Hybrid organic-inorganic photodiode interfaces have gained significant interest due to their unique physical properties such as mechanical flexibility and high photosensitivity. Two ...diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers with different backbone conformations are characterized in an inverted non-fullerene photodiode architecture using ZnO nano-patterned films as the electron transport layer. The DPP copolymer with a thienothiophene unit (PBDT-TTDPP) is more planar and rigid compared to the DPP system with a thiophene unit connecting the donor and acceptor moieties within the monomer (PBDT-TDPP). The hybrid interfaces were optimized by using poly(3-hexylthiophene) (P3HT) as the p-type layer for monitoring the critical thickness and morphology of the ZnO layer. The maximum photoresponsivity from a P3HT:ZnO photodiode was found to be 56 mA/W. The photoresponsivity of PBDT-TTDPP:ZnO photodiodes were found to be more than two orders of magnitude higher than PBDT-TDPP:ZnO photodiodes, which is attributed to an enhanced transport of carriers due to the planar backbone conformation of the PBDT-TTDPP copolymer. Capacitance-voltage measurements from hybrid Schottky barrier interfaces further shed light into the nature of photocarriers and device parameters. First-principles time-dependent density-functional theoretical calculations yield a higher absorptivity for the PBDT-TTDPP dimer compared to PBDT-TDPP.
Nanopatterned ZnO and diketopyrrolopyrrole (DPP) donor-acceptor copolymer based planar heterojunctions provide a viable route for near-infrared photodetector applications. The rigid backbone of the DPP copolymer with a thienothiophene unit enhances charge transport properties. Display omitted
•Nanopatterned ZnO films pave the way for efficient non-fullerene hybrid near IR photodetectors.•Two near IR diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers with variations in backbone conformations are synthesized.•The DPP copolymer with the thienothiophene linker shows a high photoresponsivity.•Capacitance-voltage measurements from hybrid Schottky barrier interfaces shed light into device parameters.
Abstract
We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a
z
= 0.89 galaxy using 580–1670 MHz observations from the MeerKAT Absorption Line ...Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (
z
= 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144
α
(and H163
α
) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21
σ
(14
σ
) significance. The RRL emission contains two main velocity components and is coincident in velocity with H
i
21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (
n
e
) and the volume-averaged path length (
ℓ
) of the ionized gas. We determine
log
(
n
e
)
=
2.0
−
0.7
+
1.0
cm
−3
and
log
(
ℓ
)
=
−
0.7
−
1.1
+
1.1
pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine
log
(
n
e
)
=
3.2
−
1.0
+
0.4
cm
−3
and
log
(
ℓ
)
=
−
2.7
−
0.2
+
1.8
pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of Σ
SFR
∼ 0.6
M
⊙
yr
−1
kpc
−2
or SFR ∼ 50
M
⊙
yr
−1
, consistent with a star-forming main-sequence galaxy of
M
⋆
∼ 10
11
M
⊙
. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities.
We present far ultraviolet (FUV) observations of globular cluster NGC 4147 using three FUV filters, BaF
2
(F154W), sapphire (F169M), and silica (F172M) of Ultra-Violet Imaging Telescope (UVIT) ...on-board the AstroSat satellite. We confirmed the cluster membership of the UVIT observed sources using proper motions from Gaia data release 2 (GAIA DR2). We identified 37 blue horizontal branch stars (BHBs), one blue straggler star (BSS) and 15 variable stars using UV-optical color magnitude diagrams (CMDs). We find that all the FUV bright BHBs are second generation population stars. Using UV-optical CMDs, we identify two sub-populations, BHB1 and BHB2, among the UV-bright BHBs in the cluster with stars count ratio of 24:13 for BHB1 and BHB2. The effective temperatures (
T
eff
) of BHB1 and BHB2 were derived using color-temperature relation of BaSTI-IAC zero-age horizontal branch (ZAHB). We found that BHB1 stars are more centrally concentrated than BHB2 stars. We also derive physical parameters of the detected FUV bright BSS by fitting younger age BaSTI-IAC isochrones on optical and UV-optical CMDs.
