Localization and Characterization of a Degraded Site in Crystalline Silicon Photovoltaic Cells Exposed to Acetic Acid Vapor

• Published in: IEEE journal of photovoltaics Vol. 8; no. 4; pp. 997 - 1004
• Main Authors: Tanahashi, Tadanori, Sakamoto, Norihiko, Shibata, Hajime, Masuda, Atsushi
• Format: Journal Article
• Language: English
• Published: IEEE 01.07.2018
• Subjects: AC impedance; Computer architecture; corrosion; Degradation; degradation mechanisms; Electrodes; Glass; Impedance; metallization; Microprocessors; photovoltaic (PV) cell; Silicon
• ISSN: 2156-3381; 2156-3403
• DOI: 10.1109/JPHOTOV.2018.2839259

To examine the mechanisms of degradation owing to liberated organic acid from polymer materials in crystalline silicon (c-Si) photovoltaic (PV) modules, we attempt to characterize the degraded site in a PV cell exposed to acetic acid vapor by means of ac impedance spectroscopy. The location was electrically determined at the interface between the front electrodes and emitter of a silicon wafer. Concerning this interface, two distinct electric characteristics were identified as follows: 1) the contact in this interface can rectify the current in the same direction as the p-n junction of a p-type PV cell, and 2) any linear relationship in the Mott-Schottky plot was not confirmed in the capacitance component placed in this interface, unlike in the case of that located in the p-n junction. From these characteristics, the inclusion of a layer with a voltage-independent capacitance in this interface, an inhomogeneous depth profile of impurities within the near-surface of the n + -Si layer of this contact, and/or the existence of peculiar surface/interface states in this interface were deduced. It is concluded that a crucial electrical feature involved in the degradation of c-Si PV cells/modules under acidic conditions is verified with regard to these characteristics.