Geometrically twisted intra-inter-molecular cooperative interactions for an enhanced photo-response in an ORMOSIL-based host-guest system

In situ encapsulation of the 2-(2'-hydroxylphenyl)benzothiazole (HBT) fluorophore into organically modified silica (ORMOSIL) is recognized as a potential approach to increase the photocurrent conversion efficiency. Encapsulation resulted in a twisted geometrical configuration of HBT with an efficient charge transfer and increased carrier density, resulting in a 246% photo-response enhancement.

Hollow nanostructures of metal oxides as next generation electrode materials for supercapacitors

Hollow nanostructures of copper oxides help to stabilize appreciably higher electrochemical characteristics than their solid counter parts of various morphologies. The specific capacitance values, calculated using cyclic voltammetry (CV) and charge-discharge (CD) studies, are found to be much higher than the values reported in literature for copper oxide particles showing  intriguing morphologies or even composites with trendy systems like CNTs, rGO, graphene, etc. The proposed cost-effective synthesis route makes these materials industrially viable for application in alternative energy storage devices. The improved electrochemical response can be attributed to effective access to the higher number of redox sites that become available on the surface, as well as in the cavity of the hollow particles. The ion transport channels also facilitate efficient de-intercalation, which results in the enhancement of cyclability and Coulombic efficiency. The charge storage mechanism in copper oxide structures is also proposed in the paper.

Rational design of hierarchical ZnO superstructures for efficient charge transfer: mechanistic and photovoltaic studies of hollow, mesoporous, cage-like nanostructures with compacted 1D building blocks

Exotic 3D ZnO superstructures are synthesized utilizing a biomass derived polysaccharide “sodium alginate” and their photovoltaic properties are evaluated.

Improving the photovoltaic performance of dye sensitized solar cells based on a hierarchical structure with up/down converters

A hierarchical photoanode constructed from G,TiO₂:Er³⁺,Yb³⁺ NRs and Al₂O₃:Eu³⁺ exhibits enhanced efficiency.

Ethyl Cellulose and Cetrimonium Bromide Assisted Synthesis of Mesoporous, Hexagon Shaped ZnO Nanodisks with Exposed ±{0001} Polar Facets for Enhanced Photovoltaic Performance in Quantum Dot Sensitized Solar Cells

Hexagon shaped mesoporous zinc oxide nanodisks (ZnO NDs) with exposed ±{0001} polar facets have been synthesized by using ethyl cellulose (EC) and cetrimonium bromide (CTAB) as the capping and structure directing agents. We have characterized ZnO NDs using analytical techniques, such as powder X-ray diffraction (PXRD), diffuse reflectance UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) surface area analysis and proposed a plausible mechanism for the formation of ZnO NDs. EC molecules form a colloidal solution in a 1-butanol:water (3:1) solvent system having a negative zeta potential (ζ ≈ -32 mV) value which can inhibit CTAB assisted c-axis growth of ZnO crystal and encourage the formation of ZnO NDs. In the control reactions carried out in presence of only CTAB and only EC, formation of hexagonal ZnO nanorods (NRs) and ZnO nanosheets (NSs) composed of numerous ZnO nanoparticles are observed, respectively. Photovoltaic properties of ZnO NDs as compared to ZnO NRs, ZnO NSs, and conventional ZnO nanoparticles (NPs) are investigated by co-sensitizing with CdS/CdSe quantum dots (QDs). An ∼35% increase in power conversion efficiency (PCE, η) is observed in ZnO NDs (η ≈ 4.86%) as compared to ZnO NPs (η ≈ 3.14%) while the values of PCE for ZnO NR and ZnO NS based devices are found to be ∼2.52% and ∼1.64%, respectively. Enhanced photovoltaic performance of the ZnO NDs based solar cell is attributed to an efficient charge separation and collection, boosted by the exposed ±(0001) facets apart from the single crystalline nature, better light-scattering effects, and high BET surface area for sensitizer particle adsorption. Electrochemical impedance spectroscopy (EIS) analysis further reveals that the charge recombination resistance and photoinduced electron lifetime are substantially higher in the ZnO ND based device than in ZnO NR, ZnO NP, and ZnO NS based devices, which demonstrates a slower electron-hole (e(-)-h(+)) recombination rate and faster charge migration through the single crystalline ZnO NDs.

Metal oxide semiconductors for dye- and quantum-dot-sensitized solar cells

This Review provides a brief summary of the most recent research developments in the synthesis and application of nanostructured metal oxide semiconductors for dye sensitized and quantum dot sensitized solar cells. In these devices, the wide bandgap semiconducting oxide acts as the photoanode, which provides the scaffold for light harvesters (either dye molecules or quantum dots) and electron collection. For this reason, proper tailoring of the optical and electronic properties of the photoanode can significantly boost the functionalities of the operating device. Optimization of the functional properties relies with modulation of the shape and structure of the photoanode, as well as on application of different materials (TiO2, ZnO, SnO2) and/or composite systems, which allow fine tuning of electronic band structure. This aspect is critical because it determines exciton and charge dynamics in the photoelectrochemical system and is strictly connected to the photoconversion efficiency of the solar cell. The different strategies for increasing light harvesting and charge collection, inhibiting charge losses due to recombination phenomena, are reviewed thoroughly, highlighting the benefits of proper photoanode preparation, and its crucial role in the development of high efficiency dye sensitized and quantum dot sensitized solar cells.

Highly efficient one-dimensional ZnO nanowire-based dye-sensitized solar cell using a metal-free, D-π-A-type, carbazole derivative with more than 5% power conversion

Hydrothermally grown one-dimensional ZnO nanowire (1D ZnO NW) and a newly synthesized metal-free, D-π-A type, carbazole dye (SK1) sensitizer-based photovoltaic device with a power conversion efficiency (PCE) of more than 5% have been demonstrated by employing the cobalt tris(2,2'-bipyridyl) redox shuttle. A short-circuit current density (Jsc) of ∼12.0 mA/cm(2), an open-circuit voltage (Voc) of ∼719 mV, and a fill factor (FF) of ∼65% have been afforded by the 1D ZnO NW-based dye-sensitized solar cell (DSSC) incorporating [Co(bpy)3](3+/2+) complex as the one-electron redox mediator. In contrast, the identical DSSC with traditional I3(-)/I(-) electrolyte has shown a Jsc ≈ 12.2 mA/cm(2), a Voc ≈ 629 mV, and a FF ≈ 62%, yielding a PCE of ∼4.7%. The persuasive role of the inherent superior electron transport property of 1D ZnO NWs in enhancing the device efficiency is evidenced from the impoverished performance of the DSSCs with photoanodes fabricated using ZnO nanoparticles (NPs). The DSSCs having ZnO NP-based photoanodes have achieved the PCEs of ∼3.6% and ∼3.2% using cobalt- and iodine-based redox electrolytes, respectively. The electronic interactions between the SK1 sensitizer and ZnO (NWs and NPs) to induce the photogenerated charge transfer from SK1 to the conduction band (CB) of ZnO are evidenced from the significant quenching of photoluminescence and exciton lifetime decay of SK1, when it is anchored onto the ZnO architectures. The energetics of the SK1 dye molecule are estimated by combining the spectroscopic and electrochemical techniques. The electronic distributions of SK1 dye molecule in its HOMO and LUMO energy levels are interpreted using density functional theory (DFT)-based calculations. The electron donor-π linker-acceptor (D-π-A) configuration of SK1 dye provides an intramolecular charge transfer within the molecule, prompting the electron migration from the carbazole donor to cyanoacrylic acceptor moiety via the oligo-phenylenevinylene linker group. The D-π-A-mediated electron movement witnesses the favorable photoexcited electron transfer from the LUMO of SK1 dye to the CB of ZnO through the carboxyl anchoring group.