太阳能电池中光学性能检测方案(紫外分光光度)

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Author Dr. Andrew R. Hind & Dr.Marcus Schulz Agilent Technologies， Inc. Measuring the optical properties ofphotovoltaic cells using the AgilentCary 5000 UV-Vis-NIR spectrophotometer and the ExternalDRA-2500 Application Note Introduction The term 'photovoltaic’stems from the Greek word for light (photo) and thephysicist Volta# (the inventor of the electric battery). It is applied to thedirect conversion of sunlight into energy by means of solar cells. Theconversion process is based on the photoelectric effect (discovered byBequerel* in 1839)， which involves the release of positive and negativecharge carriers in a solid when light strikes its surface. Solar cells are composed of various semi-conducting materials， with themajority (>95%) of solar cells manufactured made primarily of silicon. Toproduce a solar cell， the semiconductor is doped’. Doping involves theintentional introduction of other elements， with the aim of obtaining asurplus of either positive (p) or negative (n) charge carriers within thesemiconductor material. When two differently contaminated semiconductorlayers are combined， a so-called ’p-n’junction results at the boundary of thelayers. This junction results in an electric field which leads to the separationof the charge carriers that are released by light. By using metal contacts， anelectric charge can be drawn and， if the outer circuit is closed， direct currentflows. Silicon solar cells are generally 10×10 cm in size， with a transparentanti-reflection (AR) coating used to protect the cell and decrease reflectivelosses on the cell surface. Figure 1 shows a schematic diagram of a typicalphotovoltaic cell. Rear metal contact Figure 1. Schematic diagram of a typical solar cell In any photovoltaic cell， the current intensity obtainedincreases with higher light flux. And， whilst manyfactors can affect the efficiency of a particular cell，reflectance of light at the surface of the cell is aparameter of obvious importance. To perform thesetypes of reflectance measurements a high-performanceUV-Vis-NIR spectrophotometer equipped withintegrating sphere is required. An integrating sphere isdesigned to collect reflected radiation (diffuse or total)from a solid surface (such as a photovoltaic cell). Usingthe appropriate sampling geometry， integrating spherescan also be used for the measurement of the diffusetransmission properties of solar cells. This paper will demonstrate how the reflectanceproperties of a solar cell and its precursors can bemeasured at various stages of the manufacturingprocess using a Cary 5000 UV-Vis-NIRspectrophotometer equipped with an External DiffuseReflectance Accessory 2500 and Small Spot Kitattachment. Instrumentation1 Agilent Cary 5000 UV-Vis-NIR spectrophotometer Agilent External DRA-2500 Small Spot Kit attachment Conditions The External DRA-2500 was installed into thespectrophotometer and aligned2. UV-Vis-NIR spectrawere， in general， acquired in the region 250-2500 nmusing appropriate baseline correction (Zero/baselinecorrection). Indicative instrumental parameters were asfollows： 2 nm SBW， 0.1 s SAT， 1 nm data interval (UV-Vis) and Energy 3， 0.2 s SAT， 3 nm data interval (NIR)； 'double-beam’mode using full slit height. Thereflectance spectra were collected using a Cary 5000UV-Vis-NIR spectrophotometer equipped with anExternal DRA-2500 and a Small Spot Kit when smallbeam images were required. Discussion Figure 2 shows diffuse reflectance spectra of thefinished solar cell and its precursors. Obvious spectraldifferences are evident between the uncoated， texturedwafer (TS3)， the AR coated wafer (TS2)， and the‘finished'wafer (TS4) with metal contact grid (seeFigure 3). The spectra were acquired at two differentlocations on each sample to test for surfacehomogeneity. Figure 2. UV-Vis-NIR diffuse reflectance spectra of solar cells Figure 3. A finished solar cell with metal contact grid and anti-reflectioncoating Furthermore， additional differences are evident betweenthe 'average’reflectance spectrum of the finished cell(TS4；where the area sampled includes both cellsurface and metal contact grid)， and the spectrum ofthe cell surface only (TS4 Diff ssk； without reflectancecontribution from the reflective metal contacts). Thishighlights the advantage of being able to reduce beamsize to the point where it is small enough (~1 mmdiameter) to allow the collection of spectra from anarea between the metal contacts of the grid itself. Notsurprisingly， the results confirmed the relatively highreflectivity of the metal grid compared to the 'active’surface of the cell itself. Conclusion Both the reflectance and transmission properties ofsolar cells are readily measured using UV-Vis-NIRspectrophotometry. Using a high-performancespectrophotometer (such as the Cary 5000) equippedwith integrating sphere permits the fast acquisition ofhigh quality spectra (high resolution， low noise). For the measurement of small areas of solar cells， sometype of focusing optics are required to reduce the sizeof the beam image focused on the sample surface. TheExternal DRA-2500 with Small Spot Kit attachmentavailable from Agilent allows such measurements to bemade. References l. Part numbers： Product Part Number Agilent Cary 5000 UV-Vis-NIR spectrophotometer 0010079300 External DRA-2500 0010082000 Small Spot Kit 7910047200 2.Cary WinUV Software， online help， Version 3.0. #Allssandro Volta (1745-1827) * Alexandre-Edmond Bequerel (1820-1891) www.agilent.com/chem @ Agilent Technologies， Inc.， 2005， 2011Published March，2011Publication Number SI-A-1221 Agilent Technologies 紫外可见近红外分光光度计是表征太阳能电池各组件和电池的光学性能（反射率和透射率）必不可少的工具。本文介绍了应用高性能的光度计Cary 5000配备积分球附件快速测试电池表面的反射率，并且采用小光斑附件缩小照射到样品上的光斑尺寸，直接对电池表面电极之间的微小面积进行测试，得到了高分辨率、低噪声的高质量光谱图，比较了几种情况下电池表面反射率的变化。