Effect of Bulky Groups on the Performance of Subphthalocyanine‐Based Dye‐Sensitized Solar Cells

Cell Efficiency Table of DSSCs with Various Counter Electrode Electrocatalysts

Synthesis and characterization of perylene–bithiophene–triphenylamine triads: studies on the effect of alkyl-substitution in p-type NiO based photocathodes

Dye-sensitized solar cell (DSSC) has been widely investigated due to its low cost, simple fabrication process, and excellent photoelectric conversion efficiency. Generally, the DSSC is composed of photoanode, electrolyte and counter electrode. At present, platinum (Pt) film delivers the highest photoelectric conversion efficiency in the available counter electrode materials. However, Pt film is very expensive and prepared by relatively complicated and high-cost magnetron sputtering, which seriously hinders the large-scale applications in DSSC. Therefore, it is of highly academic and engineering significance to develop novel counter electrode materials with low cost and high photoelectric conversion efficiency to replace expensive Pt counter electrode. Previous research shows that carbon-based nanomaterials such as graphene and carbon nanotubes ard promising to be used as highly efficient counter electrode materials. However, the high-cost and complicated fabrication process restrict their practical applications in DSSC. To address such issues, here in this work, we present and fabricate a highly efficient and low-cost three-dimensional porous carbon composite, which is constructed by the relatively dense and conductive graphite film as bottom layer (PC layer), and the porous carbon nanoparticle film as top layer (CC layer). Our fabricated DSSC consists of commercial TiO<sub>2</sub> photoanode (m 4 mm×4 mm), and PC, CC, CC/PC composite, or Pt counter electrode with a size of m 8 mm×8 mm. The results show that under illumination (100 mW/cm<sup>2</sup>) provided by a solar simulator, the short circuit current densities (open circuit voltages) of DSSCs with PC, CC, CC/PC, and Pt counter electrodes are 11.45 mA/cm<sup>2</sup> (0.72 V), 11.88 mA/cm<sup>2</sup> (0.73 V), 12.00 mA/cm<sup>2</sup> (0.75 V), and 13.46 mA/cm<sup>2</sup> (0.74 V), respectively. The filling factors of DSSCs with PC, CC, and CC/PC are 56.09%, 59.80%, 65.28%, and 62.69%, respectively; the photoelectric conversion efficiencies of DSSCs with PC, CC, and CC/PC are 4.61%, 5.20%, 5.90%, and 6.26%, respectively. It is noted that compared with CC layer or PC layer counter electrode, the CC/PC counter electrode delivers better photovoltaic performance. Particularly, the filling factor of DSSC with CC/PC (65.28%) is even 4.10% higher than that of DSSC with commercial Pt (62.69%), and the photoelectric conversion efficiency of the CC/PC-based DSSC is as large as 5.90%, which reaches 94.2% of the Pt-based DSSC (6.26%). The excellent performance of DSSC with CC/PC counter electrode is attributed to the unique three-dimensional porous structure, which can not only facilitate the transfer of electrons and ions, but also provide abundant catalytic sites; these synergistic effects greatly enhance the photovoltaic conversion performance of CC/PC-based DSSC.

A computational finding on the effect of π-conjugated acceptors in thiophene-linked coumarin dyes for potential suitability in DSSC application

Dye-sensitized solar cells (DSSC) is a device which converts a solar energy to electrical energy. Different with semiconductor thin film based solar cell, DSSC utilize the sensitized-dye to absorb the photon and semiconductor such as titanium dioxide (TiO2) and zinc oxide (ZnO) as a working electrode photoanode. In this report, the preparation of TiO2 film using a facile method of spray deposition and its application in DSSC have been presented. TiO2 photoanode was synthesized by growing the droplet of titanium tetraisopropoxide diluted in acid solution on the substrate of conductive glass flourine-doped tin oxide (FTO) with variation of precursor volume. DSSC was assemblied by sandwiching both of photoanode electrode and platinum counter electrode subsequently filling the area between these electrodes with triodine/iodine electrolite solution as redox pairs. The characterization of the as prepared DSSC using solar simulator (AM 1.5G, 100 mW/cm2) and I-V source meter Keithley 2400 showed that the performance of DSSC was affected by the precursor volume.. The overall conversion efficiency of DSSC using the optimum TiO2 film was about 1.97% with the open circuit voltage (Voc) of 0.73 V, short circuit current density (Jsc) of 4.61 mA and fill factor (FF) of 0.58.

Theoretical study of T shaped phenothiazine/carbazole based organic dyes with naphthalimide as π-spacer for DSSCs.

