Electrical and Electronic measurements & instrumentation 10EE35 When external light is allowed to fall on metallic film F, it penetrates easily and at the barrier layer between the metallic film and the semiconductor, photo-electric emission occurs. The photoelectrons so emitted from the layer, move towards the metallic film. Consequently the metallic film F becomes negatively charged and the copper based plate positively charged. Hence a potential difference is developed between two and a current flows in the external circuit.The strength is proportional to the intensity of light and flows without any bias i.e. without any external source of e.m.f. USES: These cells are used in devices like Photographic exposure metre. Direct reading illuminations metre. Operation of relays. SOLAR CELLS: A cells or solar battery is basically a P–N junction diode which converts solar energy into electrical energy. It is also called a solar energy converter and is simply a photo diode operated zero bias voltage. CONSTRUCTION: A solar cell consists of a P–N junction diode generally made of Ge or Si. It may also be constructed with many other semi conducting materials like GaAs, indium arsenide and cadmium arsenide. The P–N diode so formed is packed in a can with glass windows on top so that light may fall upon P & N type materials. The thickness of P region of is kept very small so that electrons generated in this region can deffuse to the junction before the recombination takes place. Thickness of N region is also kept small to allow holes generated near the surface to diffuse to the junctions before they recombine. A heavy doping of P and N regions is recommended to obtain a large photo voltage. A nickel plated ring is provided around the P layer which acts as the positive output terminal. A metal contact at the bottom serves as the negative output terminal. WORKING: The working of solar cells may be understood with reference of figure When light is allowed to fall on a P-N junction diode, photons collide with valence electrons and impart them sufficient energy enabling them to leave there parent atoms. Thus Page 45
Electrical and Electronic measurements & instrumentation 10EE35 When external light is allowed to fall on metallic film F, it penetrates easily and at the barrier layer between the metallic film and the semiconductor, photo-electric emission occurs. The photoelectrons so emitted from the layer, move towards the metallic film. Consequently the metallic film F becomes negatively charged and the copper based plate positively charged. Hence a potential difference is developed between two and a current flows in the external circuit.The strength is proportional to the intensity of light and flows without any bias i.e. without any external source of e.m.f. USES: These cells are used in devices like Photographic exposure metre. Direct reading illuminations metre. Operation of relays. SOLAR CELLS: A cells or solar battery is basically a P–N junction diode which converts solar energy into electrical energy. It is also called a solar energy converter and is simply a photo diode operated zero bias voltage. CONSTRUCTION: A solar cell consists of a P–N junction diode generally made of Ge or Si. It may also be constructed with many other semi conducting materials like GaAs, indium arsenide and cadmium arsenide. The P–N diode so formed is packed in a can with glass windows on top so that light may fall upon P & N type materials. The thickness of P region of is kept very small so that electrons generated in this region can deffuse to the junction before the recombination takes place. Thickness of N region is also kept small to allow holes generated near the surface to diffuse to the junctions before they recombine. A heavy doping of P and N regions is recommended to obtain a large photo voltage. A nickel plated ring is provided around the P layer which acts as the positive output terminal. A metal contact at the bottom serves as the negative output terminal. WORKING: The working of solar cells may be understood with reference of figure When light is allowed to fall on a P-N junction diode, photons collide with valence electrons and impart them sufficient energy enabling them to leave there parent atoms. Thus Page 45
EEMI-QP-SOLUTION.docx