Properties Of Dye-sensitized Solar Cells Research Articles

Metal-free phenothiazine dyes with alkoxy chains modified at different position for dye-sensitized solar cells

Long alkyloxy or alkoxyphenyl chains are commonly introduced to organic dye sensitizers in dye-sensitized solar cells (DSSCs) to inhibit the aggregation of sensitizer on the TiO2, thereby minimizing charge recombination. Here, we synthesized four D-D-π-A sensitizers (TP-C6, TP-PhOC6, C6O-TP-C6, C6O-TP-PhOC6), that feature alkyl-/alkoxyphenyl- moiety in phenothiazine (PTZ) donor’s N-position, and either alkoxy or no alkoxy groups in triphenylamine (TPA) auxiliary donor. Then, their photophysical, electrochemical and DSSCs properties were investigated. The UV-Vis and electrochemical studies revealed that all four dyes exhibited good light absorption ability and appropriate HOMO-LUMO energy levels. The introduction of alkoxy at the donor or auxiliary donor can result in a significant redshift in absorption. Among them, TP-PhOC6, which incorporates an alkoxy phenyl group at the N-position of PTZ and lacks alkoxy in TPA, induces a greater redshift in ICT absorption with strong absorption intensity. Additionally, in TP-PhOC6 based DSSC, mitigated charge recombination was observed. As a result, this device exhibited the strongest and widest IPCE spectrum, the highest Jsc (12.77 mA/cm²) and Voc (0.85 V), leading to the highest PCE (6.59 %).

Exploring charge transfer effects on linear, non‐linear optical, and dye‐sensitized solar cell properties: A DFT and TD‐DFT investigation of carbazole and aniline‐based dyes

AbstractThe efficacy of aniline and carbazole‐based sensitizers used in dye‐sensitized solar cells (DSSCs) is correlated with the trends in density functional theory (DFT) based charge transfer (CT) and non‐linear optical (NLO) properties since both DSSC and NLO properties highly rely on CT properties. The aniline‐based donors showed a higher degree of planarity over carbazole‐based donor sensitizers. This improved planarity in aniline‐based sensitizers is attributed to efficient charge transfer and higher dipole moment. The efficient CT within the sensitizers is confirmed with bond‐length alternation (BLA), bond order alternation (BOA), and quinoid character (QC). A direct correlation of band‐gap (EG) with μ, ω, η, and Γ is witnessed. Time‐dependent DFT (TD‐DFT) results of vertical excitation demonstrated similar trends that are observed practically. Indeed, we observed a direct correlation between α and β and the experimentally observed DSSC efficiency. DFT and TD‐DFT methods, linear, employed for computing the CT and linear and DSSC properties as implemented in Gaussian 09. NLO properties were simulated through single‐point polar calculations. B3LYP and PBE1PBE functionals were used for geometry optimization. The linear and NLO properties were determined in various functionals, that is, global hybrid and range‐separated hybrid functionals. A polarizable continuum model (PCM) was used for solvation studies. To understand the realistic picture of the dye@TiO2 cluster, dye bound on TiO2 clusters were optimized using a LANL2DZ basis set specifically for the Ti atom.

Effects of fused thiophene Π-bridge on the electronic and optical properties of modified theaflavin natural dye

ABSTRACT Natural dye sensitizers are substances that are sensitive to light colour and can be classified into several classes based on their chemical structure. Theaflavin pigments are unexplored natural dyes used as light sensitizers derived from black tea waste. However, the efficiency of natural dye-sensitized solar cells (DSSC) is lower than that of synthetic ones. To increase the efficiency, an amine donor molecule, a thiophene bridge, and a cyanoacrylic acid anchoring group were added. This improvement was achieved by comparing the LHE values, absorption shifts towards the red spectrum, and electronic parameters before and after modification of the theaflavin structure. This study aimed to analyze the effect of a fused thiophene bridge on the colour pigment of theaflavin on the electronic and optical properties of DSSC. TDDFT was employed with the hybrid functional B3LYP and def2-SVP. The calculated results concluded that adding fused thiophene can shift the wavelength with a maximum value of 256 nm and an increase in LHE of 40%. The addition of five thiophenes can shift the absorption wavelength closer to the red spectrum and satisfy the electronic properties of the DSSC, and the number of electron donor and acceptor sites obeying the law of conservation of charge.

