The field of chemical sensing is becoming ever more dependent upon novel materials. Polymers, crystals, glasses, particles, and nanostructures have made a profound impact and have endowed modern sensory systems with superior performance. Electronic polymers have emerged as one of the most important classes of transduction materials; they readily transform a chemical signal into an easily measured electrical or optical event. Although our group reviewed this field in 2000,1 the high levels of activity and the impact of these methods now justify a subsequent review as part of this special issue. In this review we restrict our discussions to purely fluorescence-based methods using conjugated polymers (CPs). We further confine our detailed coverage to articles published since our previous review and will only detail earlier research in this Introduction to illustrate fundamental concepts and terminology that underpin the recent literature.

Chemical sensors based on amplifying fluorescent conjugated polymers.

A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

The structural and luminescence properties of porous silicon

Stability/degradation of polymer solar cells

The interaction of water with solid surfaces: Fundamental aspects

This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

The electroluminescence of organic materials

Direct measurements of electronic properties have been made for the metal/organic and organic/organic interfaces in a multilayer organic light-emitting diode (LED) using ultraviolet photoemission spectroscopy. The device configuration considered is indium–tin oxide (ITO)/copper phthalocyanine (CuPc)/N,N′-bis-(1-naphyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamne (NPB)/8-hydroxyquinoline aluminum (Alq)/Mg. For the material interfaces considered here, our result indicates that the traditional concept of vacuum-level alignment, though not valid for metal/organic interfaces, still holds at organic/organic interfaces. This implies that little charge transfer occurs at the interfaces due to the small interaction between organic molecules. The largest band offsets are observed between the lowest unoccupied state levels of the organic molecules. Based on the directly measured energy-level alignments, a model is proposed to explain the improved efficiency of multilayer organic LEDs, as compared to those with a single ...

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Interfacial electronic structures in an organic light-emitting diode

Small-molecule organic solar cells with improved stability

The energy level alignment for both Mg/8-hydroxyquinoline aluminum (Alq) and Au/Alq interfaces has been determined by the ultraviolet photoemission measurements. For both interfaces, the difference between the Fermi level and the low-energy edge of the highest occupied molecular orbital (HOMO) is around 1.7 eV. This implies that the Fermi level with respect to the HOMO edge of Alq is independent of the work function of Mg and Au despite a large difference in the metal work function. A Fermi level alignment model is proposed, invoking a charge transfer between the metal and Alq and the formation of a dipolar layer at the metal/Alq interface.

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Energy level alignment at Alq/metal interfaces

Solar cells and optical detection devices often incorporate antireflective surfaces to reduce undesired reflection and enhance optical absorption. This letter reports a “black silicon” structure of antireflective porous silicon fabricated by using electrochemical etching. The sample has a gradient-index multilayer structure, i.e., the refraction indices of the structure increase from the top (near the air) to the bottom (near the Si substrate). Reflectance below 5% is obtained over a broad wave number range (3000–28000cm−1) and the depression mechanism of the optical reflectance is analyzed by simulating the structure with the transfer matrix method. The simulated result fits the measured spectra well.

Wide-band “black silicon” based on porous silicon

The correlation between the Raman peak shift and the linewidth of porous silicon is studied. The experimental result does not fit with the relationship predicted by the phonon confinement model. By taking into account both the phonon confinement and the effect of strain, the calculated Raman line shape coincides fairly well with the measured spectrum. The built‐in strain of porous silicon varies with the porosity of the sample and is on the order of 10−3.

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Xiaoyuan Hou

Papers

Interfacial electronic structures in an organic light-emitting diode

Small-molecule organic solar cells with improved stability

Energy level alignment at Alq/metal interfaces

Wide-band “black silicon” based on porous silicon

Study of the Raman peak shift and the linewidth of light‐emitting porous silicon