Direct and inverse photoemission were used to study the impact of alkali fluoride postdeposition treatments on the chemical and electronic surface structure of Cu(In,Ga)Se2 (CIGSe) thin films used for high-efficiency flexible solar cells. We find a large surface band gap (E(g)(Surf), up to 2.52 eV) for a NaF/KF-postdeposition treated (PDT) absorber significantly increases compared to the CIGSe bulk band gap and to the Eg(Surf) of 1.61 eV found for an absorber treated with NaF only. Both the valence band maximum (VBM) and the conduction band minimum shift away from the Fermi level. Depth-dependent photoemission measurements reveal that the VBM decreases with increasing surface sensitivity for both samples; this effect is more pronounced for the NaF/KF-PDT CIGSe sample. The observed electronic structure changes can be linked to the recent breakthroughs in CIGSe device efficiencies.

There is an enormous potential in applying conjugated polymers in novel organic opto-electronic devices such as light emitting diodes and solar cells. Although prototypes and first products exist, a comprehensive understanding of the fundamental processes and energetics involved during photoexcitation is still lacking and limits further device optimisations. Here we report on a unique analysis of the excited states involved in charge generation by photoexcitation. On the model system poly(3-hexylthiophene) (P3HT), we demonstrate the general applicability of our novel approach. From photoemission spectroscopy of occupied and unoccupied states we determine the transport gap to 2.6 eV, which we show to be in agreement with the onset of photoconductivity by spectrally resolved photocurrent measurements. For photogenerated singlet exciton at the absorption edge, 0.7 eV of excess energy are required to overcome the binding energy; the intermediate charge transfer state is situated only 0.3 eV above the singlet exciton. Our results give direct evidence of energy levels involved in the photogeneration and charge transport within conjugated polymers.

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We used partially fluorinated alkyl and aromatic\ud phosphonates as model systems with similar molecular dipole\ud moments to form self-assembled monolayers (SAMs) on the\ud Zn-terminated ZnO(0001) surface. The introduced surface\ud dipole moment allows tailoring the ZnO work function to tune\ud the energy levels at the inorganic−organic interface to organic\ud semiconductors, which should improve the efficiency of charge\ud injection/extraction or exciton dissociation in hybrid electronic\ud devices. By employing a wide range of surface characterization\ud techniques supported by theoretical calculations, we present a\ud detailed picture of the phosphonates’ binding to ZnO, the\ud molecular orientation in the SAM, their packing density, as\ud well as the concomitant work function changes. We show that\ud for the aromatic SAM the interaction between neighboring molecules is strong enough to drive the formation of a more densely packed monolayer with a higher fraction of bidentate binding to ZnO, whereas for the alkyl SAM a lower packing density was found with a higher fraction of tridentate binding

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In much of the world, growth is more stable than it once was. Looking at a sample of twentyfive countries, we find that in sixteen, real GDP growth is less volatile today than it was twenty years ago.And these declines are large, averaging more than fifty per cent. What accounts for the fact that real growth has been more stable in recent years? We survey the evidence and competing explanations and find support for the view that improved inventory management policies, coupled with financial innovation, adopting an inflation targeting scheme and increased central bank independence have all been associated with more stable real growth. Furthermore, we find weak evidence suggesting that increased commercial openness has coincided with increased output volatility.

The electronic structure of the CdS/Cu2ZnSnS4 (CZTS) heterojunction was investigated by direct and inverse photoemission. The effects of a KCN etch of the CZTS absorber prior to CdS deposition on the band alignment at the respective interface were studied. We find a “cliff”-like conduction band offset at the CdS/CZTS interface independent of absorber pretreatment and a significant etch-induced enhancement of the energetic barrier for charge carrier recombination across the CdS/CZTS interface.

Over the past 20 years, macroeconomic performance has improved in industrialised and developing countries alike. In a broad cross-section of countries inflation volatility has fallen markedly while output variability has either fallen or risen only slightly. This increased stability can be attributed to some combination of more efficient monetary policy making, a reduction in the variability of supply shocks, and changes in the structure of the economy. We develop a method for allocating performance changes among these factors. For 21 of the 24 countries we study, more efficient monetary policy has been the driving force behind improved performance. Copyright 2006 Royal Economic Society.