The above design diagram is the circuit diagram of Lithium-Ion battery charger which powered using solarcell / photovoltaic as the power source.
This electronic circuit feeds a controlled the current and 6V voltage from the solarcell to a 3.6v lithium ion battery. The current is limited to 300mA and the voltage is limited to 4.2 Volts. The circuit uses a LTC1734 IC manufactured by Linear Technology. No diode is needed between the circuit and a 6 volt solar panel because the output power from solarcell already in DC form. Their SP6-200-12 cranks out about 1 watt while the SP6-300-12 can produce about 2 watts. Assuming that this circuit activated in a 6 hour sunlight day, the 2 watt panel will deviver about 1.8 amp-hours into a lithium ion battery.