This document provides an overview of LEDs and solar cells. It defines LEDs as light emitting diodes that give off visible light when forward biased using elements like gallium, phosphorus, and arsenic. It describes the internal structure of LEDs and how different colors are produced. It then defines solar cells as structures that convert solar energy directly to DC electricity. It explains the basics of solar cells including the p-n junction and how they operate in the fourth quadrant to generate power. Finally, it describes LED solar cells which can produce voltage when light falls on the LED and the advantages and disadvantages of LED solar cells.

1. LED AND SOLAR CELL
Presented by
Manjurul Haque Md.Osman Gony
Roll:1509055 Roll:1509052

2. Outlines:
Electronics and Communication Engineering 02/16
 Definition of LED
 Colors of LED
 Internal structure of LED
 Definition of Solar cell
 Basics of Solar cell
 Solar panel
 Solar cell principle
 LED Solar cell
 Advantage and disadvantage of LED solar cell

3. What is LED?
Electronics & Communication Engineering, KUET 03/16
 A light emitting diode(LED) is a
diode that gives off visible light
when forward bias.
 LED are not made from Si or Ge
like as general diode but are made
by using elements like Ga, P and
As.
Figure of LED

4. Colors of LED
04/16 Electronics & Communication Engineering, KUET
• Ga, P and As elements are used for
producing light of different wavelength
with colors that includes red,green, yellow
and blue.
• Colors and constructions:
Amber - AllnGaP
Blue - GaN
Green - GaP
Yellow - GaAsP
Red - GaAsP
White - GaNLED with different colors

5. Internal structure of LED
Electronics & Communication Engineering, KUET 05/16
When LED is forward bias as shown in
figure-
1. Electrons from the N-type materials
cross the p-n junction and recombine with
holes in the p-type materials
recall that these free electrons are in
the conduction band and at a higher
energy level than the holes in the valance
band when recombination takes place the
recombining electrons release energy in
the form of heat and light.
Fig- Internal structure of LED

6. Electronics and Communication Engineering,KUET 06/16
2. In Ge and Si diodes almost the entire energy
is given up in the form of heat and emitted light
is insignificant but in materials light GaAs the
number of photons of light energy is sufficient
to produce quiet intense visible light.
3. The figure shows the schematic symbol for a
LED.The arrows are shown as pointing away
from the diode indicating that light is being
emitted by the device when forward bias. The
schematic symbol is the same for all colors
LED.
Symbol of LED

7. Radiated light vs forward current of LED
Electronics and Communication Engineering,KUET 07/16
The figure shows the graph
between radiated light and the
forward current of the LED.It is
clear form the graph that
the intensity of radiated light is
directly proportional to the
forward current. Fig-Radiated light vs forward current

8. What is Solar cell?
Electronics and Communication Engineering,KUET 08/16
Figure of Solar cell
•A structure that converts solar
energy directly to DC electric
energy.
– It supplies a voltage and a current to a
resistive load (light, battery, motor).
•It is like a battery because it supplies
DC power.
•It is different from a battery in the
sense that the voltage supplied by
the cell changes with changes in the
resistance of the load.

9. Electronics and Communication Engineering,KUET 09/16
Basics of solar cells
• If two differently contaminated semiconductor layers are
combined, then a so-called p-n-junction results on the boundary
of the layers.
• By doping trivalent element, we get p-type semiconductor. (with
excess amount of hole)
• By doping pentavalent element, we get n-type semiconductor (
with excess amount of electron)
n-type semiconductor
p- type semiconductor
p-n junction layer

10. Electronics and Communication Engineering,KUET 10/16
Solar Cell Principle
 Operating diode in fourth quadrant generates power

11. A solar panel (or) Solar array
Electronics and Communication Engineering,KUET 11/16
Single solar cell
• The single solar cell constitute the n-type layer
sandwiched with p-type layer.
• The most commonly known solar cell is configured
as a large-area p-n junction made from silicon wafer.
• A single cell can produce only very tiny amounts of
electricity
• It can be used only to light up a small light bulb or
power a calculator.
• Single photovoltaic cells are used in many small
electronic appliances such as watches and
calculators
Single solar cell
N-type
P-type

12. Electronics and Communication Engineering,KUET 12/16
Solar panel (or) solar array (or) Solar
module
The solar panel (or) solar array is the
interconnection of number of solar
module to get efficient power.
• A solar module consists of number
of interconnected solar cells.
• These interconnected cells
embedded between two glass plate
to protect from the bad whether.
• Since absorption area of module is
high, more energy can be
produced.

13. LED solar cell
13/16 Electronics and Communication Engineering
1. When solar light is allowed to fall
through the window of an LED, the photons
in the light which has wavelength equal to
the band gap of LED penetrates deep into
the PN junction.
2. On absorbing energy from these
photons, the electron hole bond at the PN
junction breaks and result in accumulation
of electrons in the n side and holes in the p
side.
3. So, p side will be more positive than n
side. This makes anode positive and
cathode negative. Hence, LED acts as a cell.

14. 14/16 Electronics and Communication Engineering,KUET
The voltage produced by a single red LED is
around 0.7 to 1.3 volts but its output current
is very low. So, a single LED cannot be used
for powering any device.
 To increase its output current and voltage,
we will use a combination of LEDs which are
connected both in parallel and in series.
The advantage of this is that the parallel
combination increases current rating while
the series combination increases voltage
rating.
 If the current output of a single LED is
around 100uA, then 2 LEDs in parallel can
produce 200uA. Similarly, if the voltage
produced by a single LED is around 1.3 volts,
then 2LEDs in series can produce 2.6 volts.
Figure of LED solar panel circuit diagram

15. Electronics and Communication Engineering,KUET 15/16
Advantages of LED solar cell:
1. The cost incurred is low. They are economical in use.
2. They are easily available.
Disadvantages of LED solar cell:
1. If it is exposed to sunlight for long period, the LED can damage. In
order to prevent this, high power LEDs can be used.
2. All the LEDs should face the sun at the same angle. This can be done
by mounting all the LEDs on a common PCB.
3. Since the output current is low, for high power applications, more
number of LEDs must be used but this makes the circuit bulky.

16. THANK
YOU