Understanding interfacial charge injection processes is one of the key factors needed for development of efficient organic electronic devices, such as biosensors and energy conversion systems, since these processes control the electrical characteristics of these devices. Spectroelectrochemical characterization of electron transfer processes occurring at the electrode - electroactive thin film interface has been evaluated to improve our understanding of charge transfer kinetics using a novel form of electroreflectance spectroscopy, potential-modulated attenuated total reflectance (PM-ATR), which makes it possible to sensitively monitor spectroscopic changes in thin films as a function of applied potential. PM-ATR was used to evaluate three different redox-active films deposited on indium tin oxide (ITO) electrodes to investigate: i) the orientation dependence of charge transfer rates of thin films of biomolecules, ii) surface treatment and modification effects on charge transfer kinetics of conducting polymers and, iii) estimation of rates of electron injection and conduction band edge of semiconductor nanocrystalline materials. First, Prussian blue film as a model system was used successfully to examine the PM-ATR technique for determination of the charge transfer rate constant between ITO and a molecular film. Second, an anisotropic and redox active protein film, cytochrome c, was used to probe charge transfer rates with respect to molecular orientation. The electron transfer rate measured using TM polarized light was four-fold greater than that measured using TE polarized light. These data are the first to correlate a distribution of molecular orientations with a distribution of electron transfer rates in a redox-active molecular film. Third, the effects of ITO surface treatment and modification on charge transfer kinetics on a conducting polymer, poly(3,4-ethylenedioxythiophene/)/poly(styrenesulfonate) (PEDOT/PSS), were studied. The apparent interfacial charge transfer rate constant for PEDOT/PSS on ITO has been reported for the first time which cannot be measured otherwise with conventional electrochemistry due to high non-Faradaic background of PEDOT/PSS films. Fourth, PM-ATR enabled characterization of reversible redox processes between submonolayer coverages of surface-tethered, CdSe nanocrystals and ITO for the first time. Optically determined onset potentials for electron injection were used for estimation for the conduction band and valance band energies (ECB and EVB, respectively).

The overall efficiency of organic photovoltaics cells (OPVs) is influenced by the nature of the charge injection barrier at the transparent conducting oxide (TCO) bottom contact. Modification of the transparent conducting oxide (TCO)/organic interface with an electroactive molecular monolayer will potentially create a robust ohmic contact that will influence the efficiency of hole injection into the TCO. Asymmetric zinc Phthalocyanines (ZnPc) with a flexible phosphonic acid (PA) linker have been synthesized and used to modify indium tin oxide (ITO) surfaces. The adsorption of PA functionalized asymmetric ZnPcs on an ITO/waveguide was monitored using attenuated total reflectance (ATR) spectroscopy. Polarized dependent ATR spectroscopy was used to determine the orientation of these absorbed subpopulations species on ITO modified surfaces as a function of wavelength using transverse electric (TE) or transverse magnetic (TM) polarized light. The first oxidation potential on absorbed monolayers was found by cyclic voltammetry to be resolved into two peaks indicative of two electrochemically distinct subpopulations of molecules, atributed to aggregates and monomerics forms of PA functionalized ZnPcs. Potential modulated ATR (PM-ATR) spectroelechtrochemistry was employed to measure the charge transfer rates constants (k(s, app)) at ITO modified surfaces using TE and TM polarized light. Faster charge transfer rate constants were found for molecules with a smaller tunneling distance. A k(s, app) of 3.9 x 104 s−1 represents the fastest rate measured for PA functionalized ZnPc chromophore tethered to an ITO waveguide electrode by PM-ATR. We synthesized and characterized the first examples of PA functionalized RuPcs to investigate the effect of molecular orientation on charge transfer properties at an ITO/organic interface. PA functionalized RuPcs have the ability to coordinate axial ligand to suppress aggregation, providing the flexibility of connecting the anchoring group through the axial position of the metal and allowing chemisorption of the molecule in plane with ITO. Cyclic voltammetry and ATR UV/vis spectroscopy on the modified ITO surface demonstrated a surface composition of a closed-packed monolayer of monomeric species. Measurement of the charge transfer rates constants demonstrated that RuPc anchored to ITO exhibited slow rates compared to corresponding surface bound ZnPcs. Finally, we describe the synthesis and characterization of a new PA functionalized N-pyridinyl perylenediimide (PDI)-RuPc donor-acceptor dyad capable of chemisorption to ITO surfaces as a molecular-level heterojunction system to study photo induced charge separated states. The developed ensemble was proven to be stable on ITO for further study of charge injection events from the dyad to the oxide surface.

Badeker in 1907 observed that some materials are optically transparent in the visible light and electrically conducting [1]. Because of the increasing interest in electrically and electronically active materials, the search for materials and the techniques for producing semi-transparent electrically conducting films have gained much importance. In an intrinsic stoichiometric material, it is not possible to have simultaneously high transparency (>80%%) in the visible region and high electrical conductivity (>103 Ω cm-1). A variety of metals in thin film form (

With dwindling energy reserves, Photovoltaic(PV) module which is one of the most promising renewable sources of energy is slowly becoming indispensable for world's electricity production paradigm. Due to the low electrical resistance and high optical transparency in the visible range of the electromagnetic spectrum, Transparent Conducting Oxide (TCO) thin film(TF)s have found application as window electrode for fabrication of solar cell. Besides TCOs have wide application in display devices and other optoelectronic devices. This book mainly focuses on the fabrication and study of the optoelectronic properties of TCO thin films with special reference to PV application. This book also includes the fabrication and study of a heterojunction II-VI semiconductor solar cell using TCO as front electrode. It also highlights different methods used for the study of optoelectrical and structural properties of TF (e.g. SEM, XRD, thickness measurement, optical band gap, mobility, determination of carrier type, carrier concentration, conductivity etc.). This book is designed to serve as a handbook for the beginners who want to work in the field of thin film technology.