  A long operational lifetime is required for the use of solar cells in
real-life photovoltaic applications. The optimization of operational lifetimes
is achieved through understanding the inherent degradation phenomena in solar
cells. In this study, graphene/Si Schottky-junction solar cells were produced,
utilizing liquid-phase-exfoliated graphene as an active surface. The
operational and interface stability of these solar cells over a period of 5
years in ambient conditions (following ISOS-D protocols: dark storage/shelf
life) was examined, and the origin of their degradation was reported. It was
found that the dominant degradation mechanism could be attributed to the
degradation of silver contacts. This was indicated by a decrease in shunt
resistance, an increase in the ideality factor (due to a higher carrier
recombination), and a constant defect density in graphene films for up to 4
years. Measurements across the solar cell's active area during the 5-year
period revealed neither significant spatial inhomogeneity, nor shunt channel
defects.
