Browsing by Author "Toivola, Minna"
Now showing 1 - 8 of 8
Results Per Page
Sort Options
Item A carbon gel catalyst layer for the roll-to-roll production of dye solar cells(Elsevier BV, 2011) Miettunen, Kati; Toivola, Minna; Hashmi, Ghufran; Salpakari, Jyri; Asghar, Imran; Lund, Peter; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceCarbon gel catalyst layers were used in dye solar cells. These layers were prepared on flexible plastic substrates at low temperatures (130 °C). The carbon gel, demonstrated excellent flexibility which is an important feature for roll-to-roll production and special applications of dye solar cells. The use of these low cost and highly flexible catalyst layers resulted in good photovoltaic performance; only 10% lower than dye solar cells with rigid glass-based counter electrodes prepared with thermal platinization at ∼400 °C temperature.Item Considerations in Designing Dye-sensitized Solar Cell Modules(2009) Peltola, Timo; Toivola, Minna; Teknillisen fysiikan laitos; Teknillinen korkeakoulu; Helsinki University of Technology; Lund, PeterOne of the most promising alternatives to traditional silicon cells is the dye-sensitized solar cell. This type of cell should be relatively cheap, easy to manufacture and has shown promise in high efficiency. To date, a number of problems in module efficiency, stability and manufacturing have hindered the commercial adoption of this technology. A number of device structure concepts utilizing different materials and preparation methods have been proposed. Different concepts and preparation methods are briefly overviewed in this study and their advantages and disadvantages discussed. The aim of this study is to identify device concepts that can be manufactured with inexpensive materials and processing methods. Scientific publications with the addition of a couple of selected patent publications were used as references. Dye solar cells can be made on plastic, glass or metal substrates. High temperature fabrication methods yield best results but exclude the use of plastic or continuous processing on glass. Metal substrates, on the other hand, must be protected from the cell electrolyte in order to avoid corrosion problems. Cell structure configurations with different layer ordering and mechanical supports are discussed. Monolithic and back contact structures were deemed advantageous due to perceived low costs. Individual solar cells must also be integrated into a module in order to be able to power even small appliances. Three different module concepts are compared by modeling efficiency losses in them. Parallel type modules were considered to have the highest potential but difficulties in manufacturing may lead to the use of Z-type modules. Biggest efficiency losses are caused by current management structures which block sunlight. Very thin tungsten current collectors were suggested as solution to this problem and some estimates for the required conductivities were calculated. Based on these results and earlier work by other members of the research group, a new module concept was suggested. The design uses relatively low-cost materials and is suitable for roll-toroll type manufacturing. However, some material and fabrication issues need to be addressed before this concept can be realized.Item Dye Solar Cells on ITO-PET Substrate with TiO[sub 2] Recombination Blocking Layers(The Electrochemical Society, 2009) Miettunen, Kati; Halme, Janne; Vahermaa, Paula; Saukkonen, Tapio; Toivola, Minna; Lund, Peter; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceAtomic-layer-deposited TiO2 recombination blocking layers were prepared on indium tin oxide–poly(ethylene terephthalate) (ITO–PET) photoelectrode substrates for dye solar cells and were examined using several electrochemical methods. The blocking layers increased the open-circuit voltage at low light intensities. At high light intensities, a decrease in the fill factor (FF) due to the additional resistance of the current transport through the layer was more significant than the positive effect by the reduced recombination. The decrease in the FF was reduced by a thermal treatment that made the blocking layer more conductive due to a structural change from an amorphous to a crystalline form. Therefore, thinner blocking layers of this type are required for plastic cells prepared at low temperature than for conventional glass dye solar cells made with temperature processing.Item Dye-sensitized solar cells on alternative substrates(Aalto-yliopiston teknillinen korkeakoulu, 2010) Toivola, Minna; Lund, Peter, Prof.; Teknillisen fysiikan laitos; Department of Applied Physics; Aalto-yliopiston teknillinen korkeakoulu; Lund, Peter, Prof.Dye-sensitized solar cells (DSC) could become a potential alternative for the traditional silicon and thin film panels in the near future, due to the DSC's for the most part cheap materials and simple manufacturing methods. One of the challenges of this technology is, however, the heavy, expensive and inflexible glass substrate typically used in the cells. To address this problem, this thesis concentrates on transfer of the DSC technology from glass substrates to light weight, cost-efficient, and flexible plastic foils and metal sheets. Flexible solar cell would be well suited for industrial-scale mass production, for example with roll-to-roll methods and when integrated on building materials it could work as a functional coating, enabling electricity-producing roofing or façade structures. In the course of this thesis, DSCs were prepared on ITO-PET and ITO-PEN plastics, stainless steel (StS), and optical fibers. Due to the low temperature tolerance of the plastics, development and characterization of room temperature processable counter electrode materials suitable for these substrates was a part of this work. Powder suspension based on carbon nanoparticles proved to be an easily depositable, cost-efficient material with catalytic activity as high as