3,444 research outputs found
How structural factors influence the performance of copper(I) bis(diimine) based DSCs
No full textAbstract
This PhD thesis is based on the synthesis of new homoleptic copper(I) complexes and their applications in dye-sensitized-solar-cells (DSCs).
Chapter I: Is an evaluation of the anchoring ligands effect upon device performance containing ancillary ligands of 1st and 2nd generation hole transport triphenylamino-dendrons.
Chapter II: Describes the influence of six different substituents in the 6,6’-positions of the ancillary ligands on the device performance.
Chapter III: Is a short study of a more atom economic device assembling method, where the copper(I) complex is formed in situ on the TiO2 surface.
Chapter IV: Shows the influence of the dye conentration used during the dyeing process of the semi-conductor.
Chapter V: Is a study of how the enhanced photon absorption, achieved by extending the aromatic system of the ancillary ligand, affects the cell performance.
Chapter VI: Describes the use of different solvents during the dyeing process of the photoanode and their influence on DSC performance.
Chapter VII: Addresses issues concerning the TiO2 surface such as the aggregation of dye molecules and how the addition of co-adsorbants during the dyeing cycle may prohibit the formation of such aggregates.
Parts of this work have been published:
• B. Bozic-Weber, S. Y. Brauchli, E. C. Constable, S. O. Fürer, C. E. Housecroft and I. A. Wright, Phys. Chem. Chem. Phys., 2013, 13, 4500-4504.
• B. Bozic-Weber, S. Y. Brauchli, E. C. Constable, S. O. Fürer, C. E. Housecroft, F. J. Malzner, I. A.Wright and J. A. Zampese, Dalton Trans., 2013, 34, 12293-12308.
• S. Y. Brauchli, B. Bozic-Weber, E. C. Constable, N. Hostettler, C. E. Housecroft and J. A. Zampese, RSC Advances, 2014, 4, 34801-34815.
• S. Y. Brauchli, F. J. Malzner, E. C. Constable and C. E. Housecroft, RSC Advances, 2014, 4, 62728-62736.
• S. Y. Brauchli, E. C. Constable, C. E. Housecroft, Dyes and Pigments, 2015, 113, 447-450.
Summary
Within this study, 18 ligands (L1.1-L3.6) and their homoleptic copper(I) complexes [Cu(L1.1-L3.6)2][PF6] have been synthesized. They were fully characterized by 1H and 13C NMR, mass spectrometry, solution absorption spectrometry, melting point, elemental analysis and infrared spectrometry. Furthermore, all homoleptic Cu(I) complexes were electrochemically analysed by cyclic voltammetry and square-wave voltammetry.
By increasing the aromatic system in the ligands (Scheme 26), the light harvesting was effectively enhanced (e.g. going from L1.1 -> L2.1 -> L3.1). An increase in absorption by extending the aryl system was achieved in the homoleptic Cu(I) complexes, with an extinction of about twice that the free ligands.
Scheme 26: Representative ligands to illustrate the extension of the aryl system.
Furthermore, the substituents in the 6,6´-positions on the bipyridine were varied within each ligand generation (Scheme 26). All complexes were incorporated in DSCs.
In Chapter I, the first focus is on the influence of the anchoring ligand on the performance of a DSC. For this study, two representative capping ligands were introduced by treating an anchoring ligand covered photoanode with complexes [Cu(L2.1)2][PF6] and [Cu(L3.1)2][PF6]. By using these two example dyes, a set of four anchoring ligands was screened to identify the one that yielded the best conversion efficiency in the device.
Scheme 27: Set of anchoring ligands with phosphonic and carboxylic acids as anchoring groups.
It turned out that devices with anchoring ligands decorated with phosphonic acids (ALP and ALP1) generally achieve higher efficiencies than those with carboxylic acids (ALC and ALC1). Additionally, the influence of the extended aryl system on the ancillary ligands (L2.1 vs. L3.1) was examined in this set. Indeed, higher conversion efficiencies were obtained from devices incorporating the more conjugated ancillary ligand L3.1 compared to L2.1.
