Photonic light-trapping versus Lambertian limits in thin film silicon solar cells with 1D and 2D periodic patterns

Abstract

We theoretically investigate the light-trapping properties of one- and two-dimensional periodic patterns etched on the front surface of c-Si and a-Si thin film solar cells with a silver back reflector and an anti-reflection coating. For each active material and configuration, absorbance A and short-circuit current density Jsc are calculated by means of rigorous coupled wave analysis (RCWA), for different active materials thicknesses in the range of interest of thin film solar cells and in a wide range of geometrical parameters. The results are then compared with Lambertian limits to light-trapping for the case of zero absorption and for the general case of finite absorption in the active material. With a proper optimization, patterns can give substantial absorption enhancement, especially for 2D patterns and for thinner cells. The effects of the photonic patterns on light harvesting are investigated from the optical spectra of the optimized configurations. We focus on the main physical effects of patterning, namely a reduction of reflection losses (better impedance matching conditions), diffraction of light in air or inside the cell, and coupling of incident radiation into quasi-guided optical modes of the structure, which is characteristic of photonic light-trapping.

Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography

“…More specifically, for applications to photovoltaics it has been shown that trapping light beyond the commonly accepted limit of Lambertian light scattering is possible through the use of periodic photonic nanostructures [7][8]. The optical properties of such structures have been widely studied theoretically [9][10][11][12][13] and their integration has been mainly tried in a-Si, micromorph and organic based cells [14][15][16].…”

Extraordinary Light-Trapping Enhancement in Silicon Solar Cell Patterned with Graded Photonic Super-Crystals

“…Nanostructures have been used to improve light coupling from free space to silicon-based photovoltaic solar cell devices and incorporate light-trapping functionality in the solar cell so that the light absorption of the device will increase. Various nanostructures have been proposed and their mechanisms for light absorption enhancement have been investigated, which include surface plasmon induced enhancement [1], nanowire-based light trapping [2][3][4], back-reflector-based multiple pass absorption [5][6][7][8][9], and one-dimension and two-dimension photonic crystal-based structural resonances [10][11][12][13][14]. Photonic crystals are periodic structures that offer powerful photon control and manipulation capability [10,11].…”

“…Various nanostructures have been proposed and their mechanisms for light absorption enhancement have been investigated, which include surface plasmon induced enhancement [1], nanowire-based light trapping [2][3][4], back-reflector-based multiple pass absorption [5][6][7][8][9], and one-dimension and two-dimension photonic crystal-based structural resonances [10][11][12][13][14]. Photonic crystals are periodic structures that offer powerful photon control and manipulation capability [10,11]. The structural resonances in simple photonic crystals offer a series of sharp resonances at a specific wavelengths and angles [10][11][12][13][14].…”

Complex photonic structures for energy efficiency

“…This can either lead to enhanced absorption, or can reduce the amount of required material and hence reduce fabrication costs. Nanophotonics offers interesting possibilities for improving solar cell absorption [14][15][16]. Standard optics is limited by an upper thermodynamical limit [17], which can however be surpassed by nanophotonic strategies in particular when the absorbing films are extremely thin [18].…”