23 research outputs found
Conditions for efficient charge generation preceded by energy transfer process in non-fullerene organic solar cells
The minimum driving force strategy is applied to promote the exciton
dissociation in organic solar cells (OSCs) without significant loss of
open-circuit voltage. However, this strategy tends to promote F\"orster
resonance energy transfer (FRET) from the donor to the acceptor (D-A), a
consequence generally ignored until recently. In spite of the advances reported
on this topic, the correlation between charge-transfer (CT) state binding
energy and driving force remains unclear, especially in the presence of D-A
FRET. To address this question, we employ a kinetic approach to model the
charge separation in ten different D/A blends using non-fullerene acceptors.
The model considers the influence of FRET on photoluminescence (PL) quenching
efficiency. It successfully predicts the measured PL quenching efficiency for D
or A photoexcitation in those blends, including the ones for which the D-A FRET
process is relevant. Furthermore, the application of the model allows to
quantifying the fractions of quenching loss associated with charge transfer and
energy transfer. Fundamental relationships that controls the exciton
dissociation was derived evidencing the key roles played by the Marcus inverted
regime, exciton lifetime and mainly by the correlation between the driving
force and binding energy of CT state. Based on those findings, we propose some
strategies to maximize the quenching efficiency and minimize energy loss of
OSCs in the presence of D-A FRET.Comment: 44 pages, 10 figures, 3 table
FRETCalc: A Free Software and Web Server for F\"orster Resonance Energy Transfer Calculation
F\"{o}rster Resonance Energy Transfer Calculator (FRETCalc) is a program
and web server that analyzes molar extinction coefficient of the acceptor,
emission spectrum of the donor, and the refractive index spectrum of the
donor/acceptor blend. Its main function is to obtain important parameters of
the FRET process from experimental data, such as: (i) effective refractive
index, (ii) overlap integral, (iii) F\"{o}rster radius, (iii) FRET efficiency
and (iv) FRET rate. FRETCalc is license free software that can be run via
dedicated web server (nanocalc.org) or downloading the program executables (for
Unix, Windows, and macOS) from the FRETCalc repository on GitHub. The
program features a userfriendly interface, making it suitable for materials
research and teaching purposes. In addition, the program is optimized to run on
normal computers and is lightweight. An example will be given with the step by
step of its use and results obtained.Comment: 7 pages, 6 figure
Comparing C-60 and C-70 as acceptor in organic solar cells : Influence of the electronic structure and aggregation size on the photovoltaic characteristics
The difference in aggregation size of the C-60 and C-70 fullerenes affect the photovoltaic performance of devices assembled in the so-called bilayer architecture with poly [2,7-(9,9- dioctyl- dibenzosilole)- alt-4,7- bis(thiophen-2-yl)benzo- 2,1,3- thiadiazole] (PSiF-DBT) as the electron donor material. Despite the better performance of the C-70 devices, which is related to the high absorption coefficient in the visible range and the superior charge transport properties, the short-circuit current variation upon annealing treatment at 100 degrees C is approximately twice bigger when the C-60 is the acceptor. We attribute this effect to the tendency of C-60 in form smaller aggregate domains relatively to the C-70. The increased roughness on the polymeric surface after annealing results in an enhanced donor/acceptor contact area and assists the fullerene diffusion deeper inside the polymeric layer. This effect leads to a better mixing between donor and acceptor species and create a interpenetrating layer close to the so-called bulk heterojunction. Since C-60 forms smaller aggregates, this mechanism is more pronounced for this molecule. Therefore, a significant variation in the performance of the C-60 devices is observed after this kind of treatment. Density Functional Theory calculations of the potential energy of interaction between two fullerene molecules and X-Ray measurements gives evidences to support this idea. In addition, combining spectrally resolved external quantum efficiency measurements with optical modeling our results also indicate the occurrence of the bilayer interfacial mixing for PSiF-DBT/C-60.Peer reviewe
Interlaboratory comparison of methodologies for measuring the angle of incidence dependence of solar cells
The aim of this work is to compare angle of incidence (AOI) measurement setups for solar cells between laboratories with such capability. For the first time, we compare relative light transmission measurements among eight laboratories, whose measurement techniques include indoor and outdoor methods. We present the relative
transmission measurements on three 156 mm x 156 mm crystalline-Si (c-Si) samples with different surface textures. The measurements are compared using the expanded uncertainties provided by each laboratory. Five of the eight labs showed an agreement better than ±2% to the weighted mean between AOIs from -75° to 70°. At AOIs of ±80° and ±85°, the same five labs showed a worst case deviation to the weighted mean of -3% to 5% and 0% to 18%, respectively. When
measurement uncertainty is considered, the results show that measurements at the highest incidence angle of ±85° are
problematic, as measurements from four out of the six labs reporting uncertainty were found non-comparable within their stated uncertainties. At 85° AOI a high to low range of up to 75% was observed between all eight laboratories
