晶体硅太阳电池的光衰减效应研究-余学功

Light-induced degradation of crystalline silicon solar cells 晶体硅太阳电池的光衰减效应研究 State Key Laboratory of Silicon Materials Xuegong Yu (余学功 ) State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027 Outline 2 1 Introduction 2 3 Properties of LID defects Conrol strategies of LID defects 4 Conclusion Introduction 3 Al-BSF: 1-3% PERC: 5-6% Si crystal LID is a sever problem for crystalline silicon solar cells ! -+- 4 [BO] is proportional to [Bs] and [Oi]2 J. Schmidt, Physical Review B, 69 (2004) 024107. BS+ O2i = BSO2i ???? Suppression method:  Reduce [Oi]  Reduce [Bs]  Use Ga or In  Use n-type silicon  High T annealing LID defects in CZ silicon New strategy ???? 5 LID defect Characterization： Carrier lifetime BOSR Hd NN   111 0 )]e x p (1[* tRNN g e ntt  Properties of LID defects in CZ silicon 6 O2i defect characterization: LT-FTIR Properties of LID defects 7 [BO] and [O2i] vs temperature [O2ist] [O2isk] 13 12 11 10 9 3.0 6.0 9.0 12. 0 15. 0 stagg er ed dim er ske w ed dim er 1/kT ( eV -1 ) [ O 2i ] / [ O i ] 2 ( 10 - 22 cm 3 ) 1.0 2.0 3.0 4.0 5.0 E = 0.0 3 ± 0.0 1 eV E a = 0.1 7 ± 0.0 5 eV N t * / [ O i ] 2 ( 10 - 3 7 us -1 cm 6 ) T ( o C ) E = 0.1 3 ± 0.0 3 eV 650 700 750 800 850 900 950 1000 Properties of LID defects 8 [BO] and [O2ist] vs [Oi] [O i ] A B [BO] ~[Oi] has the same feature as [O2ist]~[Oi] Properties of LID defects Ge causes barrier for the Oi diffusion Effect of Ge co-doping on LID defects 1020 1050 1080 1110 0.0 0 0.0 2 0.0 4 0.0 6 0.0 8 0.1 0 CZ Abso rpti on coef f i ci ent (cm -1 ) W a v e n u mbe r ( c m -1 ) G CZ 1012 1060 1105  Ge codoping suppresses the stagger-type oxygen dimer  Ge codoping reduces the concentration of B-O defects 0 200 400 600 800 0.00 0.01 0.02 0.03 0.04 0.05 Ga- dop ed CZ Conve ntion al CZ GCZ N o r m a li z e d d e fe c t c o n . (  s -1 ) Illumination t ime (min)Effect of Ge on LID defects The LID effects of Ge-doped solar cells and modules are reduced Solar cell 180 181 182 183 184 185 GC Z Module power output (W) A s- f abri cat ed A f t er i l l um i nat i on CZ 7 16. 9 17. 0 17. 1 17. 2 17. 3 17. 4 GC Z As-f a b ri ca t e d Af t e r i l l u m i n a t i o n Ce ll ef ficie ncy (%) CZ Test of Ge-doped devices Module Effect of C codoping on LID defects Suppression of oxygen dimers R e f . C C Z 1 C C Z 2 0 .0 0 .2 0 .4 0 .6 0 .8 1 .0 N o r m . B - O c o m p le x e s c o n c . CellsEffect of C codoping on LID defects Suppression of B-O defects R e f . C C Z 1 C C Z 2 0 20 40 60 80 100 M in o r it y c a r r ie r l if e t im e   (  s ) Waf ers R e f . C C Z 1 C C Z 2 1 8 . 0 1 8 . 1 1 8 . 2 1 8 . 3 1 8 . 4 1 8 . 5 1 8 . 6 1 8 . 7 E f f b e f o r e i l l u min a t i o n E f f a f t e r i l l u min a t i o n Co n ve r si o n e f f ic ie n cy ( % ) Cells 1. 0 1. 5 2. 0 2. 5 3. 0 R a t e o f e f f i c i e n c y d e c r e a s e ( % ) Carrier lifetime solar cell efficiency Effect of C codoping on LID defects 15 Illumination or applying forward bias at elevated temperature Three states model Degraded state can be passivated by hydrogen to regeneration state So why illumination and elevated temperature is necessary? Elimination of LID defects Hydrogen passivation mechanism In p-type silicon B-O defects are mainly positively charged at low injection (BO) + is favorable to be passivated by H-/H0 Elimination of LID defects Donor level: Ec-0.16 eV Acceptor level: Em-0.07 eV quasi-Fermi level by illumination EF Illumination induces quasi-Fermi level, so reduce the ratio of H+ and raise the ratio of H0 Elevated temperature makes EF move towards the acceptor level of H and raise the ratio of H- Elevated temperature improve the diffusion ability of H Hydrogen passivation mechanism Elimination of LID defects Em 70 mW.cm-2 RT 70 mW.cm-2 150 oC Regeneration treatment is an effective way to suppress LID 70 mW.cm-2 50 oC Nt*=1/τ(t)-1/τ(0) Elimination of LID defects 19 Test of solar cells with reg. treatment 20 Grain-boundaries Dislocations Recombination activity of GBs are dominated by metal contamination. Recombination activity of defectafter Fe segregation LID defects in cast mc silicon 21 EBIC characterization 100u m EBIC image LID defects in cast mc silicon No dislocations？ EBIC temperature dependence reflects the defect recombination activity Dislocations Properties of LID defects in mc silicon Dislocation recombination activity vs metal contamination 1. Type II: No metal con. 2. Type 2: Slightly metal con. Impurity at dislocation core 3. Type 1: Medium metal con. Impurity cloud 4. Type I: Heavy metal con. Precipitate Properties of LID defects in mc silicon hydrogen passivation Limitation: type-2 Properties of LID defects in mc silicon Physical picture Properties of LID defects in mc silicon Grain boundary vs metal con. The recombination activity of GBs increases with the contamination increasing. Contamination increases Properties of LID defects in mc silicon Electric parameters of GB Properties of LID defects in mc silicon Hydrogen passivation Properties of LID defects in mc silicon 29 An effective method for industrial application ---- Regeneration treatment by forward bias Elimination of LID defects Electrode +Temperature controller Eletrode Thermocouple Elimination of LID defects