Dye-sensitized solar cells (DSSCs), quantum dot-sensitized solar cells (QDSSCs) and perovskite solar cells (PSCs) have attracted wide attention. DSSCs, QDSSCs and PSCs can be prepared by liquid phase or solid phase, which causes a certain range of interface micro-mass changes during preparation. In addition, the photoelectric conversion process occurring inside the device also inevitably causes interface micro-mass changes. Interpretation of these interface micro-mass changes can help to optimize the cell structure, improve the stability and performance repeatability of the device, as well as directly or indirectly infer, track and predict the internal photoelectric conversion mechanism of the device. Quartz crystal microbalance (QCM) is a powerful tool for studying surface mass changes, extending this technology to the fields of solar cells to directly obtain interface micro-mass changes, which makes the research more in-depth and opens up a new perspective for explaining the basic principles of solar cells. This review summarizes the research progress of QCM application in DSSCs, QDSSCs and PSCs in recent years, and explores the challenges and new opportunities of QCM application in new solar cells in the future.

Low-cost ZnO-type fiber-shaped dye-sensitized solar cells (DSSC) without transparent conductive oxide (TCO) were for the first time assembled through a low-temperature all-wet process, using a series of Ni-based composite fiber. Both Ni layer morphology and ZnO nano-array structure evidently influenced the performance of the corresponding DSSC. For applications in both liquid type and all-solid CuI type fiber-shaped DSSCs, the Ni-based photoanode is comparable with the Ti- or Fe-based photoanode. Our all-solid CuI type fiber-shaped DSSCs was even better than that of the reported all-solid Ti- or Fe-based devices with the same oxide thickness. Electrochemical analysis further indicated that side reactions on the electrode/electrolyte interface could be effectively suppressed after a layer of Ni plated. Even for Cu wire, of which its interfacial side reactions are too complicated for application in DSSC, the Cu/Ni composite fiber still works well. Similar technology can be used to fabricate many other low-cost and light-weight conductive fibers, which are potential photoanode materials for highly efficient TCO-less DSSCs.

This thesis contains complementary synthetic and computational studies of transition metal complexes with polypyridyl ligands for use either as water oxidation catalysts or for application in dye-sensitised solar cells (DSSCs). Chapter 1 introduces the reasons for researching water splitting catalysts and describes a number of current techniques used to do so; from photoelectrochemical cells to the use of transition metal polypyridyl complexes. It also introduces three commercially available types of solar cells; silicon, thin film and the dye-sensitised solar cell. Chapter 2 describes the synthesis of seven ruthenium(II) complexes with substituted 4'-(4-pyridyl)-2,2':6',2''-terpyridine ligands and their photophysical and electrochemical properties. Density Functional Theory (DFT) calculations were used to explore the compositions of the highest occupied- and lowest unoccupied molecular orbitals (HOMO and LUMO, respectively) and Time Dependent DFT (TD-DFT) was used to predict the absorption spectra of the complexes. Chapter 3 contains information on water soluble ruthenium(II) complexes, their synthesis, photophysical and electrochemical properties and their activity as water splitting co-catalysts. A mechanism to explain the variable activities of the complexes is also put forward. Chapter 4 describes the synthesis of two homoleptic Cu(I) complexes. One complex involves a simple 6,6'-dimethyl-2,2'-bipyridine ligand. The other complex contains a ligand with extended ?-conjugation. The properties of the Cu(I) complexes are studied in terms of their suitability for use in DSSCs. A strategy of ligand-exchange on the surface of titanium dioxide (TiO2) is then utilised to form surface-bound heteroleptic Cu(I) complexes and efficiences of these complexes in DSSCs were measured. Chapter 5 details the development of a suitable basis set to be used in both DFT and TD-DFT to predict the absorption spectra of the homoleptic Cu(I) complexes in Chapter 4; the accuracies of the predicted spectra are assessed. The properties of the uncharacterised, heteroleptic Cu(I) complexes were then predicted and the effects of the anchoring ligands on the overall properties of the complexes were assessed. Chapter 6 describes the synthesis of two mono-substituted bipyridine-based ligands and their corresponding homoleptic chiral copper(I) complexes. Variable temperature nuclear magnetic resonance (VT-NMR) experiments are described, along with the photophysical properties of the ligands and complexes. Chapter 7 consists of the overall conclusions and an outlook.

