Light Harvesting Nanomaterials

A complete treatment of the design, simulation, fabrication and characterization of metal nanoparticles and metal nanoparticle embedded structures is presented in this chapter. This treatment reveals that the metal nanoparticles play an important role in improving light absorption in the solar photovoltaic cell. This improves the understanding towards a promising approach to get better light trapping in solar photovoltaic cells and to enhance the power output from such a device. The examples presented here broaden the understanding of light trapping schemes and their effects.

In this chapter, recent progress in the applications of tetrapyrrolic free-base as well as its metal complexes in dye-sensitized solar cells (DSSC) is summarized and analyzed. Though ruthenium(II) complexes are dominant in DSSC, but they have certain drawbacks to necessitate the design of alternative sensitizers. Based on absorption, thermal and redox properties, tetrapyrrolic compounds are found to be alternative sensitizers to ruthenium(II) complexes. Tetrapyrroles are broadly divided into three categories and they are porphyrins, phthalocyanines and corroles. Both porphyrins and phthalocyanines are good sensitizers to wideband-gap semiconductors. Two classes of porphyrins are defined by connecting position of anchoring groups either at meso- or at pyrrole-β. The effect of efficiency of DSSC device with substituents on porphyrin ring is reviewed. Phthalocyanines are another class of tetrapyrrolic compounds and they are less explored for DSSC applications due to aggregation and solubility of macrocycle in common organic solvents. New unsymmetrical phthalocyanines are designed based on ‘push-pull’ concept is analyzed. The possibility of application of corroles as sensitizers for DSSC is also reviewed.

In recent years Nanostructured polymer and polymer-based nanocomposites are key materials for new device applications. Fabrication of nanostructured polymeric materials (e.g.: monodispersed latex, block copolymers, nanocomposites) and inorganic materials have evolved rapidly. It is already known that the inherent properties of the polymer matrix are enhanced through nanocomposite formation by the synergistic interactions between the polymer matrix and the nanoparticles. The aspect of the device applications of polymer-nanocomposites can be broadened by modifying the surface properties of nanoparticles, doping and filling the matrix with nanoparticles of both pand n-type and introducing functionalities in polymer matrix. These eBook chapter is dealing with the above observations with experimental evidences and references.

This eBook chapter also deals with synthesis of various nanocomposites by tailoring the properties of polymer materials and nanomaterials which has been explained with various examples. Fabrication of functional polymeric materials and their nanocomposites concerning their optical, electrical, mechanical and thermal properties in thin film as well as bulk morphologies using several polymerization techniques is also explained in this chapter alongwith various characterization techniques like XRD, DSC, FTIR, SEM, TEM etc. Applications of these materials for various device applications like photo diode, solar cell, light emitting diodes, magnetic storage materials etc. also explained briefly with examples in this chapter alongwith future prospects of those materials for device applications.

This chapter reviews a newly developed visible-light consisting of gold nanoparticles (NPs) and titanium(IV) oxide (Au/TiO₂), the so-called “plasmonic photocatalyst”. Unlike the hitherto studied semiconductor photocatalysts that are activated by the band gap excitation, the redox ability of the “plasmonic photocatalyst” is induced by the excitation of the localized surface plasmon resonance (LSPR) of Au NPs. Au/TiO₂ with strong and broad visible absorption well matching the solar spectrum is a very promising photocatalyst for the solar chemical transformations. Subsequently to the introduction, Section 2 describes the fundamentals of the “plasmonic photocatalyst” in the following of what the LSPR is, the photo-induced interfacial electron transfer, and coupling between LSPR and interband transition of Au NPs. Section 3 summarizes the Au/TiO₂-photocatalytic oxidation processes as organic synthesis, degradation of organic pollutants and water splitting reported so far. Section 4 deals with the important factors affecting the visible-light activity (support effect, Au particle size effect, and reaction field effect) for the design of highly active “plasmonic photocatalysts”.

C₆₀-based bulk heterojunction solar cells were fabricated, and the electronic and optical properties were investigated. C₆₀ were used as n-type semiconductors, and copper oxides, porphyrin, phthalocyanines, CuInS₂ and nano-diamond were used as p-type semiconductors. An effect of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer was also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed. Nanostructures of the solar cells were investigated by transmission electron microscopy, electron diffraction and X-ray diffraction, which indicated formation of mixed nanocrystals.