You don't want one, they're just a bad idea.
The solar panel is necessarily tiny, for its added weight its useless. It would take days of sunshine to recharge.
The heat of sun cooks the cells and ages the battery so it dies faster.
You're better either simply carrying a bigger powercore or going for a big solar panel you unfold and angle to the moving sun, and a cable to the powercore in the shade cooler.
A decent solar panel, like the Anker 21W you can't buy now, in good sunshine is as fast as a wall charge so you need typically just a few hours to recharge a significant battery. However personally I did some tests this finishing with a 3 week off-grid, and to be honest I past a wall socket often enough I think it would be less hassle, more reliable, to just carry a bigger Powercore. I carried a Powercore 10000 + 21W solar and I think I'd be better carrying a 26800 instead, as it can ingest energy fast, as fast as a pub lunch period.