https://www.independent.co.uk/tech/solar-panel-perovskite-double-sided-b2378337.html
Back side of perovskite panel achieves more than 90 per cent of the efficiency of the front side
TLDR; the front side is 23% efficient, and the rear side 20% efficient.
They don't actually give an overall efficiency but it implies a total of 43%. They compare this to typical panels also at 23% efficient, so it's really remarkable if true. Other emerging solar tech is up to about 32% but if that could also benefit from multiple layers then total efficiency could become insane.
Seems a little too good to be true, really, but great if so.
Edit: Yeah, I don't think these efficiencies can be added like that. I guess the overall efficiency will depend on how reflective the ground under the panels is, and they will extract 20% of that. Maybe that's why they don't give an overall rating.
Sure you can. That's why a UV lamp shining at the six 20% solar panels that power it can run your FTL drive.
They say the second layer retains 93% of the performance of the first using reflected light, making it 20% efficient, so, yes they are added in that case.
There isn't nearly as much light coming from the back, so you won't get that much efficiency improvement