1. Working Principle of a Solar PV Cell
A solar photovoltaic (PV) cell converts sunlight (solar energy) directly into electricity based on the photovoltaic effect.
Construction
- A solar cell is essentially a PN junction diode made from semiconductors (usually silicon).
- The base is P-type silicon, and a thin layer of N-type silicon is diffused on top.
- Metallic contacts:
- Top contact: Grid pattern (minimizing shading).
- Bottom contact: Full metal plate.
- Antireflective coating is used to minimize light loss.
Working Mechanism
- Sunlight (photons) falls on the P-N junction.
- Photons with energy > band gap excite electrons, generating electron-hole pairs.
- Electric field at the junction separates them:
- Electrons move toward N-side.
- Holes move toward P-side.
- This movement creates a potential difference (voltage) across terminals.
- When the external circuit is connected, current flows, and electrical power is generated.
2. I–V Characteristics of a Solar Cell
The I–V curve (current vs. voltage) of a solar PV cell under illumination has a unique shape.
Key Points:
- Short-Circuit Current (I<sub>SC</sub>):
- Maximum current when terminals are shorted (V = 0).
- Depends on sunlight intensity.
- Open-Circuit Voltage (V<sub>OC</sub>):
- Maximum voltage when no current flows (I = 0).
- Maximum Power Point (MPP):
- The point where the product of voltage and current is maximum.
I–V Curve Sketch
- I<sub>SC</sub>: Y-axis intercept
- V<sub>OC</sub>: X-axis intercept
- Maximum Power Point (MPP) is somewhere in the curve’s middle
Solar PV cells play a crucial role in renewable energy generation. Their PN junction structure, governed by the photovoltaic effect, enables clean and direct conversion of sunlight into electricity, with performance measured through their I–V characteristics.