S.H.ZhengX.W.ChengH.ShenDate:2013.5.21,Solar Cells And Materials,contents,1.Background 2.Introduce 3.History of solar cells 4.materials of solar cell 5.fundamental principle 6.Production Process 7.classification 8.Applications of solar cell 9.performance comparison of solar cell 10.Future prospects of solar cell,1. Background,Why should we focus on solar cells and materials ?,Since the two industrial revolutions, fossil fuels such as coal, oil, natural gas have been used wildly in succession. While these are non-renewable energy and burning to produce large amounts of carbon dioxide causing greenhouse effect.,背 景,1. It is the most abundant energy of human can make use of. 2. Where there is light,there is solar energy. 3. It is a kind of very clean energy without damage to the environment.,what about solar energy ?,The solar cell is a important way of solar energy utilization,2.Introduction,A solar cell is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect. Photovoltaics is the field of technology and research related to the application of solar cells in producing electricity for practical use.Solar cell technologies are an attractive option for clean and renewable energy generation in the form of electricity .Several technologies have been developed since 1950s and many of them are now reached to a stage of commercialization .But photovoltaic solar electricity is still not economical in comparison to the grid power we use today.,太阳能电池基本原理,Materials research studies, aimed at finding new inexpensive solar cell materials and combinations of semiconductors and semiconductor-metal junctions. Methodical research of commonly known solar cells such as Si,GaAs,Cu2S/CdS,etc.in order to improve efficiencies and find new cheap processes, both in the hope to bring down the cost of solar energy to a competitive evel with classical energy sources.,Two categories of solar cell research :,3.History of solar cell,In 1839 French physicist A. E. Becquerel discovered that light creates a bit of voltage when it strikes an electrode called the photovoltaic effect.In 1883 the first solar cell was built, by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions.The device was only around 1% efficient.In 1941 the silicon solar cell was invented by Russell Ohl. Though the efficiency of Ohls cell was only a fraction better than the selenium cells, using the less expensive silicon as a basis for solar cells was a step towards greater efficiency.,History,In 1954 Americans Pearson, Fuller and Chapin built an array of thin silicon strips, placed them in the sun and turned out energy at a six-percent efficiency rate. Their company, Bell Labs, built and deployed the first practical solar battery just one year later, eventually achieving 11-percent efficiency. In the late 1950s, Cherry and Mandelorn, working through the U.S. Signal Corps labs, helped develop workable solar cells for orbital applications. In 1973 the application of solar cell transfered to the general purpose of the peoples livelihood.,History of solar cells,Materials for solar cells include: Silicon GaAs/AlGaAs CuInSe2 (CIS) CuGaInSe2 (CGIS) CdTe etc.Advantages of Silicon Higher transfer efficiency Stability Wide spectra range Endure higher temperature,4.Materials for solar cell,敏化纳米晶太阳能电池,5.1Basic structure of a solar cell,Aproperly doped semiconductor base b (either n- or p-type) is the starting material. At the interface between b and t a space charge region will build up which leads to a rectifier characteristic,The top or front layer t can be an oppositely doped identical semi-conductor(homo-junction cell), a chemically different semiconductor with a larger gap (hetero-junction cell), or a thin metal film, typically 50-100 A thick (Schottky barrier). In the latter it has turned out to be beneficial to introduce a thin insulating barrier between the semiconductor and the metal to improve the open circuit voltage and therefore the efficiency.,敏化纳米晶太阳能电池,N-type silicon has free electrons. P-type silicon has free holes. When N-type and P-type silicon come into contact,an electric field forms within the cell.,The sun illuminates on the semi-conductors p-n junction to form a new hole-electron pairs. In the role of the p-n junction electric field , the light-generated holes flow to the p-type region , the photo-generated electronflow to the n region , connected to the circuit to form current.,敏化纳米晶太阳能电池,5.2 Solar cell operation,Key aim is to generate power by: Generating a large short circuit current, IscGenerate a large open-circuit voltage, VocMinimise parasitic power loss mechanisms (particularly series and shunt resistance).,敏化纳米晶太阳能电池,5.2.1 Short circuit current,Generation of light-generated carries Minimize reflection Absorb light in semiconductor and generate carriers Reflection and absorption depend on characteristics of sunlight, solar cell optical properties and solar cell thickness.The optical properties are key in achieving high current. To generate as many carriers possible we need to: Reduce reflection from silicon Reduce reflection from metal top surface Increase absorption of light in semiconductorCollection of light generated minority carriers Depends on material and device parameters,