Testilaitteen valmistus biodieselin tutkimiseen

Opinnäytetyö on osana 2010 syksyllä alkanutta Metropolian AMK:n ja UPM:n Concept Car -hanketta, jota Tekes on rahoittanut. Auton on suunniteltu käyttävän 100-prosenttista biodieseliä. Hankkeen yhtenä tavoitteena on selvittää biodieselin viskositeetti talvisissa olosuhteissa. Tämän insinöörityön tavoitteena oli suunnitella ja valmistaa biodieselin viskositeetin tutkimiseen soveltuva testilaite sekä koekäyttää sitä tutkimusympäristössä. Työssä paneudutaan erityisesti testilaitteessa käytettävien komponenttien toimintaan. Testilaite tehtiin Ford Fiesta 1.4 TDCi korkeapainejärjestelmän osista, jotka ovat Siemensin valmistamat. Moottorin tuottama käyttövoima korkeapainepumpulle korvattiin KLEEdriven kolmivaihesähkömoottorilla. Työn lopputuloksena syntyi mekaanisesti toimiva dieselpolttoaineen tutkimuslaite. Korkeapainepumpun ja Railin ohjauksen parantamisella sillä saataisiin vertailukelpoisia tuloksia biodieselin viskositeetistä.This thesis is a part of Helsinki Metropolia University of Applied of Science and UPM’s Concept Car project started in fall 2010. The project is funded by Tekes. The Concept Car is planned to use 100 % biodiesel. One of the project objectives is to determine the viscosity of biodiesel in winter conditions. The objective of this Bachelor’s thesis is to design and manufacture test equipment suitable for measuring biodiesel viscosity and to test the equipment in research environment. This thesis focuses on the functions of the components used in the test equipment. The test equipment is made from components of Ford Fiesta Common Rail, manufactured by Siemens. As a result of this thesis a mechanically functional device for diesel researching was made. After improving controls of the parts from Common Rail it would be possible to achieve comparable results for measuring biodiesel viscosity

Insights from Transient Optoelectronic Analyses on the Open-Circuit Voltage of Organic Solar Cells

In this Perspective, we review recent progress on the use of transient optoelectronic techniques to quantify the processes determining the open-circuit voltage (<i>V</i>_OC) of organic solar cells. Most theoretical treatments of <i>V</i>_OC include the effects of both material energetics and recombination dynamics, yet most experimental approaches are based on materials energetics alone. We show that by direct measurement of charge carrier dynamics and densities, the rate of nongeminate charge recombination may be determined within working cells and its impact on achievable <i>V</i>_OC determined. A simple fit-free device model utilizing these measurements is shown to agree (to within ±5 mV) with experimentally observed open-circuit voltages for devices comprised of a range of different photoactive layer materials and different processing conditions, and utilizing both bulk and bilayer heterojunctions. This agreement is significantly better than that obtainable from analyzing materials energetics alone, even when employing an in situ analysis of effective electronic band gap. We go on to argue that the precision of our <i>V</i>_OC calculations derives from implicitly including the impact of film microstructure on open-circuit voltage. We show that this can modulate <i>V</i>_OC by up to 200 mV, and thereby account for the limits of energy-based models in accurately predicting achievable performance

Exciton and Charge Generation in PC₆₀BM Thin Films

Transient absorption spectroscopy is employed to contrast the photophysics of [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₀BM) dispersed in a polystyrene matrix and as a neat film. For the dispersed PC₆₀BM:polystyrene film, singlet excitons are observed that undergo intersystem crossing to triplet excitons. In contrast, in the neat PC₆₀BM film, the transient absorption data indicate significant polaron generation, with photogenerated polarons exhibiting dispersive, bimolecular charge recombination on the nano- to microsecond time scales. These results are discussed in terms of their implications for charge generation from PC₆₀BM light absorption in polymer/fullerene solar cells

Concentration-Dependent Hole Mobility and Recombination Coefficient in Bulk Heterojunctions Determined from Transient Absorption Spectroscopy

A simple analytical function, based on the multiple trapping model, is used to describe the bimolecular recombination of charge carriers in a bulk heterojunction (BHJ) film in the presence of an exponential energetic tail of localized hole “trap” states. The function is used to fit charge carrier decay data from an unannealed P3HT/PCBM film measured by transient absorption. The analysis assumes that only free holes participate in recombination and transport. This implies an effective recombination rate coefficient which varies with the ratio of free to trapped holes. The fit parameters yield a bimolecular recombination constant for free holes with free electrons (<i>k</i>₀ = 3.4 × 10⁻¹² cm³ s⁻¹) and information about the distribution of trap states (trap distribution parameter β = 0.29). Assuming the Langevin recombination limit, the analysis yields a concentration-dependent effective hole mobility saturating at μ₀ ≈ 7 × 10⁻² cm² V⁻¹ s⁻¹. This approach should be useful to compare BHJs in a consistent and meaningful manner

In Situ Measurement of Energy Level Shifts and Recombination Rates in Subphthalocyanine/C₆₀ Bilayer Solar Cells

Understanding the nature and impact of internal interfaces is critical to understanding the operation of nanostructured organic devices, such as organic photovoltaics. Here, we use transient optoelectronic analyses to quantify in situ the HOMO level shifts and changes in interfacial recombination rate that occur within thermally evaporated subphthalocyanine (SubPc)/C₆₀ bilayer solar cells as the SubPc evaporation source is varied. We show how such measurements can complement ex situ optical and physical techniques to access the functional impact of device modification, particularly with respect to the resulting device open-circuit voltage (<i>V</i>_OC). We are able to explain how subtle changes in SubPc deposition conditions lead to significant modification of interfacial energetics and recombination dynamics, which in turn cause substantial changes in <i>V</i>_OC

