This is a breakout board for testing the LTC3108-1, which can boost as little as 20mv up to one of four selectable voltages: 2.5v, 3v, 3.7v, or 4.5v.
https://www.analog.com/media/en/technical-documentation/data-sheets/31081fb.pdf

The same board should also work just fine for the LTC3108, which is otherwise the same but has slightly different boosted voltages that can be selected: 2.35v, 3.3v, 4.1v, or 5v. https://www.analog.com/media/en/technical-documentation/data-sheets/LTC3108.pdf

As currently constructed this module is more appropriate for harvesting energy from a piezo device than it is from a tiny solar panel, though it should work just fine with a solar panel that can produce a continuous 3 or 4 milliamps or more of very low voltage current.