Dropping of Minority Carrier Lifetime with the Lower Resistivity of...

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江苏协鑫软控设备科技发展有限公司 Jiangsu GCL Software Control Equipment Technology Development Co.,Ltd. Dropping of Minority Carrier lifetime with the Lower Resistivity of Cz Silicon Materials Xiaochen Guo, Bayard Johnson, zhaobiao Meng Xi’an, 14th CSPV, November 8, 2018 1 New requirement on MCL Minority carrier lifetime The Relationship between Resistivity and Minority Carrier Lifetime Issues with the New Requirement of Lower Resistivity of silicon materials Content 2 Issues with the New Requirement of Lower Resistivity Structure of Al-BSF Cell and PERC Cell 100us 1 ～ 3 Ω.cm 100μs 70μs MCL Sketch of cost pressure for different resistivity PERC efficiency gain VS Cost pressure of wafers with lower reisistivity ⚫ PERC cells request lower resistivity for better FF and hence efficiency. ⚫ Lower resistivity target causes lower minority carrier lifetime of the mono-Si wafer. ⚫ CCz mono-Si wafers have narrow distribution of resistivity, when target at very low resistivity, the MCL drops significantly.0.5 ～ 1.5 Ω.cm 3 Quantitative equation of MCL for Auger recombination Ref PHYSICAL REVIEW B 86, 65202 2012 Effective MCL for p-type and n-type mono-Si with various resistivities Relationship between resis.ρ and MCLτ Intrinsic MCL ⚫ Lower τ with lower ρ. ⚫ Auger recombination becomes more important in mono-Si with lower ρ and measured by high injection. Main cause for lower τ with lower ρ 4 Relationship between ρ and τMCL for mass solidified with various ρ target ⚫ MCL degradation of CCz with increased mass solidified is slower vs RCz. ⚫ Under the same mass solidified , the lower resis. ρ, the lower MCL Tau. Features of MCL variation of CCz ingot vs mass solidified and ρ Effective MCL for p-type CCz mono-Si vs mass solidified with various resistivities MCL vs mass solidified and resis by CCz 0.8 1 1.2 1.5 0 10 20 30 40 50 60 70 80 90 100 Mass solidified /kg 50 10 0 15 0 20 0 25 0 30 0 M CL /μ S MX0 MX 50 MX100 Relationship between ρ and τ Measurement setup of BCT-400 HMI of Sinton BCT-400 Flash 1/1, ½, ¼, etc Mode Transient, QSS MCD 5E14, 1E15, etc Resis. segment ρ ⚫ Sinton BCT-400 widely used for MCL inspection of mono-Si ingot. ⚫ Different value attributed to different setup mode, MCD and flash, etc. MCL measurement tool widely used in mono-Si production 5 Relationship between ρ and τ Measurement setup of BCT-400 ⚫ Sinton BCT-400 widely used for MCL inspection of mono-Si ingot. ⚫ The higher injection, the higher MCL 6 Relationship between ρ and τ Mode transient VS QSS of BCT-400 QSS1000 Transient850 50us Cannot distinguish ⚫ We cannot distinguish 50us from 1us using Transient. ⚫ Recommended using QSS for τ1e15＜ 100us. ⚫ High injection shows better agreement at high MCL. MCL measured by mode Transient and QSS MCL variation measured using mode Transient and QSS 7 8 Measure low MCL using T850 Measure low MCL using QSS1000 ⚫ Photoconductance decay is limited by Flash decay rate. ⚫ Transient mode result is not valid. Low MCL not be distinguished by Transient Relationship between ρ and τ Transient result not valid for low MCL 28μs 10μs 9 New requirement on MCL gamma γresis.ρ/MCLτ MCL/us Resistivity/ohm.cm Within specific range of resis., minimum and min mean allowed value at different resistivities ⚫ Within specific range of resis., MCL linear variation vs resis ⚫ Enable simple averaging. ⚫ Enable linear extrapolation from few points for run termination decisions. ⚫ Proportional to cell efficiency. Focus on γ＝ ρ/τ 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 1 18 35 52 69 86 103 120 137 154 171 188 205 222 239 256 273 290 307 324 341 358 375 392 409 426 RCZ和 CCZ P型不同掺杂剂电阻率与棒长关系 RCZ/B Ω.cm CCZ/B Ω.cm RCZ/Ga Ω.cm 10 Calculated value of γ from lots of CCz runs with MCL measured at MCD 1E15 New requirement on MCL Allowed value of γ Allowed γ within certain impurity content metal, oxygen and carbon ⚫ After fitting the real data, A linear line can be draw between γ ρ/τ and charge size. ⚫ γmax ρ/τmin 0.0202 ohm.cm/μs; ⚫ρ0.7 ohm.cm of τmin＞ 35 us ⚫Need to further perform cell efficiency to confirm/revise the gamma γ and MCL limit Predicted τmin and τmin mean at different ρ according to γ MCL/us Resistivity/ohm.cm 0 25 50 75 100 γmax0.0202ohm.cm 11 New requirement on MCL gamma γresis.ρ/MCLτ ⚫ with the higher γ value, corresponding to the higher efficiency ⚫ When the γ is up to a certain value, the efficiency is no significant improvement Focus on γmaxρ/τ or γminτ/ρ 12 Conclusion ➢ MCL degrades with lower resistivity. ➢ MCL measurement by BCT-400 Use transient-850 settings and 850nm filter and report at MCD1e15cm-3. Any measurements that fall below 100us should be remeasured using QSS-1000 settings and 1000 nm filter and reported at 1e15cm-3. ➢ Use gamma γ resis. ρ/MCL τ to get MCL control value at different resis. to satisfy the cell efficiency. ➢ Need to further perform early - late run high – low MCL cell efficiency to confirm/revise the gamma γ and MCL limit. 协鑫（集团）控股有限公司 www.gcl-power.com 苏州地址江苏省苏州工业园区新庆路 28号协鑫能源中心电话 86-512-6853 6666 传真 86-512-6983 2396 上海地址上海市浦东新区世纪大道 100号环球金融中心 68楼电话 86-21-6857 9688 传真 86-21-6877 8699 香港地址香港九龙柯士甸道西一号环球贸易广场 17楼电话 852-2526 8368 传真 852-2526 7638