Renewable energy Solar_Cells_and_the_Photovoltaic_Effect Energy Solar

1. ❖ Prepared By:
- Abdullah Jubran Al-faifi. - Abdulrahman Ali Adawi.
- Waseem Ali Bashiri. - Abdulaziz Ali Qumari. - Mohammed Adawi.
❖ Instructor: Dr. Hadi Madkhali.

2. Solar Cells and the Photovoltaic Effect
What is a Solar Cell?
A solar cell is a device that converts sunlight directly into electrical energy.
How Does It Work?
Solar cells operate using the photovoltaic effect, which occurs when
sunlight is absorbed by a material (usually a semiconductor) and generates
an electric current.
What is a Photovoltaic Device?
A photovoltaic device generates voltage across a p-n junction in a semiconductor
when it absorbs light.
This process converts light energy into usable electrical power.

3. Principle of Solar Cells
Photovoltaic Effect:
Solar cells are based on the photogeneration of charge carriers due to the absorption
of light. Semiconductor Materials :P-type: Contains boron impurities (fewer
electrons).N-type: Contains phosphorus impurities (extra electrons).
Charge Movement:
❖ Holes (from P-type) diffuse to the N-type side.
❖ Electrons (from N-type) diffuse to the P-type side.
❖ This movement leaves behind charged ions.
Electric Field Creation:
❖ The charged ions create an electric field at the junction.
❖ This field allows current to flow in one direction but blocks it from flowing in the
opposite direction.

4. Generating Charges from the Sun:
Breaking Silicon Bonds:
❖ Sunlight breaks silicon bonds, creating free electrons and
holes (missing electrons).
❖ Holes act as positive charges.
Separation of Charges:
❖ The built-in electric field separates the electrons and holes,
allowing current to flow.
Connecting to a Circuit:
❖ A diode is connected to a circuit.
❖ The photocurrent flows through a resistor, causing a
voltage drop.

5. Forward Bias and Circuit Behavior:
Forward bias:
❖ Current flows in the opposite direction when the diode is forward biased.
Open Circuit Condition:
❖ When resistance (R) is very high, voltage (V) becomes large, and the
current (I) is nearly zero.
Short Circuit Condition:
❖ When resistance (R) is very low, voltage (V) is almost zero, and current (I)
equals the photocurrent (IPC).

6. Construction of Solar Cells
• Solar Cells (Crystalline Silicon) are constructed by tow layering special materials called semiconductors:
❖n type (Emitter layer).
❖p type (Base layer).
• When a solar panel exposed to sunlight , the light energies are absorbed by a semiconductor materials.
• Due to this absorbed energy, the electrons are liberated and produce the external DC current.
• The DC current is converted into 240-volt AC current using an inverter for different applications.

7. The Main Components Solar Panel
➢ Frame: Ensures structural integrity.
➢ Glass: Protects cells and lets sunlight through.
➢ Encapsulant: Holds and protects the cells.
➢ Solar Cells: Generate electricity from sunlight.
➢ Back sheet: Provides protection from the environment.
➢ Junction Box: Manages electrical connections.

8. How Solar Cells Work
▪ 1.When sunlight shines on the cell, photons bombard the upper
surface.
▪ 2. The photons (yellow dot) carry their energy down through the cell.
▪ 3. The photons give up their energy to electrons ( green dot) in the
lower, p-type layer.
▪ 4. The electrons use this energy to jump across the barrier into the
upper, n-type layer and escape out not the circuit.
▪ 5. Flowing around the circuit, the electrons make the lamp light up.

9. ➢• Open circuit voltage (Voc) .
➢• Short circuit current (Isc).
➢• Maximum power.
➢• Efficiency.
Solar Cell Properties

10. Factors Affecting Solar Cell Performance
➢• Light intensity (type of light).
➢• Light wavelength (color of light) .
➢• Angle of incident light .
➢• Surface condition of solar cells (cleanness) .
➢• Temperature on solar cells.

