Browsing by Author "Hashmi, Syed Ghufran"

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    Advanced research trends in dye-sensitized solar cells
    (ROYAL SOC CHEMISTRY, 2021-05-07) Kokkonen, Mikko; Talebi, Parisa; Zhou, Jin; Asgari, Somayyeh; Soomro, Sohail Ahmed; Elsehrawy, Farid; Halme, Janne; Ahmad, Shahzada; Hagfeldt, Anders; Hashmi, Syed Ghufran; Department of Applied Physics; New Energy Technologies; University of Oulu; Ikerbasque - Basque Foundation for Science; Uppsala University
    Dye-sensitized solar cells (DSSCs) are an efficient photovoltaic technology for powering electronic applications such as wireless sensors with indoor light. Their low cost and abundant materials, as well as their capability to be manufactured as thin and light-weight flexible solar modules highlight their potential for economic indoor photovoltaics. However, their fabrication methods must be scaled to industrial manufacturing with high photovoltaic efficiency and performance stability under typical indoor conditions. This paper reviews the recent progress in DSSC research towards this goal through the development of new device structures, alternative redox shuttles, solid-state hole conductors, TiO2 photoelectrodes, catalyst materials, and sealing techniques. We discuss how each functional component of a DSSC has been improved with these new materials and fabrication techniques. In addition, we propose a scalable cell fabrication process that integrates these developments to a new monolithic cell design based on several features including inkjet and screen printing of the dye, a solid state hole conductor, PEDOT contact, compact TiO2, mesoporous TiO2, carbon nanotubes counter electrode, epoxy encapsulation layers and silver conductors. Finally, we discuss the need to design new stability testing protocols to assess the probable deployment of DSSCs in portable electronics and internet-of-things devices.
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    Dye-sensitized solar cells with inkjet-printed dyes
    (2016-07-01) Hashmi, Syed Ghufran; Özkan, Merve; Halme, Janne; Zakeeruddin, Shaik Mohammed; Paltakari, Jouni; Grätzel, Michael; Lund, Peter D.; Department of Applied Physics; Department of Forest Products Technology; Department of Bioproducts and Biosystems; New Energy Technologies; Swiss Federal Institute of Technology Lausanne
    The slow process in which the light absorbing dye molecules are adsorbed from solution on the nanocrystalline TiO2 photoelectrode film has been a handicap to the fast and cost-effective fabrication of dye-sensitized solar cells (DSSCs) using printing techniques. Here, we report a versatile dye sensitization process, achieved by inkjet printing a concentrated dye solution over the TiO2 film, which produces solar cells with equal performance and stability as obtained using the popular dye drop casting method. In addition to allowing precise control of dye loading required for dispensing just the right amount of dye to achieve uniform and full coloration of the TiO2 films without any need for washing off the excess dye, inkjet printing also makes it possible to freely adjust the amount and position of the dye to create DSSCs with tailored transparency, color density gradients, and patterns of one or more dyes on the same electrode. The method was confirmed to be applicable also for non-transparent, high-efficiency DSSC designs that employ a light scattering layer. The inkjet-dyed DSSCs exhibited high stability, retaining almost 100% of their conversion efficiency (η = 6.4 ± 0.2%) and short circuit current density (JSC = 14.2 ± 0.6 mA cm-2) when subjected to a 1000 h accelerated aging test under 1 Sun illumination at 35 °C, followed by additional 1154 hours under 0.5 Sun at 60 °C. These results overcome one of the main hurdles in realizing fully printed DSSCs and open opportunities for entirely new DSSC designs.