Scheme 28: Ancillary ligands L1.1-L1.6 examined in Chapter II.
In Chapter II, the influence of 6 different substituents in the 6,6’-positions of the bipyridine ancillary ligands (Scheme 28) in combination with anchoring ligands ALP and ALP1 was examined. It was found that DSCs incorporating anchoring ligands ALP1 reach much higher conversion efficiencies than those with ALP. Ancillary ligands L1.3 and L1.5 reached remarkably higher efficiencies, which was attributed to the reduced charge recombination rate.
Scheme 29: Two approaches to introduce a copper metal ion and an ancillary ligand on a TiO2 coated photoanode.
In Chapter III, a new strategy for incorporating heteroleptic complexes on the TiO2 surface was tested and compared with the state of the art methodology. The state of the art method works as followed. After an anchoring ligand has been adsorbed on a semiconductor surface, the photoanode is immersed in a solution of homoleptic Cu(I) complex. Due to the labile nature of Cu(I) complexes, a ligand exchange with the previously anchored ligand occurs, leaving with heteroleptic copper dye on the surface.
In the second methodology it becomes needless to prepare the homoleptic Cu(I) complex beforehand. By using the new method (stepwise methodology), an additional step during the dyeing process is required. Nevertheless, it is more economic than the conventional process. After the anchoring ligand is bound to the TiO2 surface, the anode is immersed in a solution of [Cu(MeCN)4][PF6]. At this stage the copper(I) binds to the anchoring ligand and it is assumed that a heteroleptic complex with two coordinating acetonitrile molecules is formed. In the last step, the anode with the intermediate heteroleptic complex on the surface is immersed in a solution of pure ligand, which replaces the acetonitrile molecules due to the chelating effect. The main outcome of this survey was that devices prepared by the state of the art method achieve a higher final conversion efficiency than those prepared from the stepwise assembly. However, using this new method, devices exhibited a higher initial efficiency than those prepared from the old method.
In Chapter IV, devices were prepared from four different concentrations of dye solutions ([Cu(L2.1)2][PF6] in CH2Cl2 at 2.0, 1.0, 0.5 and 0.1 mM). Their initial efficiencies and their development over several days were compared. The results showed that devices prepared from the least concentrated dye solutions reached their maximum efficiency immediately after assembling the cells and this efficiency was maintained over the whole measuring period. Additionally, it was found that DSCs prepared from the more dilute dye solutions reach a higher maximum conversion efficiency than those prepared from concentrated dye solutions.
In Chapter V, the focus was on the change in device performance by extending the aromatic systems of the ancillary ligands. Ligands L2.1-2.6 and L3.1-3.6 were introduced into the DSCs by applying the state of the art ligand exchange method using complexes [Cu(L2.1-2.6)2][PF6] and [Cu(L3.1-3.6)2][PF6]. Except for ancillary ligand L3.1, no increase in efficiency was recorded by extending the aromatic system and increasing the absorption. Although the solid state UV-vis absorption spectra of the photoanodes showed an increase in absorption intensity, no gain in Jsc was achieved.
Chapter VI addresses the use of two different solvents during the dyeing process of the photoanodes. The cells were prepared either from acetone or CH2Cl2 dye solutions of [Cu(L2.1-2.6)2][PF6] and [Cu(L3.1-3.6)2][PF6]. By measuring solid state absorption spectra of dye loaded photoanodes, it turned out that upon using acetone during the dyeing process a severe increase of dye adsorption on the TiO2 surface was achieved. Moreover, by using acetone dye solutions the devices incorporating the more conjugated ancillary ligands (L3.1-3.6) reach generally higher efficiencies than cells with ligands L2.1-L2.6. DSCs prepared from acetone dye solutions containing capping ligands L3.1-3.6 also exhibit higher efficiencies than those with the same ancillary ligands prepared from CH2Cl2 solutions. For devices with capping ligands L2.1-2.6, no clear trend could be discovered by comparing cells prepared from acetone and CH2Cl2 dye solutions.
