Nonlinear nanostructured surfaces provide a paradigm shift in nonlinear optics with new ways to control and manipulate frequency conversion processes at the nanoscale, also offering novel opportunities for applications in photonics, chemistry, material science, and biosensing. Here, we develop a general approach to employ sharp resonances in metasurfaces originated from the physics of bound states in the continuum for both engineering and enhancing the nonlinear response. We study experimentally the third-harmonic generation from metasurfaces composed of symmetry-broken silicon meta-atoms and reveal that the harmonic generation intensity depends critically on the asymmetry parameter. We employ the concept of the critical coupling of light to the metasurface resonances to uncover the effect of radiative and nonradiative losses on the nonlinear conversion efficiency.
Polymer passivation layers can improve the open-circuit voltage of perovskite solar cells when inserted at the perovskite–charge transport layer interfaces. Unfortunately, many such layers are poor conductors, leading to a trade-off between passivation quality (voltage) and series resistance (fill factor, FF). Here, we introduce a nanopatterned electron transport layer that overcomes this trade-off by modifying the spatial distribution of the passivation layer to form nanoscale localized charge transport pathways through an otherwise passivated interface, thereby providing both effective passivation and excellent charge extraction. By combining the nanopatterned electron transport layer with a dopant-free hole transport layer, we achieved a certified power conversion efficiency of 21.6% for a 1-square-centimeter cell with FF of 0.839, and demonstrate an encapsulated cell that retains ~91.7% of its initial efficiency after 1000 hours of damp heat exposure.
Atomically
thin monolayers of transition metal dichalcogenides
(TMDs) have emerged as a promising class of novel materials for optoelectronics
and nonlinear optics. However, the intrinsic nonlinearity of TMD monolayers
is weak, limiting their functionalities for nonlinear optical processes
such as frequency conversion. Here we boost the effective nonlinear
susceptibility of a TMD monolayer by integrating it with a resonant
dielectric metasurface that supports pronounced optical resonances
with high quality factors: bound states in the continuum (BICs). We
demonstrate that a WS2 monolayer combined with a silicon
metasurface hosting BICs exhibits enhanced second-harmonic intensity
by more than 3 orders of magnitude relative to a WS2 monolayer
on top of a flat silicon film of the same thickness. Our work suggests
a pathway to employ high-index dielectric metasurfaces as hybrid structures
for enhancement of TMD nonlinearities with applications in nonlinear
microscopy, optoelectronics, and signal processing.
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