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1、Solar Cell and PhotodiodesSolar CellAdvantageslConsumes no fuellNo pollutionlWide power-handling capabilitieslHigh power-to-weight ratiolExhaustlessSolar Energy SpectrumlPower reaching earth 1.37 KW/m2UV 5% Visible 46% Near Infrared 49%Air MasslAmount of air mass through which light passlAtmosphere
2、can cut solar energy reaching earth by 50% and moreSolar cell Working PrinciplelOperating diode in fourth quadrant generates powere =(IV)m/ Pin = FF * Isc * Voc / Pin FF = ImVm/IscVoc 光电转换量子效率Schottky Barrier CelllPrinciple similar to p-n junction celllCheap and easy alternative to traditional cell
3、Limitations:lConducting grid on top of metal layerlSurface damage due to high temperature in grid-attachment techniqueGrooved Junction CelllHigher p-n junction arealHigh efficiency ( 20%)Thin Film Solar CellslProduced from cheaper polycrystalline materials and glasslHigh optical absorption coefficie
4、ntslBandgap suited to solar spectrumCdTe/CdS Solar CelllCdTe : Bandgap 1.5 eV; Absorption coefficient 10 times that of SilCdS : Bandgap 2.5 eV; Acts as window layer Limitation :Poor contact quality with p-CdTe ( 0.1 Wcm2)Inverted Thin Film Celllp-diamond (Bandgap 5.5 eV) as a window layerln-CdTe lay
5、er as an absorption layerEfficiency Losses in Solar Cell1 = Thermalization loss 2 and 3 = Junction and contact voltage loss 4 = Recombination loss Tandem CellslCurrent output matched for individual cellslIdeal efficiency for infinite stack is 86.8%lGaInP/GaAs/Ge tandem cells (efficiency 40%)Multiple
6、 E-H pairslMany E-H pairs created by incident photon through impact ionization of hot carrierslTheoretical efficiency is 85.9%Multiband CellslIntermediate band formed by impurity levels.lProcess 3 also assisted by phononslLimiting efficiency is 86.8%Multiple Quantum WelllPrinciple of operation simil
7、ar to multiband cellsThermophotonic CellslHeated semiconductor emits narrow bandwidth radiationslDiode with higher temperature has lower voltageThermo photovoltaic CelllFilter passes radiations of energy equal to bandgap of solar cell materiallEmitter radiation matched with spectral sensitivity of c
8、elllHigh Illumination Intensity ( 10 kW/m2 )Thermophotovoltaic CellslEfficiency almost twice of ordinary photocellmax=85% Carrier Temperature in Cell Tc =2470KSurface Temperature of SolarTs = 5760KEnvironment Temperature Ta =300KDye-sensitized cellThe adsorbed dye molecule absorbs a photon forming a
9、n excited state. dye*The excited state of the dye can be thought of as an electron-hole pair (exciton).The excited dye transfers an electron to the semiconducting TiO2 (electron injection). This separates the electron-hole pair leaving the hole on the dye. dye*+The hole is filled by an electron from
10、 an iodide ion. 2dye*+ + 3I- 2dye + I3-Organic solar cellFig.1Examples of organic photovoltaic materialsPhotocurrent to Temperature of photodiodes made with MEH-PPV blended with C60 and TCBZ and pure MEH-PPV IPCE quantum efficiency of photodiode at 550nm illumination at different bias voltage Photo-
11、detector DiodeOptical information transport Photol DetectorDiodeElectrical InformationIn principle, all photovoltaic devicesare also photo-detector devices.Operating in the third quadrantThe most important Factors different from photovoltaic devices:1, the ratio of the current under photo illuminated to dark stateIphoto/I dark;2, the response velocity of the device.3, the response is partially located infrared zoneSCIENCE 卷: 325 期: 5948 页: 1665- 1667 出版年: SEP 25 2009