Performance Evaluation of Modified Zinc-Phthalocyanine Groups as an Active Material in Dye-Sensitized Solar Cells

The increasing demand for energy and electricity and the depletion of fossil fuels are global problems. In recent years, dye-sensitized solar cell (DSSC) technologies have gained notoriety for their application in solar energy. DSSCs are considered a promising alternative renewable energy source to both inorganic and organic photovoltaic (PV) cells. Many types of dyes are being investigated to enhance the light-harvesting properties of DSSCs, but the actual realization of these absorbers in cell structure requires optimum parameters. The main aim of this study was to simulate proposed zinc phthalocyanine (ZnPC)-based structures to validate their design, assess their performance for commercial implementation, and optimize the cell parameters for optimum efficiency. To that end, Scaps-1D was employed to evaluate the performance of DSSCs to determine their optimum parameters. We found that ZnPC and isopropoxy ZnPC molecules outperform others molecules because of better optoelectronic properties. Several other parametric effects, such as photoactive layer thicknesses, doping densities, trap densities, and charge carrier mobilities, were also evaluated to observe their impact on device performance. The results show that moderate thickness, low defect density, moderate doping, and charge carrier mobility are favorable for better device performance due to low recombination losses, electrical losses, and better transport of charge carriers. The utmost power conversion efficiency values found for ZnPC- and ZnPC: PC70BM-based DSSCs after optimization were 9.50% and 9.81%. This paper also suggests a practical method for efficiently using DSSC cells by modifying factors that are significantly reliant on DSSC performance and output.

Synthesis of chitosan-based perylene dye material for photovoltaic solar-cell application

Renewable energy, such as solar energy, is infinite, readily available, and has extensive applications. Dye-sensitized solar cells (DSSCs) have been well developed; thus, they can be developed with low production costs, high efficiency, and facile manufacturing techniques. This study proposes a novel chitosan biopolymer-based perylene dye; the dye is modified by chitosan with perylene-3,4,9,10-tetracarboxylic anhydride using a one-pot acylation of nitrogen nucleophiles for DSSCs. The chitosan biopolymer-based perylene dyes were characterized using attenuated total reflection infrared spectroscopy, solid-state 13C CP-TOSS nuclear magnetic resonance spectroscopy, X-ray powder diffraction analysis, thermogravimetric analysis, X-ray photoelectron spectrometry, and high-resolution field-emission scanning electron microscopy. The ultraviolet-visible and fluorescence spectroscopy of chitosan biopolymer-based perylene dye exhibited a red-shift compared with perylene-3,4,9,10-tetracarboxylic anhydride and chitosan. The DSSC properties of chitosan biopolymer-based perylene dye were investigated, and it exhibited a 2.022 % power-conversion efficiency. Thus, this promising chitosan biopolymer-based perylene dye may have potential applications in solar-cell technology.

Photon up-conversion in Er3+ ion-doped ZnO-Al2O3-BaO-B2O3 glass for enhancing the performance of dye-sensitized solar cells

