Understanding the fill factor by means of characterisation and simulation Pietro P. Altermatt Leinbiz University of Hannover, Germany SPREE Seminar @ UNSW, 19th March 2015 LUH 1
Which parameters influence the fill factor? LUH
…the lumped series resistance R s LUH
… the V oc n = 1.0 R s = 0 M.A. Green, Solar Cells, 1992, (ISBN 0 85823 580 3), p. 96 M.A. Green, Solar Cells 7, 337 (1982) LUH
… der ideality factor n R s = 0 M.A. Green, Solar Cells, 1992, (ISBN 0 85823 580 3), p. 96 M.A. Green, Solar Cells 7, 337 (1982) LUH
Analytical approximation using V oc , n and R s J sc = 39 mA/cm 2 Detailed overview of analytical equations for FF: E. Sanchez and G.L. Araujo, Solar Cells 20, 1 (1987) LUH
Do we here have a „FF problem “ ? LUH
No LUH
FF in relation to V oc It is advantageous to consider FF in relation to V oc LUH
FF depends on n The idality factor may influence FF as strongly as R s . LUH
Contents (Loss)-analysis Characterization 1 2 using simulations using I-V measurements LUH
Contents Characterization 1 using I-V measurements LUH
Measurement of I-V curves Measurement V mpp Current-density [mA/cm 2 ] J sc -V oc Dark 1-sun 1-sun 1.1-sun 0.9 sun (J sc -V oc ) dark V oc Bias [V] LUH
I-V curves – logarithmic LUH
I-V curves – logarithmic LUH
I-V curves – logarithmic LUH
I-V curves – logarithmic LUH
I-V curves – logarithmic Current-density [mA/cm 2 ] V mpp J sc -V oc 1-sun dark V oc Bias [V] LUH
Extraction of R s Measurement Extraction of R s LUH
R s extraction from I-V curves Current density [mA/cm 2 ] V mpp Series resistance [ cm 2 ] J sc -V oc DLL 1-sun J sc -V oc dark V oc Bias [V] Bias [V] Overview: P.P. Altermatt et al, Prog. PV 4, 399 (1996) LUH
Tripple light-level (TLL) method K. F. Fong, K. R. McIntosh, A. W. Blakers, Prog. PV 21, 490 (2013) LUH
Tripple light-level (TLL) method K. F. Fong, K. R. McIntosh, A. W. Blakers, Prog. PV 21, 490 (2013) LUH
Large J 0 → I -V curve is higher LUH
Large J 0 → I -V curve is higher LUH
R s extraction from I-V curves V mpp Current-density [mA/cm 2 ] Series resistance [ cm 2 ] J sc -V oc DLL 1-sun J sc -V oc dark V oc Bias [V] Bias [V] If possible, use the tripple light-level method to measure R s K. F. Fong, K. R. McIntosh, A. W. Blakers, Prog. PV 21, 490 (2013) LUH
Simulation of the metallised parts Device simulation Circuit simulation Y. Yang et al, Prog. PV 20, 490 (2012) LUH
Simulation of the metallized parts Device simulation Series resistance [ cm 2 ] DLL. Circuit simulation J sc -V oc Internal R s Bias [V] LUH
Parametrization of R s Measurement Extraction Parametrization of R s of R s (V) Proper distinction between R s - and recombination losses If simulation: internal R s LUH
R s (V) as polynome 2nd degree where V 0 is offen V oc Series resistance [ cm 2 ] DLL. J sc -V oc Internal R s Bias [V] LUH
R s -corrected I-V curves Measurement Extraction Parametrization R s (V)-free of R s of R s (V) I-V curves Proper distinction R s (V) between R s - and polynome recombination losses If simulation: internal R s LUH
R s -corrected I-V curves 2 ] Current density [mA/cm 1 10 Exp R s (V mpp ) 0 10 FF Exp = 78.52 R s (V) FF R s (V) = 83.18 -1 10 0.40 0.45 0.50 0.55 0.60 0.65 External bias [V] LUH
R s -corrected I-V curves show recombination losses 2 ] Current density [mA/cm 1 10 Exp R s (V mpp ) 0 10 FF Exp = 78.52 R s (V) FF R s (V) = 83.18 FF R s (V mpp ) = 83.09 -1 10 0.40 0.45 0.50 0.55 0.60 0.65 External bias [V] LUH
