ترغب بنشر مسار تعليمي؟ اضغط هنا

Enhanced Absorption in thin silicon films by 3D photonic band gap back reflectors for photovoltaics

140   0   0.0 ( 0 )
 نشر من قبل Devashish Sharma
 تاريخ النشر 2021
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

Since thin-film silicon solar cells have limited optical absorption, we explore the effect of a nanostructured back reflector to recycle the unabsorbed light. As a back reflector we investigate a 3D photonic band gap crystal made from silicon that is readily integrated with the thin films. We numerically obtain the optical properties by solving the 3D time-harmonic Maxwell equations using the finite-element method, and model silicon with experimentally determined optical constants. The absorption enhancement relevant for photovoltaics is obtained by weighting the absorption spectra with the AM 1.5 standard solar spectrum. We study thin films either thicker ($L_{Si} = 2400$ nm) or much thinner ($L_{Si} = 80$ nm) than the wavelength of light. At $L_{Si} = 2400$ nm, the 3D photonic band gap crystal enhances the spectrally averaged ($lambda = 680$ nm to $880$ nm) silicon absorption by $2.22$x (s-pol.) to $2.45$x (p-pol.), which exceeds the enhancement of a perfect metal back reflector ($1.47$ to $1.56$x). The absorption is enhanced by the (i) broadband angle and polarization-independent reflectivity in the 3D photonic band gap, and (ii) the excitation of many guided modes in the film by the crystals surface diffraction leading to enhanced path lengths. At $L_{Si} = 80$ nm, the photonic crystal back reflector yields a striking average absorption enhancement of $9.15$x, much more than $0.83$x for a perfect metal, which is due to a remarkable guided mode confined within the combined thickness of the thin film and the photonic crystals Bragg attenuation length. The broad bandwidth of the 3D photonic band gap leads to the back reflectors Bragg attenuation length being much shorter than the silicon absorption length. Consequently, light is confined inside the thin film and the absorption enhancements are not due to the additional thickness of the photonic crystal back reflector.



قيم البحث

اقرأ أيضاً

117 - Romain Peretti 2014
The effects resulting from the introduction of a controlled perturbation in a single pattern membrane on its absorption are first studied and then analyzed on the basis of band folding considerations. The interest of this approach for photovoltaic ap plications is finally demonstrated by overcoming the integrated absorption of an optimized single pattern membrane through the introduction of a proper pseudo disordered perturbation.
We optimize multilayered anti-reflective coatings for photovoltaic devices, using modern evolutionary algorithms. We apply a rigorous methodology to show that a given structure, which is particularly regular, emerge spontaneously in a very systematic al way for a very broad range of conditions. The very regularity of the structure allows for a thorough physical analysis of how the designs operate. This allows to understand that the central part is a photonic crystal utilized as a buffer for light, and that the external layers have the purpose of reducing the impedance mismatch between the outer media and the Bloch mode supported by the photonic crystal. This shows how optimization can suggest new design rules and be considered as a source of inspiration. Finally, we fabricate these structures with easily deployable techniques.
We have performed an x-ray holotomography study of a three-dimensional (3D) photonic band gap crystal. The crystals was made from silicon by CMOS-compatible methods. We manage to obtain the 3D material density throughout the fabricated crystal. We ob serve that the structural design is for most aspects well-realized by the fabricated nanostructure. One peculiar feature is a slight shear-distortion of the cubic crystal structure. We conclude that 3D X-ray tomography has great potential to solve many future questions on optical metamaterials.
By patterning a freestanding dielectric membrane into a photonic crystal reflector (PCR), it is possible to resonantly enhance its normal-incidence reflectivity, thereby realizing a thin, single-material mirror. In many PCR applications, the operatin g wavelength (e.g. that of a low-noise laser or emitter) is not tunable, imposing tolerances on crystal geometry that are not reliably achieved with standard nanolithography. Here we present a gentle technique to finely tune the resonant wavelength of a SiN PCR using iterative hydrofluoric acid etches. With little optimization, we achieve a 57-nm-thin photonic crystal having an operating wavelength within 0.15 nm (0.04 resonance linewidths) of our target (1550 nm). Our thin structure exhibits a broader and less pronounced transmission dip than is predicted by plane wave simulations, and we identify two effects leading to these discrepancies, both related to the divergence angle of a collimated laser beam. To overcome this limitation in future devices, we distill a series of simulations into a set of general design considerations for realizing robust, high-reflectivity resonances.
We present time-resolved emission experiments of semiconductor quantum dots in silicon 3D inverse-woodpile photonic band gap crystals. A systematic study is made of crystals with a range of pore radii to tune the band gap relative to the emission fre quency. The decay rates averaged over all dipole orientations are inhibited by a factor of 10 in the photonic band gap and enhanced up to 2? outside the gap, in agreement with theory. We discuss the effects of spatial inhomogeneity, nonradiative decay, and transition dipole orientations on the observed inhibition in the band gap.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا