202 research outputs found
Monitoring Charge Exchange in P3HT-Nanotube Composites Using Optical and Electrical Characterisation
Charge exchange at the bulk heterojunctions of composites made by mixing single wall nanotubes (SWNTs) and polymers show potential for use in optoelectronic devices such as solar cells and optical sensors. The density/total area of these heterojunctions is expected to increase with increasing SWNT concentration but the efficiency of solar cell peaks at low SWNT concentrations. Most researchers use currentāvoltage measurements to determine the evolution of the SWNT percolation network and optical absorption measurements to monitor the spectral response of the composites. However, these methods do not provide a detailed account of carrier transport at the concentrations of interest; i.e., near or below the percolation threshold. In this article, we show that capacitanceāvoltage (CāV) response of (metal)-(oxide)-(semiconducting composite) devices can be used to fill this gap in studying bulk heterojunctions. In an approach where we combine optical absorption methods withCāVmeasurements we can acquire a unified optoelectronic response from P3HT-SWNT composites. This methodology can become an important tool for optoelectronic device optimization
Triplet excitations in carbon nanostructures
We show that the energy differences between the lowest optical singlet
exciton and the lowest triplet exciton in semiconducting single-walled carbon
nanotubes with diameter nm and graphene nanoribbons with widths nm are an order of magnitude smaller than in the -conjugated polymer
poly(para-phenylenevinylene). Our calculated energy gaps between the singlet
and triplet excitons are in excellent agreement with the measured values in
three different nanotubes with diameters close to 1 nm. The spatial extent of
the triplet exciton is nearly the same as that of the singlet exciton in wide
nanotubes and nanoribbons, in contrast to that in -conjugated polymers, in
which the triplet exciton exhibits strong spatial confinement. Weakly confined
behavior of the triplet state begins in nanoribbons with widths as narrow as
2.5 times the graphene unit lattice vector. We discuss possible consequences of
the small singlet-triplet energy difference in the carbon nanostructures on
device applications.Comment: 9 pages, 2 tables, 4 figure
Femtosecond Dynamics in Single Wall Carbon Nanotube/Poly(3-Hexylthiophene) Composites
Femtosecond transient absorption measurements on single wall carbon nanotube/poly(3-hexylthiophene) composites are used to investigate the relaxation dynamics of this blended material. The influence of the addition of nanotubes in polymer matrix on the ultrashort relaxation dynamics is examined in detail. The introduction of nanotube/polymer heterojunctions enhances the exciton dissociation and quenches the radiative recombination of composites. The relaxation dynamics of these composites are compared with the fullerene derivative-polymer composites with the same matrix. These results provide explanation to the observed photovoltaic performance of two types of composites
Efficiency and Stability Enhancement in Perovskite Solar Cells by Inserting Lithium-Neutralized Graphene Oxide as Electron Transporting Layer
This work proposes a new perovskite solar cell structure by including lithium-neutralized graphene oxide (GO-Li) as the electron transporting layer (ETL) on top of the mesoporous TiO2 (m-TiO2) substrate. The modified work-function of GO after the intercalation of Li atoms (4.3 eV) exhibits a good energy matching with the TiO2 conduction band, leading to a significant enhancement of the electron injection from the perovskite to the m-TiO2. The resulting devices exhibit an improved short circuit current and fill factor and a reduced hysteresis. Furthermore, the GO-Li ETL partially passivates the oxygen vacancies/defects of m-TiO2 by resulting in an enhanced stability under prolonged 1 SUN irradiation
Stability Enhancement in OPV: In-Situ Studies of Plasmonic Devices
Extended Abstract Bulk heterojunction (BHJ) organic photovoltaic (OPV) devices attracted considerable research interest due to several significant characteristics, such as their flexibility, lightweight, low environmental impact and reduced cost of large-scale production. A key aspect in OPVs is improving the device long-term stability: in this contest, novel organic materials and cell architectures are developed and a significant task is played by the development of in-situ diagnostics able to detect the driving mechanisms of device degradation, considering that the optical and transport properties of the device active elements depend on the structural, morphological and interfacial characteristics. In this work we discuss our recent results on devices incorporating metallic nanoparticles (NPs) in the photoactive layer, in order to take advantage of the ability of the metallic NPs to rise the BHJ optical absorption by the excitation of Localized Surface Plasmon Resonance. Both plasmonic and reference systems are studied and a powerful approach for addressing the role of structural/morphological and interface properties of the different layers and their interfaces is used: time-resolved Energy Dispersive X-ray Reflectivity/Diffraction (EDXR/EDXD) techniques are applied jointly with in-situ atomic force microscopy (AFM). The results of such unconventional approach, based on time-resolved EDXR/AFM cross-monitoring, showed that incorporating metallic NPs allowed to control both the bulk and the interface morphological degradation pathways References [1] B. Paci, A. Generosi, V. Rossi Albertini, G.Spyropoulos, E. Stratakis, E. Kymakis, "Enhancement of photo/thermal stability of organic bulk heterojunction photovoltaic devices via gold nanoparticles doping of the active layer,"
Self-powered, flexible and room temperature operated solution processed hybrid metal halide p-type sensing element for efficient hydrogen detection
Hydrogen (H2) is a well-known reduction gas and for safety reasons is very
important to be detected. The most common systems employed along its detection
are metal oxide-based elements. However, the latter demand complex and
expensive manufacturing techniques, while they also need high temperatures or
UV light to operate effectively. In this work, we first report a solution
processed hybrid mixed halide spin coated perovskite films that have been
successfully applied as portable, flexible, self-powered, fast and sensitive
hydrogen sensing elements, operating at room temperature. The minimum
concentrations of H2 gas that could be detected was down to 10 ppm. This work
provides a new pathway on gases interaction with perovskite materials, launches
new questions that must be addressed regarding the sensing mechanisms involved
due to the utilization of halide perovskite sensing elements while also
demonstrates the potential that these materials have on beyond solar cell
applications
High Electron Mobility Thin-Film Transistors Based on Solution-Processed Semiconducting Metal Oxide Heterojunctions and Quasi-Superlattices
High mobility thināfilm transistor technologies that can be implemented using simple and inexpensive fabrication methods are in great demand because of their applicability in a wide range of emerging optoelectronics. Here, a novel concept of thināfilm transistors is reported that exploits the enhanced electron transport properties of lowādimensional polycrystalline heterojunctions and quasiāsuperlattices (QSLs) consisting of alternating layers of In(2)O(3), Ga(2)O(3,) and ZnO grown by sequential spin casting of different precursors in air at low temperatures (180ā200 Ā°C). Optimized prototype QSL transistors exhibit bandālike transport with electron mobilities approximately a tenfold greater (25ā45 cm(2) V(ā1) s(ā1)) than single oxide devices (typically 2ā5 cm(2) V(ā1) s(ā1)). Based on temperatureādependent electron transport and capacitanceāvoltage measurements, it is argued that the enhanced performance arises from the presence of quasi 2D electron gasālike systems formed at the carefully engineered oxide heterointerfaces. The QSL transistor concept proposed here can in principle extend to a range of other oxide material systems and deposition methods (sputtering, atomic layer deposition, spray pyrolysis, rollātoāroll, etc.) and can be seen as an extremely promising technology for application in nextāgeneration large area optoelectronics such as ultrahigh definition optical displays and largeāarea microelectronics where high performance is a key requirement
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