This report results from a contract tasking Swiss Federal Institute of Technology (EPFL) as follows: The Grantee will investigate and develop a new class of polymer-gel electrolytes for use in flexible dye-sensitized solar cells in order to boost power efficiencies above the 15% light to electrical conversion efficiency.

Photovoltaic technology has been realized as a suitable renewable power source for the fulfillment of increasing world energy consumption with least impact on the environment. Dye sensitized solar cells (DSSCs) is one such photovoltaic technology which has gained a great deal of attention due to the low manufacturing cost compared tothe conventional Si-based solar cell technologies. Fabrication of DSSCs on flexible substrates enables manufacturing solar cells using cost-effective and speedy roll-to-roll processing systems and also makes the device flexible and light-weight. However,polymer-based DSSCs set restrictions to their materials and fabrication processes. In this thesis, fabrication of DSSCs on flexible polymer substrates have been extensively studied concentrating on the factors related to the slurry preparation, deposition of films and processing of electrodes to improve the mechanical and photovoltaic properties of the device.Initially, mechanically-stable, well adhered TiO2 films based on nanocrystallineP-25 TiO2 slurries were fabricated on indium tin oxide (ITO) coated plastic substrates using ball milling as a part of the processing stage, without the need for binders or high temperature annealing. The strength of the TiO2 films was examined by a novel nanoscratch technique which was developed to assess inter-particle adhesion. Interfacial and photovoltaic properties of flexible dye sensitized solar cells with a ruthenium dye involving two tetra-butyl ammonium carboxylate groups (N-719) were studied. The maximum power conversion efficiency of 4.2% is obtained under illumination of100mWcm-2, for the electrodes fabricated using 20 hour milled slurry and shorter or longer milling times were found to be less optimal.During the second stage of this work, binder-free titania pastes with high viscosity were developed for the preparation of improved quality electrodes for dye sensitized solar cells on plastic substrates. Rheological behavior of ethanol based titania pastes with theaddition of ammonia, hydrochloric acid and water was investigated. The change in the viscosity is correlated with the measured zeta potential of the colloidal titania pastes.Improved inter-particle connectivity and hence better solar cell performance was found for the pastes containing acid or water. However, no such improvements were seen for the pastes containing ammonia. Maximum light to electrical energy conversion efficiencies of 4.9% and 5.0% were obtained for the plastic based dye-sensitized solar cells fabricated using water and acid-added slurries respectively.Thirdly, chemically-sintered, mesoporous ZnO electrodes with improved interparticle connectivity were prepared in the absence of any organic binders, using ammoniaas the sole reagent to encourage interparticle connectivity. The reaction with ammoniumhydroxide was found to increase the connections between ZnO grains by forming nanorods like a structure. The enhancement of adhesion among ZnO grains was evaluated from nano-scratch technique. Two different xanthene dyes were used to sensitize ZnOelectrodes. The photo-voltage of 657 mV, fill-factor of 73 % and photo-current of 4.1mAcm-2 with the maximum light to-electrical energy conversion efficiency of 2.0 % were obtained for plastic based ZnO|Mercurochrome|electrolyte solar cell under 100 mWcm-2light intensity.One of the biggest challenges for DSSCs on plastic substrates is the difficulty in making good quality nano porous TiO2 films with both good mechanical stability and high electrical conductivity. Cold isostatic pressing (CIP) is a powder compaction technique that applies an isostatic pressure to a powder sample in all directions. It is particularly suitable for making thin films on plastic substrates and even on non-flat surfaces. During the final stage of this work, cold isostatically-pressed nanocrytallineTiO2 electrodes with excellent mechanical robustness are prepared on indium tin oxide(ITO) coated polyethylene naphthalate (PEN) substrates in the absence of organic binders, and without heat treatment. The morphology and the physical properties of theTiO2 films prepared by the CIP method were found to be very compatible with requirements for fabricating flexible DSSCs on plastics. This room-temperature processing technique has led to an important technical breakthrough in producing high efficiency flexible DSSCs. Devices fabricated on ITO/PEN films by this method using standard P-25 TiO2 films with a Ru-complex sensitizer yielded a maximum IPCE of 72%at the wavelength of 530 nm and showed high conversion efficiencies of 6.3% and 7.4%for incident light intensities of 100 and 15 mWcm-2, respectively, which are the highest power conversion efficiencies achieved so far for any DSSC on a polymer substrate using the widely-used, commercially-available P-25 TiO2 powder.

