https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...
You can get around it with multi-layer, but each layer adds diminishing returns on improvements, while the cost keeps increasing.
The best way to handle places with less solar irradiance is to have more panels. The cost per panel keeps dropping, so the economics keep improving in that way.
With more panels my setup will be more of an eye-sore, require more and longer cables, combiner boxes and the setup becomes a bigger project. So I am just being a selfish ass but I had to ask where we are.