One of the main limitations in the development of dye-sensitized solar cell (DSSC) is contributed by the optical losses that occur within the absorber layer due to spectral mismatch. DSSC typically only absorbs solar light within the visible region (i.e. up to 800 nm), while the photon energy in the infrared region remain unutilized. Here we report the integration of Er3+ ion-doped glass as up-conversion (UC) element in DSSC and study their effect on the photovoltaic performances. Several characterizations were conducted including physical, structural, optical, luminescence, and radiative properties on the glass sample, while current-voltage and incident photon-to-current conversion efficiency characterization were conducted to analyze the electrical properties of DSSC. The UC luminescence spectra of the glass sample under 800 nm excitation showed green light emissions that were located between 531 and 553 nm. The UC luminescence band of glass sample was confirmed suitable with the absorption band of Z907 dye. After placing the UC glass below the DSSC’s counter electrode side, the power conversion efficiency of DSSC were mostly positively affected by the presence of UC glass, where the highest improvement of around 7.21 % was obtained for DSSC coupled with 2.0 mol% of Er3+ ion-doped glass. The enhancement was primarily attributed to the improved light harvesting due to the UC mechanism within the device as indicated by the increase in external quantum efficiency and fill factor. Our contribution provides a simple yet versatile approach in improving DSSC performance via the application of a free standing Er3+ ion-doped up-conversion glass.

Blackberries dye-sensitized solar cells with poly(vinyl alcohol) based gel polymer electrolytes

Dye-sensitized solar cells (DSSCs) have been constructed using fluoride tin oxide (FTO) glass deposited with TiO2 and anthocyanin dye extracted from blackberries as the photoanode, platinum coated cathode, and gel polymer electrolytes (GPEs) comprising poly(vinyl alcohol) (PVA) dissolved in two different solvents, viz., dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO). GPE employing DMF solvent exhibits the highest ambient conductivity of 14.05 mS cm−1. Charge transport properties of DSSCs were studied via intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated photovoltage spectroscopy (IMVS) and electrochemical impedance spectroscopy (EIS). The highest efficiency of 0.54% is recorded for DSSC with GPE containing DMF and TBP.

Photovoltaics and its magnetic-field promotion effect in dye-sensitized solar cells with BiFeO3 + TiO2 composite photoanodes

In dye-sensitized solar cells (DSSCs), the light absorbance of photoanode is the most important factor in power conversion efficiency (PCE). Here the authors report on an alternative modified TiO2-based photoanode for obtaining enhanced photovoltaic (PV) properties in DSSCs. Multiferroics BiFeO3, which possesses excellent magnetic, electric, and photocatalytic performances, was employed to construct BiFeO3 + TiO2 composite photoanode for DSSCs. In this type of DSSCs with BiFeO3 + TiO2 composite photoanodes, BiFeO3 with suitable bandgap may also act as photoelectric conversion medium, which is generally acted by dye in DSSCs, and increases photogenerated carrier transport channels, which improves the PCE of DSSCs with BiFeO3 + TiO2 composite photoanodes. More importantly, magnetic-field enhanced PV properties in abovementioned DSSCs was firstly obtained, which may result from magnetic-field-suppression the recombination of charge carriers and magnetoresistance effect in BiFeO3. The investigated results offer both an alternative method to improve PV properties in DSSCs, and a referential train of thought to manipulate photoelectric properties of solar cells.

Expanding π-bridge and introducing auxiliary acceptor for realizing panchromatic absorption of the phenothiazine dyes in dye-sensitized solar cells

Dyes with panchromatic absorption of the solar radiation is crucial for the photovoltaic performances of dye-sensitized solar cells (DSSCs). In this paper we have constructed four phenothiazine dyes (PS1, PS2, PID1 and PID2), and applied to fabricate the DSSCs. Some important results have been found: (I) PID1 and PID2 with isoindigo as auxiliary acceptor successfully achieve nearly panchromatic absorption. (II) thieno[3,2-b]thiophene is a better π-bridge than 2,2′-bithiophene in terms of facilitating the intramolecular transport of photoexcited electrons, reducing the dye aggregation and improving the photovoltaic properties of DSSCs; (III) it is surprised that PID1 and PID2 exhibit broader absorption spectra, but achieve lower conversion efficiencies than PS2 with thieno[3,2-b]thiophene as π-bridge; (IV) The low device efficiencies of the isoindigo-based dyes might be due to the strong electron-withdrawing ability of isoindigo moiety, affecting the electron transport. These findings suggest that it might be an effective way to realize panchromatic absorption of the organic dyes by introducing isoindigo as an auxiliary acceptor, and a balanced perspective on the molecular design of dye is necessary to improve the performance of DSSCs.

