PV Training - Characterization-Fraunhofer.pdf
1PV-Training 2008 Characterization Methods / Quality Assurance PV- Training Fraunhofer Institute for Solar Energy Systems Notice: This presentation was downloaded from Internet. Translated from German to English by Zhuojian Yang. Retyped by Guizhi Zhang. Only for learning purposes. 2 Outline Loss mechanisms, characteristics, correlation Wafer / cell characterization Measuring principle of selected methods Use the methods in the production line Fault diagnosis Quantitative correlation of light-/dark-parameter Problem 1: Power too low Problem 2: Voltage too low Problem 3: Fill factor is too low PV-Training 2008 Wafer parameter Yield 3 Loss mechanisms, characteristics, relationship Parameters Wafer thickness Geometry Surface roughness Edge chips Microcracks Category Loss Mechanisms and Parameters PV-Training 2008 Wafer parameter Sf Sb Lb,τb DefectRRLZ Electrical losses 4 Lb,τb RRLZ Sb Loss mechanisms, characteristics, relationship Recombination parameter Category Parameters Sf Loss Mechanisms and Parameters PV-Training 2008 Resistance parameter Wafer parameter Rgrid ρc,fρ c,b ρbRsh Shuntsρm Electrical losses 5 Waferparameter Rekombinationsparameter Widerstandsparameter Rgrid ρb ρc,f ρc,b Rsh Shunt Parameters Category Recombination parameter Loss mechanisms, characteristics, relationship Sf Sb Lb,τb DefectRRLZ Loss Mechanisms and Parameters PV-Training 2008 Rf Rb Agrid Bgrid,Hgrid nAR,dAR Optical losses Loss mechanisms, characteristics, relationship Category Optical parameter Resistance parameter Wafer parameters Recombination parameter Rgrid ρc,fρ c,b Rsh Shuntsρm Sf Sb Lb,τb DefectRRLZ ρb Parameters Rf Rb Agrid nAR dAR Tex Hgrid Bgrid Loss Mechanisms and Parameters PV-Training 2008 Loss Mechanisms and Parameters I0e I0b I01I02RS Rp FF VOC ISC EQE IQE RS I0e Rp I02 I0b Rs Solar cell parameter Loss mechanisms, characteristics, relationship Category Optical parameter Resistance parameter Wafer parameter Recombination parameter Parameters Rgrid ρc,fρ c,b Rsh Shuntsρm Sf Sb Lb,τb DefectRRLZ ρb R f Rb Agrid nAR dAR Tex Hgrid Bgrid η PV-Training 2008 Wafer parameter 8 Category Measurement Methods 1: Wafer Parameters Parameters / Measuring Method Geometry 2D outline vision Edge-chips 2D outline vision Surface roughness metrology Mechanical stability break test Microcrack inspection Wafer thickness weighing TTV capacitive measurement Wafer-/cell characterization - Wafer parameters Recombination parameter Resistance parameter Optical parameter Solar cell parameter PV-Training 2008 9 Quasi-Steady-State Photoconduct. (QSSPC) Photoconductance Decay (MW-PCD) Carrier Density Imaging (CDI) Light-Beam Induced Current (SR-LBIC) x,y OFF x,y OFF OFF IN x,y OFF IN Measurement Methods 2 - Recombination Parameter Sf Sb Lb,τb RRLZ Measurement Methods Wafer-/cell characterization – Recombination parameters Wafer parameter Category Recombination parameter Resistance parameter Optical parameter Solar cell parameter Parameters PV-Training 2008 = + 10 10 Ndop=10 cm 10 10 10 10 10 10 10 10 1 τ rad+ Bulk Recombination τ SRH impurities τ Auger Auger τ rad radiant 1 1 1 τ bulk τ SRH τ Auger 13 14 15 16 17 18 1 3 2 Auger rad SRH bulk p-type Silicon 16 -3 EC-Et=0.5 eV k=10 τn0=10 µs -3 Bulk lifetime τbulk is a measuring of material quality Wafer-/cell characterization – Recombination parameters Carrier Lifetime - Background PV-Training 2008 10 Ndop= 10 cm 10 10 10 10 10 10 10 10 10 10 10 11 Carrier Lifetime - Background diff += 1+ surf 1 bulk 1 eff W2 2Dn diff= W 2S=surf Measured Effective Lifetime -1 0 4 -1 0 1 3 2 4 10000 100000 1000 10 100 S=0 cm/s16 -3 W = 200 µm S = varied 1 2 3 Bulk Lifetime [µs] SiN SiO2 poliert Wafer-/cell characterization – Recombination parameters τbulk Bulk lifetime Surface lifetime τdiff Diffusion to the surface. τsurf Recombination on the surface polished PV-Training 2008 Note: We always want to know τbulk of the wafer. But it’s