by sequential blue→green→red FRET (R0gr=31 Å). Finally, the authors show that the FRET processes, fundamental to have white emission, are of intermolecular nature, while intramolecular energy migration and transfer are negligible. [ABSTRACT FROM AUTHOR]

The effect of 200 MeV Ag ion irradiation on the temperature and field dependence of critical current density (J[sub C]) of high quality MgB[sub 2] thin films is studied. Substantial increase in J[sub C] is observed over a certain field range for the film irradiated at a dose of 10[sup 12] ions/cm[sup 2]. Our analysis suggests that columnar defects are not formed under irradiation conditions used in these studies, which correspond to an electronic energy loss of about 16 keV/nm. Defects clusters are likely to be responsible for the observed improvement in J[sub C].© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Analyzes the oxygen displacement in a silver ion irradiated single crystal. Significance of columnar defects on high temperature superconductors (HTSC); Techniques for nonresonant electromagnetic absorption; Mechanisms of field dependent losses in HTSC single crystals.

Examines the thermal stability and annealing of columnar defects in Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8]/Ag superconductor. Establishment of the stability of columnar defects at elevated temperatures; Details of the stages of isochronal anneals; Confirmation of recrystallization and loss of columnar defects.

Examines the transport critical current densities of oxide-powder-in-tube mono- and multifilamentary Bi-2223/Ag tapes using fission tracks from irradiation. Decrease in low field current critical values during irradiation at 0.8GeV; Effectivity of high-energy proton irradiation; Investigation of higher irradiation fluences.

Examines the enhancement of persistent currents in Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] tapes with splayed columnar defects. Irradiation of composite tapes with light energetic ions; Diameter of the splayed tracks; Indication of the magnetic hysteresis.

Examines the measurement of the anisotropic properties of Bi2223/Ag tapes with and without the silver sheath. Relationship between the resistivity anisotropy ratio and rolling plane; Use of the standard four-probe method in measuring anisotropic transport properties; Description of critical current scaling as a function of the angle theta.

Examines the enhancement of critical current density by confinement of vortices in Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub x] single crystals and thin films. Difference between the types of pinning centers; Calculation of the critical current density; Influence of the magnetic field on the current density.

Examines the transport properties of textured TlBa[sub 2]Ca[sub 2]Cu[sub 3]O[sub z] thick films before and after heavy ion irradiation. Decrease in zero field critical current; Irreversibility of line shift after the treatment; Basis for scaling the data.

Describes the increase in the pinning energy and critical current density in single superconductor crystal. Generation of defect structure other than point defects acting as pinning center; Effect of higher pinning energy on critical current density.

Presents an order-of-magnitude method for estimating the fluence that optimizes the critical current in particle-irradiated cuprate semiconductors. Relationship of the fluence to the nonionizing energy loss of a given particle; Importance of knowing incident particle type and energy; Usefulness of the ability to estimate the particle fluence.

Examines the efficacy of heavy ion damage J[sub C] of superconductors Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8]. Investigation of critical current density J[sub c] and irreversibility line using superconducting quantum interference device; Influence of linear defects on the production of the pinning of vortices; Effect of heavy ion irradiation on critical current density.

Flux pinning and anomalous magnetization peak of heavily overdoped Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2-y]Cr[sub y]O[sub 8+δ] [Cr-doping (Bi, Pb)-2212] single crystals are investigated by means of magnetization measurements with the magnetic field parallel to the c axis. Compared with undoped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] (Bi-2212) and Pb-doping Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] [(Bi, Pb)-2212] single crystals, the irreversibility line of Cr-doping (Bi, Pb)-2212 single crystals is pronouncedly shifted to high temperatures. The anomalous magnetization peak H[sub 2p] with maximum peak field near 8000 G is observed. The H[sub 2p] exhibits strong temperature dependence from 0.19 to 0.93T[sub c]. The temperature dependence of H[sub 2p] can be explained according to vortex decoupling theory. The improved flux pinning may originate from reduced anisotropy due to Pb doping and a sufficient number of effective pinning centers due to the random Cr substitution on the Cu site. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Gd and oxygen doping effects on the Josephson coupling in Bi[sub 2]Sr[sub 2]Ca[sub 1-x]Gd[sub x]Cu[sub 2]O[sub 8+δ] single crystals have been studied systematically. It was found that a pseudo-transition at temperature T[sub cJ], attributed to the Josephson coupling between CuO[sub 2] layers, shifts dramatically to lower temperature with increasing magnetic field, and the temperature dependence of the pseudo-upper-critical-field H[sub cJ] associated with the coupling shows a clear upward curvature. For the Gd-doped as compared with the oxygen-doped crystal, the value of T[sub cJ] is smaller at the same carrier density, which implies that the substitution of Gd for Ca reduces the Josephson coupling more severely. The characteristics of the pseudo-transition associated with the Josephson coupling between CuO[sub 2] layers are different from those of the superconducting transition occurring in the CuO[sub 2] layers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the isothermal, magnetic field (H|c) dependent rf power P(H) dissipation (H[sub rf]|a) in the superconducting state of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] single crystals prior to and after irradiation with 250 MeV [sup 107]Ag[sup 17+] ions. In the pristine state, P(H) shows an initial decrease with increase in field, reaches a minimum at H[sub M](T) and increases monotonically for H>H[sub M](T). This behavior arises when the electromagnetic coupling between the pancake vortices in adjacent CuO layers becomes dominant on increasing the field and minimizes the distortions of the flux lines by confining the 2D vortices. In the post irradiated state, such an initial decrease and the minimum in P(H) is not observed but only a much reduced rf dissipation that monotonically increases with field from H=0 onwards is seen. We attribute this difference to the strong enhancement of the tilt modulus C[sub 44] of the flux lines on irradiation when the pancake vortices in adjacent CuO bilayers are pinned along the track forming a well-stacked flux line in the field direction (|c). We have also observed that the rf dissipation disappears at a certain temperature T[sub sf], at which the normal core of the flux line becomes commensurate with the columnar track diameter. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]