Presentation Details
| Direct Observation of Electrical Passivation on TOPCon Solar Cells by Kelvin Probe Force Microscopy Chun-Sheng Jiang, Dana Kern, Rebecca Wai, Harvey Guthrey, John Mangum, Steve Johnston. National Laboratory of the Rockies, Golden, CO, USA |
Abstract
Surface passivation is critical for reducing efficiency loss for photovoltaics, which has been achieved for Si cells by chemical passivation such as hydrogen, oxygen, or nitrogen termination of dangling bonds and other defects, and by electrical field that repulses minority carriers away from the interface. Our group has recently observed UV-induced degradation and associated metastability of efficiency gain and loss due to UV short expose and longtime dark storage, on a commercial n-type TOPCon module. We here focus on potential imaging for the metastability on cross-sections of the cell using Kelvin probe force microscopy. The results show a potential trough on the Al2O3 dielectric on the textured Si surface, directly demonstrating electrical passivation in p-type emitter. Half of the electrical charge is balanced with adjacent Si hole accumulation, and half with positive charges in the adjacent dielectric on the other side. The potential amplitude is location-dependent, the largest (~300 mV) in flat and parallel area to the cell surface as appeared on the cross-section, smaller (~250 mV) in the “valley” area of the textured surface, and further smaller (~200 mV) in the “peak” area, reflecting location-dependent charge-trapping density. The charging was excited by short UV illumination and decayed slowly, during the UV-excited metastability. Two types of cells from the same module show significantly different charge decay time constants of 666 or 252 minutes, corresponding to the different degrees of metastability and degradation in less or more susceptibility to UV.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.
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