difficult to directly measure it because of surface recombination. Measured Effective Lifetime [µs] 10 Ndop= 10 cm 10 10 10 10 10 10 10 10 10 10 10 12 SiO2 -1 0 4 -1 0 1 3 2 4 50 µm 500 200 100 S=0 cm/s16 -3 W = varied S = 100 cm/s 1 2 3 Bulk Lifetime [µs] Wafer-/cell characterization – Recombination parameters Measured Effective Lifetime τbulk Bulk lifetime Surface lifetime τdiff Diffusion to the surface. τsurf Recombination on the surface Carrier Lifetime - Background PV-Training 2008 diff += 1+ surf 1 bulk 1 eff W2 2Dn diff= W 2S=surf Measured Effective Lifetime [µs] 10 10 Ndop= 10 cm 10 10 10 10 10 10 10 10 10 10 13 SiO2 -1 0 4 -1 0 2 1 4 3 200 100 50 µm S=0 cm/s 500 16 -3 W = varied S = 100 cm/s 1 2 3 Bulk Lifetime [µs] Wafer-/cell characterization – Recombination parameters Measured Effective Lifetime Direct correspondence with If τbulk is small If τbulk is large Passivation should be good wafer thickness should be large Carrier Lifetime - Background PV-Training 2008 diff += 1+ surf 1 bulk 1 eff W2 2Dn diff= W 2S=surf Quasi-Steady-State Photoconductance(QSSPC) Si Test Wafer Reference Cell RF Bridge PC Data Analysis Storage Oscilloscope 14 Flash Lamp Coil Excitation Flash lamp (0-500 Suns) Detection / measurements Flash intensity Isuns(t) Reference solar cell Sample conductivity σ(t) Inductive / oscillator circuit Measurement Setup Wafer-/cell characterization – Recombination parameters Measuring Principle PV-Training 2008 15 (t) q(n +p)n(t) = Quasi-Steady-State Photoconductance (QSSPC) Measuring Methods 0.000 0.002 0.004 0.000 0.004 0.008 Time [s] Illumination Photoconductance Transient Mode PCD technique Time [s] Illumination Photoconductance Quasi-Steady-State QSSPC technique Wafer-/cell characterization – Recombination parameters Excitation Flash lamp (0-500 Suns) Detection / measurements Flash intensity Isuns(t) Reference solar cell Sample conductivity σ(t) Inductive / oscillator circuit Outputs Measuring Principle PV-Training 2008 16 (t) q(n +p)n(t) = Quasi-Steady-State Photoconductance (QSSPC) Measuring Modes / Basic Equation 0.000 0.002 0.004 0.000 0.004 0.008 Time [s] Illumination Photoconductance Transient Mode PCD technique Time [s] Illumination Photoconductance Quasi-Steady-State QSSPC technique n(t) eff = U(t) = n(t) t n(t) eff G(t) =U(t) = Wafer-/cell characterization – Recombination parameters Excitation Flash lamp (0-500 Suns) Detection / measurements Flash intensity Isuns(t) Reference solar cell Sample conductivity σ(t) Inductive / oscillator circuit Outputs Measuring Principle PV-Training 2008 17 Typical Measurement Curve 1013 10 14 10 15 1016 1017 2x10 -5 4x10 -5 8x10 6x10 -5 -5 10-4 p-Type Cz-Silicon ρ = 0.85 Ω cm Auger-Recombination SRH-Recombination Trapping Max. Flash Intensity 500 suns 50 suns 5 suns Under average injection → Material Quality Under low injection → Measurement artifact Under high injection → Intrinsic property Required Sample Structure Bare wafer Passivated Wafer Diffused wafers Metallized wafer Wafer-/cell characterization – Recombination parameters Injection level △ n [cm-3] Ef fect ive life tim e τ eff [s] Quasi-Steady-State Photoconductance (QSSPC) PV-Training 2008 NA=2.9× 10 cm = C × FeB Fei ncrossover= 2× 10 cm 18 1 1 [Fe]total Metastable Defect States FeB Fei + Bs QSSPC Application – Fingerprint of Iron 10 12 1013 1014 1015 1016 10 17 101 102 103 After dark storage (FeB) After Illumination (Fei) 13 -3 14 -3 p-type Silicon Fe-contaminated -3 Decomposition of FeB pairs Lighting / Injection Annealing at T 150 ° C Formation of FeB pairs Dark storage at T TW Bail, Brendel, 16th EU-PVSEC, 2000 Wafer-/cell characterization – Recombination parameters PV-Training 2008 26 IR Camera Lock-in System Optics Fiber of Generation laser Carrier Density Imaging (CDI) Hotplate Wafer Tb Tw Tb Tw Tb Tw Tb Tw Tb Tw Wafer-/cell characterization – Recombination parameters PV-Training 2008
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