ISE Solar Cells for Portable Electronic Devices Dr. Christopher Hebling (email: hebling@ise.fhg.de) Ulf Groos (email: groos@ise.fhg.de) Micro-Energy Technology Fraunhofer Institute for Solar Energy Systems ISE Oltmannsstr.5 79100 Freiburg, Germany Internet: www.mikroenergietechnik.de
Micro-Energy Technology at Fraunhofer-ISE ISE High-Efficiency Solar Cell Modules Small Fuel Cells Thermophotovoltaics
Characteristics of ISE Solar Cells and Fuel Cells ISE Solar Cells Fuel Cells Modular design (mw to MW) Modular design (mw to MW) High conversion efficiency (20%) Independant of fuels Integratable into the surface of the housing High conversion efficiency (50%) Storage capacity of fuels independent of output power Variable geometry - adaptable to the cavities in the devices No self-discharge Environmentally sound High aging proof $ 20 per installed W p in production (estimated) Environmentally sound High aging proof Potential for low production costs
Principle of ISE solar cells Generation and separation of charge carriers in a semiconductor Power density: V oc = 700 mv, J sc = 40 ma/cm 2 (mono-si) 25 mw/cm 2 (1 sun illum.) Conversion efficiency: 24.5 % (world record on mono-si) Module efficiency in production: 12-16 % Anti Reflection Coating Emitter Light - - + - Hole + - - n + p Electron Metal - - Base - + + - + - Metal
ISE high-efficiency vs standard solar cell technology Conversion Efficiency Standard technologies on Multi-Si: Multicrystalline silicon Mono-Si: Monocrystalline silicon a-si : Amorphous silicon material Illumination mw/cm² Sunny, outdoor 100 Indoor, near window 10 Office illumination 3 Conversion Efficiency [%] 25 20 15 10 5 0 ISE Multi-Si Mono-Si a-si 1 10 100 Illumination [mw/cm²]
ISE high-efficiency vs standard solar cell technology Open Circuit Voltage Standard technologies on Multi-Si: Multicrystalline silicon Mono-Si: Monocrystalline silicon a-si : Amorphous silicon material Open Circuit Voltage Voc [mv] 900 800 700 600 500 400 ISE Multi-Si Mono-Si a-si Illumination mw/cm² Sunny, outdoor 100 Indoor, near window 10 Office illumination 3 300 1 10 100 Illumination [mw/cm²]
Research Topics: Inverted pyramids as anti-reflection measure Moth-eye structure on a solar module Solar Cells: - Reduction of optical and electrical losses - Innovative technologies (random pyramids, laser ablation) - Cost-effective production (automatization) Modules: - Series connection of the cells - Encapsulation / Surface Structuring - Production technology Device Integration: High-efficiency DC/DCconverter - Electronic Energy Management - Charge controllers - High -efficiency DC/DC - converters
Processing of High-efficiency Solar Cells Usual process (LBSF - Pearl): 23.3% max. conversion efficiency Texture Boron LBSF Local Emitter Emitter Oxide Rear Side Front Side Electroplating Diffusion Diffusion Diffusion Passivation Metallization Metallization pm pm pm pm pm pm (photo masking) ISE Process (RP-PERC): 21.9% max. conversion efficiency (2-3 times less costly) (pm) pm pm
ISE Module Structure - Shingle technique for minimal shadowing losses - Curved surfaces possible - Minimal thickness 1.5 mm - 20 % conversion efficiency PMMA / PC Silicone High Efficiency Solar Cell Insulation Foil
Prototype of a Solar Powered Personal Digital Assistant Autonomous of external electricity supply* * Illumination conditions apply
Performance of ISE PV-modules under different illumination Power [mw] 400 350 300 250 200 150 100 1000 W/m² 100 W/m² 30 W/m² Illumination W/m 2 Sunny, outdoor 1000 50 0 0 20 40 60 80 100 Indoor, near window 100 Office illumination 30 Area of the PV-module [cm²]
Prototype of a Solar Powered Cell Phone Unlimited stand-by time* * Illumination conditions apply Cooperation with SIEMENS company
Stand-by Behaviour of a Typical Cell Phone for 800 Different Illumination 768 700 600 Time / h 500 400 300 200 Cell Parameter @ 1000 W/m²: J mpp = 36,75 ma/cm², V oc = 670 mv Module Parameter: A: 15 cm² 100 0 144 Without Solar Cell Module With ISE Solar Cell Module
Summary Solar cells are powerful energy converter as a supplement or a substitute to batteries due to: - highly developed technological standard - modularity of power - integratable into housings - mass production possible - easily applicable for customers