Metal cluster enhanced organic solar cells

Surface plasmons are collective oscillations of free electrons localized at surfaces of structures made of metals. Since the surface plasmons induce fluctuations of electric charge at surfaces, they are accompanied by electromagnetic oscillations. Electromagnetic fields associated with surface plasmons are localized at surfaces of metallic structures and significantly enhanced compared with the excitation field. These two characteristics are ingredients for making good use of surface plasmons in plasmonics. Plasmonics is a rapidly growing and well-established research field, which covers various aspects of surface plasmons towards realization of a variety of surface-plasmon-based devices. In this paper, after summarizing the fundamental aspects of surface plasmons propagating on planar metallic surfaces and localized at metallic nanoparticles, recent progress in plasmonic waveguides, plasmonic light-emitting devices and plasmonic solar cells is reviewed.

https://iopscience.iop.org/article/10.1088/0022-3727/45/43/433001/pdf

Plasmonics: visit the past to know the future

Transparent electrodes composed of ultrathin, unpatterned metal films are investigated in planar heterojunction (PHJ) and bulk heterojunction organic photovoltaic (OPV) cells. Optimal electrode composition and thickness are deduced from electrical and optical models and experiments, enabling a PHJ-OPV cell to be realized using a silver anode, achieving power conversion efficiency parity with an analogous cell that uses an indium tin oxide anode. Beneficial aspects of smooth, unpatterned metal films as transparent electrodes in OPV cells are also discussed in the text.

Transparent and conductive electrodes based on unpatterned, thin metal films

Flexible organic electronics operated at extreme mechanical conditions are crucial for the next generation of smart foldable electronic applications. Kim et al. show non-volatile organic memory devices that are subject to sharp bending deformation without protection from a stress-release layer.

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Non-volatile organic memory with sub-millimetre bending radius

Key approaches to the synthesis of merocyanine dyes are summarised. The dependence of the dye properties on their chemical structure, the solvent nature and the aggregation type is analysed. The main methods of studying the electronic structure of merocyanines are considered. Attention is focused on polyene–polymethine electron transitions. The applications of merocyanines in modern research, including the design of new materials and technologies (non-linear optics, photovoltaics, holography, etc.) are presented.

https://iopscience.iop.org/article/10.1070/RC2009v078n02ABEH003900/pdf

Merocyanine dyes: synthesis, structure, properties and applications

Enhanced photocurrent due to the excitation of surface plasmons (SPs) in organic photoelectric cells of MgF2/Al/copper phthalocyanine (CuPc)/Ag structure has been investigated. SPs were excited both at Ag/air and at Al/MgF2 interfaces, using the attenuated total reflection (ATR) method. The enhancement of the photocurrent due to SP excitation depended considerably upon the wavelengths of incident light. The origin of the enhancement is discussed, comparing the experimental results with the calculations of the light absorption in the cells. The results suggested that excitation of SPs induced an increase in the light absorption at the CuPc layer, which led to the enhanced photocurrent. It was found that the light absorption by SP excitation was substantially effected by the anomalous dispersion of the CuPc dye.

Surface Plasmon-Enhanced Photocurrent in Organic Photoelectric Cells.

The tilt angles of liquid crystal molecules, 5CB, have been investigated in liquid crystal cells with rubbing-free aligning layers of polyimide (PI) Langmuir-Blodgett (LB) films on aluminum electrodes using the attenuated total reflection (ATR) measurement method. The surface plasmon polariton (SPP) and/or the guided wave excitation modes (GWEM) were observed in the ATR curves of the liquid crystal cells when various DC voltages were applied to the cell. The ATR properties were evaluated from the SPP and the GWEM. The tilt angles of the liquid crystal molecules were calculated by fitting the theoretical ATR curves to the experimental ones using various models of the liquid crystal layer structure. Furthermore, the electric field intensities in the cell were calculated at several incident angles in the ATR curves. The ATR measurement is very useful for evaluating the alignment properties of liquid crystal molecules in liquid crystal cells.

http://iopscience.iop.org/article/10.1143/JJAP.37.2581/pdf

Evaluation of Tilt Angles of Nematic Liquid Crystal Molecules on Polyimide Langmuir-Blodgett Films using the Attenuated Total Reflection Measurement Method

Enhancement of optical absorption and photocurrents in solar cells of merocyanine Langmuir–Blodgett films utilizing surface plasmon excitations

Attenuated total reflection properties and structures in squarylium LB films

We present an interpretation that differs from an accepted explanation for resonance excitation of surface plasmons (SPs) on a metal using an attenuated total reflection (ATR) method. The metal ATR phenomenon is well expressed in terms of wave optics and accompanies an enhanced evanescent field. The ATR curves and the electric field and absorption distributions in the film layer for the noble metals are simulated numerically using electromagnetic wave analysis. The calculation results provide interpretation that the ATR dips are caused by an absorption loss of the metals produced by enhanced electric fields rather than the energy loss of a transfer excitation to the SPs: the damping loss converted into the SPs or the damping absorption of the once-converted propagation SPs. The sharp ATR dips do not necessarily demonstrate the high-resonance excitations of the SPs, and the metal ATR phenomenon is not restricted to the SPR.

Takashi Wakamatsu

Papers

Surface Plasmon-Enhanced Photocurrent in Organic Photoelectric Cells.

Evaluation of Tilt Angles of Nematic Liquid Crystal Molecules on Polyimide Langmuir-Blodgett Films using the Attenuated Total Reflection Measurement Method

Enhancement of optical absorption and photocurrents in solar cells of merocyanine Langmuir–Blodgett films utilizing surface plasmon excitations

Attenuated total reflection properties and structures in squarylium LB films

Interpretation of attenuated-total-reflection dips observed in surface plasmon resonance