Optimized TiO2 blocking layers for dye-sensitized solar cells (DSSC)

In recent years much attention has been paid to dye-sensitized solar cells due to their low cost and wide applicability. The modest efficiencies achieved by these devices are caused by several phenomena including electronic losses due to parasitic electronic reactions. One of the most common way to reduce the electronic losses is to introduce a compact layer of conductive material (blocking layer) between the transparent conductive substrate and the sensitized semiconductor film. Aim of this work was to asses the correlation between the most common deposition processes and the final properties of the blocking layers produced by them. The blocking layer of TiO2 was prepared on FTO glass using two of the most commonly used colloidal deposition processes: dip and spin coating. The results obtained with the conventional dip coating were compared with the ones coming from spin coating of two different solutions of TiCl4 (50 mM). These solutions were characterized in terms of viscosity, surface tension and contact angle. The spin coating parameters were optimized on the basis of these analysis. The influence of subsequent cycles of deposition (2,4,6) was also evaluated. The TiO2 films obtained were deeply characterized (AFM, SEM, UV-vis and electrochemical measurement) in order to assess the best conditions needed to obtain an efficient blocking layer (BL)

Geopolymer oxygen carriers for chemical-looping combustion

One of the best alternatives to reduce the economic cost of CO2 capture is represented by the chemical looping combustion (CLC). This technology accomplishes indirect fuel combustion by use of a solid oxygen carrier (OC), generally a metal oxide having the capability of transporting the oxygen needed for the combustion from an air reactor to a fuel reactor, usually designed as two coupled fluidized beds. The combustion takes place in the fuel reactor through the reaction between the fuel and the solid OC, which is consequently reduced to a lower oxidation state. The reduced OC is then transferred to the air reactor, where it is regenerated by oxidation in air at high temperature. Therefore, the CLC process enables the inherent separation of the produced CO2, the stream exiting the fuel reactor being only composed of CO2 and H2O, easily separable by water condensation. Please click Additional Files below to see the full abstract

Morphological and electrochemical characterization of TiO2 blocking layers in Dye Sensitized Solar Cells

In recent years much attention has been paid to dye-sensitized solar cells due to their low cost and wide applicability. The modest efficiencies achieved by these devices are caused by several phenomena, including electronic losses due to parasitic electronic reactions. One of the most common way to reduce the electronic losses is to introduce a compact layer of conductive material (blocking layer) between the transparent conductive substrate and the sensitized semiconductor film. Aim of this work was to asses the correlation between the most common deposition processes (spin coating and dip coating) and the morphological and electrochemical properties of the blocking layers produced by them. The blocking layer of TiO2 was prepared on FTO glass, and the results obtained with the conventional dip coating were compared with the ones coming from spin coating of two different solutions of TiCl4 (50 mM). The TiO2 films obtained were deeply characterized in particular from the electrochemical point of view in order to assess the best conditions needed to obtain an efficient blocking layer. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to understand the electrochemical behavior of the blocking layer (BL

Processi di deposizione di blocking layers di TiO2 per Dye - Sensitized Solar Cells (DSSC)

Le Dye – Sensitized Solar Cells (DSSC) sono attualmente considerate tra le alternative più promettenti al fotovoltaico tradizionale. I ridotti costi di produzione e l’elevata versatilità di utilizzo rappresentano i punti di forza di questi dispositivi innovativi. Ad oggi la ricerca è concentrata prevalentemente sull’incremento delle prestazioni delle DSSC, ottenibile solamente attraverso un miglioramento delle funzioni dei singoli componenti e dell’interazione sinergica tra questi. Tra i componenti, ha recentemente assunto particolare interesse il blocking layer (BL), costituito generalmente da un film sottile di TiO2 depositato sulla superficie dell’anodo (FTO) e in grado di ottimizzare i fenomeni all’interfaccia FTO/TiO2/elettrolita. Nel corso di questo lavoro di tesi si è rivolta l’attenzione prevalentemente sulle caratteristiche del BLs (ad esempio proprietà morfologico – strutturali) cercando di mettere in correlazione il processo di deposizione con le caratteristiche finali del film ottenuto. A questo scopo è stato ottimizzato un processo di deposizione dei film via spin coating, a partire da soluzioni acquosa o alcolica di precursore (TiCl4). I film ottenuti sono stati confrontati con quelli depositati tramite un processo di dip coating riportato in letteratura. I BLs sono stati quindi caratterizzati tramite microscopia (SEM – AFM), spettrofotometria (UV.- Vis) e misure elettrochimiche (CV – EIS). I risultati ottenuti hanno messo in evidenza come i rivestimenti ottenuti da soluzione acquosa di precursore, indipendentemente dalla tecnica di deposizione utilizzata (spin coating o dip coating) diano origine a film disomogenei e scarsamente riproducibili, pertanto non idonei per l’applicazione nelle DSSC. Viceversa, i BLs ottenuti via spin coating dalla soluzione alcolica di TiCl4 sono risultati riproducibili, omogenei, e uniformemente distribuiti sulla superficie di FTO. Infine, l’analisi EIS ha in particolare evidenziato un effettivo aumento della resistenza al trasferimento di carica tra elettrodo FTO ed elettrolita in presenza di questi BLs, fenomeno generalmente associato ad un efficace blocking effect

Optimized TiO2 blocking layer for dye-sensitized solar cells

A thin compact layer of TiO2 deposited on the conductive transparent substrate of a dye-sensitized solar cell photoanode, (blocking layer, BL) can enhance the performances of the entire device. In this paper, an optimized spin coating process using an alcoholic TiCl4 solution was developed and correlated to the final properties of the layer. The physicochemical characteristics of the precursor solution and the spin coating parameters were optimised to obtain a uniform layer. XRD, FE-SEM, UV–Vis spectroscopy, AFM, cyclic voltammetry and electrochemical impedance spectroscopy were used to evaluate the influence of the number of deposition cycles on the TiO2 layer. The results were compared with those obtained using a conventional dip coating technique, showing that the newly developed spin coating process produces blocking layers with superior properties. Finally, analyses of the photovoltaic performances of the complete cell confirmed that an optimized blocking layer can lead to an improvement of the solar conversion efficiency of about 84%

Nano-to-macroporous TiO 2 (anatase) by cold sintering process

Cold Sintering Process (CSP) was applied on commercial nanopowders to produce nanostructured TiO 2 anatase with nano-to-macro porosity. Nanoporous TiO 2 based materials were obtained by applying CSP at 150 °C and pressures up to 500 MPa on three TiO 2 nanopowders with different specific surface area (s.s.a. = 50, 90 and 370 m 2 /g), using water as transient aqueous environment. Although TiO 2 is insoluble in water, a density of 68% and s.s.a. = 117 m 2 /g were achieved from the powder with the highest specific surface area. A post annealing process at 500 °C increased the density up to 73% with a s.s.a. = 59 m 2 /g, and the crystallites dimensions passed from 110 Å in the powder to 130 Å in CSP material and 172 Å after post annealing. Finally, macroporosity was produced by using thermoplastic polymer beads as sacrificial templates within TiO 2 nanopowder during CSP, followed by a debonding at 500 °C