Molecular Semiconductors: Photoelectrical Properties and Solar Cells

ISBN-13: 9783642700149 / Angielski / Miękka / 2011 / 290 str.

J. Simon; J. -J Andre; J. M. Lehn

Opis

During the past thirty years considerable efforts have been made to design the synthesis and the study of molecular semiconductors. Molecular semiconductors - and more generally molecular materials - involve interactions between individual subunits which can be separately synthesized. Organic and metallo-organic derivatives are the basis of most of the molecular materials. A survey of the literature on molecular semiconductors leaves one rather confused. It does seem to be very difficult to correlate the molecular structure of these semiconductors with their experimental electrical properties. For inorganic materials a simple definition delimits a fairly homogeneous family. If an inorganic material has a conductivity intermediate between that of an 12 1 1 3 1 1 insulator - 10- n- cm- ) and that of a metal (> 10 n- cm- ), then it is a semiconductor and will exhibit the characteristic properties of this family, such as junction formation, photoconductivity, and the photovoltaic effect. For molecular compounds, such simplicity is certainly not the case. A huge number of molecular and macromolecular systems have been described which possess an intermediate conductivity. However, the various attempts which have been made to rationalize their properties have, more often than not, failed. Even very basic electrical properties such as the mechanism of the charge carrier formation or the nature and the density ofthe dopants are not known in detail. The study of molecular semiconductor junctions is very probably the most powerful approach to shed light on these problems."

Spis treści

I Basic Notions of Solid State Physics.- I.1 Dark Conductivity: Generalities.- I.2 Conduction in Metals: Drude and Sommerfeld Models.- I.3 Band Model of Conduction.- I.4 Limitations to Band Theory.- I.5 Hopping and Tunneling Mechanisms of Charge Migration.- I.6 Charge Carrier Trapping Processes.- a Molecular Crystals.- b Polymers.- II Photoelectric Phenomena in Molecular Semiconductors.- II. 1 Light Absorption.- II.2 Energy Migration in Molecular Materials.- a Mechanisms of Energy Migration.- b Effect of Traps.- II.3 Photogeneration of Charge Carriers.- II.4 Semiconductor Junctions.- a p-n Junctions: Formation and Electrical Properties.- b Schottky Junctions: Semiconductor-Metal Contacts.- c Insulator-Metal Contacts.- II.5 Photovoltaic Effect.- a Molecular Solar Cells: Classical Formulation.- b Molecular Solar Cells: Localized States Formulation.- c Effect of Surface States.- d Characterization of Junctions by the Capacitance Method.- III Metallophthalocyanines.- III. 1 Syntheses and Physico-Chemical Properties.- a Syntheses.- b Structure and Morphology.- c Spectroscopic Properties.- d Photoelectron Spectroscopy.- e Oxidation-Reduction Properties.- f Electron Spin Resonance Measurements (ESR).- III.2 Dark Electrical Properties.- a Energy Band Structures.- b Electrical Properties: Intrinsic Case.- c Determination of the Trapping Levels.- d Doping of PcM by O2.- e Doping of PcM by other Doping Agents.- III.3 Photovoltaic Effect and Solar Cells.- a Photoelectrical Properties.- b Photovoltaic Effect: Generalities.- c Junction in the Dark.- d Junction Studies under Illumination.- e Effect of Doping on the Performances of Molecular Solar Cells.- f Solar Energy Conversion Efficiencies of Molecular Solar Cells.- IV Poly acetylene.- IV. 1 Synthesis and Physico-Chemical Properties of Polyacetylene.- a Synthesis.- b Morphology.- c Molecular Weight and Length of the Conjugated Sequences.- d Stability of Polyacetylene and Effect of O2.- e Isomers.- f Crystalline Structures.- IV.2 Theoretical Properties.- a Origin of the Band Gap.- b Band Structure.- c Bond Length Alternation Defects in Polyenes: the Solitons.- IV.3 Properties of Doped Polyacetylene.- a Dopants and Doping Processes.- b Structural Features.- c Optical Properties.- d Magnetic Properties.- IV.4 Transport Properties of Polyacetylene.- a Conduction Mechanisms at Low Doping Levels.- b Semiconductor-Metal Transition.- c Metallic Domain.- d Comparison of the Models with the Experimental Results in the Low Dopant Concentration Domain.- IV. 5 Photoelectric Properties and Solar Cells.- a Luminescence and Photoconductive Properties of Cis- and Trans- Poly acetylene.- b Junctions Properties and Molecular Solar Cells.- V The Main Other Molecular Semiconductors.- V. l Aromatic Hydrocarbons and Graphite.- V.2 Metallo-Organic Derivatives.- V.3 Charge Transfer Systems.- a Different Types of Charge-Transfer Systems.- b Charge Distribution.- c Charge-Transport Properties.- d Tetrathiofulvalene-tetracyanoquinodimethane (TTF-TCNQ) and Related Complexes.- e (Tetramethyltetraselenofulvalene)2-X and Related Radical-Ion Salts.- V.4 Polysulfurnitride and Polydiacetylene.- V.5 Polymethines.- V.6 Polymeric Conjugated Systems.- a Polyphenylene and Related Materials.- b Substituted Polyacetylenes, Phenylacetylene.- c Pyrolyzed Polyacrylonitrile.- d Polypyrroles.- V.7 Molecular Solar Cells.- a Squaric Acid and Merocyanine.- b Aromatic Derivatives.- c Aromatic Liquid Crystals.- d Chlorophylls and Porphyrins.- e Polymeric Systems.- Conclusion.- References.