30 research outputs found
Bulk Heterojunction versus Diffused Bilayer: The Role of Device Geometry in Solution p-Doped Polymer-Based Solar Cells
We exploit the effect of molecular p-type doping of P3HT in diffused bilayer (DB) polymer solar cells. In this alternative device geometry, the p-doping is accomplished in solution by blending the F<sub>4</sub>-TCNQ with P3HT. The p-doping both increases the film conductivity and reduces the potential barrier at the interface with the electrode. This results in an excellent power conversion efficiency of 4.02%, which is an improvement of ∼48% over the p-doped standard bulk heterojunction (BHJ) device. Combined <i>V</i><sub>OC</sub>–light intensity dependence measurements and Kelvin probe force microscopy reveal that the DB device configuration is particularly advantageous, if compared to the conventional BHJ, because it enables optimization of the donor and acceptor layers independently to minimize the effect of trapping and to fully exploit the improved transport properties
Charge Carrier Generation and Extraction in Hybrid Polymer/Quantum Dot Solar Cells
Here we investigate charge carrier
generation and extraction processes
in hybrid polymer/nanocrystal solar cells by means of time-resolved
optical and photoelectrical techniques. We addressed the role of both
polyÂ(3-hexylthiophene) and colloidal arenethiolate-capped PbS quantum
dots, which constitute the hybrid composite nanomaterial, in the photoinduced
processes most relevant to device operation by changing the compositional
ratio and applying chemical and thermal postdeposition treatments.
The carrier generation processes were found to be wavelength-dependent:
excitons generated in the polymer domains led to long-lived weakly
bound charge pairs upon electron transfer to PbS nanocrystals; whereas
charge carrier generation in the nanocrystal domains is highly efficient,
although effective separation required the application of external
electric field. Overall, charge carrier generation was found efficient
and almost independent of the strength of applied electric field;
therefore, competition between separation of electron–hole
pairs into free carriers and geminate recombination is the major factor
limiting the fill factor of nanocomposite-based solar cells. Device
efficiency improvements thus require faster interfacial charge transfer
processes, which are deeply related to the refinement of nanocrystal
surface chemistry
Multilayered Magnetic Nanobeads for the Delivery of Peptides Molecules Triggered by Intracellular Proteases
In
this work, the versatility of layer-by-layer technology was combined
with the magnetic response of iron oxide nanobeads to prepare magnetic
mesostructures with a degradable multilayer shell into which a dye
quenched ovalbumin conjugate (DQ-OVA) was loaded. The system was specifically
designed to prove the protease sensitivity of the hybrid mesoscale
system and the easy detection of the ovalbumin released. The uptake
of the nanostructures in the breast cancer cells was followed by the
effective release of DQ-OVA upon activation via the intracellular
proteases degradation of the polymer shells. Monitoring the fluorescence
rising due to DQ-OVA digestion and the cellular dye distribution,
together with the electron microscopy studying, enabled us to track
the shell degradation and the endosomal uptake pathway that resulted
in the release of the digested fragments of DQ ovalbumin in the cytosol
[1]Benzothieno[3,2‑<i>b</i>]benzothiophene-Based Organic Dyes for Dye‑Sensitized Solar Cells
Three new metal-free organic dyes with the [1]ÂbenzothienoÂ[3,2-<i>b</i>]Âbenzothiophene (BTBT) Ï€-bridge, having the structure
donor-Ï€-acceptor (D-Ï€<i>-</i>A) and labeled
as <b>19</b>, <b>20</b> and <b>21</b>, have been
designed and synthesized for application in dye-sensitized solar cells
(DSSC). Once the design of the π-acceptor block was fixed, containing
the BTBT as the π-bridge and the cyanoacrylic group as the electron
acceptor and anchoring unit, we selected three donor units with different
electron-donor capacity, in order to assemble new chromophores with
high molar extinction coefficients (ε), whose absorption features
well reflect the good performance of the final DSSC devices. Starting
with the <b>19</b> dye, which shows a molar extinction coefficient
ε of over 14,000 M<sup>–1</sup> cm<sup>–1</sup> and takes into account the absorption maximun at the longer wavelength,
the substitution of the BFT donor unit with the BFA yields a great
enhancement of absorptivity (molar extinction coefficient ε
> 42,000 M<sup>–1</sup> cm<sup>–1</sup>), until reaching
the higher value (ε > 69,000 M<sup>–1</sup> cm<sup>–1</sup>) with the BFPhz donor unit. The good general photovoltaic
performances
obtained with the three dyes highlight the suitable properties of
electron-transport of the BTBT as the π-bridge in organic chromophore
for DSSC, making this very cheap and easy to synthesize molecule particularly
attractive for efficient and low-cost photovoltaic devices
Shape and Morphology Effects on the Electronic Structure of TiO<sub>2</sub> Nanostructures: From Nanocrystals to Nanorods
We carry out an accurate computational analysis on the nature and distribution of electronic trap states in shape-tailored anatase TiO<sub>2</sub> structures, investigating the effect of the morphology on the electronic structure. Linear nanocrystal models up to 6 nm in length with various morphologies, reproducing both flattened and elongated rod-shaped TiO<sub>2</sub> nanocrystals, have been investigated by DFT calculations, to clarify the effect of the crystal facet percentage on the nanocrystal electronic structure, with particular reference to the energetics and distribution of trap states. The calculated densities of states below the conduction band edge have been very well fitted assuming an exponential distribution of energies and have been correlated with experimental capacitance data. In good agreement with the experimental phenomenology our calculations show that elongated rod-shaped nanocrystals with higher values of the ratio between (100) and (101) facets exhibit a relatively deeper distribution of trap states. Our results point at the crucial role of the nanocrystal morphology on the trap state density, highlighting the importance of a balance between the low-energy (101) and high-energy (100)/(001) surface facets in individual TiO<sub>2</sub> nanocrystals
Stark Effect in Perovskite/TiO<sub>2</sub> Solar Cells: Evidence of Local Interfacial Order
To
unveil the mechanisms controlling photovoltaic conversion in
high-performing perovskite-based mesostructured solar cells, we focus
on the key role played by the mesoporous oxide/perovskite interface.
