It might be worth checking whether you need a boost converter or MPPT at all. Often, the efficiency of these low voltage converters is not all that great. If the maximum power point of these solar cells is close to the voltage of your LiPo, you could hook the panel up to your LiPo directly through a FET. The maximum panel current is your maximum charge current. Once the cell reaches full voltage, you turn off the FET.
You need battery cell protection though, and of course monitor the battery temperature. Also, it's smart to choose your battery cutoff voltage conservatively (for example 4.0V instead of 4.2V).