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    High performance low temperature carbon composite catalysts for flexible dye sensitized solar cells
    (ROYAL SOC CHEMISTRY, 2013) Hashmi, Syed Ghufran; Halme, Janne; Saukkonen, Tapio; Rautama, Eeva-Leena; Lund, Peter; Department of Applied Physics; Department of Chemistry; Department of Mechanical Engineering
    Roll-to-roll manufacturing of dye sensitized solar cells (DSSCs) requires efficient and low cost materials that adhere well on the flexible substrates used. In this regard, different low temperature carbon composite counter electrode (CE) catalyst ink formulations for flexible DSSCs were developed that can be simply and quickly coated on plastic substrates and dried below 150 degrees C. The CEs were investigated in terms of photovoltaic performance in DSSCs by current-voltage measurements, mechanical adhesion properties by bending and tape tests, electro-catalytic performance by electrochemical impedance spectroscopy and microstructure by electron microscopy. In the bending and tape tests, PEDOT-carbon composite catalyst layers exhibited higher elasticity and better adhesion on all the studied substrates (ITO-PET and ITO-PEN plastic, and FTO-glass), compared to a binder free carbon composite and a TiO2 binder enriched carbon composite, and showed lower charge transfer resistance (1.5-3 Omega cm(2)) than the traditional thermally platinized CE (5 Omega cm(2)), demonstrating better catalytic performance for the tri-iodide reduction reaction. Also the TiO2 binder enriched carbon composite showed good catalytic characteristics and relatively good adhesion on ITO-PET, but on ITO-PEN its adhesion was poor. A DSSC with the TiO2 binder enriched catalyst layer reached 85% of the solar energy conversion efficiency of the reference DSSC based on the traditional thermally platinized CE. Based on the aforementioned characteristics, these carbon composites are promising candidates for replacing the platinum catalyst in a high volume roll-to-roll manufacturing process of DSSCs.
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    Progress on electrolytes development in dye-sensitized solar cells
    (MDPI AG, 2019-06-02) Iftikhar, Haider; Sonai, Gabriela Gava; Hashmi, Syed Ghufran; Nogueira, Ana Flávia; Lund, Peter David; Department of Applied Physics; New Energy Technologies; Universidade Estadual de Campinas
    Dye-sensitized solar cells (DSSCs) have been intensely researched for more than two decades. Electrolyte formulations are one of the bottlenecks to their successful commercialization, since these result in trade-offs between the photovoltaic performance and long-term performance stability. The corrosive nature of the redox shuttles in the electrolytes is an additional limitation for industrial-scale production of DSSCs, especially with low cost metallic electrodes. Numerous electrolyte formulations have been developed and tested in various DSSC configurations to address the aforementioned challenges. Here, we comprehensively review the progress on the development and application of electrolytes for DSSCs. We particularly focus on the improvements that have been made in different types of electrolytes, which result in enhanced photovoltaic performance and long-term device stability of DSSCs. Several recently introduced electrolyte materials are reviewed, and the role of electrolytes in different DSSC device designs is critically assessed. To sum up, we provide an overview of recent trends in research on electrolytes for DSSCs and highlight the advantages and limitations of recently reported novel electrolyte compositions for producing low-cost and industrially scalable solar cell technology.
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    Sub-wavelength coatings on metals by ALD
    (2009) Hashmi, Syed Ghufran; Chekurov, Nikolai; Mikro- ja nanotekniikan laitos; Teknillinen korkeakoulu; Helsinki University of Technology; Tittonen, Ilkka
    The equations that describe reflection and transmission of electromagnetic field on various interfaces of transparent materials can be found from almost any textbook on optics. A lot less known problems are related to the behavior of e.m. field on such interfaces where one part is a dielectric material and the other one metal layer. In such cases one can for example modify the colour of the metal in the reflected visible light by varying the film thickness. In most common cases the metal surface is being oxidized either spontaneously or by a controlled treatment. Then the visible light normally becomes transmitted through the oxide layer and may experience a number of internal reflections between the metal/oxide and the oxide/air boundaries leading to scattering and absorption losses and to a large phase change. In this thesis the main focus has been to calculate and experimentally test the effect of an oxide layer on the reflected light by taking into account higher order reflection events in the analysis One motivation was to test the applicability of the atomic layer deposition method for modifying the optical response of metal surfaces by highly controllable sub-wavelength metal oxide coatings. The atomic layer deposition (ALD) has become a prominent technique for conformal deposition of thin films. By using ALD one can get pinhole free films of almost perfectly uniform thickness in this work ALD was used to deposit optical oxide coatings with the main emphasis on very thin sub-wavelength thick films on metals. One application of optical coatings that was tested in this work is an optical polarizer. The idea is to reduce one polarization component of light as effectively as possible. In order to find the behavior of the two polarization components of the light field in thin optical coatings the physical system was simulated using Matlab. In the experimental part of the work, a polarizing component was fabricated by using ALD to make a 229 nm thick A1203 film it was also experimentally tested by measuring reflected light using the monochromatic (635 nm laser) source in a setup that included a goniometer Rather satisfactory agreement between the experimental reflectance curve and the simulated data was found.
