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

We present the first demonstration of interlayer, or vertical, directional grating coupling using a permanently incorporated corrugated layer grating. Based on an InP/InGaAsP antiresonant reflecting optical waveguide (ARROW) geometry grown by chemical beam epitaxy and metalorganic chemical vapor deposition, we have achieved a large mode contradirectional grating‐coupled waveguide photodetector with a spectral response peak 9 A wide. The ‘‘optical bus’’ capabilities of the vertically coupled ARROW structure make this device suitable for optical integration.

Wavelength selective interlayer directionally grating-coupled InP/InGaAsP waveguide photodetection

With the increasing complexity of high density WDM and TDM networks, large amount of optical amplifiers are required for each, switch fabric.

Two section semiconductor optical amplifier as optical power equalizer with high output power

Operating characteristics are described for broad contact double‐heterostructure (DH) lasers grown by molecular beam epitaxy (MBE), with In0.53Ga0.47As active layers lattice matched to InP. These were operated at T≊293 K, with (low duty cycle) pulses of current from 1.5 to 3Ith. The lowest threshold current density, Jth ≊2800 A/cm2, is some 40% higher than an ideal cavity expectation. Under these strong pulse conditions, a multimode output was observed, with pronounced spatially filamentary characteristics. The output was plane polarized perpendicular to the active layer, indicative of TM mode dominance. This nontypical polarization, considered in conjunction with an indicated trend of external differential quantum efficiency increasing with length, is consistent with polarization‐selective internal losses or polarization‐dependent gain as the mode‐controlling feature, rather than facet reflection losses.

High‐output room‐temperature pulsed operation for broad contact InP/In0.53Ga0.47As/InP lasers grown by molecular beam epitaxy

Active mode-locking of a broadly tunable monolithic semiconductor laser based on a grating assisted vertical coupler filter resulted in 10 - 12 ps pulses at a repetition rate of 15.8 GHz. Mode-locking was achieved at discrete wavelengths from 1544.5 nm to 1564.7 nm.

Broadly tunable (202 /spl Aring/) mode-locked monolithic laser with an integrated vertical coupler filter

A 1 × 2 digital optical switch in InGaAsP multiple-quantum-wells with an 8 GHz bandwidth is demonstrated, which may also be operated as a wavelength-, polarisation-, and drive-voltage insensitive modulator. The total length of the switch/modulator device is 3 mm which includes passive fan-outs for fibre interconnection. The on-chip insertion loss is 3 dB out of which the Y-branch excess loss is only 0.7 dB. The measured switch crosstalk is –18 dB for a 4 V push-pull bias. Further crosstalk reduction is expected from a more optimised design and improved fabrication processes.

Barry Miller

Papers

Wavelength selective interlayer directionally grating-coupled InP/InGaAsP waveguide photodetection

Two section semiconductor optical amplifier as optical power equalizer with high output power

High‐output room‐temperature pulsed operation for broad contact InP/In0.53Ga0.47As/InP lasers grown by molecular beam epitaxy

Broadly tunable (202 /spl Aring/) mode-locked monolithic laser with an integrated vertical coupler filter

High-speed digital Y-branch switch/modulator with integrated passive tapers for fibre pigtailing