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Diffractive gratings for crystalline silicon solar cells—optimum parameters and loss mechanisms
Author(s) -
Peters Marius,
Rüdiger Marc,
Hauser Hubert,
Hermle Martin,
Bläsi Benedikt
Publication year - 2012
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.1151
Subject(s) - materials science , grating , silicon , optoelectronics , absorption (acoustics) , reflector (photography) , optics , solar cell , planar , light source , physics , composite material , computer graphics (images) , computer science
In this paper, we present guidelines for the design of backside gratings for crystalline silicon solar cells. We use a specially developed method based on a combination of rigorous 3D wave optical simulations and detailed semiconductor device modeling. We also present experimental results of fabricated structures. Simulation‐based optimizations of grating period Λ and depth d of a binary grating and calculations of the optical and electrical characteristics of solar cells with optimized gratings are shown. The investigated solar cell setup features a thickness of d bulk = 40 µm and a flat front surface. For this setup, we show a maximum increase in short‐circuit current density of Δ j SC = 1.8 mA/cm² corresponding to an efficiency enhancement of 1% absolute. Furthermore, we investigate different loss mechanisms: (i) an increased rear surface recombination velocity S 0,b because of an altered surface caused by the introduction of the grating and (ii) absorption in the aluminum backside reflector. We analyze the trade‐off point between gain due to improved optical properties and loss due to corrupted electrical properties. We find that, increasing the efficiency by 1% absolute due to improved light trapping, the maximum tolerable recombination velocity is S 0,b(max) = 5.2 × 10 3 cm/s. From simulations and measurements, we conclude that structuring of the aluminum backside reflector should be avoided because of parasitic absorption. Adding a dielectric buffer layer between silicon and the structured aluminum, absorption losses can be tuned. We find that for a planar reflector, the thickness of a SiO 2 buffer layer should exceed d SiO 2 = 120 nm. Copyright © 2011 John Wiley & Sons, Ltd.