Photon Energy (Electromagnetic energy) c 1 m /sec E = hν = h J sec = J sec = J λ sec m 34 h= 6.626X10 J s Planck s Constant hν - Smallest amount of energy for the light with the frequency (ν) - Quantum of energy for light. - Energy of a photon. Although light behaves like a wave, having both a wavelength and a frequency, a series of experiments by Planck and Einstein in the early 1900s showed that it also exhibits particle-like behavior. These light particles are called photons, and the energy of a given particle of light can be computed from the simple relationship http://www.cartage.org.lb/en/themes/sciences/chemistry/generalchemistry/atomic /Electronicstructure/Atomicstructure/Photonenergy/Photonenergy.htm Review: Semiconductor E C C E F E C E D E i E F E i E i E V Intrinsic n-type p-type E V E A E F E V n= p= ni E = E F n i is too small to be useful in devices Doping i EF Ei n= ni exp kt Ei EF p= ni exp kt P P e - B B - h (E F -E i ) Shallow donor n p (E F -E i ) deep donor n (E i -E F ) Shallow acceptor (E F -E i ) deep acceptor p
PN Junctions Jump from VB Majority carrier E C E i E C E F E i E F E V Majority carrier When the P and N regions are joined, diffusion currents flows due to the carrier gradients. E V dn Jn = qµ nnε qdn = 0 dx Drift Diffusion Jump from VB -Moving of carriers leave behind charged donor and acceptor atom (P or B - ) -Electric field builds up until it balances the diffusion process PN Junctions (Formation) 2 ni np = p E C E i E F E V p p = p N A Depletion region (Space charge region) Mobile carrier concentration is very small - - - - - - - - - - --B - - - - - P n n = N D 2 np = n i charged acceptor charged donor x= x p x= xn p n = 2 i n n n p n n i
PN Junctions (Physical Meaning) P - N - - - - - - Solar Cell (Photo Diode) using PN Junction hυ hυ P - I N - Conduction band Valence band Light of sufficient energy Electron transfer from VB to CB The electron readily rolls down to N region due to the high electric field in the depletion region The hole readily rolls up to P region Some electrons(or holes) recombine (do not contribute to the current) Some electrons(or holes) within the diffusion length contribute the current The contribution of photocurrent became small as increasing the length from depletion region To reduce the electron consumption by recombination, the defect in semiconductor should be minimized. (e.g. [defect] may diffuse up to 200 µm [defect] diffusion length reduces to 10µm) From Hummel, Electronic Properties of Materials
Solar Cell : Schematics Convert Light (Photon) Into Electricity (Voltage) Photovoltaic effect Materials for Energy and Environment http://acre.murdoch.edu.au/refiles/pv/text.html (2006) Solar Cell: Applications Thanks to Government initiatives, it is estimated that 7000 home in Japan have installed solar power systems. The system can be attached to a roof with metal fittings and supports, or already come built-in. D/C electricity is converted to usable A/C using a power conditioner. No electricity is wasted as excess electricity is sold to power generating companies and during rainy weather or at nighttime, can be bought back. Example. 3.34kW Example. 4.25kW www.ecoflag.com/feature/ feature0208_3e.html
Solar Cell: remote island Solar Cell: high mountain
Solar Cell: satellite Solar Cell: handheld charger http://www.violetta.com/
Solar Cell: handheld charger http://www.solarion.co.kr/ Solar Cell: wireless street lamp - 램프 : 18/26W, 저압나트륨램프. - 태양전지모듈 : 100Watt / 150Watt/225Watt. -AM 1.5(1000W/m²) 의태양광조건하에서, 3 시간충전시, 7~10 시간점등이가능합니다. - 두개의 12V 100Ah 충전지는최대 5 일까지흐린날에도작동을할수있도록도움을드립니다. - 충전, 방전조정및자동점 소등과과열방지가가능합니다. http://www.solarcell.co.kr/