that of platinum. With metal materials, the main problem is the corrosive, iodine-based electrolyte conventionally used in the DSC. This is why, in the beginning of this work, the corrosion resistance of some widely used building materials such as zinc-coated carbon steels, copper, and StS was studied with soaking tests in the electrolyte. StS passed the soaking tests and was chosen for further research. StS has also other benefits such as good electrical conductivity and mechanical sturdiness. Substrate-mediated leakage current is also smaller from StS than from glass substrates. With a DSC configuration where the StS sheet worked as the photoelectrode substrate efficiencies comparable to all-glass cells, near 5 %, were obtained so this configuration was chosen also for the cell size upscaling tests. The largest StS photoelectrode cells prepared in the course of this thesis were 6 cm × 6 cm and their efficiencies over 3 % at their best. This is already a promising value considering the ohmic losses bound to happen at the counter electrode, due to the sheet resistance of the counter electrode substrate. To minimize these losses, additional current collector structures were integrated on the counter electrode substrate with inkjet-printing with silver nanoparticle ink. 50 % reduction in the total ohmic losses of the cell was achieved with the current collector structures and 80 % with replacing the photoelectrode glass substrate with the StS sheet. StS-based DSC would seem like a feasible concept even for industrial-scale mass production but special emphasis should be put, in the future research, on the long term stability of the cells and its improvement. Room for improvement still exists in efficiencies also - a research challenge in which for example some recently developed carbon nanomaterials might provide progress.Item The effect of temperature and air humidity on the aging of dye solar cells prepared on glass and metal substrates(2011) Neuvonen, Lauri; Toivola, Minna; Perustieteiden korkeakoulu; Lund, PeterItem Loss mechanisms and optimization of dye-sensitized solar cells deposited on stainless steel substrates(2006) Miettunen, Kati; Toivola, Minna; Teknillisen fysiikan ja matematiikan osasto; Teknillinen korkeakoulu; Helsinki University of Technology; Lund, PeterTämä tutkimus keskittyy väriaineherkistettyihin aurinkokennoihin, joilla on yksinkertaisista valmistusmenetelmistä johtuen alhaisemmat valmistuskustannukset verrattuna moniin perinteisempiin aurinkokennotekniikoihin. Väriainekennojen rakentaminen metalli- ja muovisubstraateille on eräs keino vähentää kustannuksia entisestään. Tämä työ keskittyy ruostumattomaan teräkseen, sillä sen on havaittu olevan yksi stabiileimmista metallisubstraateista. Valoelektrodien rakentaminen muoville on ongelmallista, koska ne eivät kestä tavanomaista, 450-500 °C suoritettavaa sintrausprosessia. Toisin kuin muovit, ruostumaton teräs voidaan sintrata. Lisäksi ruostumaton teräs tarjoaa tukevamman alustan TiO2-kerrokselle tehden kennosta kestävämmän. Tämän vuoksi ruostumatonta terästä käytettiin valoelektrodin substraattina ja muovia vastaelektrodin substraattina. Geelielektrolyyttejä käytettiin perinteisten neste-elektrolyyttien sijaan parantamaan kennon stabiiliutta entisestään. Tämän työn tarkoituksena oli häviömekanismien määritys eri komponenteissa ja kennon suorituskyvyn parantaminen. Ensinnäkin tutkittiin varauksensiirtoa eri kennokomponenteissa. Toiseksi tarkasteltiin optisia häviöitä, sillä teräsvaloelektrodin tapauksessa valon täytyy tulla kennoon vastaelektrodin puolelta, mikä puolestaan tarkoittaa sitä, että vastaelektrodi ja elektrolyytti varjostavat valoelektrodia. Tutkimus on jaettu kolmeen osaan kennokomponenttien mukaan: valoelektrodi, elektrolyytti ja vastaelektrodi. Lopuksi esitetään optimoidun kennon tulokset ja eritellään häviömekanismien vaikutukset. Mittauksia varten valmistettiin aurinkokennoja, vastaelektrodi-vastaelektrodi -kennoja sekä optisia näytteitä. Tutkimuksessa käytettiin seuraavia mittaustekniikoita: aurinkosimulaattori, sähkökemiallinen impedanssispektroskopia ja optinen spektroskopia. Valitulla kennotyypillä saavutettiin parhaimmillaan 2.4 % hyötysuhde. Tutkimuksissa huomattiin, että ruostumattomalla teräksellä on pienet vuotovirrat ja se näyttäisi toimivan valoelektrodin substraattina muutenkin hyvin. Pitkäaikaisstabiiliusmittauksia on tosin vielä tarpeen suorittaa. Ohuemman elektrolyyttikerroksen käyttö ja trijodidin konsentraation pienentäminen nostivat virtaa 26 %. Vastaelektrodin huomattiin rajoittavan kennojen toimintaa merkittävästi ja lisätutkimusta sekä kehittämistä tarvitaan vielä.Item New materials and upscaling issues in flexible, all-plastic dye solar cells(2010) Salpakari, Jyri; Toivola, Minna; Informaatio- ja luonnontieteiden tiedekunta; Lund, PeterItem Stability of Dye Solar Cells with Photoelectrode on Metal Substrates(The Electrochemical Society, 2010) Miettunen, Kati; Ruan, Xiaoli; Saukkonen, Tapio; Halme, Janne; Toivola, Minna; Guangsheng, Huang; Lund, Peter; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceIn this study, the stability of dye solar cells (DSCs) with different kinds of metals as the photoelectrode substrate is studied. Stainless steels (StSs), Inconel, and titanium substrates were tested to find stable substrate options. Photovoltaic characterization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy, and substrate polarization measurements were used in the characterization. DSCs based on different grades of StS suffered from rapid degradation of efficiency within few hours in light soaking. Good stability was demonstrated with DSCs with Inconel and Ti photoelectrode substrates. The Inconel substrates have a thick passive oxide layer, which is likely related to good stability. However, according to the EIS analysis, the oxide layer of Inconel substrates increased resistive losses, which caused a lower fill factor and photovoltaic efficiency compared to the Ti-based cells.