Items necessary to make a solar cell phone charger

Today I made a video of items that I have to make the charger. Check it out:

• a PV solar cell - 6 V, 200 mA
• wires
• a diode
• a USB connector
• a soldering iron
• a box
• glue
• a digital multimeter 

Q: Why should the PV solar cell be 6 Volts? A voltage should be 5.5-6 volts to charge a cell phone. I tested my PV solar cell's voltage with a multimeter in different conditions and this is what I've got:

• On a sunny day: 6.2 V
• On a cloudy day: 5.3-5.7 V
• Under a lamp: 4.2-4.8 V

So, my solar cell should work, right?

FUNNY fact of the day: One can make such handmade solar cell phone chargers for all phones but iPhones :) I saw a video of how one man actually found a way around it. He didn't make it himself though. Watch the video from the minute 1 to see how to charge apple products with solar energy: