The current of 4 cells will not always be higher then the current of 1 cell.
It does depend on the U-I characteristic of the PV-cells and the load.
F.e. if the 100 Ohm resistor is choosen to get the absolute maximal current of ONE PV-cell, 4 identical pieces in series will not be able to generate more current by definition.
Voltage sources put parallel with identical voltage (parallel, not anti-parallel) will not cancel out each other. I.e., the voltage is the same as with 1 voltage source, but no current will flow. The statement, that the current will be canceled out is correct. This case is fully symmetrical, no current can flow in either direction since the symmetry would be broken.