We employ several spectroscopic techniques to design a complete scenario
and corroborate our results with first principle density functional
theory calculations. In particular Stark spectroscopy, a powerful
tool allowing interface-sensitive analysis is employed to prove the
existence of oriented permanent dipoles, consistent with the hypothesis
of an ordered perovskite layer, close to the oxide surface. The existence
of a structural order, promoted by specific local interactions, could
be one of the decisive reasons for highly efficient carriers transport
within perovskite films
Role of Polymer in Hybrid Polymer/PbS Quantum Dot Solar Cells
Hybrid
nanocomposites (HCs) obtained by blend solutions of conjugated
polymers and colloidal semiconductor nanocrystals are among the most
promising materials to be exploited in solution-processed photovoltaic
applications. The comprehension of the operating principles of solar
cells based on HCs thus represents a crucial step toward the rational
engineering of high performing photovoltaic devices. Here we investigate
the effect of conjugated polymers on hybrid solar cell performances
by taking advantage from an optimized morphology of the HCs comprising
lead sulfide quantum dots (PbS QDs). Uncommonly, we find that larger
photocurrent densities are achieved by HCs incorporating wide-bandgap
polymers. A combination of spectroscopic and electro-optical measurements
suggests that wide-bandgap polymers promote efficient charge/exciton
transfer processes and hinder the population of midgap states on PbS
QDs. Our findings underline the key role of the polymer in HC-based
solar cells in the activation/deactivation of charge transfer/loss
pathways
Sustainability of Organic Dye-Sensitized Solar Cells: The Role of Chemical Synthesis
The
synthesis of a novel and efficient π-extended D-A-π-A
organic sensitizer (<b>G3</b>, η = 8.64%) for dye-sensitized
solar cells has been accomplished by applying the green chemistry
pillars, aiming at overriding traditional routes involving organometallic
intermediates with innovative synthetic strategies for reducing the
waste burden and dye production costs. It has been demonstrated that
the obtainment of a complex target sensitizer can be exclusively pursued
via direct arylation reactions. Green metrics comparison with those
of a traditional synthetic pathway clearly indicates that the new
approach has a lower environmental impact in terms of chemical procedures
and generated wastes, stressing the importance of the synergy between
the molecular design and the synthetic plan in the framework of environmentally
friendly routes to back up sustainable development of third-generation
photovoltaics. Additionally, the stability of the <b>G3</b>-based
photovoltaic devices was also investigated in aging tests on large
area devices, evidencing the excellent potentialities of the proposed
structure for all practical applications involving inorganic semiconductor/organic
dye interfaces
Electrochemical Assessment of the Band-Edge Positioning in Shape-Tailored TiO<sub>2</sub>‑Nanorod-Based Photoelectrodes for Dye Solar Cells
Three families of linear shaped TiO<sub>2</sub> anatase
nanocrystals
with variable aspect ratio (4, 8, 16) and two sets of branched TiO<sub>2</sub> anatase nanocrystals (in the form of open-framework sheaf-like
nanorods and compact braid-like nanorod bundles, respectively) were
employed to fabricate high-quality mesoporous photoelectrodes and
then implemented into dye-sensitized solar cells to elucidate the
intrinsic correlation holding between the photovoltaic performances
and the structure of the nanocrystal building blocks. To this aim,
the chemical capacitance and the charge-transfer resistance of the
photoelectrodes were extrapolated from electrochemical impedance spectroscopy
measurements and used to draw a quantitative energy diagram of the
dye-sensitized solar cells realized, on the basis of which their photovoltaic
performances have been discussed. It has thus been revealed that photoanodes
made from braid-like branched-nanorod bundles exhibited the most favorable
conditions to minimize recombination at the interface with the electrolyte
due to their deep distribution of trap states, whereas linear-shaped
nanorods with higher aspect-ratios result in more remarkable downshift
of the conduction band edge
Mid-Infrared Plasmonic Excitation in Indium Tin Oxide Microhole Arrays
Transparent
conducting oxides (TCOs) are emerging as possible alternative
constituent materials to replace noble metals such as silver and gold
for low-loss plasmonic applications in the near-infrared (NIR) and
mid-infrared (MIR) regimes. In particular, TCO-based nanostructures
are extensively investigated for biospectroscopy exploiting their
surface-enhanced infrared absorption (SEIRA). The latter enhances
the absorption from vibrational and rotational modes of nearby biomolecules,
making TCO nanostructures a promising candidate for IR sensing applications.
Nevertheless, in order to produce inexpensive devices for lab-on-a-chip
diagnostics, it would be favorable to achieve surface-enhanced infrared
absorption with very simple microstructures not requiring nanosize
control. In this work, we attempt to demonstrate a SEIRA effect with
the least challenging fabrication, μm-scale instead of nm-scale,
by tailoring both device design and charge density of the indium tin
oxide (ITO) film. We show that microperiodic hole arrays in a ITO
film are able to produce SEIRA via grating coupling. Such a study
opens the way for innovative and disrupting biosensing devices