Effect of organic dyes on the performance of ZnO based dye-sensitized solar cells

Experimental and theoretical studies of the influence of alkyl groups on the photovoltaic properties of (E)-6-((2, 3-dihydroxylnaphthalene)diazenyl)-1H-benzoisoquinoline-1,3-dione-based organic solar cell

The manipulation of the active dye material for application in dye-sensitized solar cell (DSSC) using simple or bulky group substituents is necessary for improved dye performance. Herein, we carried out a combined experimental and theoretical studies of different alkylated novel reactive (E)-6-(2,3-dihydroxyl naphthalene diazinyl)-1H-benzoisoquinoline-1,3-dione azo-based dyes using spectral (FTIR, UV-visible, and NMR) analysis and electronic structure theory method based first principle density functional theory (DFT) calculations to investigate the molecular electronic properties, structural analysis, excitation behavior, and the theoretical potential application in photovoltaic cell. The synthesized azo dye (azoD) was theoretically modeled by varying the number of alkyl chains denoted as AzoD₁, AzoD₂, AzoD₃, and AzoD₄ to represent azo dyes having ten (10), twelve (12), fourteen (14), and sixteen (16) alkyl chain length respectively. From the natural bond orbital (NBO) analysis, the higher stabilization energies, 227.80 and 227.77 kcal/mol respectively, recorded for AzoD₁ and AzoD₄ may be due to extra orbital contribution by π*(N₂₁-N₂₂) to π*C₅₄-C₅₆ 31.19 eV for AzoD₁ and π*(N₂₁-N₂₂) → π*(C₅₃-C₅₅) 31.43 eV AzoD₄ confirming that chain length affected the orbital interaction of the molecules. The driving force (ΔG_inject) of electron injection into the TiO₂ surface (- 1.92 to - 1.93) shown in this study is indicative that alkylated azo dyes are good for improved DSSCs performance. Again, the open circuit voltage (V_oc) of 1.090 (AzoD₁), 1.092 (AzoD₂), 1.093 (AzoD₃), and 1.095 (AzoD₄) are also evidence of the suitability of azo dyes as photosensitizers. All the spectroscopic analysis, FTIR, UV-visible, and NMR combined with theoretical calculations, provided accurate data for characterizing the titled azo dye compound and showed that it has good photophysical properties. The presence of alkyl groups and chain length promoted the stability of the dyes thereby making them suitable for application in DSSCs. Increase in chain length as well enhanced the electron injection into the conduction band of the semiconductor.

ZnO nanostructured materials for emerging solar cell applications

Zinc oxide (ZnO) has been considered as one of the potential materials in solar cell applications, owing to its relatively high conductivity, electron mobility, stability against photo-corrosion and availability at low-cost. Different structures of ZnO materials have been engineered at the nanoscale, and then applied on the conducting substrate as a photoanode. On the other hand, the ZnO nanomaterials directly grown on the substrate have been attractive due to their unique electron pathways, which suppress the influence of surface states typically found in the former case. Herein, we review the recent progress of ZnO nanostructured materials in emerging solar cell applications, such as sensitized and heterojunction architectures, including those embedded with promising perovskite materials. The remarkable advancement in each solar cell architecture is highlighted towards achieving high power conversion efficiency and operational stability. We also discuss the foremost bottleneck for further improvements and the future outlook for large-scale practical applications.

Organophilicity of Graphene Oxide for Enhanced Wettability of ZnO Nanorods

Interfacing two-dimensional graphene oxide (GO) platelets with one-dimensional zinc oxide nanorods (ZnO) would create mixed-dimensional heterostructures suitable for modern optoelectronic devices. However, there remains a lack in understanding of interfacial chemistry and wettability in GO-coated ZnO nanorods heterostructures. Here, we propose a hydroxyl-based dissociation-exchange mechanism to understand interfacial interactions responsible for GO adsorption onto ZnO nanorods hydrophobic substrates. The proposed mechanism initiated from mixing GO suspensions with various organics would allow us to overcome the poor wettability (θ ∼ 140.5°) of the superhydrophobic ZnO nanorods to the drop-casted GO. The addition of different classes of organics into the relatively high pH GO suspension with a volumetric ratio of 1:3 (organic-to-GO) is believed to introduce free radicals (-OH and -COOH), which consequently result in enhancing adhesion (chemisorption) between ZnO nanorods and GO platelets. The wettability study shows as high as 75% reduction in the contact angle (θ = 35.5°) when the GO suspension is mixed with alcohols (e.g., ethanol) prior to interfacing with ZnO nanorods. The interfacial chemistry developed here brings forth a scalable tool for designing graphene-coated ZnO heterojunctions for photovoltaics, photocatalysis, biosensors, and UV detectors.

Efficiency Investigations of Organic/Inorganic Hybrid ZnO Nanoparticles Based Dye-Sensitized Solar Cells

The present research study focuses upon the synthesis, characterization, and performances of optoelectronic properties of organic-inorganic (hybrid) ZnO based dye sensitized solar cells. Initially, polymer dye A was synthesized using condensation reaction between 2-thiophenecarboxaldehyde and polyethylenimine and was capped to ZnO nanoparticles. Size and morphology of polymer dye A capped ZnO nanoparticles were analyzed using DLS, SEM, and XRD analysis. Further, the polymer dye was added to ruthenium metal complex (RuCl3) to form polymer-ruthenium composite dye B. Absorption and emission profiles of polymer dye A and polymer-ruthenium composite dye B capped ZnO nanoparticles were monitored using UV-Vis and fluorescence spectroscopy. Polymer dye A and polymer-ruthenium composite dye B capped ZnO nanoparticles were further processed to solar cells using wet precipitation method under room temperature. The results of investigations revealed that, after addition of ruthenium chloride (RuCl3) metal complex dye, the light harvesting capacity of ZnO solar cell was enhanced compared to polymer dye A capped ZnO based solar cell. The polymer-ruthenium composite dye B capped ZnO solar cell exhibited good photovoltaic performance with excellent cell parameters, that is, exciting open circuit voltage (Voc) of 0.70 V, a short circuit current density (Jsc) of 11.6 mA/cm2, and a fill factor (FF) of 0.65. A maximum photovoltaic cell efficiency of 5.28% had been recorded under standard air mass (AM 1.5) simulated solar illuminations for polymer-ruthenium composite dye B based hybrid ZnO solar cell. The power conversion efficiency of hybrid ZnO based dye sensitized solar cell was enhanced by 1.78% and 3.88% compared to polymer dye A (concentrated) and polymer dye A (diluted) capped ZnO based dye sensitized solar cells, respectively. The hybrid organic/inorganic ZnO nanostructures can be implemented in a variety of optoelectronic applications in the future of clean and green technology.