In Chapter VII, the main attempt was to minimize the dye aggregation on the surface by adding a co-adsorbant (chenodeoxycholic acid) to the dye solution during the dyeing process of the photoanode. The homoleptic complexes [Cu(L3.1)2][PF6] and [Cu(L3.5)2][PF6] served as example dyes. Additionally, cells were prepared again from acetone and CH2Cl2 dye solutions. Interestingly, all devices prepared from CH2Cl2 in the presence of cheno showed a clear increase in efficiency compared to the control devices without co-adsorbant. Furthermore, the device with ancillary ligand L3.5 prepared from acetone dye solution with cheno showed a higher conversion efficiency than its control cell. The device with the capping ligand L3.1 obtained from an acetone dye solution with cheno did not show an increased performance.
Conclusion
It has been shown that by increasing the aromatic system of the ancillary ligand, a gain in absorption intensity and an increase in conversion efficiency was achieved under certain circumstances. The studies revealed the huge number of possible tuning sites of DSCs, such as structural properties of the dye, dye concentration and solvent used during the dyeing cycle, and aggregation issues concerning the molecular size of the dye. Nevertheless, this work showed that a dye that does not seem to yield a reasonable conversion efficiency at first might reveal its full potential after some time. Screening of dyes is quite delicate because it is simply impossible to know the optimal conditions for every dye and it is likely to miss a potentially good dye.
Outlook
For the future, one may want to think to test more solvents during the dyeing process of the photoanode in order to obtain even higher device performances. Additionally, it might be reasonable to add a co-adsorbant to all of the synthesized dyes during the dyeing process of the photoanode in order to reduce dye aggregation, reduce charge recombination and increase the efficiency. Furthermore, that it is also sensible to test new electrolytes in combination with these dyes in attempt to obtain, for example, a higher Voc
Constable Anthony
No full textConstable Anthony, who served in Woody Point in the early 1900’s. Standing in front of traditional picket fence. Date of photo unknown
Octyl-decorated Fréchet-type dendrons : a general motif for visualisation of static and dynamic behaviour using scanning tunnelling microscopy
No full textFirstly, a short overview on supramolecular chemistry including definitions, basic principles and examples taken from the literature of 2D and 3D self-assembly processes is given in Chapter 1. The introduction is completed by some general ideas of dendrimer chemistry. In the second Chapter the techniques used in this thesis are introduced with a special focus on scanning tunnelling microscopy (STM). Besides the mode of operation and the data processing, the historical background is briefly described. The following four Chapters present STM studies of monolayers formed by different types of compounds, all functionalised with Fréchet-type dendrons. Not only static features of monolayers such as conformational analysis of single molecules have been investigated, but also dynamic processes such as delayed conversion of a whole domain and conformational changes by protonation have been examined. The 2D properties of monolayers on a graphite surface have been compared with the X-ray data of 3D single crystals. For two compounds, the same molecular arrangement has been detected in monolayers on graphite and in single crystals. Together with organic molecules, the self-assembly of metal complexes possessing tpy ligands and organometallic species with platinum(II) bis(alkynyl) units has been examined. Not all of these metal complexes were stable under the scanning conditions used in STM. A synthetic programme leading to dendrimer-functionalised organic and organometallic compounds has been developed. Discussions of synthetic routes are given at the beginning of each Chapter. Chaptercompares X-ray diffraction methods with STM, the two main analysis tools used for investigation of self-organised assemblies in the solid state in this thesis. In the second part of Chapter 7, the results presented in the previous Chapters are discussed with some general reflections on the self-assembling properties of Fréchet-type dendrimers with pendant octyl groups. Additional to the studies of self-assembled