In this work, we have successfully cross-linked the different weight ratio of Chitosan-PVA blend with sulfuric acid. The effect of cross-linker on the properties of blends are studied by using ...different experimental technique. The cross-linked membrane provides higher ion exchange capacity due to the procurement of extra ionic hooping sites in the membrane. The compatibility of the blends are confirmed from the FTIR and DSC analysis. The crosslinking reaction fastening the phase transition behavior of the blends which reduces the glass transition temperature. The highly compatiblized cross-linked blend provides higher tensile strength and lower modulus at moderate temperature. The significant reduction of weight loss was observed in a cross-linked membrane which enhances thermal stability of the blend. The group which are responsible for higher methanol cross-over are consumed by the cross-linking reaction and a drastic reduction of methanol cross-over was observed. The proton conductivity of the blends are obtained by performing experiment in a four probe impedance analyzer and fitting the EIS data in an equivalent circuit model. At moderate temperature, the cross-linked membrane provides higher proton conductivity than the pure membrane and the proton transport was controlled by Grotthus mechanism. The cross-linked membrane provides higher proton conductivity and membrane selectivity which is beneficial for DMFC design.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We present the far ultraviolet (FUV) imaging of the nearest Jellyfish or Fireball galaxy IC3418/VCC 1217, in the Virgo cluster of galaxies, using Ultraviolet Imaging Telescope (UVIT) onboard the ...AstroSat satellite. The young star formation observed here in the 17 kpc long turbulent wake of IC3418, due to ram pressure stripping of cold gas surrounded by hot intra-cluster medium, is a unique laboratory that is unavailable in the Milky Way. We have tried to resolve star forming clumps, seen compact to GALEX UV images, using better resolution available with the UVIT and incorporated UV-optical images from Hubble Space Telescope archive. For the first time, we resolve the compact star forming clumps (fireballs) into sub-clumps and subsequently into a possibly dozen isolated stars. We speculate that many of them could be blue supergiant stars which are cousins of SDSS J122952.66+112227.8, the farthest star (~17 Mpc) we had found earlier surrounding one of these compact clumps. We found evidence of star formation rate (4–7.4 × 10
–4
M
☉
yr
–1
) in these fireballs, estimated from UVIT flux densities, to be increasing with the distance from the parent galaxy. We propose a new dynamical model in which the stripped gas may be developing vortex street where the vortices grow to compact star forming clumps due to self-gravity. Gravity winning over turbulent force with time or length along the trail can explain the puzzling trend of higher star formation rate and bluer/younger stars observed in fireballs farther away from the parent galaxy.
Acetamidinium-substituted methylammonium lead iodide (MAPI) based perovskite solar cells (PSCs) have shown promising performance. This work demonstrates acetamidinium-substituted MAPI-based PSCs ...fabricated on stainless-steel substrate which can be used for various flexible applications. The preliminary fabrication runs exhibited the power conversion efficiency (PCE) upto 5.3%. The short circuit current density (J sc ), open circuit voltage (V oc ) and fill factor (FF) obtained for the best PCE device are −12.69 mA/cm 2 , 0.77 V and 54% respectively. The work is currently in progress to obtain better performing solar cell devices and understand the responsible physical mechanisms behind their behavior.
Resonance energy transfer (RET) can potentially improve the device efficiencies of ternary blend organic solar cells (TBSCs). However, several parameters, such as domain morphology, exciton lifetime, ...energy and charge transfer, influence the resulting photophysics. Owing to this, spectroscopic studies on TBSCs have not unambiguously deconvolved the role of RET in the observed enhancement of photocurrent densities, often downplaying the mechanistic aspects of the RET associated enhancement. In this perspective, we discuss and analyse the role of RET in enhancing the device efficiency by taking a few recent examples of TBSCs. Taking analogy from natural photosynthetic systems, we argue that deviations in the observed RET rates from a Förster type mechanism may be at play. We suggest new strategies to systematically correlate the Förster critical distance (
R
0
) with increments in current density (Δ
J
SC
) in order to gain mechanistic insights to optimize RET enhanced photocurrent for high efficiency organic solar cells.
Resonance energy transfer in ternary blend organic solar cells is discussed by drawing parallels from natural photosynthetic proteins.
