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Experimental evidence of parasitic shunting in silicon nitride rear surface passivated solar cells
Author(s) -
Dauwe Stefan,
Mittelstädt Lutz,
Metz Axel,
Hezel Rudolf
Publication year - 2002
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.420
Subject(s) - passivation , silicon nitride , materials science , open circuit voltage , short circuit , optoelectronics , solar cell , current density , silicon , optics , voltage , electrical engineering , nanotechnology , layer (electronics) , physics , engineering , quantum mechanics
Many solar cells incorporating SiN x films as a rear surface passivation scheme have not reached the same high level of cell performance as solar cells incorporating high‐temperature‐grown silicon dioxide films as a rear surface passivation. In this paper, it is shown by direct comparison of solar cells incorporating the two rear surface passivation schemes, that the performance loss is mainly due to a lower short‐circuit current while the open‐circuit voltage is equally high. With a solar cell test structure that features a separation of the rear metal contacts from the passivating SiN x films, the loss in short‐circuit current can be reduced drastically. Besides a lower short‐ circuit current, dark I–V curves of SiN x rear surface passivated solar cells exhibit distinct shoulders. The results are explained by parasitic shunting of the induced floating junction (FJ) underneath the SiN x films with the rear metal contacts. The floating junction is caused by the high density of fixed positive charges in the SiN x films. Other two‐dimensional effects arising from the injection level dependent SRV of the Si/SiN x interfaces are discussed as well, but, are found to be of minor importance. Pinholes in the SiN x films and optical effects due to a different internal rear surface reflectance can be excluded as a major cause for the performance loss of the SiN x rear surface passivated cells. Copyright © 2002 John Wiley & Sons, Ltd.