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)

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

Multi-phase (Zr,Ti,Cr)B2solid solutions: Preparation, multi-scale microstructure, and local properties

Multi-phase ceramics based on ZrB2, TiB2 and doped with CrB2 and SiC were prepared by powder metallurgy and hot pressing to explore the possibility of obtaining multi-scale microstructures by super-saturation of complex (Zr,Ti,Cr)B2 solid solutions. Core–shell structures formed in TiB2 grains, whereas ZrB2 appeared to form a homogeneous solid solution with the other metals. Precipitation of nano-inclusions within both micron-sized borides was assessed by transmission electron microscopy and thermodynamics elucidated the preferential formation of boride inclusions due to the specific sintering atmosphere. In addition, atomic size factors explicated the precipitation of CrB2 nano-particles into ZrB2-rich grains and of ZrB2 nano-particles into TiB2-rich grains. The hardness of the constituent phases measured by nanoindentation ranged from 36 to 43 GPa

Whose Ocean? Exploring multidisciplinary perspectives towards ocean sustainability and implications for the un(der)represented

The ocean's significance encompasses crucial ecosystem services including climate regulation, oxygen production and food supply. The ocean is also a major player in the global economy. However, human activities continue to harm the ocean, jeopardising these vital functions. In July 2022, the United Nations Ocean Conference adopted a political declaration entitled "Our ocean, our future, our responsibility," emphasising the need for sustainable ocean management and protection. However, an important initial question arises: who are the “Our”? or, rephrased “Whose ocean” is it? This study presents first answers to this question, based on interviews with ocean professionals from diverse backgrounds. Their responses showcased the complexity of the issue, with differing opinions on ocean “ownership” and “control”. Despite the diversity of perspectives, a shared emphasis emerged: shifting from profit-driven decision-making to prioritising marine ecosystem health. Proposed approaches to build a sustainable relationship between people and the ocean include promoting ocean literacy and marine research and ensuring global accountability. These voices offered valuable insights towards ocean sustainability, guiding future academic, educational and policy-making efforts

3D Engineered Photoanodes for Dye-Sensitized Solar Cells

Questa tesi di dottorato è stata incentrata principalmente su due aspetti: (i) produzione di energia elettrica dal sole mediante l’uso di celle solari a coloranti organici (DSCs) e (ii) produzione dei loro fotoanodi mediante processi non convenzionali e rispettosi dell'ambiente come il wet-powder spray (WPS) e le tecniche additive come il robocasting (micro-estrusione) e il material jetting (basato sulla stampa a getto d'inchiostro). Queste tecniche sono state utilizzate per l’ingegnerizzazione tridimensionale di fotoanodi per DSCs, costituiti da uno strato mesoporoso realizzato via WPS e da strutture tridimensionali ordinate (micro-pillars) che mirano ad aumentare le prestazioni del dispositivo. Grazie alle sue eccellenti prestazioni, il biossido di titanio(TiO2) è il materiale di riferimento per queste applicazioni; in esse è tradizionalmente utilizzato in forma di film nanocristallino prodotto via screen-printing. Il lavoro di tesi è stato rivolto in primo luogo alla sostituzione di quest’ultimo processo utilizzando la tecnica WPS. Inizialmente è stata studiata un appropriata sospensione per la tecnica spray, derivante dalla modifica di un prodotto commerciale; in particolare, la sua distribuzione delle dimensioni delle particelle ed il potenziale ζ sono stati analizzati per valutarne la stabilità. Quindi, le interazioni sospensione-substrato sono state quantificate attraverso misure di angolo di contatto. Infine, la relazione tra i parametri del processo di deposizione ed i film ottenuti è stata definita in termini di trasparenza e microstruttura del fotoanodo; il film più adatto è stato quindi sensibilizzato e utilizzato per produrre un prototipo DSC completo. Successivamente, micro-pillars a base di TiO2 sono stati sviluppati mediante micro-estrusione. L'obiettivo è stato raggiunto formulando un inchiostro ad alto contenuto di solido avente le giuste caratteristiche reologiche; queste ultime sono state studiate al variare della quantità e della composizione del sistema legante. Inoltre, l'ottimizzazione della deposizione è stata effettuata lavorando sui principali parametri di processo come il flusso di materiale, la velocità di deposizione, ecc. Le strutture prodotte, costruite sul film mesoporoso ottimizzato, sono state caratterizzate in termini di aspect ratio, microstruttura ed infine testate in un prototipo DSC. Un miglioramento delle prestazioni è stato effettivamente registrato a causa di un progressivo aumento sia della densità di corrente che della tensione a circuito aperto (Voc) delle celle. La sezione conclusiva della tesi ha visto la formulazione e la deposizione di un inchiostro a base acquosa per la stampa a getto d'inchiostro. Quest'ultima è una tecnica digitale estremamente potente che è stata selezionata come metodo di deposizione adatto per creare strutture 3D ad alto aspect ratio che garantiscano migliori performance. La stabilità dell'inchiostro, la sua reologia e l'interazione con il substrato sono state studiate dettagliatamente. Alcune limitazioni introdotte dalla presenza di acqua come solvente hanno però portato a considerare un approccio completamente diverso basato su un solvente con ridotto impatto ambientale. In aggiunta sono stati applicati trattamenti di macinatura piuttosto energici al fine di aumentare efficacemente la stabilità dell'inchiostro e garantirne la stampabilità. I risultati preliminari sono stati positivi ed indicano che questo approccio alternativo può essere adeguato agli scopi desiderati.This PhD thesis was focused on two main fields of interest: (i) energy production by improved Dye-sensitized Solar Cells (DSCs) and (ii) the DSC photoanode production by using unconventional and environmental friendly processes like wet-powder spray (WPS) and additive manufacturing techniques such as robocasting (micro-extrusion) and material jetting (based on DoD inkjet printing). These techniques were used to develop 3D-engineered DSCs photoanodes constituted by a mesoporous sprayed layer and well-ordered three-dimensional structures (micro-pillars) aiming at increasing the device performance. Due to its superior performance, TiO2 is the reference material for DSC applications for which it is traditionally used in the form of flat nanocrystalline supported layer produced by screen-printing. This work was firstly directed at the substitution of the screen-printed layers by using WPS. Initially, a suitable spray suspension, derived from the modification of a commercial product, was investigated; in particular, particle size distribution and ζ potential were analyzed to evaluate its stability. Then, the suspension-substrate interactions were evaluated through contact angle measurements. Finally, the relationship between the deposition process parameters and the obtained films was defined in terms of transparency and microstructure; the most suitable film was then sensitized and used to produce a complete DSC prototype. Afterwards, coarse TiO2-based 3D micro-pillars were developed by using the robocasting technique. The goal was achieved through the formulation of a high-solid loaded ink that possessed proper rheological characteristics; the effects of the binder amount and composition were principally investigated. Moreover, the deposition optimization was carried out working on the main process parameters such as material flow, velocity, etc. The as-produced 3D structures, built on the optimized mesoporous sprayed film, were characterized in terms of aspect ratio, microstructure and finally tested in functioning DSCs prototypes. A performance improvement was recorded due to a progressive increase of both the current density and open circuit voltage (Voc) of the cells. The conclusive section of the thesis involved the formulation and deposition of an aqueous-based ink for inkjet printing. The latter is an extremely powerful digital technique that was selected as suitable deposition method to create high-aspect ratio 3D structures ensuring improved performance. The ink stability, rheology and interaction with the substrate were investigated. However, some limitations introduced by the presence of water as liquid carrier leaded to consider a completely different approach based on a solvent with reduced environmental impact. Heavy milling treatments were also applied to effectively increase the ink stability and ensure its printability. Preliminary positive results indicated that this alternative approach can be adequate to the purpose

