The carrier collection efficiency (ηc) and energy conversion efficiency (ηe) of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C60 or its functionalized derivatives. Composite films of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and fullerenes exhibit ηc of about 29 percent of electrons per photon and ηe of about 2.9 percent, efficiencies that are better by more than two orders of magnitude than those that have been achieved with devices made with pure MEH-PPV. The efficient charge separation results from photoinduced electron transfer from the MEH-PPV (as donor) to C60 (as acceptor); the high collection efficiency results from a bicontinuous network of internal donor-acceptor heterojunctions.

/pdf/polymer-photovoltaic-cells-enhanced-efficiencies-via-a-2lwj3yarfe.pdf

Polymer photovoltaic cells : enhanced efficiencies via a network of internal donor-acceptor heterojunctions

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

Evidence for photoinduced electron transfer from the excited state of a conducting polymer onto buckminsterfullerene, C(60), is reported. After photo-excitation of the conjugated polymer with light of energy greater than the pi-pi* gap, an electron transfer to the C(60) molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components, consistent with photo-excited charge transfer. A photoinduced electron spin resonance signal exhibits signatures of both the conducting polymer cation and the C(60) anion. Because the photoluminescence in the conducting polymer is quenched by interaction with C(60), the data imply that charge transfer from the excited state occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures.

https://science.sciencemag.org/content/sci/258/5087/1474.full.pdf

Photoinduced electron transfer from a conducting polymer to buckminsterfullerene.

The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

An overview of semiconductor photocatalysis

Preface Acknowledgements Notation Part I. Overview and Background Topics: 1. Introduction 2. Overview 3. Theoretical background 4. Periodic solids and electron bands 5. Uniform electron gas and simple metals Part II. Density Functional Theory: 6. Density functional theory: foundations 7. The Kohn-Sham ansatz 8. Functionals for exchange and correlation 9. Solving the Kohn-Sham equations Part III. Important Preliminaries on Atoms: 10. Electronic structure of atoms 11. Pseudopotentials Part IV. Determination of Electronic Structure, The Three Basic Methods: 12. Plane waves and grids: basics 13. Plane waves and grids: full calculations 14. Localized orbitals: tight binding 15. Localized orbitals: full calculations 16. Augmented functions: APW, KKR, MTO 17. Augmented functions: linear methods Part V. Predicting Properties of Matter from Electronic Structure - Recent Developments: 18. Quantum molecular dynamics (QMD) 19. Response functions: photons, magnons ... 20. Excitation spectra and optical properties 21. Wannier functions 22. Polarization, localization and Berry's phases 23. Locality and linear scaling O (N) methods 24. Where to find more Appendixes References Index.

Electronic Structure: Basic Theory and Practical Methods

Application of Isosurface Concentration Voltammetry at a Rotating Disk Electrode to Simple Electron Transfer Kinetics

Ba1−xKxBiO3 is to date the highest Tc member of a class of superconductors which, it could be argued, belong in the same class of materials as the copper oxides. While there are striking differences between the bismuthates and the cuprates, there are some similarities. In this paper, we will report the results of our tunneling measurements on BKBO. The determination f the energy gap in this material suggests that it is a relativity weakly coupled BCS superconductor - a similar conclusion is reached in the sister compound BaPb1−xBixO3. These results are substantailly different from similar measurements in the cuprates. In addition, we have studied the background tunneling conductance in four of the compounds in this class (BaPbO3, BaPb1−xSbxO3, BaPb1−xBixO3 and Ba1−xKxBiO3) and find a remarkable correlation between the strength of the linear conductance and the superconducting transition temperature. Finally, the Josephson tunneling in these compounds will be discussed.

Tunneling spectroscopy in Ba1−xKxBiO3

We demonstrate a novel modulation scheme in which both data-encoding and pulse generation are achieved using a single, wavelength tunable, integrated semiconductor laser/modulator. Data-encoded, near-transform limited 66 ps pulses are obtained at 2.5 Gbit/s and BER performance is reported. >

A 2.5-Gbit/s return-to-zero integrated DBR laser/modulator transmitter

High‐power semi‐insulating blocked planar buried‐heterostructure (SIPBH) lasers were grown entirely by atmospheric organometallic vapor phase epitaxy (OMVPE) by using a novel dilution scheme for the trimethylgallium and AsH3. Current thresholds as low as 20 mA and differential quantum efficiencies ≥20% per facet at 1.3 and 1.5 μm were obtained with power outputs of about 25 mW/facet. These results are similar to SIPBH lasers where liquid phase epitaxy was used to grow the active layer, but because of the better planarity and uniformity of OMVPE‐grown material, it appears possible to grow material that can give a high yield of distributed feedback lasers.

InGaAsP/InP high-power semi-insulating blocked planar buried-heterostructure lasers grown entirely by atmospheric organometallic vapor phase epitaxy

We propose and demonstrate a novel high-speed and wavelength insensitive Y-branch modulator in InGaAsP multiple-quantum-wells that exhibits negligible chirp and is also suitable for achieving controllable chirp. We raise the refractive index on one arm via applied bias and use the unbiased arm as a modulator. As the light switches to the biased arm, the modulated light in the unbiased arm experiences little phase change and therefore exhibits negligible chirp. Tunable chirp may be achieved using a push-pull bias configuration. We demonstrate that our modulator chirp is /spl sim/10 times lower than that of typical electroabsorption modulators.

Barry Miller

Papers

Application of Isosurface Concentration Voltammetry at a Rotating Disk Electrode to Simple Electron Transfer Kinetics

Tunneling spectroscopy in Ba1−xKxBiO3

A 2.5-Gbit/s return-to-zero integrated DBR laser/modulator transmitter

InGaAsP/InP high-power semi-insulating blocked planar buried-heterostructure lasers grown entirely by atmospheric organometallic vapor phase epitaxy

A novel high-speed and wavelength insensitive Y-branch modulator with reduced and controllable chirp