6:30 Charge is conserved. An electron-hole pair has zero net charge. When the hole and electron get swept out of the depletion region, the electron will give the N-region a -1 charge, and the hole gives the P-region a +1 charge. To "equalize" this charge imbalance, it requires only one electron to flow around the exterior circuit. 9:30 The electrons in the external circuit due to recombination are in the opposite direction from the light generated electrons flowing through the external circuit. That is why you subtract them to get the total diode current. I had to think about this for a while, so I thought a comment might be helpful to someone else.
The dark current under short circuit conditions is supposed to be 0. Whenever there is electron/ hole recombination an electron flows into the external circuit, leading to dark current flow. I don't understand how recombination of photo generated carriers under short circuit conditions does not lead to dark current, but recombination when electrons/ holes are injected to the p/ n side in a forward bias diode does.
