Umer Mehmood

Recent Advances in Dye Sensitized Solar Cells

Solar energy is an abundant and accessible source of renewable energy available on earth, and many types of photovoltaic (PV) devices like organic, inorganic, and hybrid cells have been developed to harness the energy. PV cells directly convert solar radiation into electricity without affecting the environment. Although silicon based solar cells (inorganic cells) are widely used because of their high efficiency, they are rigid and manufacturing costs are high. Researchers have focused on organic solar cells to overcome these disadvantages. DSSCs comprise a sensitized semiconductor (photoelectrode) and a catalytic electrode (counter electrode) with an electrolyte sandwiched between them and their efficiency depends on many factors. The maximum electrical conversion efficiency of DSSCs attained so far is 11.1%, which is still low for commercial applications. This review examines the working principle, factors affecting the efficiency, and key challenges facing DSSCs.

Density functional theory study on dye-sensitized solar cells using oxadiazole-based dyes

Abstract. Density functional theory (DFT) and time-dependent DFT(TD-DFT) modeling techniques are used to conduct a computational study of the geometry and electronic structure of oxadiazole-based organic sensitizers. A DFT study on the thermodynamic aspects of the charge transport processes associated with dye-sensitized solar cells (DSSCs) suggests that the system with 1,2,4-oxadiazole has a balance among the different crucial factors and may result in the highest incident photon to charge carrier efficiency. The dye/(TiO2)8 anatase clusters were also simulated to illustrate the electron injection efficiency at the interface. This study provides basic understanding of the impact of molecular design on the performance of oxadiazole dyes in DSSCs.

Enhanced Photovoltaic Performance of Dye-Sensitized Solar Cells Using TiO 2 -Graphene Microplatelets Hybrid Photoanode

Hybrid photoanodes for dye-sensitized solar cells (DSSCs) were prepared by simple addition of graphene (GR) microplatelets to TiO2 nanoparticulate paste. Transmission electron microscopy was used to confirm the presence of GR in composite films after heating at 450°C for 30 min. TiO2/GR-based DSSCs were fabricated using an N749 photosensitizer. The UV-Visible absorption spectroscopy, photocurrent-voltage (I-V) characteristic, and electrochemical impedance spectroscopy measurements were carried out to characterize the cells. The results indicate that the GR/TiO2 photoanode improves the performance of the solar cell. This is because the GR/titania electrode accelerates electronic transportation and suppresses the charge recombination. Under optimal conditions, the solar cell based on GR/TiO2 shows power conversion efficiency (PCE) of 4.1%, which is about 30% greater than the cell based on the pristine TiO2 electrode (3.16%). The objective of this study is to develop a fast, cheap, and an effective means to increase the PCE of DSSCs. Density functional theory was used to calculate the bandgap of TiO2 and graphnene-TiO2.

Density Functional Theory Study on the Electronic Structures of Oxadiazole Based Dyes as Photosensitizer for Dye Sensitized Solar Cells

The molecular structures and UV-visible absorption spectra of complex photosensitizers comprising oxadiazole isomers as the π-bridges were analyzed by density functional theory (DFT) and time-dependent DFT. The ground state and excited state oxidation potentials, HOMOs and LUMOs energy levels, and electron injection from the dyes to semiconductor TiO2 have been computed in vacuum here. The results show that all of the dyes may potentially be good photosensitizers in DSSC. To justify the simulation basis, N3 dye was also simulated under the similar conditions. Simulated absorption spectrum, HOMO, LUMO, and band gap values of N3 were compared with the experimental values. We also computed the electronic structure properties and absorption spectra of dye/(TiO2)8 systems to elucidate the electron injection efficiency at the interface. This work is expected to give proper orientation for experimental synthesis.

Enhanced photovoltaic performance with co-sensitization of a ruthenium(II) sensitizer and an organic dye in dye-sensitized solar cells

Co-sensitization is demonstrated to be an effective technique to enhance the efficiency of dye-sensitized solar cells, where an efficiency of 9.23% is achieved by mixing N3 and RK-1 dyes. The assembled solar cells are characterized by UV-vis absorption measurements, current–voltage characteristics, and electrochemical impedance spectroscopy. The co-sensitized solar cell shows an enhanced photovoltaic performance as compared to the devices sensitized by individual dyes. Upon optimization, the device made of 0.3 mM N3 + 0.2 mM RK-1 yielded Jsc = 18.1 mA cm2, Voc = 888 mV, FF = 57.44, and η = 9.23%. This performance is superior to that of solar cells sensitized with either N3 (6.10%) or RK-1 (5.82%) fabricated under the same conditions. The enhanced efficiency can be attributed to the decrease of the competitive light absorption by I−/I3−, dye aggregation, and charge recombination.