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    Super-Droplet-Repellent Carbon-Based Printable Perovskite Solar Cells
    (Wiley-VCH Verlag, 2024-07-10) Mai, Cuc Thi Kim; Halme, Janne; Nurmi, Heikki A.; da Silva, Aldeliane M.; Lorite, Gabriela S.; Martineau, David; Narbey, Stéphanie; Mozaffari, Naeimeh; Ras, Robin H.A.; Hashmi, Syed Ghufran; Vuckovac, Maja; Department of Applied Physics; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; New Energy Technologies; Soft Matter and Wetting; University of Oulu; Solaronix SA; Monash University Australia
    Despite attractive cost-effectiveness, scalability, and superior stability, carbon-based printable perovskite solar cells (CPSCs) still face moisture-induced degradation that limits their lifespan and commercial potential. Here, the moisture-preventing mechanisms of thin nanostructured super-repellent coating (advancing contact angle >167° and contact angle hysteresis 7°) integrated into CPSCs are investigated for different moisture forms (falling water droplets vs water vapor vs condensed water droplets). It is shown that unencapsulated super-repellent CPSCs have superior performance under continuous droplet impact for 12 h (rain falling experiments) compared to unencapsulated pristine (uncoated) CPSCs that degrade within seconds. Contrary to falling water droplets, where super-repellent coating serves as a shield, water vapor is found to physisorb through porous super-repellent coating (room temperature and relative humidity, RH 65% and 85%) that increase the CPSCs performance for 21% during ≈43 d similarly to pristine CPSCs. It is further shown that water condensation forms within or below the super-repellent coating (40 °C and RH 85%), followed by chemisorption and degradation of CPSCs. Because different forms of water have distinct effects on CPSC, it is suggested that future standard tests for repellent CPSCs should include rain falling and condensate formation tests. The findings will thus inspire the development of super-repellent coatings for moisture prevention.
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    Towards metal free counter electrodes for dye-sensitized solar cells
    (Aalto University, 2014) Hashmi, Syed Ghufran; Halme, Janne, Dr., Aalto University, Department of Applied Physics, Finland; Miettunen, Kati, Dr., Aalto University, Department of Applied Physics, Finland; Teknillisen fysiikan laitos; Department of Applied Physics; New Energy Technologies Group (NEW); Perustieteiden korkeakoulu; School of Science; Lund, Peter, Prof. Aalto University, Department of Applied Physics, Finland
    This thesis provides a technical overview of results from addressing the critical steps in preparing counter electrodes for dye-sensitized solar cells (DSC) on flexible substrates (mainly plastics) to pave the way towards low-cost DSCs. The aim was to develop low-temperature counter electrode inks and pastes that could be suitable for high volume manufacturing processes. A special focus was given on the mechanical stability (flexibility and adhesion) of the materials that were deposited through a low-temperature route. Different low temperature inks and pastes based on carbon composites were tested as a replacement to expensive platinum nanoparticles based catalyst layer and showed good mechanical stability, comparable photovoltaic performance and low charge transfer resistance in complete dye-sensitized solar cells. Indium doped tin oxide (ITO) layer that is normally used as a conductor on plastic substrates was successfully replaced with a single walled carbon nanotube (SWCNT) film deposited as a low-temperature curable ink on polyvinyl chloride (PVC) substrate. The SWCNT films exhibited remarkably good mechanical stability when subjected to bending and tape adhesion tests. Coating the film with a thin layer of conducting polymer poly (3, 4-ethylenedioxythiophene (PEDOT) increased its catalytic performance comparable to a reference platinum counter electrode. Relevant to scaling up DSC preparation, a two way electrolyte filling method was studied as a means to suppress performance losses that occur due to non-homogenous distribution of electrolyte components. The method enhanced the photovoltaic performance of a segmented measurement cell by up to 42% compared to traditional one way filling of the electrolyte. The aforementioned results provide pathways for the future development of robust flexible counter electrodes that can be beneficial especially from the perspective of high throughput roll-to-roll processing of flexible DSCs on polymer substrates.