Of course it's sustainable. The notion that landfilling somehow isn't sustainable is based mostly on silly aesthetics.
About the only concern with sustainability in PV is silver for contact wires, but that can be substituted for. It's being used now because it's marginally cheaper.
To clarify: not the landfill in itself, but the materials are finite. If we don't reuse them, we'll run out of them eventually. Future generations will have to dig through our landfills to recycle them. And that will be quite expensive. That's the future bill I'm mostly concerned about.
So, exactly which material for PV were you concerned about?
This also goes against your original expression about lifecycle cost. Later shortage of some critical material doesn't affect the lifecycle cost of PV built now.
About the only concern with sustainability in PV is silver for contact wires, but that can be substituted for. It's being used now because it's marginally cheaper.