High-Speed Imaging/Mapping Spectroscopic Ellipsometry for In-Line Analysis of Roll-to-Roll Thin Film Photovoltaics

Shan, Ambalanath and Fried, Miklós and Juhász, György and Major, Csaba and Polgár, Olivér and Németh, Ágoston and Petrik, Péter (2013) High-Speed Imaging/Mapping Spectroscopic Ellipsometry for In-Line Analysis of Roll-to-Roll Thin Film Photovoltaics. IEEE JOURNAL OF PHOTOVOLTAICS, 4 (1). pp. 355-361. ISSN 2156-3381

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Abstract

An expanded-beam spectroscopic ellipsometer has been developed and applied toward in-situ, high-speed imaging/ mapping analysis of large area spatial uniformity for multilayer coated substrates in roll-to-roll thin film photovoltaics (PV). Slower speed instrumentation available in such analyses applies a 1D detector array for spectroscopic mapping and involves width-wise translation of the ellipsometer optics over the moving coated substrate surface, measuring point-by-point in a time-consuming process. The expanded-beam instrument employs instead a 2D detector array with no moving optics, exploiting one array index for spectroscopy and the second array index for line imaging across the width of a large area sample. Thus, the instrument enables imaging width-wise and mapping length-wise for uniformity evaluation at the high linear substrate speeds required for real-time, in-situ, and on-line analysis in roll-to-roll thin film PV. In this investigation, we employ the expanded beam technique to characterize the uniformity of the Ag, ZnO, and n-type hydrogenated amorphous silicon (a-Si:H) layers of an a-Si:H n-i-p structure deposited on a flexible polyimide substrate in the roll-to-roll configuration. Spectroscopic ellipsometry data across a line image were collected as the substrate was translated by a roll-to-roll mechanism. Coated areas as large as 12 cm × 45 cm were analyzed in this study for layer thickness and optical properties by applying the appropriate analytical models for the complex dielectric functions of the Ag, ZnO and n-type a-Si:H layers.

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