Dye-sensitized solar cells (DSSCs) have been intensively studied since their discovery in 1991. DSSCs have been extensively researched over the past decades as cheaper alternatives to silicon solar cells due to their high energy-conversion efficiency and their low production cost. However, some problems need to be solved in order to enhance the efficiency of DSSCs. In particular, the electron recombination that occurs due to the contact between the transparent conductive oxide (TCO) and a redox electrolyte is one of the main limiting factors of efficiency. In this work, we report for the first time the improvement of the photovoltaic characteristics of DSSCs by doping TiO2 with Al2O3. DSSCs were constructed using composite particles of Al2O3-doped TiO2 and TiO2 nanoparticles. The DSSCs using Al2O3 showed the maximum conversion efficiency of 6.29% due to effective electron transport. DSSCs based on Al2O3-doped TiO2 films showed better photovoltaic performance than cells fabricated with only TiO2 nanoparticles. This result is attributed to the prevention of electron recombination between electrons in the TiO2 conduction band with holes in the dye or the electrolyte. There mechanism is suggested based on impedance results, which indicated improved electron transport at the TiO2/dye/electrolyte interface.

In this work, we have introduced a star‐shaped sensitizer for dye sensitized solar cells (DSSCs) consist of three anchoring groups of benzene sulfonic acid with a significant improvement of interfacial electron transfer rate of dye/TiO 2 ‐ anatase nanostructures compared to corresponding sensitizers containing only one anchoring group. Physical chemistry aspect of the robust star‐shaped sensitizer has been investigated, employing the Current over Voltage analysis (I−V) and Transient Absorption Spectroscopy (TAS) methods. The computational studies based on density functional theory (DFT) and quantum calculations were clearly indicated that the rate of the Interfacial electron transfer (IET) significantly depends on the binding mode of a sensitizer to semiconductor surface and the nature of the electronic population in lowest unoccupied molecular orbitals (LUMOs) that initially localized on the adsorbate molecule, which is in a good agreement with experimental results. Our main result is that, among different possible binding modes of anchoring group to TiO 2 surface, the bridging mode has the shortest life time of 28 fs in the presence of visible light as the excitation source. To investigate negative effect of the sensitizer molecules aggregation on TiO 2 surface, on the performance of the cell, was examined the dye loading time on TiO 2 surface for 10, 16 and 20 hours, which 16 hours of dye loading on surface exhibited the best DSSC performance. Moreover, transient absorption studies consistently show that the star‐shaped dye (consist of three anchoring groups) has better performance compared to the other dyes (consist of one anchoring groups) (1 and 3), in all aspects of critical parameters for DSSCs, including electron lifetime in TiO 2 , electron injection, dye regeneration and recombination resistance. The present work explains the fundamental physical chemistry aspects of the excited‐state in star‐shaped ruthenium polypyridyl complexes, along with opening new insight into the design of new sensitizers for enhancing the interfacial electron transfer rate and lowering the charge recombination process, which results in high power conversion efficiency of DSSC.

Tin oxide (SnO2) is a promising candidate for dye-sensitized solar cell (DSSC) application due to its wide band gap, high stability and high electron conductivity. Despite of its remarkable benefits, a detailed discussion on electron transfer mechanism inside SnO2-based DSSC is still needed. Electrochemical impedance spectroscopy (EIS) analysis have been widely employed to understand the electron transport processes and performance of DSSC by correlating the impedance spectrum with its equivalent circuit model. The scope of this review provides an insight overview on the photovoltaic potential of SnO2 as photoanode in DSSC application followed by a detailed review on the application of EIS analysis in morphologically modified SnO2-based DSSC and hybrid structure of SnO2-based DSSC.

Construction of nickel molybdenum sulfide (NiMoS3)/bio carbon (BC) heterostructure photoanodes and optimization of light scattering to improve the photovoltaic performance of dye sensitized solar cells (DSSCs)

The control of the loss mechanism in a dye sensitised solar cell (DSSC) via recombination of the injected electron with the oxidised dye was investigated by incorporating a redox-active ligand, 6,7-bis(methylthio)tetrathiafulvalene dithiolate (TTF(SMe)(2)), into a ruthenium bipyridyl dye. A series of dyes with general formula [Ru(4,4'-R-bpy)(2)(TTF(SMe)(2)], where R = H, CO(2)Et and CO(2)H, were synthesised and characterised using electrochemistry, absorption and emission spectroscopy, spectroelectrochemistry and hybrid-DFT calculations. In addition, the performance of the acid derivative in a DSSC was investigated using IV measurements, as well as transient absorption spectroscopy. These complexes showed significant TTF-ligand character to the HOMO orbital, as deduced by spectroelectrochemical, emission and computational studies. Upon adsorption of the acid derivative to TiO(2) a long-lived charge-separated state of 20 ms was observed via transient absorption spectroscopy. Despite this long-lived charge-separated state, the dye yielded extremely low DSSC efficiencies, attributed to the poor regeneration of the neutral dye by iodide. As a result, the complex forms a novel long-lived charge separated state that persists even under working solar cell electrolyte conditions.

A Study on the Growth of ZnO Nanorods for the Application to Dye-sensitized Solar Cells