Study of detached back reflector designs for thin‐film silicon solar cells

Abstract

We present a precise and flexible method to investigate the impact of diverse detached reflector designs on the optical response of p–i–n thin‐film silicon solar cells. In this study, the term detached reflectors refers to back reflectors that are separated from the silicon layers by an intermediate rear dielectric of several micrometers. Based on the utilization of a highly conductive n‐doped layer and a local electrical contact scheme, the method allows the use of non‐conductive rear dielectrics such as air or transparent liquids. With this approach, diverse combinations of back reflector and rear dielectric can be placed behind the same solar cell, providing a direct evaluation of their impact on the device performance. We demonstrate the positive effect of a rear dielectric of low refractive index on the light trapping and compare the performance of solar cells with an air/Ag and a standard ZnO/Ag back reflector design. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells

“…All solar cells have poor conversion efficiency for wavelengths near the active-layer bandgap, motivating many previous light-management studies for non-heterojunction silicon devices. 6,7,[9][10][11][12][13][14][15][16] However, IR light management in silicon heterojunction solar cells is neither like that in diffused-junction crystalline silicon solar cells nor like that in thin-film silicon cells. Heterojunction cells and monocrystalline diffused-junction cells share the same random pyramid texture at the silicon surfaces, so that the angular distribution of light paths-and thus the probability of absorption in the wafer or escape out the front-is similar in both devices in the absence of parasitic absorption.…”

Silver versus white sheet as a back reflector for microcrystalline silicon solar cells deposited on LPCVD‐ZnO electrodes of various textures

“…In the case of a metallic BR, parasitic absorption usually occurs in the metal because of texture-mediated or roughness-mediated plasmonic interactions [19][20][21]. It has been shown that a dielectric layer with a low refractive index inserted between the silicon layers and the metal reduces the plasmonic losses in the metal layer [19,20,[22][23][24][25][26]. Most commonly, an~100-nm-thick layer of sputtered aluminum-doped ZnO or of sub-stoichiometric silicon oxide is combined with an opaque Ag layer [1][2][3][4][5][6][7][8]27,28].…”

Investigation of the impact of the rear‐dielectric/silver back reflector design on the optical performance of thin‐film silicon solar cells by means of detached reflectors

“…The strong and simultaneous increase in the absorptance, of 5.4% and 9.1% at 750 nm, indicates that the enhancement of the EQE is mainly caused by an improvement of the light trapping in the active layer of the solar cell rather than an enhanced reflectivity of the BR. More details about this explanation are given in Reference [21]. The improvement of the light-trapping properties for lower n rd is confirmed by the significant enhancement of the Haze, measured in the reflection mode of the complete solar cell (not shown).…”

“…Despite this result, the highest optical cell performance obtained so far by our group was found by using a detached textured Ag BR in combination with air as a rear dielectric. This BR design was found to outperform the commonly used 80 nm‐ZnO/Ag BR design and even a 110 nm‐SiO 2 /Ag BR design, showing noticeably reduced parasitic losses . In the long wavelength range ( λ > 800 nm), the experimental results show a significantly reduced cell absorptance with air as a rear dielectric rather than with a thin layer of SiO 2 .…”