It is better then 5v.
Charging li ion batteries with solar panel.
A pwm or mppt solar charge controller is used to regulate the charging of the battery in a stand alone solar photovoltaic system.
Let s say i have a battery pack made from 3 lithium ion cells connected in a series making a battery with around 12 volts.
A lithium ion solar charge controller is used when a li ion battery is used as power storage in the system.
Tp4056 then charges the battery from the solar power itself.
Material links are affilliate.
So you can choose 500 mah solar cell or 1 ah solar cell.
That battery pack has a pcb with balancing function and also protects the battery from over charging over discharging and short circuit by interrupting the input output to from the battery when needed.
For li ion.
Otherwise it may lead to explosion also.
Charging lithium batteries with solar panels.
Charging lithium ion batteries is a tricky affair and too with solar power because lithium ion batteries are dangerous and require controlled charging environments.
The input to tp4056 can be in the range of 4v to 8v which is the range of the output of the solar panel.
Here i am going to build a 18650 lithium ion battery charger harnessing solar energy.
I find good website with tests lithium ion.
Lithium ion batteries 18650.