Chương SOLAR CELL THUẬN LỢI VÀ KHÓ KHĂN  Thuận lợi + Nguồn lượng sạch, không ô nhiễm + Dồi dào Theo một tính toán, lượng mặt trời chiếu trái đát vòng 30 ngày bằng tổng lượng nhiên liệu hóa thạch hành tinh kể cả đã sử dụng và chưa sử dụng!  Khó khăn + Ánh sáng mặt trời chiếu sáng khác theo thời gian và không gian + Năng lượng mặt trời phân tán, không tập trung + Để giải quyết vấn đề này: 1) collection, 2) conversion, 3) storage Solar Source • The average solar power incident on Continental US is 1600 x 1012 W This is 500x the power consumption in US (3.3 x 1012 W) • If we cover 2% of the continental US with 10% efficient PV systems, we would make all the energy we need • FYI: • 1.5% of Continental US is covered by roads Solar Energy to Heat Living Spaces  Proper design of a building is for it to act as a solar collector and storage unit This is achieved through three elements: insulation, collection, and storage Photovoltaics (PV) Photo + voltaic = convert light to electricity Solar cell = convert sun to electricity Solar Cells Background  1839 - French physicist A E Becquerel first recognized the photovoltaic effect  1883 - first solar cell built, by Charles Fritts, coated semiconductor selenium with an extremely thin layer of gold to form the junctions  1954 - Bell Laboratories, experimenting with semiconductors, accidentally found that silicon doped with certain impurities was very sensitive to light Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the first practical device for converting sunlight into useful electrical power Resulted in the production of the first practical solar cells with a sunlight energy conversion efficiency of around 6%  1958 - First spacecraft to use solar panels was US satellite Vanguard http://en.wikipedia.org/wiki/Solar_cell Driven by Space Applications in Early Days Worldwide PV Growth Source: European Commission meeting Dec 2004 The first generation photovoltaic, consists of a large-area, single layer p-n junction diode, which is capable of generating usable electrical energy from light sources with the wavelengths of sunlight These cells are typically made using a silicon wafer Inorganic pn Junction Solar Cell (First Generation) Silicon Shared electrons Si Si Si Si Si Si Si Si - Si  Silicon is group IV element – with electrons in their valence shell  When silicon atoms are brought together, each atom forms covalent bond with silicon atoms in a tetrahedron geometry Extrinsic Semiconductor, n-type Doping Conducting band, Ec Si Si Si As Si Si Si Extra Electron Ed ~ 0.05 eV Eg = 1.1 eV Si - Si Valence band, Ev  Doping silicon lattice with group V elements can creates extra electrons in the conduction band — negative charge carriers (n-type), As- donor  Doping concentration #/cm3 (1016/cm3 ~ 1/million) Extrinsic Semiconductor, p-type doping Conducting band, Ec Si Si Si Hole Si Eg = 1.1 eV B Si Ea ~ 0.05 eV Si Si - Si Electron Valence band, Ev  Doping silicon with group III elements can creates empty holes in the conduction band — positive charge carriers (p-type), B(acceptor) THE PHOTOVOLTAIC CHARACTERISTICS OF THE SOLAR CELLS How the device works? The p-n junction under illumination (on the right) A photon induced hole-electron pair is separated by the local field of the junction Taken from: F C TREBLE (Editor); Generating Electricity from the Sun; Pergamon Press, Inc.;New York; 1991 The second generation of photovoltaic materials is based on the use of thin-film deposits of semiconductors These devices were initially designed to be high-efficiency, multiple junction photovoltaic cells Inorganic Thin Film Solar Cells (Second Generation) Third generation photovoltaics are very different from the previous semiconductor devices as they not rely on a traditional p-n junction to separate photogenerated charge carriers These new devices include photoelectrochemical cells, polymer solar cells, and nanocrystal solar cells Dye-sensitized solar cells are now in production Examples include Amorphous silicon, Polycrystalline silicon, micro-crystalline silicon, Cadmium telluride, copper indium selenide/sulfide Dye-sensitized solar cells: Operation Dye electrons are excited by solar energy absorption They are injected into the conduction band of TiO2 Get to counter-electrode (cathode) through the external circuit I3-  2e  3I- : Redox regeneration at the counter-electrode (oxidation)  3I  I3  2e : Dye regeneration reaction (reduction) Potential used for external work: Vext  EF  Vredox Red=IOx =I3- Ionic Liquid [bmim]+ I - Fourth generation Composite photovoltaic technology with the use of polymers with nano particles can be mixed together to make a single multispectrum layer Then the thin multi spectrum layers can be stacked to make multispectrum solar cells more efficient and cheaper based on polymer solar cell and multi junction technology used by NASA on Mars missions [...]... junction photovoltaic cells Inorganic Thin Film Solar Cells (Second Generation) Third generation photovoltaics are very different from the previous semiconductor devices as they do not rely on a traditional p-n junction to separate photogenerated charge carriers These new devices include photoelectrochemical cells, polymer solar cells, and nanocrystal solar cells Dye-sensitized solar cells are now in... light sources with the wavelengths of sunlight These cells are typically made using a silicon wafer Inorganic pn Junction Solar Cell (First Generation) Silicon Shared electrons Si Si Si Si Si Si Si Si - Si  Silicon is group IV element – with 4 electrons in their valence shell  When silicon atoms are brought together, each atom forms covalent bond with 4 silicon atoms in a tetrahedron geometry Extrinsic... silicon, micro-crystalline silicon, Cadmium telluride, copper indium selenide/sulfide Dye-sensitized solar cells: Operation 1 Dye electrons are excited by solar energy absorption 2 They are injected into the conduction band of TiO2 3 Get to counter-electrode (cathode) through the external circuit 4 I3-  2e  3I- : Redox regeneration at the counter-electrode (oxidation)  5 3I  I3  2e : Dye regeneration... the use of polymers with nano particles can be mixed together to make a single multispectrum layer Then the thin multi spectrum layers can be stacked to make multispectrum solar cells more efficient and cheaper based on polymer solar cell and multi junction technology used by NASA on Mars missions ... Electron Valence band, Ev  Doping silicon with group III elements can creates empty holes in the conduction band — positive charge carriers (p-type), B(acceptor) THE PHOTOVOLTAIC CHARACTERISTICS OF THE SOLAR CELLS How the device works? The p-n junction under illumination (on the right) A photon induced hole-electron pair is separated by the local field of the junction Taken from: F C TREBLE (Editor); Generating