I've got my hands on a bunch of old garden lights with solar panels, and of course I disassembled them and found that they use just one 1.5V accumulator cell to light up the LED.
Just for illustration
I've managed to get the schematic from the PCB (I hope it's correct):
R1 ... 10k R2 ... 100k R3 ... 5k1 C1 ... 100pF (marking 101) L1 ... 150uH (translated from colors) L2 ... 410uH (translated from colors) T1,T2 ... S8050D D1 ... 1N5819
I thought I'd replicate it to get a simple and cheap 1.5V -> ~ 3V converter, but I'm not really sure how it works. Also, there's some logic to turn it off during day and on at night, which I'd rather remove.
The R and K wires (red and black) are connected to the 1.5V cell, and B and K (blue and black) wires are connected to the solar cell.
Some ideas, maybe wrong:
I assume the diode prevents current from flowing through the solar cell at night, but I'm not sure about T2's purpose. Could it be that it inhibits the converter when the solar cell is in sunlight?
Then of course the converter is a big enigma to me, but I'll just take it that it works somehow – I'm not really good with transistors.