Understanding the Apparent Charge Density Dependence of Mobility and Lifetime in Organic Bulk Heterojunction Solar Cells

Energetic disorder in organic semiconductors leads to strong dependence of recombination kinetics and mobility on charge density. However, observed mobilities and reaction orders are normally interpreted assuming uniform charge carrier distributions. In this paper, we explore the effect of the spatial distribution of charge on the determination of mobility and recombination rate as a function of average charge density. Since the spatial gradient changes when the thickness of a device is varied, we study thickness series of two different polymer:fullerene systems and measure the charge density dependence of mobility and lifetime. Using simulations, we can show that the high apparent reaction orders frequently observed in the literature result from the spatial gradient of charge density at open circuit. However, the mobilities, measured at short circuit, are less affected by the gradients and therefore may show substantially different apparent charge density dependence than the recombination constants, especially for small device thicknesses

Analysis of the Relationship between Linearity of Corrected Photocurrent and the Order of Recombination in Organic Solar Cells

We address the claim that the dependence of the “corrected photocurrent” (defined as the difference between the light and dark currents) upon light intensity can be used to determine the charge recombination mechanism in an organic solar cell. We analyze a poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) device using corrected photocurrent and transient photovoltage experiments and show that whereas the corrected photocurrent is linear in light intensity the charge recombination rate scales superlinearly with charge carrier density. We explain this apparent discrepancy by measuring the charge carrier densities at different applied voltages and light intensities. We show that it is only safe to infer a linear recombination mechanism from a linear dependence of corrected photocurrent on light intensity under the following special conditions: (i) the photogenerated charge carrier density is much larger than the dark carrier density and (ii) the photogenerated carrier density is proportional to the photogeneration rate

On the Differences between Dark and Light Ideality Factor in Polymer:Fullerene Solar Cells

Ideality factors are derived from either the slope of the dark current/voltage curve or the light intensity dependence of the open-circuit voltage in solar cells and are often a valuable method to characterize the type of recombination. In the case of polymer:fullerene solar cells, the ideality factors derived by the two methods usually differ substantially. Here we investigate the reasons for the discrepancies by determining both ideality factors differentially as a function of voltage and by comparing them with simulations. We find that both the dark and light ideality factors are sensitive to bulk recombination mechanisms at the internal donor:acceptor interface, as is often assumed in the literature. While the interpretation of the dark ideality factor is difficult due to resistive effects, determining the light ideality factor <i>differentially</i> indicates that the open-circuit voltage of many polymer:fullerene solar cells is limited by surface recombination, which leads to light ideality factors decreasing below one at high voltage

Electron Diffusion Length in Mesoporous Nanocrystalline TiO₂ Photoelectrodes during Water Oxidation

A long electron diffusion length (<i>L</i>) relative to film thickness is required for efficient collection of charge in photoelectrodes. <i>L</i> was measured in a nanocrystalline, mesoporous TiO₂ electrode during photochemical water splitting by two independent methods: (1) analyzing the ratio of incident photon conversion efficiency (IPCE) measured under back and front side illumination, and (2) analyzing transient photovoltage rise and decay measurements. These gave values of <i>L</i> that agreed (<i><i>L</i> = </i> 8.5−12.5 μm between −0.15 and 0.1 V vs Ag/AgCl 3 M KCl at pH 2). The transient measurements were consistent with trap limited transport and recombination of electrons as previously observed in dye-sensitized solar cells. <i>L</i> ∼ 10 μm is sufficient to collect separated electrons with minor electrolyte recombination losses in thin electrodes. However, charge collection may limit performance in doped mesoporous electrodes with weak visible light absorption where thicker films are required

Il neolitico medio ligure e le influenze chasseane

The kinetic competition between electron–hole recombination and water oxidation is a key consideration for the development of efficient photoanodes for solar driven water splitting. In this study, we employed three complementary techniques, transient absorption spectroscopy (TAS), transient photocurrent spectroscopy (TPC), and electrochemical impedance spectroscopy (EIS), to address this issue for one of the most widely studied photoanode systems: nanostructured hematite thin films. For the first time, we show a quantitative agreement between all three techniques. In particular, all three methods show the presence of a recombination process on the 10 ms to 1 s time scale, with the time scale and yield of this loss process being dependent upon applied bias. From comparison of data between these techniques, we are able to assign this recombination phase to recombination of bulk hematite electrons with long-lived holes accumulated at the semiconductor/electrolyte interface. The data from all three techniques are shown to be consistent with a simple kinetic model based on competition between this, bias dependent, recombination pathway and water oxidation by these long-lived holes. Contrary to most existing models, this simple model does not require the consideration of surface states located energetically inside the band gap. These data suggest two distinct roles for the space charge layer developed at the semiconductor/electrolyte interface under anodic bias. Under modest anodic bias (just anodic of flatband), this space charge layer enables the spatial separation of initially generated electrons and holes following photon absorption, generating relatively long-lived holes (milliseconds) at the semiconductor surface. However, under such modest bias conditions, the energetic barrier generated by the space charge layer field is insufficient to prevent the subsequent recombination of these holes with electrons in the semiconductor bulk on a time scale faster than water oxidation. Preventing this back electron–hole recombination requires the application of stronger anodic bias, and is a key reason why the onset potential for photocurrent generation in hematite photoanodes is typically ∼500 mV anodic of flat band and therefore needs to be accounted for in electrode design for PEC water splitting