monolayers, the formation of metallomacrocycles has been investigated using two novel homoditopic tpy ligands. This work is presented in Chapter 8. It was demonstrated that the ring-size depends on the metal used for the cyclisation. Furthermore, some of the macrocycles formed self-assembled monolayers on graphite, which have been examined using STM. One homoditopic ligand formed a molecular square by complexation with an iron(II) salt which was analysed using single crystal X-ray diffraction. This thesis has brought together the realms of chemical design with studies of the physical behaviour of the envisioned molecules on the surface. It has been demonstrated that Fréchet-type dendrimers with octyl end-groups are a general motif for visualisation of static and dynamic behaviour using STM
Constable, E J, NX19458
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/378449Surname: CONSTABLE
Given Name(s) or Initials: E J
Military Service Number or Last Known Location: NX19458
Missing, Wounded and Prisoner of War Enquiry Card Index Number: 1755192262
Item: [2016.0049.10743] "Constable, E J, NX19458
Constable, G A, QX9851
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/378450Surname: CONSTABLE
Given Name(s) or Initials: G A
Military Service Number or Last Known Location: QX9851
Missing, Wounded and Prisoner of War Enquiry Card Index Number: 34911192263
Item: [2016.0049.10744] "Constable, G A, QX9851
A marine electromagnetic survey to detect gas hydrate at Hydrate Ridge, Oregon
No full textGas hydrates are a potential energy resource and hazard for drilling and infrastructure, yet estimates of global volume vary by over three orders of magnitude. Hydrates are electrically resistive compared to water saturated sediment and so electromagnetic methods provide an additional tool to seismic surveys and drilling for determining hydrate saturations. A marine electromagnetic survey was carried out at Hydrate Ridge, Oregon, USA, with the aim of testing the use of controlled source electromagnetic (CSEM) and magnetotelluric (MT) methods to map gas hydrate and free gas below the gas hydrate stability zone. A 2-D CSEM inversion supports the scenario deduced from previous seismic and drilling results, which indicate two mechanisms of hydrate emplacement: a transport-dominated and reaction-dominated regime. A prominent resistive region of 2.5–4 ?m at a depth of about 130 mbsf, near the seismic bottom simulating reflector (BSR), suggests that 27 to 46 per cent of the bulk volume is filled with hydrate, depending on whether Archie's Law or the Hashin-Strikman bounds are used. This is representative of a reaction-dominated regime for hydrate emplacement, and where a significant low velocity zone exists based on a seismic tomography inversion, suggests large quantities of free gas below the BSR. Electrical resistivity logging while drilling (LWD) data show general agreement with the CSEM inversion model except for a CSEM-derived resistive region at seismic horizon A, known to transport free gas into the gas hydrate stability zone. Inversion of MT data collected simultaneously during the CSEM survey provides a complimentary low-resolution image of the shallow sediments and shows folding in the accretionary complex sediments similar to that imaged by a tomographic seismic velocity model
Constable, G W, 214408
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/378444Surname: CONSTABLE
Given Name(s) or Initials: G W
Military Service Number or Last Known Location: 214408
Missing, Wounded and Prisoner of War Enquiry Card Index Number: V-994192257
Item: [2016.0049.10738] "Constable, G W, 214408
Constable, R G, 2791005
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/378447Surname: CONSTABLE
Given Name(s) or Initials: R G
Military Service Number or Last Known Location: 2791005
Missing, Wounded and Prisoner of War Enquiry Card Index Number: SEA-4315192260
Item: [2016.0049.10741] "Constable, R G, 2791005
Constable, G A, 235125
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/378445Surname: CONSTABLE
Given Name(s) or Initials: G A
Military Service Number or Last Known Location: 235125
Missing, Wounded and Prisoner of War Enquiry Card Index Number: SEA-3010192258
Item: [2016.0049.10739] "Constable, G A, 235125
Electrical resistivity structure of the Valu Fa Ridge, Lau Basin, from marine controlled-source electromagnetic sounding
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