Near-field study of optical modes in randomly textured ZnO thin films |
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Authors: | K Bittkau R Carius |
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Institution: | aInstitut für Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany |
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Abstract: | We report on near-field scanning optical microscopy measurements on randomly textured ZnO thin films. These films are commonly used as transparent conducting oxide in thin-film solar cells. Textured interfaces are used to increase the scattering of light, which leads to a better light trapping in the solar cell. Here, both the topography and the local transmission are measured with a tapered fiber tip with very high spatial resolution. By varying the distance of the tip and the wavelength of the incident light, the optical profile is visualized and reveals a strong confinement of light on a subwavelength scale which corresponds to ridges in the surface structure. The confinement of light results from guided optical modes in the ZnO which are accompanied by a modulated evanescent field in air. No corresponding structure to this modulation is found in the topography. These results give new insight for further improvement of light trapping in solar cells. |
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Keywords: | Near-field microscopy Thin-film solar cell ZnO Random surface Light trapping |
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