Bright, room‐temperature stable, on‐demand, and highly directional light sources are essential for quantum optical technologies. A design methodology to enhance the emission and collection efficiencies for given collection optics is proposed and demonstrated. Hyperbolic metamaterials (HMMs) offer manipulation of local density of states to improve the emission as well as coupling of emission to high‐K modes. However, metallic losses limit the efficiencies achieved. The HMM structure designed for large, broadband Purcell enhancement with limited metallic losses as well as HMM and antenna design to optimize the collection efficiency is presented. 200 times emission enhancement is reported from CdSeS/ZnS core/shell alloyed quantum dots embedded in a planar HMM structure with cylindrical silver (Ag) patch antenna on the top. 40% collection efficiency is demonstrated for a lens with a numerical aperture of 0.9 and the emission enhancement is about an order of magnitude higher than the previous reports.
A new property of the trapped mode (bound state in the continuum, BIC) supported by a dielectric resonant metasurface, which changes its lattice symmetry, is uncovered. The transformation of a metasurface composed of identical nanodisk resonators into a “diatomic” structure when one half of the nanodisks change their diameters is studied. The resulting folding of the Brillouin zone in the k‐space transforms the trapped (BIC) mode to quasi‐BIC resonances manifested in the polarization‐independent response. This novel feature is verified experimentally in the transmission of the metasurfaces illuminated by light with both linear and circular polarizations.
The
nanomorphology of bulk heterojunction (BHJ) blends based on
poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is systematically
varied by using the volume fraction of the solvent additive 1,8-diiodooctane
(DIO) from 0 to 20 vol % in chlorobenzene to prepare organic solar
cells (OSCs). Blends prepared without DIO forms large phase-separated
domains of PC71BM which are suppressed on addition of 3
vol % DIO, resulting in improved nanoscale features. Addition of 20
vol % DIO results in a finer interconnected morphology along with
increased roughness due to polymer aggregation, which contrasts with
previous reports. With increase in addition of DIO the photoluminescence
(PL) from the blend is reduced; however, a relative increase in PL
from 750 nm onward is observed for blends with 20 vol % DIO. As quenching
of the blend PL is related to the donor/acceptor interface, structural
characterizations in real-space (microscopy) and k-space (scattering) are performed to unravel the nanomorphology and
correlate it with photophysical and charge transport processes. Electron-transport
length scales measured by scanning photocurrent microscopy are found
to increase with the addition of up to 3 vol % DIO associated with
the breakup of the large PC71BM agglomerates, while the
hole-transport length is found to increase on adding DIO up to 20
vol % due to aggregation of polymer chains. Hence, this work represents
a unique set of results systematically examining the effect of nanomorphology
on structural and solar cells properties of BHJ blends, which can
have a direct implication on better understanding of the emerging
high-efficiency OSC systems.
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