A Review on Gel Polymer Electrolytes for Dye-Sensitized Solar Cells.

Significant growth has been observed in the research domain of dye-sensitized solar cells (DSSCs) due to the simplicity in its manufacturing, low cost, and high-energy conversion efficiency. The electrolytes in DSSCs play an important role in determining the photovoltaic performance of the DSSCs, e.g., volatile liquid electrolytes suffer from poor thermal stability. Although low volatility liquid electrolytes and solid polymer electrolytes circumvent the stability issues, gel polymer electrolytes with high ionic conductivity and enduring stability are stimulating substitutes for liquid electrolytes in DSSC. In this review paper, the advantages of gel polymer electrolytes (GPEs) are discussed along with other types of electrolytes, e.g., solid polymer electrolytes and p-type semiconductor-based electrolytes. The benefits of incorporating ionic liquids into GPEs are highlighted in conjunction with the factors that affect the ionic conductivity of GPEs. The strategies on the improvement of the properties of DSSCs based on GPE are also presented.

A synergistic effect of NaYF4:Yb,Er@NaGdF4:Nd@SiO2 upconversion nanoparticles and TiO2 hollow spheres to enhance photovoltaic performance of dye-sensitized solar cells

Introducing upconversion nanoparticles (UCNPs) or fabricating TiO2 hollow spheres (TiO2-HSs) are considered two feasible strategies to enhance the photovoltaic performance of dye-sensitized solar cells (DSSCs). However, studies investigating a combination of UCNPs and TiO2-HSs for the application in DSSCs are still scarce. In this contribution, NaYF4:Yb,Er@NaGdF4:Nd@SiO2 UCNPs and TiO2-HSs were synthesized and respectively applied as upconversion layers and scattering layers on the TiO2 photoanode of DSSCs. The influence of different doping ratios of UCNPs on cell performance was explored. The present results reveal that the DSSCs device based on conventional P25 photoanode films incorporating the UCNPs with 10% can achieve a photovoltaic efficiency of 6.65%, showing 29.63% enhancement in comparison to the device without UCNPs. When the TiO2-HSs are used as scattering layers above the P25 film, the DSSCs device obtains a higher photovoltaic efficiency of 6.97%. More importantly, combining the UCNPs and TiO2-HSs can further enhance the photoelectrical property of DSSCs, realizing an optimal efficiency of 8.17%. Such an improvement can be attributed to a synergistic mechanism arising from the upconversion effect of UCNPs and the light scattering effect of TiO2-HSs. This work opens a new way of preparing composite photoanode films to improve the photovoltaic performances of DSSCs.

Surface Plasmon Resonance and Increased Interfacial Electron Transfer of 3D AgNWS@TiO2NS Structure for Enhanced Photocatalytic and DSSC Properties

Ag nanowires coated with TiO2 nanosheets (AgNWS@TiO2NS, AWT) have been successfully synthesized via a one-pot hydrothermal synthesis. Importantly, the prepared AWT shows enhanced photocatalytic activity compared with Degussa P25, which is attributed to its continuous hierarchical structures, special conductive channel and localized surface plasmon resonance (SPR). Additionally, these prepared AWT were exploited as an electron conductor and scattering material in the TiO2 composite photoanodes of dye-sensitized solar cells (DSSCs). The highest energy conversion efficiency of 6.98% was achieved when the AWT doping rate in the photoanode slurry was 5 wt%. Both enhanced Isc and Voc are attributed to the increased photo-absorption efficiency from the localized SPR. The potential enhanced light-scattering effect and faster photoelectric transmission efficiency of the AWT in the photoanode.

