solar-cell-太阳能电池介绍.ppt

Solar Cell (Photovoltaics), : 20075418 Ju Dae-Hyun,Nonrenewable Enargy, (Renewable Energy), (Nonrenewable Energy),Renewable,What is a 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). Power = Current x Voltage=Current2 x R= Voltage2/R It is like a battery because it supplies DC power. It is not like a battery because the voltage supplied by the cell changes with changes in the resistance of the load.,Basic Physics of Solar Cells,Silicon (Si) is from group 4 of the period table. When many Si atoms are in close proximity, the energy states form bands of forbidden energy states. One of these bands is called the band gap(Eg) and the absorption of light in Si is a strong function of Eg.,The Sun daily provides about 10 000 times more energy to the Earth than we consume Photovoltaic technology directly converts solar energy into electricity No moving parts no noise no emissions long lifetime Large industrial potential - cost reductions needed Feedstock for PV industry is silicon - the second most abundant element in the crust of the Earth,The Sun as Energy Source,Solar Energy status,Market is exploding The solar industry is very profitable Lack of highly purified silicon (polysilicon) Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency,Actual Growth vs. Historic Forecasts,Solar Energy status,Market is exploding The solar industry is very profitable Lack of highly purified silicon (polysilicon) Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency,- Gross revenue development,Solar Energy status,Market is exploding The solar industry is very profitable Lack of highly purified silicon (polysilicon) Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency,Solar Grade Silicon Supply-Demand (MT/year),Solar Energy status,Market is exploding The solar industry is very profitable Lack of highly purified silicon (polysilicon) Cost of solar electricity is too high, R&D focus on reducing cost and increasing efficiency,Cost reductions existing technologies,Thinner wafers - Wire sawing - Laser cutting and etching Higher efficiencies - Semiconductor technologies on single crystal wafers (examples Sanyo / SunPower) Thin film technologies (flat panel display),Public incentives are important,Cost goals for third generation solar cells,Efficiency and cost projections for first-, second- and third generation photovoltaic technology (wafers, thin-films, and advanced thin-films, respectively) Source: University of New South Wales,Next generation technology,Silicon nanostructures Bandgap engineering of silicon. Applications could be tandem solar cells and energy selective contacts for hot carrier solar cells. Fabrication of silicon nanostructures consisting of quantum well and quantum dot super lattices to achieve band gap control,Up/Down converters Luminescent materials that: EITHER absorb one high energy photon and emit more than one low energy photon just above the bad gap of the solar cell (down-conversion) OR that absorb more than one low energy photon below the band gap of the cell and emit one photon just above the band gap (up-conversion).,Next generation technology (cont.),Understanding cell efficiency,Hot carrier Cells This concept tackles the major PV loss mechanism of thermalisation of carriers. The purpose is to slow down the rate of photoexcited carrier cooling caused by phonon interaction in the lattice to allow time for the carriers to be collected whilst they are still hot, and hence increasing the voltage of a cell.,Next generation technology (cont.),Thermoelectric solar cells Application of the concept of energy selective electron transport used in hot carrier solar cells, to develop thermo electrics and thermo-ionics devices.,Next generation technology (cont.),The PV Value Chain (multi-crystalline),Prices are actually increasing,How does solar energy work? Solar Electric or Photovoltaic Systems convert some of the energy in sunlight directly into electricity. Photovoltaic (PV) cells are made primarily of silicon, the second most abundant element in the earths crust, and the same semiconductor material used for computers. When the silicon is combined with one or more other materials, it exhibits unique electrical properties in the presence of sunlight. Electrons are excited by the light and move through the silicon. This is known as the photovoltaic effect and results in direct current (DC) electricity. PV modules have no moving parts, are virtually maintenance-free, and have a working life of 20 - 30 years.,Silicon Solar cell,Photovoltaics,Most current solar cells are photovoltaic Typically made from silicon or amorphous silicon. Typical efficiency 12%. Best efficiency ever in laboratory: 30%. Theoretical maximum, including concentrating light: 43% Generic design: doped pn junction. Photons come in and photoionize donors. Built-in electric field at junction causes carriers to flow, building up a potential (voltage) btw the p and n sides. Clearly one can play with different band gap systems to arrive at materials with different absorption spectra. Also, good mobility of charge essential for this to work well - trapping of charge or poor mobility will kill efficiency.,Principle p-n Junction Diode.,Silicon Solar cell,Ref. Soft Condensed Matter physics group in univ. of Queenland, : Si ingot 330m 2cm x 2cm Surface cleaning,Texturing : chemical v-groove,p-n junction : POCl3 (900C),ITO increasing minorty carrier correction, ARC,Poly-Si Solar cell Making process,Back Surface Field Deposition Al and Ag ohmic-contact,Forward surface Electrode,Anti-reflection coating (ARC) TiO2 deposition,H2 diffusion dangling bond H2 bonding Decreasing recombination,Measure,- An individual PV cell typically produces between 1 and 2 watts,Solar Cell, Module, Array,decrease the area of solar cell material being used in a system,Concentrator collectors,Flat-plate collectors typically use large numbers or areas of cells that are mounted on a rigid, flat surface. substrate ; metal, glass, plastic,They are simpler to design and fabricate. They do not require special optics, specially designed cells, or mounting structures that must track the sun precisely. plus, flat-plate collectors can use all the sunlight,Flat-Plate Systems,Uses for Solar Energy,Solar Home Systems,Space,Water Pumping,Telecom,Main Application Areas Off