Near-Infrared Active Lead Chalcogenide Quantum Dots: Preparation, Post-Synthesis Ligand Exchange, and lications in Solar Cells

Quantum dots (QDs) of lead chalcogenides (e.g. PbS, PbSe, and PbTe) are attractive near‐infrared (NIR) active materials that show great potential in a wide range of applications, such as, photovoltaics (PV), optoelectronics, sensors, and bio‐electronics. The surface ligand plays an essential role in the production of QDs, post‐synthesis modification, and their integration to practical applications. Therefore, it is critically important that the influence of surface ligands on the synthesis and properties of QDs is well understood for their applications in various devices. In this Review we elaborate the application of colloidal synthesis techniques for the preparation of lead chalcogenide based QDs. We specifically focus on the influence of surface ligands on the synthesis of QDs and their solution‐phase ligand exchange. Given the importance of lead chalcogenide QDs as potential light harvesters, we also pay particular attention to the current progress of these QDs in photovoltaic applications.This work was financially supported by the Australian Research Council Discovery Projects DP110102877 and DP140104062, DP150101939 and Discovery Early Career Award DE16010056

Sulfur-doped graphene with iron pyrite (FeS 2 ) as an efficient and stable electrocatalyst for the iodine reduction reaction in dye-sensitized solar cells

As an alternative to platinum (Pt), hybrid electrocatalysts based on sulfur-doped graphene with FeS2 microspheres (SGN-FeS2) were used as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). Benefiting from the high conductivity of SGN and excellent electrocatalytic activity of the FeS2, the bifunctional hybrid electrocatalyst-based device displays a power conversion efficiency (PCE) of 8.1%, which is comparable to that (8.3%) of traditional Pt CE-based DSSC, while also exhibiting excellent stability in ambient conditions. These characteristics, in addition to its low-cost and facile preparation, make the SGN–FeS2 hybrid an ideal CE material for DSSCs

Characterization of porous membranes via porometry

Gas-liquid porometry is the most common method for characterizing microfiltration membranes. This thesis provides a new approach to analyze data from gas-liquid porometry. Here, we combine porometry results with porosity measurement to determine the transport through the membranes. The pore size distribution and porosity measurements were performed for a range of membranes from straight through to asymmetric membranes. There was high discrepancy between the measured pore size and manufacturer data. Our study also examined the effect of asymmetry in pore size distribution of the membranes as compared to symmetric membranes. The asymmetric membranes were found to give smaller pore size compared to symmetric membranes. The orientation of asymmetric membranes provided different results for the mean pore size. A comparison between the classical approach and modified approach to analyze the data and thus in the estimation of transport parameter was made. Better correlation of measured and estimated transport parameter was found for modified approach as compared to classical approach. In addition modified approach determines the tortuosity for each pore size range during the estimation of transport parameters. The average tortuosity of the membranes under study varied from 0.707 to 6.48 with larger nominal pore membranes having higher values compared to smaller ones. This research also studied the transport of particles through the symmetric membranes. Theoretical model based on sieving was examined. The actual rejection increased for more tortuous membranes in comparison to theoretical rejection prediction with the difference being greater for the highest tortuosity. With this study, we hope to further elucidate the characterization of membranes via porometry and hope to provide useful information regarding the development and end use of these membranes

