This has been confusing me a lot lately. I built a type of battery derived from a solar cell that outputs a constant voltage of 0.5 Volts. My original plan was to work out a method to boost this voltage to around 1V to power a joule thief and light an LED using a capacitor charged by the cell. However upon testing the cell with some capacitors I found that it would charge a variety of different capacitors all the way up to 1.6V if left connected for long enough (It would greatly slow after about 1.4V). Now this doesn't make much sense to me as it isn't possible to charge capacitors to a higher voltage than the input. I took all measurements with the same multimeter and have verified that the charged capacitors are indeed 1.6V (they will briefly light up the LED in the joule thief that only works down to 0.8V).