Plan to DIY a solar charger, but the voltage is unstable, how to make him stable to 5V, and, the voltage is stable, will the current be unstable, such as?

First of all, you need to use a few more photovoltaic panels, so that the voltage output is at least 7V or more, and then access the 5V regulator, and the 5V after voltage regulation can charge the mobile phone. As for the size of the output current, it is only related to the charging speed and slow time.