Surfactant assisted approach to development of efficient WO3 photoanode for natural dye sensitized solar cell

Herein, the single-step hydrothermal route has been successfully implemented to design a surfactant-assisted WO3 photoanode for dye-sensitized solar cell (DSSC). The influence of surfactant on growth and photoresponse properties of the dye-sensitized WO3 have been studied. Optical absorption study shows a direct allowed type of electronic transition with band gap energy lies in the range of 2.82–2.38 eV. The formation of pure hexagonal crystal with tuning in the surface morphology from nanospheres to nanoflowers were obtained in the structural and morphological investigation. The compositional analysis confirms the formation of stoichiometric films with respective valence states of W+6 and O2–. Photovoltaic performance of dye-sensitized WO3 demonstrates improved photocurrent from 1.53 to 2.61 mA/cm2 corresponding to photovoltage of 690–764 mV. The best photo-conversion efficiency of 3.52% was obtained for the W-SDS sample of DSSC. The IPCE measurement are well supported to PEC performance of the DSSC. The stability of the prominent W-SDS photoanode was performed to confirm the suitability and reproducibility of photoelectrode. The charge transfer properties of DSSC were analyzed by electrochemical impedance spectroscopy (EIS).

Hollow NiSe2 nanospheres grown on graphene with unconventional dual-vacancies in dye-sensitized solar cells

Although nickel-based counter electrodes display good catalytic properties in dye-sensitized solar cells (DSSCs), there are challenges to achieve efficient activity for practical device. Except that, vacancy can effectively regulate electrocatalytic efficiency for the catalytic reactions, which take place on the surface of catalysts. Thereby, the hollow Ni0.85Se nanospheres grown on the reduced graphite oxide (RGO) were designed to attain the composites utilizing a facile hydrothermal strategy, and followed by heating within argon atmosphere at 400 °C (NiSe2-400) and 450 °C (NiSe2-450), forming NiSe2/RGO composite catalysts with abundant vacancies. Importantly, the resultant NiSe2-400 as counter electrode (CE) exhibits superior electrochemical properties in DSSCs, thus yielding a remarkable photovoltaic performance (8.93%), which may originate from the existence of the appropriate Ni-Se dual vacancies, accelerating the I3− reduction. The work would provide a strategy for the synthesis of other non-noble metal compounds with unconventional dual vacancies to develop the application of DSSCs.

New tetrazole based dyes as efficient co-sensitizers for dsscs: Structure-properties relationship

Two new compounds based on the phenyltetrazole system, 5-(4-decyloxyphenyl)tetrazole ( LTz-4 ) and N , N -diethyl-4-{[(2′-nitro-4′-tetrazoyl)phenyl]diazenyl}aniline ( SD - 6 ), were synthesized and characterized as co-adsorbents in Dye-Sensitized Solar Cells (DSSCs). The effects of hydrophobic chain length and anchoring group on the properties of DSSCs containing the previously reported dye HD-14 and compared with the benchmark deoxycholic acid ( DCA ) are described. The charge-transfer resistance of dye/TiO 2 interface followed the order HD-14 – SD - 6 > HD-14 – LTz-4 > HD-14 – DCA . However, the V OC for the dye HD-14 with co-adsorbent DCA was 0.71 V, for the and the dye HD-14 with co-adsorbent LTz-4 was 0.70 V and for the dye HD-14 with co-adsorbent SD - 6 was 0.67 V. Co-adsorbents LTz-4 and SD - 6 achieved mean solar-to-power conversion efficiencies (%η), for three devices, of 9.20 and 7.48, respectively, compared to 9.14 for DCA under the same experimental device conditions. For LTz-4 co-adsorbent, the results can be attributed to the repellent effect of the long alkyl chain that prevents the charge recombination on the semiconductor surface. For SD - 6 , the molecular volume of the co-adsorbent and the presence of the nitro group in a lateral position should make it difficult to form a more compact layer with the dye. The sum of these contributions would allow the electrolyte to approach, reducing the efficiency of electron injection into TiO 2 . • Compact layer with charge-transfer from dye to the co-adsorbent system by π-π stacking interactions. • Co-adsorbent allows of photons capture and injection of electrons into TiO 2 . • The change in the length of the hydrophobic chain of the phenyl thetrazole co-adsorbent does not produce significant changes in efficiency in dye-sensitized solar cells (DSSC). • The use of tetrazole anchor group in co-adsorbent allows increasing efficiency in DSSCs.

