by means of characterisation and simulation Pietro P. Altermatt - PowerPoint PPT Presentation

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