Volume is indexed by Thomson Reuters BCI (WoS).The development of photovoltaic technology is expected to solve problems related to energy shortages and environmental pollution caused by the use of fossil fuels. Dye-sensitizedsolar cells (DSSCs) are promising next-generation alternatives to conventional silicon-based photovoltaic devices owing to their low manufacturing cost and potentially high conversion efficiency. This special topic volume addresses recent advances in the research on dye-sensitized solar cells. The focus of this special topic volume is on materials development (sensitizers, nanostructured oxide films, and electrolyte), but commercialization. This work illustrates a new pathway to achieve highly efficient DSSCs for practical applications.

Photovoltaic technologies use light from the sun to create electricity, using a wide range of materials and mechanisms. The generation of clean, renewable energy using this technology must become price competitive with conventional power generation if it is to succeed on a large scale. The field of photovoltaics can be split into many sub-groups, however the overall aim of each is to reduce the cost per watt of the produced electricity. One such solar cell which has potential to reduce the cost significantly is the dye sensitised solar cell (DSC), which utilises cheap materials and processing methods. The reduction in cost of the generated electricity is largely dependent on two parameters. Firstly, the efficiency that the solar cell can convert light into electricity and secondly, the cost to deposit the solar cell. This thesis aims to address both factors, specifically looking at altering the transparent conducting oxide (TCO) and substrate in the solar cell. One method to improve the overall conversion efficiency of the device is to implement the DSC as the top cell in a tandem structure, with a bottom infra-red absorbing solar cell. The top solar cell in such a structure must not needlessly absorb photons which the bottom solar cell can utilise, which can be the case in solar cells utilising standard transparent contacts such as fluorine-doped tin oxide. In this work, transparent conducting oxides with high mobility such as titanium-doped indium oxide (ITiO) have been used to successfully increase the amount of photons through a DSC, available for a bottom infra-red sensitive solar cell such as Cu(In, Ga)Se2 (CIGS). Although electrically and optically of very high quality, the production of DSCs on this material is difficult due to the heat and chemical instability of the film, as well as the poor adhesion of TiO2 on the ITiO surface. Deposition of a interfacial SnO2 layer and a post-deposition annealing treatment in vacuum aided the deposition process, and transparent DSCs of 7.4% have been fabricated. The deposition of a high quality TCO utilising cheap materials is another method to improve the cost/watt ratio. Aluminium-doped zinc oxide (AZO) is a TCO which offers very high optical and electronic quality, whilst avoiding the high cost of indium based TCOs. The chemical and thermal instability of AZO films though present a problem due to the processing steps used in DSC fabrication. Such films etch very easily in slightly acidic environments, and are susceptible to a loss of conductivity upon annealing in air, so some steps have to be taken to fabricate intact devices. In this work, thick layers of SnO2 have been used to reduce the amount of etching on the surface of the film, whilst careful control of the deposition parameters can produce AZO films of high stability. High efficiency devices close to 9% have been fabricated using these stacked layers. Finally, transferring solar cells from rigid to flexible substrates offers cost advantages, since the price of the glass substrate is a significant part of the final cost of the cell. Also, the savings associated with roll to roll deposition of solar cells is large since the production doesn't rely on a batch process, using heavy glass substrates, but a fast, continuous process. This work has explored using the high temperature stable polymer, polyimide, commonly used in CIGS and CdTe solar cells. AZO thin films have been deposited on 7.5um thick polyimide foils, and DSCs of efficiency over 4% have been fabricated on the substrates, using standard processing methods.

Several forms of thin-film solar cells are being examined as alternatives to silicon-solar cells-one of the most promising technologies is the dye-sensitized solar cell (DSC), with proven efficiencies that approach 11%. This book, which provides a comprehensive look at this promising technology, aims to provide both a graduate level text that bring

Dye-Sensitized Solar Cells: Mathematical Modelling and Materials Design and Optimization presents the latest information as edited from leaders in the field. It covers advances in DSSC design, fabrication and mathematical modelling and optimization, providing a comprehensive coverage of various DSSC advances that includes different system scales, from electronic to macroscopic level, and a consolidation of the results with fundamentals. The book is extremely useful as a monograph for graduate students and researchers, but is also a comprehensive, general reference on state-of-the-art techniques in modelling, optimization and design of DSSCs. Includes chapter contributions from worldwide leaders in the field Offers first-principles of modelling solar cells with different system scales, from the electronic to macroscopic level References, in a single resource, state-of-the-art techniques in modelling, optimization and design of DSSC