Your understanding is correct about charging.
To use a solar charger you would have to use some small circuit either into the battery VCC and GND lines or a simpler method would be to use the micro USB port as you could feed from a regulated solar input of 5V.
The TP4056 if used as one of those Chinese modules (or similar) gives you that regulated charge that you would need to avoid over charging (bad thing with LiPo's).
There are similar modules that allow a closer match to a battery and depending on the battery capacity that would be a better option as they are usually have some adjustment or extra capacity.