Lead sulfide quantum dots and their application for solar cells

Quantum dot sensitized solar cells (QDSSCs) are interesting third generation solar cells that have potential to address the current energy related issues due to their low manufacturing cost, ease of fabrication as well as good performance. Quantum dots (QDs) offer several advantages such as size tunable band gaps across a wide range of energy levels, high molar extinction coefficients and enhanced stability. Among them, colloidal near infrared (NIR) QDs of lead sulfide (PbS) are attractive due to their narrow bulk bandgap, large exciton Bohr radii and the possibility of multiple exciton generation. Utilizing these QDs in solar cells with extendable IR absorption is promising. However, the progress of PbS QDSSCs is lacking due to the limited understanding regarding the synthesis and surface chemistry of QDs. The development of QDSSCs is also hindered by lack of proper counter electrode materials for the reduction of electrolytes. Hence, further developments in the synthesis and application of new materials for QDSSCs are necessary. This PhD project focuses on the materials development for PbS QDSSCs such as PbS QD synthesis, surface ligand exchange of PbS QDs, and the development of new counter electrode materials. The following researches are included in this thesis: 1) A robust method to synthesize monodisperse lead sulfide (PbS) QDs is presented. PbS QDs with different sizes is produced by stepwise heating of the preformed seed QDs in the presence of excess oleic acid. A combination of "living" monomer addition and Ostwald ripening is identified as the mechanism for such QD growth processes. 2) The detailed synthesis mechanism of PbS QDs is investigated. Here, the various synthesis parameters influencing the nucleation and growth of PbS QDs are elucidated. In addition, the detailed understanding of the synthesis mechanism is used to guide the synthesis of PbS QDs at ultra-small regime. 3) A versatile solution phase ligand exchange of PbS QDs in the presence of Pb-thiolate as the exchanging ligands is presented. The ligand exchange procedure better preserves the optical properties of PbS QDs and is applicable to a number of ligand/solvent systems. 4) The implementation of PbS QDs in QDSSCs is presented. The treatment of PbS QD photoelectrodes with cadmium salts is necessary to maintain the stability of PbS QDs in polysulfide based electrolytes. In addition, the number of cycles of CdS and ZnS treatment is optimized to achieve a photoconversion efficiency of 1.77 %. 5) Finally, N-doped CNₓ/CNT hetero-electrocatalyst materials using polydopamine is synthesized, which are explored as counter electrode materials for dye-sensitized solar cell (DSSC). These CNₓ/CNTs material show excellent electrocatalytic activities towards the reduction of tri-iodide electrolytes with the optimized solar devices using CNₓ/CNTs showing comparable performance (7.3 %) to reference Pt based devices (7.1 %).Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2016

Nahinfrarotaktive Bleichalkogenid‐Quantenpunkte: Herstellung, postsynthetischer Ligandenaustausch und Anwendungen in Solarzellen

Quantenpunkte (QDs) von Bleichalkogeniden (z. B. PbS, PbSe und PbTe) sind nahinfrarotaktive Materialien, die großes Potenzial für einen breiten Bereich von Anwendungen wie Photovoltaik, Optoelektronik, Sensorik und Bioelektronik zeigen. Oberflächenliganden spielen eine wesentliche Rolle bei der Herstellung und postsynthetischen Modifizierung von QDs sowie bei deren Einsatz in Anwendungen. Daher ist ein gutes Verständnis des Einflusses von Oberflächenliganden auf die Synthese und Eigenschaften von QDs für deren Anwendungen in verschiedenen Bauelementen unerlässlich. Der vorliegende Aufsatz beschäftigt sich mit der Anwendung kolloidaler Synthesetechniken zur Herstellung von bleichalkogenidbasierten QDs. Der Schwerpunkt liegt auf dem Einfluss von Oberflächenliganden auf die QD‐Synthese sowie dem Ligandenaustausch in Lösung. Angesichts der Bedeutung von Bleichalkogenid‐QDs als möglichen Lichtsammlern richten wir unsere Aufmerksamkeit besonders auf die aktuellen Fortschritte von PV‐Anwendungen mit diesen QDs

Back Cover: Solar RRL 3-4∕2017

Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. This is the back cover of Solar RRL 3-4∕2017 with an image relating to the article Sulfur-Doped Graphene with Iron Pyrite (FeS 2 ) as an Efficient and Stable Electrocatalyst for the Iodine Reduction Reaction in Dye-Sensitized Solar Cells (https://dspace.lboro.ac.uk/2134/24841)Dye-sensitized solar cells (DSSCs) were first reported almost thirty years ago and considerable efforts have gone into improving every component in that time. Despite all these efforts, the improvements from the early designs have been marginal and there are still considerable issues to overcome. One such issue is the use of platinum (Pt) as the counter electrode due to its expense and catalytic properties. Here, Batmunkh et al. (Article No. 1700011) used hybrid electrocatalysts based on sulfur-doped graphene with FeS2 microspheres (SGN-FeS2) as a counter electrode (CE) in DSSCs, instead of Pt. Because of the high conductivity of SGN and excellent electrocatalytic activity of the FeS2, the bifunctional hybrid electrocatalyst based device displays a power conversion effi ciency (PCE) comparable to that of traditional Pt CE based DSSC, while also exhibiting excellent stability in ambient conditions. These characteristics, in addition to the fact that the new hybrid is relatively cheap and easy to prepare, mean the SGN-FeS2 hybrid is an ideal CE material for DSSCs