11. Solar cell process flow
• n-type Silicon Wafers: Start with silicon doped with phosphorus for extra
electrons.
• Cleaning: Use chemicals (sulfuric-peroxide, hydrofluoric acid, hydrochloric acid)
to remove contaminants.
• Spin-on Boron: Apply a boron solution to introduce p-type impurities for
forming the p-n junction.
• Annealing (1000°C): Heat the wafer to diffuse boron, creating the p-n junction.

12. Solar cell process flow
• Metallization: Deposit aluminum for electrical contacts.
• Patterning: Use photoresist and UV light to define metal
contacts.
• Metal Etching: Remove excess metal, leaving behind the
contacts.
• Final Annealing (400°C): Anneal again to improve contact
conductivity.

13. Doping
What are doping ?
Doping is the process of introducing impurity atoms into the silicon lattice to manipulate its electrical
properties.
Can we know how this is done?
Yes , This is done by substituting silicon atoms with elements that have either three or five valence
electrons, such as boron or phosphorus.

14. What type of element are phosphorus and
boron?
Phosphorus (n-type doping): It has five valence electrons. When
introduced into the silicon lattice, four of these electrons form bonds with
neighboring silicon atoms, leaving one free electron. This free electron
increases the concentration of electrons in the silicon, making it an n-type
semiconductor, where electrons are the majority carriers.
Boron (p-type doping): It has three valence electrons. When introduced, it
can accept an electron from a nearby silicon-silicon bond to complete its
bonds, creating a “hole” in the process. This hole can move through the
lattice, increasing the concentration of positive charge carriers (holes),
making the material a p-type semiconductor, where holes are the majority
carriers.

15. Carrier concentrations
• Semiconductor Operation:
Depends on charge carriers (electrons and holes) for electrical
currents.
Precise knowledge of carrier concentration is crucial.
• Equilibrium State:
No external forces (e.g., voltage or magnetic field) applied.
Semiconductor properties remain constant over time.

16. Energy Bands and Charge Transport
• Valence Band (VB): Holds electrons bound in
covalent bonds.
• Conduction Band (CB): Contains free electrons that
enable current flow.
• Band Gap : Separates the VB and CB, and defines
the energy required for an electron to move from
VB to CB.

17. Key Equations Summary (4.1 – 4.18)
1. Fermi-Dirac Distribution:
Describes the probability of electron occupancy:
𝑓 𝐸 =
1
1 + 𝑒(𝐸−𝐸𝐹)/𝑘𝑇
2. Intrinsic Carrier Concentration
𝑛 = 𝑝 = 𝑛𝑖(Intrinsic semiconductor)
Relationship: 𝑛 × 𝑝 = 𝑛𝑖
2

18. 3. Doping Effects:
n-type: Adds electrons, shifts 𝐸𝐹 closer to CB.
p-type: Adds holes, shifts 𝐸𝐹 closer to VB.
4. Charge Neutrality Equation:
Ensures balance between carriers and dopants:
𝑛 − 𝑝 + 𝑁𝐴
−
− 𝑁𝐵
+
= 0
5. Fermi Energy Shift:
Doping changes the position of 𝐸𝐹:
n-type: 𝐸𝐹→𝐸𝑐
p-type: 𝐸𝐹 → 𝐸𝑣
The Fermi energy shift for an n-type material can be calculated using the equation:
∆𝐸𝐹 = 𝐸𝐶 − 𝐸𝐹 = 𝑘𝑇 ln(
𝑁𝐶
𝑁𝐷
)

19. Example
A silicon wafer is uniformly doped with 1 × 1017𝑐𝑚−3 phosphorus atoms. Phosphorus acts as a donor,
providing free electrons. Given the intrinsic carrier concentration 𝑛𝑖 = 1.5 × 1010𝑐𝑚−3 , calculate:
1. Electron concentration 𝑛. 2. Hole concentration 𝑝.
Solution:
Electron Concentration : 𝑛 ≈ 𝑁𝐷 = 1 × 1017𝑐𝑚−3.
Hole Concentration : 𝑛 × 𝑝 = 𝑛𝑖
2
, 𝑝 =
𝑛𝑖
2
𝑛
=
(1.5×1010)2
1×1017 = 2.25 × 103𝑐𝑚−3.

21. Thank You