11,140 research outputs found
Broadband Quantum Efficiency Enhancement in High Index Nanowires Resonators
Light trapping in sub-wavelength semiconductor nanowires (NWs) offers a
promising approach to simultaneously reducing material consumption and
enhancing photovoltaic performance. Nevertheless, the absorption efficiency of
a NW, defined by the ratio of optical absorption cross section to the NW
diameter, lingers around 1 in existing NW photonic devices, and the absorption
enhancement suffers from a narrow spectral width. Here, we show that the
absorption efficiency can be significantly improved in NWs with higher
refractive indices, by an experimental observation of up to 350% external
quantum efficiency (EQE) in lead sulfide (PbS) NW resonators, a 3-fold increase
compared to Si NWs. Furthermore, broadband absorption enhancement is achieved
in single tapered NWs, where light of various wavelengths is absorbed at
segments with different diameters analogous to a tandem solar cell. Overall,
the single NW Schottky junction solar cells benefit from optical resonance,
near bandgap open circuit voltage, and long minority carrier diffusion length,
demonstrating power conversion efficiency (PCE) comparable to single Si NW
coaxial p-n junction cells11, but with much simpler fabrication processes
Observer and Command-Filter-Based Adaptive Fuzzy Output Feedback Control of Uncertain Nonlinear Systems
State-independent quantum contextuality with projectors of nonunit rank
Virtually all of the analysis of quantum contextuality is restricted to the
case where events are represented by rank-one projectors. This restriction is
arbitrary and not motivated by physical considerations. We show here that
loosening the rank constraint opens a new realm of quantum contextuality and we
demonstrate that state-independent contextuality can even require projectors of
nonunit rank. This enables the possibility of state-independent contextuality
with less than 13 projectors, which is the established minimum for the case of
rank one. We prove that for any rank, at least 9 projectors are required.
Furthermore, in an exhaustive numerical search we find that 13 projectors are
also minimal for the cases where all projectors are uniformly of rank two or
uniformly of rank three.Comment: 9+9 pages, 4 figures. Published versio
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