Silicon nanowires (NWs) and microwires (MWs) are cost-effectively integrated on a 4-inch wafer using metal-assisted electroless etching for solar cell applications. MWs are periodically positioned using low-level optical patterning in between a dense array of NWs. A spin-on-doping technique is found to be effective for the formation of heavily doped, thin n-type shells of MWs in which the radial doping profile is easily delineated by low voltage scanning electron microscopy. Controlled tapering of the NWs results in additional optical enhancement via optimization of the tradeoff between increased light trapping (by a graded-refractive-index) and increased reflectance (by decreasing areal density of NWs). Compared to single NW (or MW) arrayed cells, the co-integrated solar cells demonstrate improved photovoltaic characteristics, i.e. a short circuit current of 20.59 mA cm −2 and a cell conversion efficiency of ∼7.19% at AM 1.5G illumination.
We present the two-photon recording of microholograms in new cationic initiated photopolymer material. The experimental results show that the material has a square-law dependence of the refractive index change on intensity, and also the threshold character of recording. Both such dependence and the threshold character of recording make it possible to improve the microhologram localization at recording and to reduce the crosstalk at reading. Besides that, the use of two-photon absorption increases the homogeneity on depth recording and provides high values of refractive index change Δn = 3.3 × 10−3. We also describe the recording/reading of microholograms in ten layers of the designed material, and present data on reading errors and their distribution on depth.
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