Nanowires (NW)/nanopillars (NP) have unique optical and electrical properties that make them attractive for
photovoltaic applications. Important factors such as diameter, length and array density of the nanowires have
investigated in the recent years or their effect on light trapping. In this work, we study the effect of varying
the NWs top tip morphology, and find significant differences in optical response, both via simulations and
experiments. In the simulations, optical performance of NW with flat top and spherical top were investigated.
The simulated 3D model is a CNT/Cr/a-Si/ITO coaxial structure with total diameter of 760nm. Our results
show that as the spacing of the NWgets smaller, the influence of the top morphology on the nanowires’ reflectance
becomes more significant. For narrow spacing arrays (p<2d, where p is the period and d is the diameter of NWs)
NW device with spherical top shows better antireflection performance than the one with flat top. This is due to
the biomimetic antireflection (AR) effect introduced by the spherical top . For large spacing arrays (p<2d), AR
effect introduced by spherical tops was almost negligible. It can be ascribed to the low volume concentration
of the spherical top comparing to that of the planar surface. In addition, effect of structural defects were also
Indium tin oxide (ITO) films were deposited on sapphire substrates at temperatures ranging from 30°C to 700°C and oxygen background pressure changing from 0.05 Pa to 0.25 Pa by femtosecond pulsed laser deposition (PLD). The films were characterized using metallurgical microscope, film resistance meter and Fourier transform infrared spectrometer to study the effect of substrate temperature and oxygen background pressure on the surface topography, sheet resistance and infrared transmission. The photographs of metallurgical microscope show that substrate temperature plays a dominant role on the surface morphology of the films. The sheet resistance test suggests that the sheet resistance of the film decreases with increase of substrate temperature but increases with increase of oxygen background pressure. The results of infrared transmission show that the infrared transmission through the ITO film is about 40% at the wavelength of 1.5μm to 1.8μm and is very low at other infrared band. The films deposited at higher substrate temperatures show lower value of transmittance, and which at higher oxygen background pressure show higher value of transmittance.
Minimizing surface reflection loss is critical when designing high efficiency solar cells. In recent years, biomimetic
antireflection nanostructures (such as moth-eye structures), with their extraordinary broadband and omnidirectional
antireflection properties, have caught much attention. Single side biomimetic antireflection (AR) coatings
show good performance in suppressing broadband reflection between air and glass interface. However, reflection
from the interface between absorption layer and transparent window layer still remains. In this study,
we proposed a double-side gradient-index nanostructure, and examined its reflection spectrum in comparison
with different biomimetic nanostructures using a finite-difference time-domain (FDTD) simulation and effective
medium theory (EMT). In order to minimize surface reflection, all abrupt interfaces were replaced by gradientindex
biomimetic nanostructures, including air/glass interface and absorber/glass interface. Monolayer of silica
spheres serve as double-side gradient-index nanostructures, partially immersed into photoabsorbing material.
Spheres with diameter smaller than incoming light wavelength show excellent antireflection properties. From
simulation results, in normal incidence, average reflection rate of optimized AR coating structure was lower to
around 5% compared to originally above 25% within visible spectrum region (350nm – 850nm). Details of how
to apply such biomimetic nanostructures in thin film solar cells were also discussed.
A series of InSb thin films were fabricated on the sapphire substrate by femtosecond pulsed laser deposition (fsPLD)
method with the laser of 110 fs pulse width. The laser incident energy is near 1mJ. The target is one kind of heavily
doped n-type InSb. The substrate temperature changes from 80 ºC to 400 ºC, Laser frequency changes from 1 Hz to 1 kHz and laser energy density changes from 0.1 J/cm2 to 1 J/cm2. The effects of different laser frequencies, substrate temperature and laser energy density on the surface morphology and optical property have been investigated separately. The surface morphology of InSb thin films was observed by metallurgical microscope and scanning electron microscope (SEM). The thin film with better surface morphology is obtained when the laser frequency is 10 Hz, substrate temperature is 80 ºC and laser energy density is 0.1 J/cm2. X-ray diffraction (XRD) demonstrates that the InSb thin film has a good single crystal structure. The infrared transmittance of InSb thin films is measured by an infrared spectrometer. The results show that good InSb thin films can be prepared by fsPLD. It is found that the mid-wavelength Infrared transmission through the InSb thin films is near 55% and it almost does not change under the different growing conditions.
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