4 research outputs found
Transparent Long-Pass Filter with Short-Wavelength Scattering Based on <i>Morpho</i> Butterfly Nanostructures
We
combine the principles of moth-eye antireflection, Bragg scattering,
and thin-film interference to design and fabricate a short-wavelength
scattering/long-pass filter with sharp cutoff, high transmission of
infrared light, and strong reflection of visible light into high angles.
Based on the lamellae-edge features on <i>Morpho didius</i> butterfly wings, nanostructures are self-assembled via sequential
one-chamber chemical vapor deposition, metal nanoparticle formation,
and wet-chemical etching. Finite-element modeling demonstrates strong
(>45%) reflection into the first diffracted order for short wavelengths,
while retaining >80% transmission for longer wavelengths. Fabricated
nanostructures couple more than 50% of reflected light into angles
of >10° while enabling broadband long-pass transmission. Such
structures have potential applications in light trapping for tandem
solar cells, stealth, and signals processing
Ultralow Absorption Coefficient and Temperature Dependence of Radiative Recombination of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Perovskite from Photoluminescence
Spectrally resolved photoluminescence
is used to measure the band-to-band
absorption coefficient α<sub>BB</sub>(ℏω) of organic–inorganic
hybrid perovskite methylammonium lead iodide (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>) films from 675 to 1400 nm. Unlike other methods
used to extract the absorption coefficient, photoluminescence is only
affected by band-to-band absorption and is capable of detecting absorption
events at very low energy levels. Absorption coefficients as low as
10<sup>–14</sup> cm<sup>–1</sup> are detected at room
temperature for long wavelengths, which is 14 orders of magnitude
lower than reported values at shorter wavelengths. The temperature
dependence of α<sub>BB</sub>(ℏω) is calculated
from the photoluminescence spectra of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> in the temperature range 80–360 K. Based on
the temperature-dependent α<sub>BB</sub>(ℏω), the
product of the radiative recombination coefficient and square of the
intrinsic carrier density, <i>B</i>(<i>T</i>)
Ă— <i>n</i><sub><i>i</i></sub><sup>2</sup>, is also obtained
Inverted Hysteresis in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Solar Cells: Role of Stoichiometry and Band Alignment
J–V
hysteresis in perovskite solar cells is known to be
strongly dependent on many factors ranging from the cell structure
to the preparation methods. Here we uncover one likely reason for
such sensitivity by linking the stoichiometry in pure CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>) perovskite cells
with the character of their hysteresis behavior through the influence
of internal band offsets. We present evidence indicating that in some
cells the ion accumulation occurring at large forward biases causes
a temporary and localized increase in recombination at the MAPbI<sub>3</sub>/TiO<sub>2</sub> interface, leading to inverted hysteresis
at fast scan rates. Numerical semiconductor models including ion accumulation
are used to propose and analyze two possible origins for these localized
recombination losses: one based on band bending and the other on an
accumulation of ionic charge in the perovskite bulk
Supplement 1: Total absorption of visible light in ultrathin weakly absorbing semiconductor gratings
Supplemental document Originally published in Optica on 20 June 2016 (optica-3-6-556