Theoretical and Conceptual Framework to Design Efficient Dye-Sensitized Solar Cells (DSSCs): Molecular Engineering by DFT Method

Herein, eight new donor-π-acceptor organic dyes namely M1–M8 have been theoretically investigated for their potential in optoelectronic properties. The M1–M8 were designed through structural modification of π-conjugated bridge of reference reported molecule IC2. The designed molecules contain Indolo[3,2,1-jk]carbazole as core donor unit and end capped cyanoacrylic acid as acceptor unit. DFT and TDDFT calculations using B3LYP, CAM-B3LYP, ωB97XD and M062X functional were performed to evaluate the photophysical and photovoltaic properties. Results indicate that HOMO–LUMO energy gaps in M1–M8 have been found smaller than IC2. Among all, M7 is a material with lowest energy gap 2.61 eV, red shifted absorption wavelength value 436 nm. Results of the calculated redox potential of the ground state, vertical excitation energy of the dye, oxidation potential of the dye in the excited state, free energy change for electron injection, dye regeneration and open circuit photovoltage and light harvesting efficiency indicates that π-bridges in M1–M8 would show better power conversion efficiency than IC2. Especially, dye M7 with π-bridge 5-(thiazol-5yl)thiazole is found to be the most promising candidate for highly effective DSSCs properties. This theoretical framework may provide new ways for experimentalists to design high-performance DSSCs materials for optoelectronic applications.

Dye-sensitized solar cells based on graphene oxide and natural plant dye extract

The world is advancing quickly in terms of population and technology and this has placed a high demand on energy. The exploitation of conventional sources of energy such as fossil fuel, has proven to be harmful to the environment and its biota. Consequently, there is a need to exploit clean, renewable and sustainable sources of energy like the sun. Dye-sensitized solar cells (DSSCs) have been of particular interest owing to their low price-to-performance ratio, relatively low cost of fabrication, availability of raw materials and eco-friendliness. The performance of the cell is highly dependent on the materials used for each of its components: the sensitizer, photoanode, counter electrode and the electrolyte. This work was carried out to study the photovoltaic properties of DSSCs based on TiO2-GO photoanodes sensitized with natural dye pigments. Graphene oxide (GO), synthesized from graphite by Hummer’s method, was incorporated into the photoanodes to study the effects of its varying composition on the photovoltaic performance of the cells. GO was incorporated into the photoanodes by forming a nanocomposite layer (GO-TiO2) onto a pristine TiO2 nanoparticle layer to form double-layer sensitized photoanodes. The synthesized GO was characterized by UV–vis spectroscopy showing an absorbance peak at 221 nm wavelength, characteristic of GO. Mimosa pudica dye, a chlorophyll dye, was extracted from the leaves of the photosensitive green plant to sensitize the photoanodes. The photovoltaic properties of the cells were evaluated by current density–voltage (JV) curves. Promising results were observed. Generally, the incorporation of GO in the double layer photoanodes enhanced the photovoltaic properties of the cells. This led to a 41% improvement in efficiency for 0.71 wt% GO double layer based DSSC compared to the single layer nanoparticle based DSSC. The highest efficiency was recorded for the double layer (DL) photoanode with 0.71 wt% GO composition (Voc = 0.284, Jsc = 16.085, FF = 0.00035, η = 0.1%). Furthermore, single-layer chlorophyll-sensitized photoanodes were compared with single-layer anthocyanin-sensitized photoanodes using Rhoeo spathacea and Hibiscus rosa-sinensis dye extracts. The highest efficiency was recorded for the TiO2/ Hibiscus rosa-sinensis (Voc = 0.468, Jsc = 0.039, FF = 0.485, η = 0.55%).

