Comparison of metal/polymer back reflectors with half-sphere, blazed, and pyramid gratings for light trapping in III-V solar cells

Abstract

We report on the fabrication of diffraction gratings for application as back contact reflectors. The gratings are designed for thin-film solar cells incorporating absorbers with bandgap slightly lower than GaAs, i.e. InAs quantum dot or GaInNAs solar cells. Light trapping in the solar cells enables the increase of the absorption leading to higher short circuit current densities and higher efficiencies. We study metal/polymer back reflectors with half-sphere, blazed, and pyramid gratings, which were fabricated either by photolithography or by nanoimprint lithography. The gratings are compared in terms of the total and the specular reflectance, which determine their diffraction capabilities, i.e. the feature responsible for increasing the absorption. The pyramid grating showed the highest diffuse reflection of light compared to the half-sphere structure and the blazed grating. The diffraction efficiency measurements were in agreement with the numerical simulations. The validated model enables designing such metal/polymer back reflectors for other type of solar cells by refining the optimal dimensions of the gratings for different wavelength ranges.

Efficient broadband light absorption in thin-film a-Si solar cell based on double sided hybrid bi-metallic nanogratings

“…A key technique for obtaining good light trapping and enhancing the efficiency of solar cells is to engineer the light behavior by using photonic crystals, 4 diffraction gratings, 5 anti-reection coatings, 6 surface texturing, 7 and metallic nanoparticles. 3,8 Plasmonic nanogratings among other structures show a substantial progress as they can be used either as an innovative back reector patterned on a metal mirror [9][10][11][12] and/or on transparent and conductive oxides (TCO), [13][14][15][16] to improve both the optical path length and optical absorption over a broad spectrum. The effective coupling between metallic nanograting modes and the incident light essentially presents an efficient light trapping developing from surface plasmon resonances and their resultant near-eld light concentration.…”

Enhancing intermediate band solar cell performances through quantum engineering of dot states by droplet epitaxy

“…Moreover, light-trapping techniques can be exploited to further increase first and second photon optical transitions, increasing the short-circuit current and preserving the open circuit voltage thanks to the improved ratio between optical and thermal extraction rates from the IB. 31,38,39…”

Rational and key strategies toward enhancing the performance of graphene/silicon solar cells

“…Thanks to its significant reflectance, flat Si surfaces have a high absorption loss of 30-40% in the visible range. 136 To improve light trapping, silicon substrates were designed with various nano and micro-textured structures such as pyramid texture, [137][138][139][140][141][142] nanowires, 143,144 nanopillars, 145,146 and, a porous surface. 147,148 The utilization of Si nano-or micro-textured can significantly improve light trapping ability due to the powerful light-collecting effect that stifles the reflection of the junction area in the visible and near-infrared range and enhances the light-collecting efficiency.…”