ECN publication
MWT Cells for shade-linear, diode-free modules
Newman, B.K.; Bende, E.E.; Loffler, J.; Wang, J.; Zhai, jinye; Liu, D.; Wang, Z.; Chen, Y.; Shi, J.
Published by: Publication date:
ECN Solar Energy 10-6-2016
ECN report number: Document type:
ECN-M--16-043 Conference Paper
Number of pages: Full text:
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Metal wrap through (MWT) technology is an all back contact cell technology where the front emitter contact is extended through a laser-drilled via to the rear cell surface. The vias act as a pathway for current under both forward and reverse bias voltage conditions. Through engineering the vias, we tune the resistivity under reverse bias voltage of nMWT cells such that the vias act as in-cell bypass diodes without impacting the 21% light conversion efficiency. In this contribution, back contact foil laminates made from these cells are tested under partial shade conditions as part of a simulated string with bypass diodes. The laminates with low resistance in reverse bias survive simulated hot spot testing without performance degradation or mechanical failure. The temperature distribution suggests power dissipation well distributed through the vias. The dissipated power under reverse biasing as a function of shade fraction agrees well with an analytical model. Further, the reverse voltage does not exceed the bypass diode threshold voltage under any single cell shade conditions. From these tests and simulations we show that modules made from nMWT cells with high current in reverse bias can be implemented in a shade-linear, diode-free module concept.

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