Natural dyes as photo-sensitizer in solar cells

The objective of this research is to employ the natural dyes in dye-sensitized solar cell (DSSC). On account of eco-friendly, renewable, and non-hazardous properties of natural dyes over silicon, a semiconductor, photo-sensitizer in conventional solar cells, cyclohexane extract of Terminalia alata, a natural dye, was employed as photo-sensitizer. The photoanodes ZnO and 5% Al-doped ZnO for DSSCs were developed by spray pyrolysis. The X-ray diffraction (XRD) has shown hexagonal wurtzite structure of ZnO with lattice constants a = 3.2487 Å and b = 5.1518 Å having particle size 25.85 nm for ZnO and 33.17 nm for Al-doped ZnO. The DSSC properties such as solar conversion efficiency (η), short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) were found to be 0.31%, 2.10 mA/cm2, 0.73V, and 45% for ZnO photoanode and 0.37%, 2.25mA/cm2, 0.70 V, and 52.10% for 5% Al-doped photoanode respectively.
 BIBECHANA 17 (2020) 27-32

Preparation and Characterization of Submicron Star-Like ZnO as Light Scattering Centers for Combination with ZnO Nanoparticles for Dye-Sensitized Solar Cells

Submicron star-like ZnO (ZnO SZ) was synthesized via a facile hydrothermal method, and a series of composite photoanode materials with different ZnO SZ concentrations in the range from 0 wt.% to 0.20 wt.% were synthesized by a mechanical mixing method. The as-prepared samples were characterized by x-ray diffraction analysis, scanning electron microscopy, ultraviolet–visible (UV–Vis) absorption spectroscopy, etc. The results clearly showed that the mean diameter of the ZnO SZ was approximately 300 nm while its length was in the micrometer range, and the ZnO SZ was embedded homogeneously into the ZnO nanoparticle photoanode. Although UV–Vis spectral analysis revealed that increasing the ZnO SZ content decreased the dye adsorption density of the composite photoanode, the photocurrent density–voltage (J–V) characteristic indicated that dye-sensitized solar cells (DSSCs) using the ZnO SZ/ZnO composite photoelectrode exhibited significantly improved photovoltaic performance compared with those using pure ZnO nanoparticles. Electrochemical measurements revealed that DSSCs using 0.10 wt.% ZnO SZ showed improved efficiency of light energy conversion of 1.38%, being 43.75% higher than when using pure ZnO. All these results prove that incorporation of ZnO SZ into the ZnO nanoparticle photoelectrode represents a highly effective method for improving the photovoltaic properties of DSSCs.

Prediction of Second-Order Nonlinear Optical Properties of D–π–A Compounds Containing Novel Fluorene Derivatives: A Promising Route to Giant Hyperpolarizabilities

Herein, first attempt has been made to utilize fluorene-based dye-sensitized solar cell (DSSCs) dye JK-201 as potential nonlinear optical (NLO) material and for the theoretical designing of novel NLO chromophores JK-D1–JK-D12. DFT/TDDFT calculations were performed to compute the effect of π-linkers and acceptors-steered modulation on electronic, photophysical and NLO properties of JK-201 and JK-D1–JK-D12. Results illustrate that computed λmax (484.74 nm) and experimentally calculated λmax (481 nm) of JK-201 was found in good agreement. Maximum red shifted absorption spectrum was observed in JK-D12 with 599.38 nm. JK-D1–JK-D12 showed narrow energy gap and broader absorption spectrum as compared to JK-201. NBO analysis confirmed the formation of charge separation state due to robust range of electrons/charge transfer from donor to acceptor via π-bridge. Giant NLO response was observed in all compounds. Particularly, JK-D12 displayed surprisingly large 〈α〉 and βtot computed 1376.74 (a.u.) and 405,731.84 (a.u.) respectively. Although literature is flooded with D–π–A compounds investigated for their DSSCs properties, but research reports on their NLO properties and utilization as NLO materials are completely deserted. Our research will open new horizons to explore DSSCs materials for NLO applications. This theoretical framework also exposed that fluorene-substituted chromophores are excellent NLO candidates for modern hi-tech applications.