Recent Advances in Nanoparticles Enhanced Oil Recovery: Rheology, Interfacial Tension, Oil Recovery, and Wettability Alteration

Chemically enhanced oil recovery methods are utilized to increase the oil recovery by improving the mobility ratio, altering the wettability, and/or lowering the interfacial tension between water and oil. Surfactants and polymers have been used for this purpose for the last few decades. Recently, nanoparticles have attracted the attention due to their unique properties. A large number of nanoparticles have been investigated for enhanced oil recovery applications either alone or in combination with surfactants and/or polymers. This review discusses the various types of nanoparticles that have been utilized in enhanced oil recovery. The review highlights the impact of nanoparticles on wettability alteration, interfacial tension, and rheology. The review also covers the factors affecting the oil recovery using nanoparticles and current challenges in field implementation.

New 1,3,4-Oxadiazole Based Photosensitizers for Dye Sensitized Solar Cells (DSSCs)

1,3,4-Oxadiazole based photosensitizers with biphenyl, naphthalene, anthracene, and triphenylamine as the electron-donating moiety were synthesized for solar cell applications. In these photosensitizers, cyano groups were introduced as the electron acceptor and the anchor group because of their high electron-withdrawing ability and strong bonding to the semiconductor. Oxadiazole isomers were used as the π-conjugation system, which bridges the donor-acceptor systems. The electrochemical and optical properties of the sensitizers were investigated both in their native form and upon incorporation into dye sensitized solar cells. The results of UV-visible absorption spectroscopy, electrochemical impedance spectroscopic measurements, and photocurrent voltage characteristics indicate that 1,3,4-oxadiazole pi-spacer with the anthracene moiety has the highest efficiency of 2.58%. Density functional theory was employed to optimize the structures of the sensitizers and the TiO2 cluster.

Enhancing Power Conversion Efficiency of Dye-Sensitized Solar Cell Using TiO 2 -MWCNT Composite Photoanodes

The aim of this work is to improve the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) using composite films consisting of titanium oxide (TiO2) nanoparticles and multiwalled carbon nanotubes (MWCNTs). A transmission electron microscope (TEM) was used to confirm the dispersion of carbon nanotubes (CNTs) in TiO2. Composite photoanode-based solar cells were characterized by UV-Visible absorption spectroscopy, photocurrent-voltage (I-V) characteristics, and electrochemical impedance spectroscopy. It was found that the PCE (ηc) of DSSCs strongly depends on the concentration of CNTs in the nanocomposite films. The solar cell assembled with photoanode containing 0.06% MWCNTs shows the highest efficiency of 5.25%, which is 46% greater than unmodified photoanode. The density functional theory (DFT) quantum modeling technique was used to compute the band gap of TiO2 and CNT-TiO2 clusters.

Derivatization and diffusive motion of molecular fullerenes: Ab initio and atomistic simulations

Using first principles density functional theory in combination with the nonequilibrium Greens function formalism, we study the effect of derivatization on the electronic and transport properties of C60 fullerene. As a typical example, we consider [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which forms one of the most efficient organic photovoltaic materials in combination with electron donating polymers. Extra peaks are observed in the density of states (DOS) due to the formation of new electronic states localized at/near the attached molecule. Despite such peculiar behavior in the DOS of an isolated molecule, derivatization does not have a pronounced effect on the electronic transport properties of the fullerene molecular junctions. Both C60 and PCBM show the same response to finite voltage biasing with new features in the transmission spectrum due to voltage induced delocalization of some electronic states. We also study the diffusive motion of molecular fullerenes in ethanol solvent and inside...

Transparent Conductive Oxide Films for High-Performance Dye-Sensitized Solar Cells

In this paper, atmospheric pressure chemical vapor deposition of fluorine-doped tin oxide (FTO) thin films of various thicknesses and dopant levels is reported. The deposited coatings are used to fabricate dye-sensitized solar cells, which exhibited reproducible power conversion efficiencies in excess of 10%. No surface texturing of FTOs or any additional treatment of dye-covered films is applied. In comparison, the use of commercial FTOs showed a lower cell efficiency of 7.11%. Detailed analysis showed that the cell efficiencies do not simply depend on the resistivity of FTOs but instead rely on a combination of carrier concentration, thickness, and surface roughness properties.