Most organic dyes synthesized for dye-sensitized solar cells (DSC) use a single linker group to bind to the metal oxide photo-anode. Here we describe the synthesis and testing of two new triphenylamine dyes containing either two carboxylic acids 5-[2-(4-diphenylamino-phenyl)-vinyl]-isophthalic acid (10) or two cyanoacrylic acids (2Z, 2′Z)-3, 3′-(5-((E)-4-(diphenylamino) styryl)-1, 3-phenylene) bis (2-cyanoacrylic acid) (8) as linker groups. Full characterization data are reported for these dyes and their synthetic intermediates. DSC devices have been prepared from these new dyes either by passive or fast dyeing and the dyes have also been tested in co-sensitized DSC devices leading to a PCE (η = 5.4%) for the double cyanoacrylate linker dye (8) co-sensitized with D149. The dye:TiO₂ surface interactions and dye excitations are interpreted using three modelling methods: density functional theory (at 0 K); molecular dynamics (at 298 K); time dependent density functional theory. The modelling results show the preferred orientation of both dyes on an anatase (1 0 1) TiO₂ surface to be horizontal, and both the simulated and experimental absorption spectra of the dye molecules indicate a red shifted band for (8) compared to (10). This is in line with broader light harvesting and J_sc for (8) compared to (10).

Whilst the highest power conversion efficiency (PCE) perovskite solar cell (PSC) devices that have reported to date have been fabricated by high temperature sintering (>500 °C) of mesoporous metal oxide scaffolds, lower temperature processing is desirable for increasing the range of substrates available and also decrease the energy requirements during device manufacture. In this work, titanium dioxide (TiO₂) mesoporous scaffolds have been compared with metal oxide oxidation catalysts: cerium dioxide (CeO₂) and manganese dioxide (MnO₂). For MnO₂, to the best of our knowledge, this is the first time a low energy band gap metal oxide has been used as a scaffold in the PSC devices. Thermal gravimetric analysis (TGA) shows that organic binder removal is completed at temperatures of 350 °C and 275 °C for CeO₂ and MnO₂, respectively. By comparison, the binder removal from TiO₂ pastes requires temperatures >500 °C. CH₃NH₃PbBr₃ PSC devices that were fabricated while using MnO₂ pastes sintered at 550 °C show slightly improved PCE (η = 3.9%) versus mesoporous TiO₂ devices (η = 3.8%) as a result of increased open circuit voltage (V_oc). However, the resultant PSC devices showed no efficiency despite apparently complete binder removal during lower temperature (325 °C) sintering using CeO₂ or MnO₂ pastes.

This study describes the utilization of near edge X‐ray absorption fine structure (NEXAFS) to investigate the hole transporting material (HTM) 2,2ʹ,7,7ʹ‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐ 9,9ʹ‐spirobifluorene (Spiro‐OMeTAD) and its most common dopants, lithium bis‐(trifluoromethylsulfonyl) imide (LiTFSI), 4‐tert‐butylpiridine (tBP), and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ). By changing the angle of the sample with respect to the beam, the orientation of the molecules on the surface can be observed. The data suggest that it is difficult to determine any orientational preference for Spiro‐OMeTAD deposited on a surface due to the 3D propeller‐like geometry of this molecule. Both doped and undoped samples show thermal stability beyond the glass transition temperature of the molecules. Significant changes to the Spiro‐OMeTAD spectra are observed with the addition of the dopants, in particular the C K‐edge. Differences are also observed in the valence band spectra when dopants are added. It is also demonstrated how the doping combination of LiFTSI with tBP and, F4‐TCNQ act as p‐type dopants by altering the position of the HOMO levels. The F4‐TCNQ induces a larger change in the HOMO levels when compared to the LiTFSI and tBP. These results are important to increase the understanding of Spiro‐OMeTAD and the effect dopants have on this material for next generation solar cells.

We report the synthesis of organometal halide perovskites by milling CH₃NH₃I and PbI₂ directly with an Al₂O₃ scaffold to create hybrid Al₂O₃-CH₃NH₃PbI₃ perovskites, without the use of organic capping ligands that otherwise limit the growth of the material in the three dimensions. Not only does this improve the ambient stability of perovskites in air (100 min versus 5 min for dimethylformamide (DMF)-processed material), the method also uses much fewer toxic solvents (terpineol versus dimethylformamide). This has been achieved by solid-state reaction of the perovskite precursors to produce larger perovskite nanoparticles. The resulting hybrid perovskite–alumina particles effectively improve the hydrophobicity of the perovskite phase whilst the increased thermal mass of the Al₂O₃ increases the thermal stability of the organic cation. Raman data show the incorporation of Al₂O₃ shifts the perovskite spectrum, suggesting the formation of a hybrid 3D mesoporous stack. Laser-induced current mapping (LBIC) and superoxide generation measurements, coupled to thermogravimetric analysis, show that these hybrid perovskites demonstrate slightly improved oxygen and thermal stability, whilst ultra-fast X-ray diffraction studies using synchrotron radiation show substantial (20×) increase in humidity stability. Overall, these data show considerably improved ambient stability of the hybrid perovskites compared to the solution-processed material.