ABSTRACT
We present a detailed analysis of 99 optically thin C iii absorption systems at redshift 0.2 ≤ z ≤ 0.9 associated with neutral hydrogen column densities in the range 15 ≤ log ...$N({\rm{H\,{\small I}}})$ (cm−2) ≤ 16.2. Using photoionization models, we infer the number density (nH), C-abundance (C/H), and line-of-sight thickness (L) of these systems in the ranges −3.4 ≤ log nH (cm−3) ≤ −1.6, −1.6 ≤ C/H ≤ 0.4, and 1.3 pc ≤ L ≤ 10 kpc, respectively, with most of the systems having sub-kpc scale thickness. We combine the low-z and previously reported high-z (2.1 ≤ z ≤ 3.3) optically thin C iii systems to study the redshift evolution and various correlations between the derived physical parameters. We see a significant redshift evolution in nH, C/H, and L. We compare the redshift evolution of metallicity in C iii systems with those of various types of absorption systems. We find that the slope of C/H versus z for C iii absorbers is steeper compared to the redshift evolution of cosmic metallicity of the damped Ly α sample (DLA) but consistent with that of sub-DLAs. We find the existence of strong anticorrelation between L and C/H for the combined sample with a significance level of 8.39σ. We see evidence of two distinct C/H branch C iii populations (low-C/H branch, $\mathrm{ C/H}\, \le -1.2$, and high-C/H branch, $\mathrm{ C/H}\, \gt -1.2$) in the combined C iii sample when divided appropriately in the L versus $N({\rm{C\,{\small III}}})$ plane. Further studies of C iii absorbers in the redshift range 1.0 ≤ z ≤ 2.0 are important to map the redshift evolution of these absorbers and gain insights into the time evolution physical conditions of the circumgalactic medium.
ABSTRACT
We have studied ultraviolet (UV) bright sources in the Galactic globular cluster (GGC) NGC 4590 using Ultraviolet Imaging Telescope onboard the AstroSat satellite. Using UV-optical ...colour–magnitude diagrams (CMDs), we have identified and characterized the sources of different evolutionary stages i.e. blue horizontal branch stars (BHBs), extremely blue horizontal branch stars (EHBs), blue straggler stars (BSs), variable stars, etc. We estimated effective temperature (Teff), gravity (log (g)), luminosity (Lbol), and hence the radius (R) of these hot stars by fitting spectral energy distribution with the help of stellar atmosphere models. Two new far-UV bright cluster member stars situated near the core of the cluster have been detected; one of them is an EHB star and the other one is either in its post-blue hook evolutionary phase or in white dwarf phase. The evolutionary status of all the hot stars, identified in the cluster, has been investigated by using various evolutionary models. We find the massive and younger BSs are concentrated at the centre of the cluster whereas the older and less massive BSs are distributed throughout the cluster. The BSs normalized radial distribution seems to be bi-modal with a minimum located at rmin = 4.3 rc. We calculated A+ parameter of the cluster which is obtained using cumulative normalized radial distribution of horizontal branch stars (HBs) and BSs. We measured this value up to half-mass radius of the cluster to be +0.13, which indicates that NGC 4590 is one of the youngest clusters among dynamically intermediate age GGCs with a dynamical age of 0.423 ± 0.096 Gyr.
ABSTRACT
We present detailed photometric observations of the Galactic globular cluster NGC 7492 using the data obtained with two far-ultraviolet (FUV; 1300–1800 Å) and three near-ultraviolet (NUV; ...2000–3000 Å) filters of Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. We confirmed the cluster membership of the extracted sources using Gaia data release 2 (Gaia DR2) proper motion data. We have used colour–magnitude diagrams (CMDs) using UVIT and GAIA filters to separate out different evolutionary stages of the stars present in the cluster. We have identified a new extreme horizontal branch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The estimated distance modulus of the cluster is 16.95 ± 0.05 obtained by fitting BaSTI isochrones with cluster parameters, Fe/H = −1.8 dex and age =12.0 Gyr on the V − I versus V CMD. Interestingly, only the EHB star and blue horizontal branch stars (BHBs) among the UV-bright hot sources are detected in FUV filters of UVIT. We have derived the effective temperature of BHBs using colour–temperature relation and spectral energy distributions (SEDs) of multiband filters, which are in the range from 8000 to 10 500 K. We find a variation of He abundance of BHBs by fitting the BaSTI ZAHB (zero-age horizontal branch). The range in the He abundance of the BHBs corresponding to the best-fitting isochrones is from 0.247 to 0.350. We have estimated various physical parameters of the newly identified EHB star in the cluster using SED fit and post-HB evolutionary tracks. We have studied the radial distribution of all the sources of the cluster detected in UVIT. The sources detected in FUV filters extend beyond the half-light radius (1.15 arcmin) of the cluster, whereas the sources detected in NUV filters extend beyond the tidal radius (9.2 arcmin) of the cluster.
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