Manual therapy for chronic migraine: a pragmatic randomised controlled trial study protocol
Introduction Chronic migraine is a largely refractory condition affecting between 1 and 2.2% of the overall population worldwide, with females more affected than males. There are also high health and socioeconomic costs associated both for the individual and society. The mainstay of chronic migraine management is pharmacological, but the options available have limited efficacy and there are often unwanted side effects. There is some evidence for manual therapy as a treatment option for migraine, but its effectiveness for chronic migraine is unknown. Therefore, we have designed a pragmatic randomised control trial to investigate whether adding manual therapy to the tertiary specialist treatment of chronic migraine improves patient-reported outcomes. Methods A pragmatic, randomised controlled trial in a hospital tertiary headache clinic. Participants will be randomised into one of two groups: treatment as usual or treatment as usual plus manual therapy. The primary outcome measure will be a change in the Headache Impact Test score. Secondary outcomes will also be measured over the 12-week study period including changes in headache frequency, migraine specific quality of life and reductions in relevant medicine consumption. The manual therapy group will have five treatment sessions each lasting 30 min. The recruitment target of 64 participants will allow power at 80% with p = 0.05 using minimal clinical difference for Headache Impact Test of 3.7 and includes provision for a 10% dropout rate. Recruitment will take place between August 2018 and February 2019. The results will form part of a doctoral study and be published in peer-reviewed journals and presented at national/international conferences. Discussion Current pharmacological approaches have limited effects in the management of chronic migraine and there is a requirement to improve treatment options and reduce the health and economic burden of the condition. Manual therapy has been shown to be effective in other chronic pain conditions as well as other primary headaches. This study will explore the effectiveness of manual therapy as an adjunctive approach to the management of chronic migraine. Trial registration The trial has received a favourable opinion from the UK Health Research Authority (IRAS 228901) and is registered at ClinicalTrials.gov.number NCT03395457. Registered 1st March 2018
Conformational Change on a Bithiophene-Based Copolymer Induced by Additive Treatment: Application in Organic Photovoltaics
In recent years the use of solvent
additives for fabrication of
polymer-based solar cells has become an important procedure to induce
morphological changes at the system nanoscale, a critical step to
improve device performance. Yet the actual effects of those additives
on the polymer’s backbone conformations (with coupled variations
on the electronic structure) remain very elusive. By combining different
experimental and theoretical techniques, we show that the use of the
solvent additive 1,8-diiodooctane (DIO) might influence the conformation
of polyÂ[(9,9-dioctylfluorenyl-2,7-diyl)-<i>co</i>-bithiophene]
(F8T2) chains resulting in improved properties of the film. We correlate
this conformational variation with the photovoltaic response of F8T2:fullereneÂ(C<sub>60</sub>) devices prepared using different DIO concentrations. We
find that the efficiency of the devices increases more than 100%,
and the hole mobility in the F8T2 films increases almost 1 order of
magnitude with the use of DIO. A comparison between experimental data
and the properties of the calculated structures suggests that the
additive induces a higher density of syn conformers in the bithiophene
unit of the copolymer backbone, planarizing the polymer’s geometry.
The simulations indicate that this transition is very likely mediated
by the electrostatic interaction between the iodine atom of the DIO
and the heteroatoms of the bithiophene moiety. The higher degree of
electronic delocalization and the enhancement of the interchain interactions
improve the transport and the photovoltaic features of F8T2 layers.
The use of solvent additive treatments to control conformational variations
of the backbone might be a promising strategy to improve the optoelectronic
properties of polymer-based devices
Interlaboratory comparison of methodologies for measuring the angle of incidence dependence of solar cells
The aim of this work is to compare angle of incidence (AOI) measurement setups for solar cells between laboratories with such capability. For the first time, we compare relative light transmission measurements among eight laboratories, whose measurement techniques include indoor and outdoor methods. We present the relative transmission measurements on three 156 mm x 156 mm crystalline-Si (c-Si) samples with different surface textures. The measurements are compared using the expanded uncertainties provided by each laboratory. Five of the eight labs showed an agreement better than ±2% to the weighted mean between AOIs from -75° to 70°. At AOIs of ±80° and ±85°, the same five labs showed a worst case deviation to the weighted mean of -3% to 5% and 0% to 18%, respectively. When measurement uncertainty is considered, the results show that measurements at the highest incidence angle of ±85° are problematic, as measurements from four out of the six labs reporting uncertainty were found non-comparable within their stated uncertainties. At 85° AOI a high to low range of up to 75% was observed between all eight laboratories