The development of organic photovoltaics (OPVs) has attracted a lot of attention due to their potential to create a low cost flexible solar cell platform. In general, an OPV is comprised of a number of layers of thin films that include the electrodes, active layers and barrier films. Thus, with all of the interfaces within OPV devices, the potential for failure exists in numerous locations if adhesion at the interface between layers is inherently low or if a loss of adhesion due to device aging is encountered. To date, few studies have focused on the basic properties of adhesion in organic photovoltaics and its implications on device reliability. In this dissertation, we investigated the adhesion between interfaces for a model multilayer barrier film (SiNx/PMMA) used to encapsulate OPVs. The barrier films were manufactured using plasma enhanced chemical vapor deposition (PECVD) and the interfacial fracture toughness (Gc, J/m2) between the SiNx and PMMA were quantified. The fundamentals of the adhesion at these interfaces and methods to increase the adhesion were investigated. In addition, we investigated the adhesive/cohesive behavior of inverted OPVs with different electrode materials and interface treatments. Inverted OPVs were fabricated incorporating different interface modification techniques to understand their impact on adhesion determined through the interfacial fracture toughness (Gc, J/m2). Overall, the goal of this study is to quantify the adhesion at typical interfaces used in inverted OPVs and barrier films, to understand methods that influence the adhesion, and to determine methods to improve the adhesion for the long term mechanical reliability of OPV devices.

In this work two different solution based methods have been used for synthesis ofoxide-wires and homogeneous heterometallic oxides of transparent conductingmaterials. The first method used is an aqueous chemical growth (ACG) method for synthesis ofmicrorods and nanowires of zinc oxide and tin dioxide useful for detection of toxicgases. No desired films have been obtained but some new interesting structures withnew surfaces at the a,b-plane, especially for zinc oxide where a jagged surface hasbeen observed. For low metal-concentrations of zinc, a band-like structure with 120 °angles has been observed to grow along the a- and b-axis instead of the preferredc-axis. The rod- and wire films have been characterized by SEM and XRD. The other solution-based method used is an inorganic sol-gel type where aheterometallic oxide of 80 mol% zinc and 20 mol% tin manufactured for CIGS solarcells acts as an absorption layer. The alkoxide was prepared by first synthesizing a zincmethoxy-ethoxide solution from diethylzinc and methoxy-ethanol and then mixing itwith tin tert-butoxide to get a heterometallic alkoxide solution. Films and powderhave been prepared either in humidified argon atmosphere or in air and characterizedby SEM, TGA and XRD. The XRD pattern just show the two expected phases of zincoxide and the heterometallic zin-tin oxide which improves the homogeneity of theheterometallic oxide. But the TGA show that some carbonating species formed. This method seems promising for large scale manufacturing of absorption layer toCIGS solar cell for commercially use due to low-cost materials, low temperatures andcheap equipment.

Today many buildings and it´s nearby surroundings are designed to achieve some kind of environmental goal.The issue concerning energy consumption is currently at focus and it is relevant that we start increase the share of renewable energy. Solar energy is an infinite resource and should therefore be considered when selecting an energy supplier.   Uppsala University hospital is facing major restructuring when parts of the existing buildings will be refurbished and a large new building will be constructed. White Architects have developed a study concerning the new building and for some of the existing buildings on the hospital campus. Uppsala County requires tough energy measures and wants the new building to be classified as an eco-building in Whites following work. The classifications will involve high energy source requirements.   This work has been conducted to see if solar power can be envisaged as a supplementary energy source for the University hospital and also to investigate the aesthetic impact of solar cells on the new building. In this report, solar cells integrated on the facade and PV modules on the roofs have been studied. Focus has been to evaluate the potential of what each option can produce and what opportunity they have to become an intrinsic part of the architecture   The type of solar cell module, which in this case study has been proven to generate most electricity is stand-alone modules on roofs. These are however, more difficult to reconcile with the architecture. Solar cells on the facades should therefore still be considered as an alternative application.The result shows that the potential energy that can be generated by solar panels on the new building is large but not in relation to hospital´s electricity use. It is for that reason questionable whether solar installation, applied on the new building, can be seen as a good additional source of energy or if it will more become a matter of public relations.

