1 KIER-Min Gu Kang

2019. 06. 04. M.S. Jeong1,2, M.G. Kang1, S. Park1, J.T. Jeong1, J.I. Lee1, H. Song1 1 Korea Institute of Energy Research, 2 Korea University Ref) ITRPV 2019 ▪ The front recombination current density is expected to decrease from 100 fA/cm2 to 40 fA/cm2. ▪ Emitter sheet resistance is expected to increase from 100 Ω/sq to 140 Ω/sq. ▪ To achieve this with increasing the efficiency, accurate analysis of the electronic properties on the front side is required. 2 Ideal Non-ideal ▪ In case of ideal contact, there is no etching of emitter during the metallization. ▪ Ideal contact has low leakage currents and good electronic properties. ▪ During real process, not only the passivation layer but also the emitter layer is etched. ▪ Non-ideal contact increases both J01 and J02. 3 ▪ Recombination current at the front side can be divided by metal fraction and passivation fraction. ▪ Surface recombination velocity is proportional to the recombination current. ▪ As the contact area of the metal electrode increases, the surface recombination velocity increases. Smetal Metal contact Smetal 𝑺𝒆𝒇𝒇 = 𝑱𝒐𝑵𝑨𝒒𝒏 𝒊 𝟐 Total J0 is the sum of all J0 component J0 = J0.bulk + J0.BSF + J0.metal (fm) + J0.pass (1-fm) J0.Front 4 0.0 5 0.1 0 0.1 5 0.2 0 0.2 5 1100 1200 1300 1400 J 0 ( fA/cm 2 ) Metal f racti on Me asu re d J 0 v alue Lin ea r f it E q u at i on y = a + b * x P l ot B W ei g h t I n s t r u m en t al I n t er c ep t 11 46 . 55 96 3 ?4 . 18 73 8 S l op e 67 8. 89 90 8 ?2 5. 57 28 8 R es i d u al S u m of S q u ar es 0. 10 09 2 P ea r s on s r 0. 99 78 8 R - S q u ar e( C O D ) 0. 99 57 6 A d j . R - S q u ar e 0. 99 43 5 J0 = J0.bulk + J0.BSF + J0.metal (fm) + J0.pass (1-fm) Slope = J0.metal – J0.pass ∴ J0.metal = Slope + J0.pass ➢ J0.metal was extracted by the relationship between metal fraction and J0. 5 Ref) I. B. Copper et al., IEEE J. PHOTOVOLT., 4(1), 134, 2014 Ref) Mohamed M. Hilali et al., J. Electrochem. Soc., 153(1), A5, 2006 ▪ Previous studies were qualitative analysis of Ag crystallite imprint and contact resistance. ▪ In this presentation, relationship of doping profile and quantified Ag crystallites will be talk. 6 N type Si Texturing POCl3 doping & PSG removal ( Sample A = 8.82E20 atom/cm3, 60Ω/sq Sample B = 6.24E20 atom/cm3, 120Ω/sq Reference = 2.11E20 atom/cm3, 85Ω/sq) Anti-reflection coating ( SiNx 80nm, double side ) Screen printing (Ag paste, metal fraction = 0 - 25%, size = 4 X 4cm2 ) Firing ( peak temperature = 875, 925 and 975℃ ) Metal removal ( HNO3 68%, 15min ) Laser cutting ( size = 4 X 4cm2 ) Characterization ( QSSPC, SEM, SIMS, TEM, TLM, ICP-OES ) P type, 1 - 3 Ω·cm N type Si SiNx SiNx Ag crystalliteGlass frit 7 0 100 200 300 400 500 1E 17 1E 18 1E 19 1E 20 1E 21 P concentrati on ( atom/ cm 3 ) Depth (nm) Sam pl e A ( 60  s q. Surfac e c onc entration 8 .82E+ 20) Sam pl e B (120  s q. Surfac e c onc entration 6 .24E+ 20) Reference ( 85  s q. Surfac e c onc entration 2 .11E+ 20) ▪ Normally, when using the emitter, the process is based on the sheet resistance. ▪ Doping concentration profile is more important to the device characteristics than the sheet resistance. ▪ We prepare the samples with higher and lower Rsh than reference, but they have higher surface doping conc. 8 Sa mple A Sa mple B Refere nce 0 500 1000 1500 J 0.pa ss ( fA/cm 2 ) • As surface doping concentrations decrease, J0.pass decreases. • J0.pass depends on surface doping concentration, not sheet resistance. 0 100 200 300 400 500 1E 17 1E 18 1E 19 1E 20 1E 21 P concentrati on ( atom/ cm 3 ) Depth (nm) Sam pl e A ( 60  s q. Surfac e c onc entration 8 .82E+ 20) Sam pl e B (120  s q. Surfac e c onc entration 6 .24E+ 20) Reference ( 85  s q. Surfac e c onc entration 2 .11E+ 20) A B Reference N type Si P type, 1 - 3 Ω·cm N type Si SiNx SiNx 9 Sa mple A Sa mple B Refere nce 0 500 1000 1500 2000 J 0.me ta l ( fA/cm 2 ) Peak tem p. 87 5 ° C Peak tem p. 92 5 ° C Peak tem p. 97 5 ° C J 0 .p a s s v alue • As surface doping concentration decreases, J0.metal decreases. • As firing peak temperature increases, J0.metal increases. 0 100 200 300 400 500 1E 17 1E 18 1E 19 1E 20 1E 21 P concentrati on ( atom/ cm 3 ) Depth (nm) Sam pl e A ( 60  s q. Surfac e c onc entration 8 .82E+ 20) Sam pl e B (120  s q. Surfac e c onc entration 6 .24E+ 20) Reference ( 85  s q. Surfac e c onc entration 2 .11E+ 20) A B Reference 10 • At the higher firing peak temperatures, Ag crystallites was larger. • It was not easy to distinguish which sample has more Ag crystallites depending on the doping concentration. • Another evaluation was needed to make quantitative analysis. 11 Sa mple A Sa mple B Refere nce 0.0 0.5 1.0 1.5 2.0 Ag concen trat ion ( mg/L) Peak tem p. 87 5 ° C Peak tem p. 92 5 ° C Peak tem p. 97 5 ° C • ICP-OES was used to quantitatively analyze the Ag crystallites on the surface. • Surface doping concentration and amount of Ag crystallites were positively correlated. • As Ag crystallites concentration was increased, J0,metalwas increased. Sa mple A Sa mple B Refere nce 0 500 1000 1500 2000 J 0.me ta l ( fA/cm 2 ) Peak tem p. 87 5 ° C Peak tem p. 92 5 ° C Peak tem p. 97 5 ° C J 0 .p a s s v alue 12 975℃ 925℃ 875℃ AgSi O Pb • At the higher firing peak temperature, emitter was more etched by glass frit. Using reference sample 13 Sa mple A Sa mple B Refere nce 0 2 4 6 8 Con tact resi stance ( m Ω  cm 2 ) Peak tem p. 87 5 ° C Peak tem p. 92 5 ° C Peak tem p. 97 5 ° C • Larger Ag crystallites at higher peak temperature means → emitter surface was more etched. → silicon and Ag crystallite was contacted deeply. → it made high contact resistance. 