Comparison of pseudo-FF with 1FF FF Exp = 78.52 FF R s (V) = 83.18 FF R s (V mpp ) = 83.09 FF n=1 = 83.28 pFF n = 1.0 is often smaller R s = 0 than 1FF M.A. Green, Solar Cells, 1992, (ISBN 0 85823 580 3), p. 96 M.A. Green, Solar Cells 7, 337 (1982) LUH
Loss analysis Loss analysis Measurement Extraction Parametrization R s (V)-free of R s of R s (V) I-V curves Predictions Proper distinction R s (V) Recombination between R s - and polynome losses recombination losses pFF If simulation: internal R s 1FF LUH
Content (Loss)-Analysis 2 using simulations LUH
Domain & discretization Finger 2D Domain Entire cell LUH
Reproduction of the ideality factor Ultimate test S. Steingrube et al. Energy Procedia 8, 263 (2011) LUH
Which is the most likely current-path? dark V applied forward bias LUH
Exponentially increasing recombination rates LUH 39
Dark I-V curve = recombination rate Number of defects 40 many few 2 ] Stromdichte [mA/cm 30 20 10 0 -100 0 100 200 300 400 500 600 700 Spannung [mV] LUH
Illuminated I-V curve is shifted to 4th quadrant LUH
Think of G – R G LUH
J(V) = G – R(V) J(V) = G – R(V) R(V) G LUH
Losses in the various cell regions R(V) Recombination current [mA/cm 2 ] Total Emitter Base Al-BSF Voltage [V] LUH
Predictions Loss analysis Measurement Extraction Parametrization R s (V)-free of R s of R s (V) I-V curves Predictions LUH
After improvement of the emitter in a PERC cell Standard cell Improved emitter Recombination current [mA/cm 2 ] Total Emitter Base Al-BSF Bias [V] Bias [V] V oc = 614 mV V oc = 633 mV FF = 76.3 FF = 75.4 LUH
Losses in the p-type Cz base LUH
Injection dependent lifetime in the p-type base ( n n n ) ( p p n ) p 0 1 n 0 1 ( ) n SRH n p n 0 0 B-dotiertes Cz-Si N dop =5.1x10 15 cm -3 N dop =5.1 10 15 cm -3 n p Lebensdauer eff [µs] nach Tempern 10 -4 (200°C 10 min) B-O complex Effective lifetime p / n =10 nach Beleuctung (1Sonne 60 Stunden) 10 -5 n 10 12 10 13 10 14 10 15 10 16 10 17 Ladungsträgerkonzentration n [cm -3 ] Injection density n [cm -3 ] J. Schmidt, A. Cuevas, J. Appl. Phys. 86 (1999) 3175 S. Rein, S.W. Glunz, Appl. Phys. Lett. 82 (2003) 1054 K. Bothe R. Sinton, J. Schmidt, Prog. PV 13 (2005) 287 LUH
Deactivated B-doped Cz wafers D. Waler et al, Appl. Phys. Lett. 104, 042111 (2014) LUH 49
Improved emitter → smaller FF because of base! Standard cell Improved emitter Recombination current [mA/cm 2 ] Total Emitter Base Al-BSF Bias [V] Bias [V] V oc = 614 mV V oc = 633 mV FF = 76.3 FF = 75.4 LUH
FF, pFF und 1FF Two cells with low FF Mainly due to R s pFF is close to 1FF 1) Mainly due to n pFF is far from1FF 2) Determine FF and pFF, if possible using R s (V), and 1FF LUH
More recent progress of PERC cells (1) Inital Improved emitter 79.69 80.38 LUH 52
More recent progress of PERC cells (2) Improved emitter Improved base and rear 80.80 80.38 LUH 53
More recent progress of PERC cells (3) Improved base and rear Improved base 80.80 81.46 LUH 54
Emitter losses increase… Inital Improved emitter… …base and rear …base LUH 55
…because V mpp increases Inital Improved emitter… …base and rear …base LUH 56
Main points • Extraction of R s (V) from three I-V curves (TLL method) • Clear distinction between R s (V) and recombination losses • R s (V)-corrected I-V curve → pFF < 1FF ? • Further analysis and prediction with simulations FF is not only determined by R s , but also by the ideality factor, i.e.by recombination, especially in good cells (where the base or the rear surface dominates) LUH
Thank you! altermatt@solar.uni-hannover.de LUH
Recommend
More recommend
