1,721,260 research outputs found
Photovoltaic characterization of organic solar cells
No full textIn recent years organic solar cells (SCs) have reached power conversion efficiencies above
10% [1]. Organic photovoltaics is indeed an intensively pursued research field because it
promises high efficiency and low cost SCs. Organic materials have unique and useful
optoelectronic properties, their chemical synthesis can be cheap and easy, and can be
deposited in the form of thin films even on flexible plastic substrates by simple deposition
techniques such as spinning, ink-jet printing and high vacuum thermal evaporation. Here we
report results of the photovoltaic characterization of organic SCs having the donor
(D)/acceptor (A) heterojunction structure [2]. The SCs, fabricated by vacuum thermal
deposition on Indium Tin oxide (ITO)-coated glass substrates, have the structure and layer
thicknesses ITO/CuPc (20 nm)/C60 (40 nm)/BCP (12 nm)/Al (80 nm) where CuPc is Copper
phtalocyanine used as D organic material, C60 is fullerene used as A organic material and
BCP is bathocuproine used as exciton blocking layer [3].
The measurement system shown in Fig.1 is used to test the organic SCs, straight after being
taken out from the high vacuum deposition chamber, in ambient atmosphere and without
encapsulation. A calibrated halogen lamp (cold light) is used as light source because its
spectrum, shown in Fig.2, is very close to the solar spectrum except for a lower power in the
NIR with wavelengths above 700 nm. The calibration of the halogen lamp, i.e. the
extrapolation of its optical power density, is carried out by using a calibrated Newport
818-UV Si photodiode with 1 cm2 area and known spectral responsivity i.e. photocurrent over
incident optical power at each wavelength. The “equivalent responsivity” of the photodiode
corresponding to the halogen lamp is calculated by simply weighting the photodiode
responsivity with the normalized optical spectrum of the halogen lamp. The desired incident
optical power density can be set by simply varying the distance D in Fig.1 between the lamp
and the SC surface [4]. The illumination condition used is AM1.0, i.e. vertical incidence and a
standard value of 100 mW/cm2 for the optical power density.
The current density J vs. forward voltage V under illumination is measured by a source-meter
Keithley 6487 for increasing incident optical power density. The J-V characteristics of the
organic SC is shown in Fig. 2 where one notices that the current density increases with
increasing incident optical power density, meaning there are little saturation effects at the used
values of incident optical power density. The organic SC exhibits a good photovoltaic effect
and this can be ascribed to the fullerene layer used as acceptor and, more important, to the
insertion of the exciton blocking layer. The SC exhibits VOC = 0,43 V and JSC = 2,35 mA/cm2
with a fill factor FF ≈ 50%, an external quantum efficiency (electrons/s over incident
photons/s) EQE ≈ 5% and a power conversion efficiency ≈ 0,5%. The not-encapsulated SCs
are very much sensitive to oxygen and humidity induced degradation and we observed the
degradation process in a time interval of 48 hr. Of course the solution to the oxygen and
humidity induced degradation problem is the encapsulation of the organic SCs in an inert
atmosphere (glove box) with an air tight packaging of the devices. However our results are
certainly a good starting point for further improvements. References
[1] Martin A. Green et al., “Solar cell efficiency tables (version 49)”, Prog. Photovolt: Res. Appl.,
Vol.25, 2017, pp.3-13
[2] C. W. Tang et al., “Two-Layer Organic Photovoltaic Cell”, Appl. Phys. Lett. Vol.48(2), 1986,
pp.183-185
[3] B. P. Rand J. Li J. Xue R. J. Holmes M. E. Thompson S. R. Forrest, “Organic
Double‐ Heterostructure Photovoltaic Cells Employing Thick Tris(acetylacetonato)ruthenium(III)
Exciton‐ Blocking Layers,” Adv. Mater., Vol.17, 2005, pp. 2714-2718.
[4] P. Cona, “Realizzazione e caratterizzazione fotovoltaica di celle solari organiche”, Master Degree
Thesis in Electronic Engineering, University of Palermo, A.A. 2005-200
Clinostratificazione o inclinazione tettonica degli strati? Rivisitazione dei conglomerati del Serravalliano medio-Tortoniano inferiore dei Mt. Peloritani e implicazioni paleogeografiche.
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Nonlinear Disorder Mapping Through Three-Wave Mixing
No full textWe implement a simple and powerful approach to characterize the domain distribution in the bulk of quadratic ferroelectric crystals via far-field second-harmonic spectroscopy. The approach is demonstrated in a lithium tantalate sample with periodic electric field poling and random mark-to-space ratio
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Dai geositi al geoparco: proposta di protezione e valorizzazione del patrimonio geologico della provincia di Ragusa
No full textNovel Configuration for a C-Band Axial Vircator With High Output Power
Full text linkWe present a novel configuration for an axial virtual cathode oscillator (Vircator) operating in the C-band and designed for high output power applications. In order to enhance the efficiency, we have employed a geometry with up to seven reflectors along the drift space. While in previous research works this optimization process has been
performed only varying the reflectors radii while using a fixed distance between reflectors,in our work we propose an optimization in terms of both reflectors radii and distances. Our optimized structure for the axial Vircator is able to provide an efficiency up to 15.6% and an output power of 1.6 GW in the C-band, with a working voltage of 510 kV and a cathodic current of 24 kA
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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