  In this article, we investigate the effect of prolonged light exposure on
silicon heterojunction solar cells. We show that, although light exposure
systematicallyimproves solar cell efficiency in the case of devices using
intrinsic and p-type layers with optimal thickness, this treatment leads to
performance degradation for devices with an insufficiently thick (p) layer on
the light-incoming side. Our results indicate that this degradation is caused
by a diminution of the (i/p)-layer stack hole-selectivity because of light
exposure. Degradation is avoided when a sufficiently thick (p) layer is used,
or when exposure of the (p) layer to UV light is avoided, as is the case of the
rear-junction configuration, commonly used in the industry. Additionally,
applying a forward bias current or an infrared light exposure results in an
efficiency increase for all investigated solar cells, independently of the
(p)-layer thickness, confirming the beneficial influence of recombination on
the performance of silicon heterojunction solar cells.
