LED and Solar cell

It is my first presentation slide. So it is important memory more than importance

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 - GaN LED 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 LED s 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 100 uA, then 2 LED s in parallel can produce 200 uA. Similarly, if the voltage produced by a single LED is around 1.3 volts, then 2 LED s 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