This research is to synthesize polyaniline (PANI) thin film for polymer solar cells as a hole transport layer by using potentiostatic deposition of electrochemical method. In our previous studies, we have shown that the power conversion efficiencies of the solar cell device were improved for the slow polymerization rate. We choose the potentiostatic deposition method to improve the polymerization rate of PANI for the application in industry. In this study, we investigated optical transmittance, absorption spectrum, Highest Occupied Molecular Orbital (HOMO), surface roughness, and surface morphology of the PANI thin film by changing voltages and to discuss the factors on device efficiency. Then, we compared the device structures with hole transport layer PEDOT: PSS by spin-coating process. We found PANI thin films synthesized from different voltages, and the transmittance measurement results were similar. In addition, we found HOMO, surface roughness, and surface morphology of PANI thin film that varies with different voltages. The power conversion efficiencies of the device mainly were affected by the surface roughness and morphology of PANI thin film surface. Comparing to other parameters, PANI thin film polymerized at 0.8V owns the most appropriate surface roughness and surface morphology. The power conversion efficiency was up to 1.52% under AM 1.5G illumination based on ITO (150 nm) / PANI (75 nm) / P3HT: PCBM (100 nm) / Al (200 nm), and the device area of 0.16 cm2.

Thin film solar cells, if film thickness is thinner than the optical absorption length, typically give lower cell performance. For the thinner structure, electric current loss due to light penetration can offset the electric current gain obtained from higher built-in electric field. Light trapping schemes can increase the effective optical absorption length and thus enhance the electric current for thinner solar cells. Here a new light trapping scheme based on light trapping transparent conducting oxide layer (LT-TCO) is proposed to enhance the performance of thin film solar cells. Three different configurations of integrating the LT-TCO layer in solar cells are proposed and evaluated. This research aims to develop the LT-TCO layer with surface texture and good conductivity by pulsed laser deposition (PLD) technique at low temperature. The LT-TCO layer is fabricated by PLD deposition of Al-doped ZnO to achieve multilayer films by tuning of oxygen pressure. The light trapping effect is examined by optical transmittance measurement and the surface texture is characterized by transmission electron microscopy (TEM) technique. The conductivity of LT-TCO layer is measured by resistivity measurement. Thin film CdTe/CdS solar cells are fabricated by PLD technique to develop baseline solar cells for integration of LT-TCO layer. The as-deposited thin film solar cells show relatively low performance and are further processed with various post-deposition treatments to seek efficiency enhancement. The effects of different processes on cell performance are examined by electrical, optical, and microstructure studies. Air annealing of CdS layer and CdCl2 treatment of CdTe layer combined are found to yield the best cell performance. The fabrication issues that limit the cell performance are discussed and future optimizations in fabrication processes are suggested.

The thesis discusses how to utilize Sol-gel method to prepare nano-sized TiO2 films of photoelectrodes and the their use in Dye-Sensitized Solar Cells. The main goal is the study on the production of TiO2 photoelectrodes. When making nano-sized TiO2 films of photoelectrodes, we have to first produce TiO2 sol via the Sol-gel method optical thin films are then made by spin coating. After its spin coating, we study the crystalline phase and morphology of nano-sized TiO2 films of photoelectrodes in terms of two ways: Supercritical drying and oven drying. Among the Dye-Sensitized Solar Cells that are made with different drying methods, owing to higher porosity and surface area, the nano-sized TiO2 films of photoelectrodes made by supercritical drying adsorb more dye molecules and are thus more efficient.

Photovoltaic (PV) conversion of solar energy appears to be one of the most promising ways of meeting the increasing future energy demand. In space, photovoltaic power source is the only alternative. The demand for higher power has necessitated the use of high speed switching charge controller and power conditioner. To design an efficient and reliable switching charge controller, the static (I-V) and dynamic (AC) characteristics of a solar cell need to be understood. The AC parameters of a solar cell can be measured either by Frequency Domain technique or by Time Domain technique. In frequency domain technique, a small signal is applied about the operating point and the AC parameters are measured. Hence, in the frequency domain technique the steady state values of AC parameters at a particular operating condition are measured. In time domain technique, a transient measurement is made where the cell voltage varies from short-circuit to open circuit or vice versa. Hence, this technique gives only the time constant of a solar cell. The impedance spectroscopy is a frequency domain technique widely used in electro chemistry to study battery characteristics. In the present investigation, the impedance spectroscopy is proposed for measuring the AC parameters of solar cells. An experimental set-up has been developed to measure the solar cell AC parameters. The AC parameters of Silicon (BSR and BSFR) solar cells and GaAs/Ge solar cells are measured using impedance spectroscopy (IS). The cell capacitance, the parallel resistance and the series resistance are measured and compared. GaAs/Ge solar cell has shown only transition Capacitance throughout its operating range while silicon (BSR and BSFR) solar cells exhibited both transition and diffusion capacitances. Theoretical and experimental values of the cell parallel resistance are compared and are in good agreement. While the diode factor in silicon solar cell varies from 2 to 1, where as in GaAs/Ge solar cell it varies from 4 to 2 to 1. Measurements conducted using open circuit voltage buildup (time domain technique) on silicon BSR solar cell shows that the collected data can be used for the restricted purpose of measuring cell transient response. The dime domain technique could not estimate the solar cell. It may be noted that the impedance spectroscopy assumes piece-wise linearity of the solar cell characteristics, lending itself for easy measurement and modeling. This assumption is valid as the signal amplitude is less than thermal voltage (VT). Since, the parameters are measured under steady state, the values are more stable and accurate. An attempt has also been made to correlate the measured AC parameters with the requirements of switching charge controllers. These correlations can be used to design the switching controllers for device rating, circuit stability and other aspects.