Photoelectrochemical Hydrogen Production by Screen-Printed Copper Oxide Electrodes

In this work, copper oxides-based photocathodes for photoelectrochemical cells (PEC) were produced for the first time by screen printing. A total 7 × 10−3 g/m2 glycerine trioleate was found as optimum deflocculant amount to assure stable and homogeneous inks, based on CuO nano-powder. The inks were formulated considering different binder amounts and deposited producing films with homogenous thickness, microstructure, and roughness. The as-produced films were thermally treated to obtain Cu2O- and Cu2O/CuO-based electrodes. The increased porosity obtained by adding higher amounts of binder in the ink positively affected the electron transfer from the surface of the electrode to the electrolyte, thus increasing the corresponding photocurrent values. Moreover, the Cu2O/CuO system showed a higher charge carrier and photocurrent density than the Cu2O-based one. The mixed Cu2O/CuO films allowed the most significant hydrogen production, especially in slightly acid reaction conditions

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%

An Investigation on Gel-State Electrolytes for Solar Cells Sensitized with β-Substituted Porphyrinic Dyes

The presence of a liquid electrolyte in dye-sensitized solar cells (DSSCs) is known to limit the time stability of these devices due to leakage and evaporation phenomena. To overcome this issue, gel-state electrolytes may represent a good solution in order to maintain stability and good performances, albeit at lower costs. In the present work, two different kinds of gel-electrolytes, based on poly (methyl methacrylate) (PMMA) and nanoclay agents, were investigated in DSSC-devices sensitized using β-substituted Zn-porphyrins (namely ZnPC4 and ZnPC12) with enveloping alkoxy chains of different lengths, able to produce a coverage of the photoanode surface. The highest power conversion efficiency (PCE) values equal to 1.06 ± 0.04% and 1.55 ± 0.26% were obtained for ZnPC12 (with longer alkoxy chains) with PMMA- and nanoclay-based electrolytes respectively. The properties of the photoanode/electrolyte interface as well as the influence of the gelling agents on the final properties of the obtained devices were thoroughly characterized

Multi-Phase (Zr,Ti,Cr)B2 Solid Solutions: Preparation, Multi-Scale Microstructure, and Local Properties

Multi-phase ceramics based on ZrB2, TiB2 and doped with CrB2 and SiC were prepared by powder metallurgy and hot pressing to explore the possibility of obtaining multi-scale microstructures by super-saturation of complex (Zr,Ti,Cr)B2 solid solutions. Core–shell structures formed in TiB2 grains, whereas ZrB2 appeared to form a homogeneous solid solution with the other metals. Precipitation of nano-inclusions within both micron-sized borides was assessed by transmission electron microscopy and thermodynamics elucidated the preferential formation of boride inclusions due to the specific sintering atmosphere. In addition, atomic size factors explicated the precipitation of CrB2 nano-particles into ZrB2-rich grains and of ZrB2 nano-particles into TiB2-rich grains. The hardness of the constituent phases measured by nanoindentation ranged from 36 to 43 GPa