Solar cell: A solar cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. Solar cell is a p-n junction fabricated from silicon. The energy conversion consists of absorption of light (photon) energy producing electron-hole pairs in the p−n junction and charge carrier separation.
I-V Characteristics:

Solar cell I-V characteristic curves are graphs of output voltage versus current.
VOC : This is the maximum voltage that the array provides when the terminals are not connected to any load (an open circuit).
ISC : The maximum current provided by the PV array when the output connectors are shorted together (a short circuit condition).
Working of solar cell: A solar cell is a junction of n-type silicon (blue) and p-type silicon (red).

It generates electricity by using sunlight to make electrons move across the junction between the different types of silicon :
1. When sunlight shines on the cell, photons bombard the upper surface.
2. The photons carry their energy from n-type layer to p-type layer through p-n junction of the cell.
3. The photons transfer their energy to electrons in the p-type layer.
4. The electrons use this energy to move across the barrier into the n-type layer and flow out into the circuit.
5. This flow of electrons through the circuit gives rise to flow of current in the external circuit.
OR
A centre-tapped full wave rectifier system consists of :
1. Centre-tapped Transformer
2. Two Diodes
3. Resistive Load

Centre-tapped Transformer: It is a normal transformer with an additional tap in the secondary winding known as centre tap. Centre tap is always at zero potential. For one half cycle of AC voltage applied to the primary coil, one end on the secondary coil positive potential is developed and at the other end a negative potential is developed. For the other half cycle, the polarity get reversed.
When AC voltage is applied to the primary coil, during the positive half-cycle, the terminal A is at positive potential, centre-tap is at zero potential and terminal B is at negative potential. During this cycle, the diode D1 is forward biased- and causes current to flow through it. During this time, diode D2 is in reverse bias and does not conduct. The current flow path is shown below.

During the negative half-cycle of the input AC voltage, terminal B is at positive potential, centretap is at zero potential and terminal A is at negative potential. During this cycle, diode D2 is reverse biased and causes current to flow through it. During this time, diode D1 is in reverse bias and does not conduct. The current flow path is shown below.

As a result, the current flow through the load resistance is unidirectional for the complete cycle.
Hence, the output is a DC voltage.
The output waveforms are as follows: