The paper presents the investigation on the anti-reflection property of 2-dimensional periodic structures on silicon
surface for high efficiency solar cells. The characteristics of micron-to-submicron periodic surface-relief structures for
broadband anti-reflection silicon layers are studied theoretically and experimentally. Theoretical analysis is carried out to
determine the appropriate sturcture period. Hexagonal and cross grating structures were fabricated on the surfaces of
silicon wafers using hologrpahic and wet etching techniques. Measurement on the silicon wafers with fabricated
structures shows significant reduction of surface reflection for the wavelength from 300 nm to 1100 nm.
Using 2-dimensional (2D) photonic crystal with hexagonal lattice to extract guided waves inside slab waveguides is
investigated in the paper. Since 2D hexagonal lattice structure is circularly symmetrical, the effect of light extraction can
be regarded as the same for guided waves propagating toward different directions on the plane of the slab. Theoretical
analysis was carried out under the assumption that a hexagonal lattice consists of many groups of gratings with different
periods and orientations. Based on the assumption, the simulations of the extracted light-spot distributions on the
waveguides for the guided waves with different reflection angles inside the slab were obtained. The simulations are
consistent with the experimental result, verifying that the observed spot array above the slab surface, where 2D
hexagonal lattice was fabricated, was generated by the diffraction of the lattice. The light extraction method can be used
to separate a laser beam into many distributed beams for optical network interconnection applications and to extract
trapped light inside LEDs. Theoretical analysis indicates that to obtain efficient light extraction via hexagonal lattice,
lattice constant should be properly chosen. Method for choosing desired lattice constant is provided.
One of the more intriguing of solar collection techniques, holographic concentration, has been addressed in many ways,
but it has so far met with only limited success. The major attraction of holography is that unlike conventional
concentrators, the holographic concentrator can track the sun across the sky while remaining completely stationary. A
simple system using holographic Fresnel lenses (HFLs) was proposed in this paper. We present the theoretical analysis
and the technique for fabricating HFLs used for solar concentrator. Several HFLs fabricated using corresponding
recording geometries, resulted in a combined device that collects light at any angle, with each lens responsible for
gathering sunlight for a certain portion of the day. Three HFLs with different fringe pattern were achieved, which
operates in the morning, at noon and in the afternoon, respectively. The primary experimental results of the concentrator
were presented, which effectively concentrates the visible spectrum over a 60 degrees daily angular variation. Several
advantages of the holographic concentrator we obtained include longer lifetime, low cost, and the small size of a flat
piece of film compared to a mirror or lens. The dispersive characteristics applied to photovoltaic power generation would
offer a novel type of generator with high conversion efficiencies.
A new method for reducing surface reflectance of multicrystalline silicon wafers is presented. The method using
holographic lithography and wet etching to fabricate 2-dimensional (2D) photonic crystal (PC) on the surface of
multicrystalline silicon. 2D hexangonal PC structures with micron scale lattice constant exhibit significant reduction of
the surface reflectance. In the method, 2D hexagonal PC structure is firstly recorded in photoresist, which is coated on
the surface of Si wafer, using holographic 3-beam interference technique. After exposure and development the wafer is
put into acid solution to transfer the lattice structure into the silicon. Experiments with different exposure angles and
etching times were carried out to form different lattice period and structure depth for obtaining optimal lattice parameters.
PC with 1.3 μm lattice constant and 0.5 μm depth has achieved a reflectance below 6%. The holographic technique used
in the work allows large-area lattice fabrication with only one process. The proposed method has the advantages of low
production cost and high throughput, enabling industrial mass production of Si solar cells.
In this paper, we propose an improved hologrpahic technique for fabricating 2D hexagonal and 3D hexagonal packed
photonic crystals (PhCs). The key element in the fabrication system is an off-axis holographic lens group (OHLG)
consisting of three off-axis holographic lenses. Under the illumination of an expanded laser beam, three collimated
beams can be generated by the OHLG to form a uniform hexagonal lattice pattern without using a collimating lens. The
utilization of OHLG in the system eliminates the noise in the interference pattern resulted from the collimating lens so
that lattice quality is enhanced. The system is simple and stable and can be used to fabricate large-size PhCs.
A technique using a holographic optical element to split one incident laser beam into hundreds is proposed. The holographic optical element is fabricated with hexagonal packed lattice structure using 4-beam interference method. When the element is illuminated by a single laser beam with normal incidence, hundreds of beams are generated by diffraction. The element has the potential to be used as the device for interconnection and clock distribution in optical and electronic systems.
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