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Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm² exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically.

Significant progress in nanotechnology stimulated extensive research on novel Si-based photonic structures for optoelectronic devices and promising new technologies for the development of solar energy harvesting architectures in thin film photovoltaic applications [1 -8]. The substantial challenge is the development of inexpensive and easily scalable fabrication methods for the controlled implementation of such patterns into high quality Si thin film devices. Lithographic patterning and anisotropic etching processes as well as vapor -liquid -solid processes have been explored to prepare and successfully implement arrays of crystalline Si wires in device structures [5 -7]. However, the existing methods either rely on high-quality substrates, or face scalability challenges, or do not comply with the standards of a low-cost production process. This Letter presents a versatile and scalable preparation process for tailored periodic arrays of Si crystals on imprinted glass templates by employing exclusively low-cost large-area fabrication techniques, such as nanoimprint lithography, high-rate electron-beam (e-beam) evaporation, solid phase crystallization (SPC) and etching. Nanoimprint lithography is an elegant and scalable technique to economically prepare well-defined structures on large areas with abundant design possibilities [8 -10]. The preparation of solid phase crystallized Si is a promising approach for the fabrication of solar cells with high electronic quality, yielding a conversion efficiency of 10% for Si deposited by plasma enhanced chemical vapor deposition (PECVD) [11]. Recently, we successfully demonstrated that the PECVD process can be replaced by high-rate e-beam evaporation utilizing deposition rates of 600 nm/min [12]. The singular combination of nanoimprint lithography with the emerging high-rate deposition technique e-beam evaporation of amorphous Si enables the controlled design of periodic Si nanostructures.A two-dimensional periodic pattern with a 2 µm pitch was imprinted in a sol-gel coated glass template by repli-By combining nanoimprint lithography with the emerging high-rate deposition technique electron-beam evaporation of amorphous Si, we developed a low-cost fabrication process for the design of periodic arrays of Si crystals on large areas of 50 cm 2 in a solid phase crystallization and subsequent selective etch process. The method allows for precise control over the feature size of the crystals. The promising absorption properties of the features and the versatility and simplicity of the preparation process inspire the development of threedimensional solar cell architectures and tailored large-area photonic crystals.Cross-sectional SEM image of periodic arrays of Si crystals on nanoimprinted glass.

Emerging low cost and large area periodic texturing methods promote the fabrication of complex absorber structures for thin film silicon solar cells. We present a comprehensive numerical analysis of a 2 μm square periodic polycrystalline silicon absorber architecture designed in our laboratories. Simulations are performed on the basis of a precise finite element reconstruction of the experimentally realized silicon structure. In contrast to many other publications, superstrate light trapping effects are included in our model. Excellent agreement to measured absorptance spectra is obtained. For the inclusion of the absorber into a standard single junction cell layout, we show that light trapping close to the Yablonovitch limit can be realized, but is usually strongly damped by parasitic absorption.