<p>Potential electrolytes for dye-sensitized photoelectrochemical solar cells have been synthesized and their applicability has been investigated. Different experimental techniques were used in order to characterize the synthesized electrolytes, such as elemental analysis, electrospray ionisation/mass spectrometry, cyclic voltammetry, dynamic viscosity measurements, as well as impedance, Raman and NMR spectroscopy. Some crystal structures were characterized by using single crystal X-ray diffraction.</p><p>In order to verify the eligibility of the ionic compounds as electrolytes for photoelectrochemical solar cells, photocurrent density/photovoltage and incident photon-to-current conversion efficiency measurements were performed, using different kinds of light sources as solar simulators. In electron kinetic studies, the electron transport times in the solar cells were investigated by using intensitymodulated photocurrent and photovoltage spectroscopy. The accumulated charge present in the semiconductor was studied in photocurrent transient measurements.</p><p>The ionic liquids were successfully used as solar cell electrolytes, especially those originating from the diethyl and dibutyl-alkylsulphonium iodides. The highest overall conversion efficiency of almost 4 % was achieved by a dye-sensitized, nanocrystalline solar cell using (Bu₂MeS)I:I₂ (100:1) as electrolyte (Air Mass 1.5 spectrum at 100 W m^-2), quite compatible with the standard efficiencies provided by organic solvent-containing cells. Several solar cells with iodine-doped metal-iodidebased electrolytes reached stable efficiencies over 2 %. The (Bu₂MeS)I:I₂-containing cells showed better long-term stabilities than the organic solvent-based cells, and provided the fastest electron transports as well as the highest charge accumulation.</p><p>Several polypyridyl-ruthenium complexes were tested as solar cell sensitizers. No general improvements could be observed according to the addition of amphiphilic co-adsorbents to the dyes or nanopartices of titanium dioxide to the electrolytes. For ionic liquid-containing solar cells, a saturation phenomena in the short-circuit current densities emerged at increased light intensities, probably due to inherent material transport limitation within the systems.</p><p>Some iodoargentates and -cuprates were structurally characterized, consisting of monomeric or polymeric entities with anionic networks or layers. A system of metal iodide crownether complexes were employed and tested as electrolytes in photoelectrochemical solar cells, though with poorer results. Also, the crystal structure of a copper-iodide-(12-crown-4) complex has been characterized</p>

<p>This thesis is divided into four parts with organic chromophores for dye sensitized solar cells as the common feature and an introduction with general concepts of the dye sensitized solar cells.</p><p>The first part of the thesis describes the development of an efficient organic chromophore for dye sensitized solar cells. The chromophore consists of a triphenylamine moiety as an electron donor, a conjugated linker with a thiophene moiety and cyanoacrylic acid as an electron acceptor and anchoring group. During this work a strategy to obtain an efficient sensitizer was developed. Alternating the donor, linker or acceptor moieties independently, would give us the tool to tune the HOMO and LUMO energy levels of the chromophores. The following parts of this thesis regard this development strategy.</p><p>The second part describes the contributions to the HOMO and LUMO energy levels when alternating the linker moiety. By varying the linker the HOMO and LUMO energy levels was indeed shifted. Unexpected effects of the solar cell performances when increasing the linker length were revealed, however.</p><p>The third part describes the investigation of an alternative acceptor group, rhodanine-3-acetic acid, in combination with different linker lengths. The HOMO and LUMO energy level tuning was once again successfully shifted. The poor electronic coupling of the acceptor group to the semiconductor surface proved to be a problem for the overall efficiency of the solar cell, however.</p><p>The fourth part describes the contributions from different donor groups to the HOMO and LUMO energy levels and has so far been the most successful in terms of reaching high efficiencies in the solar cell. A top overall efficiency of 7.1 % was achieved.</p>

Thesis (M.S.)--University of Delaware, 2009. / Principal faculty advisor: Stephen P. Bremner, Dept. of Electrical & Computer Engineering. Includes bibliographical references.