Halloysite nanotubes (HNTs) can be used as stable support materials for gold and silver nanoparticles (Au/Ag-NPs) without distinction given to the morphology of the tubular HNTs, i.e. polygonal prismatic or cylindrical. The present study aimed to use direct visualization techniques to observe and compare the adsorption sites and behaviors of the two tubular morphologies with both Au- and Ag-NPs. Au/Ag-NPs were surface engineered with methyl-, carboxylate-, or phosphonate-terminated linker groups and reacted with halloysite nanotubes with two different morphologies, forming composite materials HNTs@Au-NPs and HNTs@Ag-NPs. Transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy were used to investigate the sorption reactions. Au-NPs disperse well into individual particles while the Ag-NPs show a tendency to agglomerate, making them less suitable probes for adsorption onto HNTs. The results also indicate that polygonal prismatic HNTs show greater sorption than cylindrical HNTs, where NPs were detected on the external walls of the nanotubes. This sorption is suggested to occur at the steps and edges of the particles, at the termini of the tubes, and in the hollow inner lumina. For the varying linker groups, carboxylate- and phosphonate-derivatized Au-NPs show similar sorption behavior on HNTs, while no surface sorption was observed for the methyl-terminated linkers. This justifies the hypothesis that the carboxylate and phosphonate moieties chemisorb to the hydroxyls of the aluminol groups at the edge sites, steps, and lumina of polygonal prismatic HNTs, identifying these as key anion bonding sites on HNTs, while non-ionic, methyl-terminated Au-NPs do not adsorb. Identification of these specific anionic bonding sites on two different HNT morphologies highlights the importance of HNT morphology in their use as stable support materials in applications such as catalysis, anion sorption, and drug delivery, amongst others.

This work details the synthesis of several bespoke materials to derivatise the surface of titania (TiO2) in order to obtain greater understanding of the sensitisation process in dye-sensitised solar cells and how this can influence device performance. In particular, this work has combined synthetic (dye synthesis), experimental (AR-XPS) and theoretical experiments (computer modelling) in order to investigate the self-assembly of organic dyes onto titania surfaces in dye-sensitised solar cell (DSC) devices. To test the dyes and other materials in this thesis both liquid and solid-state dye-sensitised solar devices were made. The standard liquid DSC device utilised TEC 8 glass (3 cm x 1.5 cm) for both the photo and counter electrode. On the photoelectrode a mesoporous TiO2 layer is deposited and sensitised with N719 dye. The counter electrode is coated with a thin layer of platinum PT-1 paste (GreatCellsolar). The two electrodes are bound together by melting 20 µm surlyn and a standard triiodide electrolyte is injected to the cell and the cell sealed. With this method we have managed to achieve 6.5 % using N719 dye. Solid-state dye-sensitised solar cell (ssDSC) devices we made using TEC 7 glass (2.8 cm2). Onto the glass a compact layer of TiO2 has been deposited via spray coating, thereafter a thin layer of mesoporous TiO2 is spin coated and sensitised overnight in a dye bath. After which, a thin layer of Spiro-OMeTAD is deposited via spin coating, after which Au is deposited under vacuum. With this method 4.0 % has been achieved using LEG4 dye. This thesis reports the first synthesis of ten novel half-squaraine (HfSQ) dyes, five containing a benzothiazole backbone and another five identical dyes with a dimethyl-derivatised carbon. These new dyes have been purified using various preparative (column and flash) chromatography. Once purified the dyes have been analysed using nuclear magnetic resonance (NMR), attenuated total reflectance infra-red (ATR-IR), ultraviolet-visible spectroscopy (UV-Vis) and mass spectrometry. These novel dye materials have then been used to derivatise the titania surface in DSC devices. The dyes have been designed so that a sulphur heteroatom can be used as an atomic probe of the dye-TiO2 interface in order to study surface coverage, dye orientation and dye-electrolyte interactions in dye-sensitized solar cell (DSC) devices. X-ray single crystal structural and opto-electronic data have also been correlated with density functional theory/computer modelling to better understand the widely reported but poorly understood influence of S heteroatoms on dye photochemistry, DSC device performance and lifetime. To the best of our knowledge, for the first time, the S heteroatom in the dyes has been used as a molecular probe along with angle-resolved X-ray photoelectron (ARXPS) data to study how the dye-TiO2 orientation varies with the position of the carboxylate linker on the dye periphery. In further work, a one-step synthesis has been used to link two dye-sensitized solar cell (DSC) dyes together through an anhydride moiety. The dyes we have attempted to combine are triphenylamine dye “Yellow dye” to another Yellow dye and squaraine dye SQ2 to other moieties such as Chenodeoxycholic acid and stearic acid. To the best of our knowledge, this is also the first time this has been attempted in DSC dyes. The resulting anhydride precursor has been used to self-assemble the two dyes onto TiO2 surfaces in a controlled manner. Hence, this represents a brand-new method of sensitising two dyes, in a single sorption process; providing a new method to control dye-sorption kinetics, dye loading and surface organisation. When two dyes are introduced to the titania surface at the same time it is possible to control the positions of the two dyes without the need of bulky co-sorbents (e.g. CDCA) to supress dye aggregation. This one-step synthesis method was applied to combine two different dye materials into one anhydride moiety. Attempts have been made to combine SQ2 dye to co-adsorbent CDCA and SQ2 dye to stearic acid. The photo-physical properties of the anhydride and its precursor dyes have been studied (via UV-Vis, ATR-IR NMR and tested in ssDSC devices) and compared highlighting the potential of this new method for co-sensitisation.