Back cover: Solar RRL 3-4∕2017

Dye-sensitized solar cells (DSSCs) were first reported almost thirty years ago and considerable efforts have gone into improving every component in that time. Despite all these efforts, the improvements from the early designs have been marginal and there are still considerable issues to overcome. One such issue is the use of platinum (Pt) as the counter electrode due to its expense and catalytic properties. Here, Batmunkh et al. (Article No. 1700011) used hybrid electrocatalysts based on sulfur-doped graphene with FeS2 microspheres (SGN-FeS2) as a counter electrode (CE) in DSSCs, instead of Pt. Because of the high conductivity of SGN and excellent electrocatalytic activity of the FeS2, the bifunctional hybrid electrocatalyst based device displays a power conversion effi ciency (PCE) comparable to that of traditional Pt CE based DSSC, while also exhibiting excellent stability in ambient conditions. These characteristics, in addition to the fact that the new hybrid is relatively cheap and easy to prepare, mean the SGN-FeS2 hybrid is an ideal CE material for DSSCs

Electrocatalytic activity of a 2D phosphorene-based heteroelectrocatalyst for photoelectrochemical cells

Research into efficient synthesis, fundamental properties, and potential applications of phosphorene is currently the subject of intense investigation. Herein, solution-processed phosphorene or few-layer black phosphorus (FL-BP) sheets are prepared using a microwave exfoliation method and used in photoelectrochemical cells. Based on experimental and theoretical (DFT) studies, the FL-BP sheets are found to act as catalytically active sites and show excellent electrocatalytic activity for triiodide reduction in dye-sensitized solar cells. Importantly, the device fabricated based on the newly designed cobalt sulfide (CoS ) decorated nitrogen and sulfur co-doped carbon nanotube heteroelectrocatalyst coated with FL-BP (FL-BP@N,S-doped CNTs-CoS ) displayed an impressive photovoltaic efficiency of 8.31 %, outperforming expensive platinum based cells. This work paves the way for using phosphorene-based electrocatalysts for next-generation energy-storage systems

One-step synthesis of porous transparent conductive oxides by hierarchical self-assembly of aluminum-doped ZnO nanoparticles

Transparent conductive oxides (TCOs) are highly desirable for numerous applications ranging from photovoltaics to light-emitting diodes and photoelectrochemical devices. Despite progress, it remains challenging to fabricate porous TCOs (pTCOs) that may provide, for instance, a hierarchical nanostructured morphology for the separation of photoexcited hole/electron couples. Here, we present a facile process for the fabrication of porous architectures of aluminum-doped zinc oxide (AZO), a low-cost and earth-abundant transparent conductive oxide. Three-dimensional nanostructured films of AZO with tunable porosities from 10 to 98% were rapidly self-assembled from flame-made nanoparticle aerosols. Successful Al doping was confirmed by X-ray photoemission spectroscopy, high-resolution transmission electron microscopy, elemental mapping, X-ray diffraction, and Fourier transform infrared spectroscopy. An optimal Al-doping level of 1% was found to induce the highest material conductivity, while a higher amount led to partial segregation and formation of aluminum oxide domains. A controllable semiconducting to conducting behavior with a resistivity change of more than 4 orders of magnitudes from about 3 × 102 to 9.4 × 106 ω cm was observed by increasing the AZO film porosity from 10 to 98%. While the denser AZO morphologies may find immediate application as transparent electrodes, we demonstrate that the ultraporous semiconducting layers have potential as a light-driven gas sensor, showing a high response of 1.92-1 ppm of ethanol at room temperature. We believe that these tunable porous transparent conductive oxides and their scalable fabrication method may provide a highly performing material for future optoelectronic devices.</p