Solar Cell: meteorological station http://my.dreamwiz.com/dj112/buoy.htm Solar Cell : The Needs The Need for Solar Cells -the need for low maintenance, long lasting sources of electricity suitable for places remote from both the main electricity grid and from people; eg satellites, remote site water pumping, outback telecommunications stations and lighthouses; -the need for cost effective power supplies for people remote from the main electricity grid; eg Aboriginal settlements, outback sheep and cattle stations, and some home sites in grid connected areas. -the need for non polluting and silent sources of electricity; eg tourist sites, caravans and campers -the need for a convenient and flexible source of small amounts of power; eg calculators, watches, light meters and cameras; -the need for renewable and sustainable power, as a means of reducing global warming. http://acre.murdoch.edu.au/refiles/pv/text.html
Solar Cell: Amorphous or Crystalline Amorphous Si -Deposition on glass from reactive gas such as SiH 4-13% in Market -Efficiency: 6-9% Polycrystalline Si - Casting process (molten silicon is poured into a mold.) - 86% in market - Efficiency: 11-16% Easy to fabricate in a large area There has been progress in fabrication. http://acre.murdoch.edu.au/refiles/pv/text.html http://www.cse.ucsc.edu/~tara/ugradsummerresearch01/dawn_hettelsater.pdf Solar Cell: the comparison with other energy sources Falling water..rivers, ocean tides Wave motion..in ocean Wind motion..of air Solar radiation..from the sun Fossil fuels..coal, oil, natural gas Fission nuclear energy..splitting atoms Fusion nuclear energy..combining atoms Characteristic features - Environmentally Friendly - Proper energy source in Isolated and Sunny place - Climate-dependent (Hybrid with battery) - Should increase the energy conversion efficiency
Dye-Sensitized Solar Cell: The flexible solar cell - Overall conversion efficiency : up to 11% - Convenient and easy manufacturing - Flexibility - Low cost fabrication - Polymer foil is used as substrate instead of glass Enables roll to roll production Enables flexible solar cell Can be used in power generation in wearable computer and flexible display http://www.ecn.nl/docs/library/report/2000/rx00020.pdf Dye-Sensitized Solar Cell: Working Principle http://www.ecn.nl/docs/library/report/1998/rx98040.pdf Photon Excitation of dye Fast electron injection into C.B. of TiO 2, SnO 2 Injected electrons percolate through the TiO 2 and are fed into external circuit At counter electrode I 3-2e - 3I - Iodide(3I - ) reduces the oxidized dye on the surface of TiO 2 by electron injection
Dye-Sensitized Solar Cell: Easy Fabrication Process roll-to-roll, high volume manufacturing process produces thin, flexible cells "In 2005 we will go to market with our first product based on dye-sensitized cell chemistry which currently is on par with today's commercially available thin-film." - Daniel Patrick McGahn, Executive Vice President and Chief Marketing Officer at Konarka Konarka Contracted for Hybrid Solar PV Cells Lowell, Massachusetts - February 18, 2004 [SolarAccess.com] Konarka Technologies has been selected by The Defense Advanced Research Projects Agency (DARPA) to receive a contract in excess of US$6 million for basic research in developing new materials for hybrid photovoltaic (PV) cells. http://www.konarkatech.com/ Dye-Sensitized Solar Cell: Application to OLED OLED Display / Organic Solar Cells The anticipated advantages of organic and nano solar cells have prompted