Silicon Photovoltaics Using Conducting Photonic Crystal Back‐Reflectors

Abstract

Currently, research is being directed towards thinning conventional 200–300µm thick silicon photovoltaic cells by an order of magnitude or more. The benefits of reducing the cell thickness include decreased material costs, enhanced cell flexibility, and reduced effects of light‐induced degradation. However, one of the major challenges associated with reducing the active region to this extent is the corresponding reduction of light absorption. To mitigate this effect it has been proposed that the cell should incorporate enhanced light‐trapping strategies. One potential approach to enhance light trapping in thin photovoltaic cells is to structure the back‐reflector in the form of a photonic crystal (PC). It has recently been shown that two fundamental attributes of PC back‐reflectors optically coupled to thin semiconductor films contribute to enhanced absorption in the semiconductor: (i) the PC back‐reflector behaves as a perfect mirror, exhibiting complete reflection over stop‐gap frequencies; and (ii) the PC–semiconductor film interface couples incident light into resonant states that propagate along the plane of the film, thereby further enhancing the absorption. Although the ability of PC back‐reflectors to enhance absorption is encouraging, significant challenges arise when attempting to incorporate this light trapping technique in photovoltaic devices. Herein, we describe the underlying physical mechanisms that give rise to absorption enhancements in thin Si wafers featuring PC back‐reflectors, and describe hurdles that will have to be surmounted in order to reduce‐to‐practice a PC back‐reflector into an actual PV device.

Modulated photonic-crystal structures as broadband back reflectors in thin-film solar cells

“…Photonic crystals ͑PCs͒ have been suggested as promising candidates for improving the optical performance of solar cells. [1][2][3][4][5][6][7] While two-or three-dimensional PCs exhibit a high potential for efficient light scattering, 1,5 one-dimensional ͑1D͒ PCs can be used as distributed Bragg reflectors with high optical reflectance ͑close to 100%͒. 2,7 A regular 1D PC is a periodiclike multilayer structure consisting of two alternating layers each with a different refractive index ͑n 1 , n 2 ͒ and thickness ͓d 1 where m is the number of alternating-layer pairs ͑periods͒ in the PC structure and n 1 and n 2 are their refractive indices.…”

Bottom-Up Assembly and Applications of Photonic Materials

“…The use of photonic structures to manage light and optimize optical and electro-optical properties in photovoltaic devices has been widely studied [117][118][119][120][121][122]. Photonic structures can enable the "trapping" of photons and consequently enhance the photocurrent of a solar cell [120].…”

Efficiently Harvesting Sun Light for Silicon Solar Cells through Advanced Optical Couplers and A Radial p-n Junction Structure

“…The short-circuit current enhancement of such a design can reach levels of 28.3% and 45.2 % for cells with thicknesses of 5 m and 2 m, respectively. Some researchers have described the underlying physical mechanisms that give rise to absorption enhancements in thin silicon film featuring PC back-reflectors, and have described hurdles that researchers must surmount in order to reduce-to-practice a PC back-reflector operating as an actual PV device [23,24]. Figure 4.…”