Color image sensing is commonly carried out by an array of color pixels. Each of the color pixels consists of at least three sensing elements in combination with optical filters for red, green and blue. The filters are arranged sideby-side limiting the total quantum efficiency of a color pixel to 1/N, where N is the number of color channels per color pixel. Hence, in the most basic filter arrangement, just consisting of a red, green, and blue filter, the upper limit of the quantum efficiency is equal to 1/3, limiting the dynamic range and color contrast of the detected optical input signal. In order to increase the quantum efficiency and improve the image quality, an alternative sensor device is proposed, which can be realized by using current semiconductor technology. The proposed sensor uses silicon optical antennas to detect the incident light. The sensor allows for detecting the color information, with quantum efficiencies approaching unity. The design of the optical antennas is described, and optimization strategies are discussed.

Abstract:The optics of axial silicon nanowire solar cells is investigated and compared to silicon thin-film solar cells with textured contact layers. The quantum efficiency and short circuit current density are calculated taking a device geometry into account, which can be fabricated by using standard semiconductor processing. The solar cells with textured absorber and textured contact layers provide a gain of short circuit current density of 4.4 mA/cm 2 and 6.1 mA/cm 2 compared to a solar cell on a flat substrate, respectively. The influence of the device dimensions on the quantum efficiency and short circuit current density will be discussed.

A hybrid energy-harvesting system is proposed that combines photosynthesis and photovoltaics. First, the light passes through a spectrally selective solar cell, which absorbs almost all green light but absorbs almost no blue and red light. The blue and red light are absorbed by a photosynthesis executing plant. The solar cell is tailored in such a way that the photosynthetic process is almost unaffected by the generation of electrical energy. The spectrally selective solar cell consists of an array of inorganic optical antennas. By combining a spectrally selective solar cell and a photosynthetic executing plant, a hybrid energy system is formed, which absorbs almost 100% of the visible light, while the energy conversion efficiency of the solar cell reaches up to 50% of their nonspectrally selective counterparts. Guidelines are provided on how to realize both the highly efficient spectrally selective solar cells and hybrid energy-harvesting systems. The proposed solution allows for the realization of new greenhouses or gardens covered with spectrally selective transparent solar cells that produce chemical energy in the form of fruits and vegetables and electrical energy.

The optics of core / shell nanowire solar cells was investigated. The optical wave propagation was studied by finite difference time domain simulations using realistic interface morphologies. The interface morphologies were determined by a 3D surface coverage algorithm, which provides a realistic film formation of amorphous silicon films on zinc oxide nanowire arrays. The influence of the nanowire dimensions on the interface morphology and light trapping was investigated and optimal dimensions of the zinc oxide nanowire were derived.

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