accelerated research to leverage the link between organic solar cells and organic LED (light emitting diode). Organic solar cells absorb light and convert it to electricity, while organic LEDs (OLED) use the same materials to perform the reverse process they conduct electricity to emit light. There is great scientific and commercial interest in OLEDs because they make color displays cheaper, sharper, thinner, and mechanically more flexible in consumer devices such as cell phones, personal digital assistants, and car dashboards. OLED technology also uses significantly less energy than current electronic displays, enabling longer battery life and increased usefulness of the products. http://www.powerlight.com/newsletters/2004/winter/newsletter_industry.htm
Dye-Sensitized Solar Cell: Combination with fuel cell Capturing sunlight to make enough hydrogen fuel to power cars and buildings has been brought a step closer by a British research company. 1 Ultraviolet sunlight passes through glass skin of cell 2 Light is captured in glass coated with nano-crystalline film 3 Nano-coating properties enable the glass to conduct electricity, which is used to separate the water into oxygen and hydrogen 4 Hydrogen gas is stored for later use as a power source http://news.bbc.co.uk/1/hi/sci/tech/3536156.stm Why H 2 should be prepared by solar energy? If you use a battery, then chances are that the battery was charged with electricity produced by burning fossil fuels, so that the hydrogen you produce isn't produced cleanly. If you use a solar cell, however, then the hydrogen will be produced cleanly, except for any pollutants that were emitted when the cell was made (we say that the solar cell has no "point-of-use" emissions). Burning fossil fuels on the other hand, always results in carbon monoxide (CO) and/or carbon dioxide (CO 2 ), which is produced when the carbon atoms combine with oxygen. These compounds are now considered pollutants because they are greenhouse gases - that is, they help trap heat near the Earth's surface, causing the Earth's surface temperature to rise, i.e. global warming. http://www.nmsea.org/curriculum/7_12/electrolysis/electrolysis.htm
http://www.hygen.com/images/flowcht.jpg Two obstacles to a hydrogen-economy There are two obstacles to a hydrogen-economy. It takes a lot of volume (or energy) to store hydrogen - usually five times or so the volume, at reasonable pressures, needed to store an equivalent amount of energy with gasoline. (It triggered the researches on hydrogen storage materials.) There is no hydrogen infrastructure: Making the transition to a hydrogen economy might mean having to scrap the fossil fuel infrastructure that we have already developed. (The in-situ reforming becomes big issue.) http://www.nmsea.org/curriculum/7_12/electrolysis/electrolysis.htm
미래의핵심대체에너지인수소ㆍ연료전지및태양광, 풍력등 3대사업분야사업단이 19일공식출범식을갖고본격적인연구를시작했다. 이날한국과학기술연구원 (KIST) 에서개최된사업단출범식에서각사업단장에는수소ㆍ연료전지분야에홍성안한국과학기술연구원박사, 태양광분야에김동환고려대교수, 풍력은이수갑서울대교수가각각임명됐다. 산업자원부는이날 3대사업단의운영계획을함께발표하고올해 371억원을포함, 향후 5년간약 2,500억원을투자하기로했다. 이는단일사업으로는최대규모의정부연구개발 (R&D) 사업이다. 산자부관계자는 11개신ㆍ재생에너지원중기술중요성이크면서연평균 20~30% 급성장하고있는수소ㆍ연료전지, 태양광, 풍력 3대분야를집중육성키로하고사업단을구성했다 고설명했다. 산자부에다르면정부는 2012년까지 수소ㆍ연료전지분야에서연료전지자동차 3,200여대, 수소충전소설치, 전력용연료전지 300기, 가정용연료전지 1만기를 태양광분야에서주택용 10만기, 건물용 700기, 산업용 1,400기를 풍력분야는해상풍력 680MW, 육상풍력 1,570MW 등총2,250MW를보급하는것을목표로하고있다. 사업단측은현재사업자선정을위한공모절차를진행중이며과제에는기술개발뿐아니라표준화, 성능평가등기반조성사업도포함돼있다고밝혔다. 한편이날행사에서는관련분야육성에기여한공로로 수소ㆍ연료전지분야 = 임태원현대자동차연료전지개발팀장, 임희천한국전력책임연구원 태양광분야 = 안병태한국과학기술원교수, 이박일 포톤반도체에너지대표이사 풍력분야 = 전중환포항공대교수, 공창덕조선대교수가각각산자부장관표창을받았다. ( 서울경제 2004년 5월 19일 )