Fahim Faisal Amio's document summarizes the basics of solar cells in 3 sentences or less: A solar cell converts light energy into electrical energy through the photovoltaic effect using a p-n junction diode. Common materials used in solar cells include silicon, GaAs, CdTe, and CuInSe2 which have band gaps close to 1.5eV. External factors like photon transmission through protective layers, intensity of light, and cell area influence solar cell efficiency.

1. Name: Fahim Faisal Amio
MS in Mechanical Engineering
Student id: 22240126
E-mail: fahimfaisal@yu.ac.kr
║Materials For Machine║
Basics of Solar cells

2. Contents
• Introduction
• Photon
• Solar Spectrum at Earth Surface
• Irradiance
• PN Junction
• Silicon Solar Cell 6 Volt Panel Series-Parallel Design
• Materials of Solar cell
• Advantages, Disadvantages and Uses
• External Factors Influencing Solar Cell Efficiency

3. Introduction
A solar cell (also known as a photovoltaic cell or PV cell) is defined as an electrical device that converts light energy
into electrical energy through the photovoltaic effect. A solar cell is basically a p-n junction diode. Solar cells are a form
of photoelectric cell, defined as a device whose electrical characteristics – such as current, voltage, or resistance –vary
when exposed to light.

4. A light particle having energy. Sunlight is a spectrum of photons.
Photon Energy, E = hn or hc/ l [Joules or eV (electron-volts)]
Photon
(higher frequency = higher energy)
(lower energy)

5. Solar Spectrum at Earth Surface (noon time)
E (eV) = hc/l
l = hc/E
Visible range
.75 mm (red) - .4 mm (purple)
1.6 eV - 3.1 eV
Solar Spectrum at Earth Surface
.5 eV - 3.6 eV
2.6 mm (infrared) - 0.34 mm (ultraviolet)
visible
ultraviolet
inrfared
Solar Spectrum
at Earth Surface
(noon time)
925 W/m2

6. Amount of power over a given area, Watts/m2
Irradiance
Energy of 1 red photon = hc/l = (6.63 x 10-34 J-s)(2.99 x 108 m/
s)/(0.80 x 10-6 meters)
= 2.48 x 10-19 J = 1.55 eV
Irradiance = Power/Area = (4 photons/sec)(Energy of 1 photon)/
2.00 m2
= 4.96 x 10-19 W/m2
Typical sunlight irradiance is 0.093 W/cm2 = 930 W/m2 at l = .5
5 mm
4 red photons every second
Area = 2.00 m2

7. PN Junction in Thermal Equilibrium
(No Applied Electric Field)
metallurgical
junction
• Free electrons from n-region diffuse to p-region leaving donor atoms behind.
• Holes from p-region diffuse to n-region leaving acceptor atoms behind.
• Internal Electric Field is created within Space Charge Region.
P-type N-Type
metallurgical
junction
E field
Space Charge Region
p n
Initial Condition
Equilibrium Condition
+
+
+
+
-
-
-
-

8. PN Junction Hole and Electron Injection
Reversible Process
Forward biased voltage applied to a PN junction creates hole and
electron injection carriers within the space charge region.
External photon energy absorbed in space charge region creates hole
and electron injection carriers.

9. PN Junction Solar Cell Operation
Step 1
Photon
hn > Eg
Space Charge Region
+
+
+
+
+
E field
p n
e-
e-
e-
e-
e-
• Photons create hole-electron pairs in space charge region
• Created hole-electron pairs swept out by internal E field

10. PN Junction Solar Cell Operation
Step 2
• Creates excess holes in p-region
• Creates excess electrons in n-region
• Einjected is created by excess holes and electrons
Photon
hn > Eg
Space Charge Region
E field
p n
E injected
+
+
+
+
+
e-
e-
e-
e-
e-

11. PN Junction Solar Cell Operation
Step 3
• Attaching a resistive load with wires to the PN Junction allows
current flow to/from p-n regions
• Photocurrent, IL, is in reverse bias direction
• Iforwad is created by Einjected
• Icell = IL - Iforward
Photon
hn > Eg
Space Charge Region
E field
p n
Resistor
Vcell
IL
Icell
IForwad
+ -
E injected
+
+
+
+
+
e-
e-
e-
e-
e-

12. Typical Silicon Solar Cell Design
N-type
Silicon
Wafer
P-type
Doping
Protective High Transmission Layer
To load
Wires
4-6 inches
Photons
• Photons transmit through thin protective layer and
thin P-type doped layer and create hole-electron
pairs in space charge region
• Typical Silicon Single Cell Voltage Output = ~ 0.5 volts

13. Silicon Solar Cell 6 Volt Panel Series-Parallel Design
12 cells in series = 6 volts
6 volts
p to n connection
-
+

14. Materials Used in Solar Cell
The materials which are used for this purpose must have band gap close to 1.5ev. Commonly
used materials are-
1.Silicon.
2.GaAs.
3.CdTe.
4.CuInSe2
Criteria for Materials to be Used in Solar Cell
1.Must have band gap from 1eV to 1.8eV.
2.It must have high optical absorption.
3.It must have high electrical conductivity.
4.The raw material must be available in abundance and the cost of the material must be low.
Materials of Solar cell

15. Advantages of Solar Cell
1.No pollution associated with it.
2.It lasts for a long time.
3.No maintenance cost.
Disadvantages of Solar Cell
1.It has high cost of installation.
2.It has low efficiency.
3.During cloudy days, the energy cannot be produced, and at night, we will not get solar energy.
Uses of Solar Generation Systems
1.Add energy to the electricity supply grid.
2.Used in light meters.
3.It is used in power calculators and wrist watches.
4.Electric vehicles
5.Household applications
6.Small Industrial applications
Advantages, Disadvantages and Uses

16. External Factors Influencing Solar Cell Efficiency
 Photon transmission, reflection, and absorption of protective layer
• Maximum transmission desired
• Minimum reflection and maximum absorption desired
 Polarization of protective layer
• Minimum polarized transmission desired
 Photon Intensity
• Increased intensity (more photons) increases cell current, Icell
• Cell voltage, Vcell, increases only slightly
• Larger cell area produces larger current (more incident photons)
 Theoretical Silicon Solar Cell Maximum Efficiency = 28%
 Typical Silicon Solar Cell Efficiency = 10-15%

17. Thank You