925℃ 975℃ Cross section of Sample B 14 1E13 1E14 1E15 1E16 0 200 400 600 800 Su rf ac e reco mbina tion velo city (cm/s) Exc es s ca rr ier de ns ity ( cm -3 ) Samp le A ( 8.8 2E+20 cm -3 ) Calcu late d S e ff (S e ff = 0) Bef or e m eta llization (8 75 o C) Afte r m eta llization (8 75 o C) Bef or e m eta llization (9 25 o C) Afte r m eta llization (9 25 o C) Bef or e m eta llization (9 75 o C) Afte r m eta llization (9 75 o C) • Conversion of QSSPC data to Seff • The higher the surface doping conc., the greater the difference in Seff • As the doping conc. increases, the Seff does not change much even if the firing temperature changes. • However, if the recombination is not limited by the doping conc., the firing condition affects the Seff. 1E13 1E14 1E15 1E16 0 200 400 600 800 Samp le B ( 6.2 4E+20 c m -3 ) Su rf ac e reco mbina tion velo city (cm/s) Exc es s ca rr ier de ns ity ( cm -3 ) 1E13 1E14 1E15 1E16 0 200 400 600 800 Referen ce ( 2.1 1E+20 c m -3 ) Su rf ac e reco mbina tion velo city (cm/s) Exc es s ca rr ier de ns ity ( cm -3 )1E13 1E14 1E15 1E16 0 200 400 600 800 Su rf ac e reco mbina tion velo city (cm/s) Exc es s ca rr ier de ns ity ( cm -3 ) Samp le A ( 8.8 2E+20 cm -3 ) Calcu late d S e ff (S e ff = 0) Bef or e m eta llization (8 75 o C) Afte r m eta llization (8 75 o C) Bef or e m eta llization (9 25 o C) Afte r m eta llization (9 25 o C) Bef or e m eta llization (9 75 o C) Afte r m eta llization (9 75 o C) 1E13 1E14 1E15 1E16 0 200 400 600 800 Su rf ac e reco mbina tion velo city (cm/s) Exc es s ca rr ier de ns ity ( cm -3 ) Samp le A ( 8.8 2E+20 cm -3 ) Calcu late d S e ff (S e ff = 0) Bef or e m eta llization (8 75 o C) Afte r m eta llization (8 75 o C) Bef or e m eta llization (9 25 o C) Afte r m eta llization (9 25 o C) Bef or e m eta llization (9 75 o C) Afte r m eta llization (9 75 o C) 15 • Using QSSPC measurements, J0,metal were extracted with J0 extrapolation by the metal fraction. • The firing peak temperature and surface concentration affect metal-Si interface and J0,metal values. Quantitative analysis of Ag crystallite was characterized by ICP-OES. • The lower surface doping concentration is much important to reduce the recombination velocity than high sheet resistance. 16 17 Thank you for your kind attention. mgkang@kier.re.kr 0% 5% 10% 15% 20 % 25 % Metal fraction ARC Emitter Bulk Emitter ARC • Ag printing on front side • Firing at the same time • Cutting with laser 19 • Surface doping concentration decreases → High initial Voc (because J0 is low) • Increase of metal fraction → J0.metal increase, the Voc decreases 𝑽𝒐𝒄 = 𝒌𝑻𝒒 𝒍𝒏 𝑱𝒔𝒄𝑱 𝟎 +𝟏 0 5 10 15 20 25 608 610 612 614 616 Vo c (mV) Meta l Frac tion (% ) 875 ° C 925 ° C 975 ° C Firi ng tem perature Sample A ( 8.82E+20 cm -3 ) 0 5 10 15 20 25 628 630 632 634 636 638 Vo c (mV) Meta l Frac tion (% ) 875 ° C 925 ° C 975 ° C Firi ng tem perature Sample B ( 6.24E+20 cm -3 ) 0 5 10 15 20 25 640 642 644 646 648 Vo c (mV) Meta l Frac tion (% ) 875 ° C 925 ° C 975 ° C Firi ng tem perature Referenc e ( 2.11E+20 cm -3 ) 20 21 N type Si P type, 1 - 3 Ω·cm N type Si SiNx SiNx Ag crystalliteGlass frit Etching glass frit with HF N type Si P type, 1 - 3 Ω·cm N type Si SiNx SiNx Ag crystallite Etching Ag crystallite with HNO3 N type Si P type, 1 - 3 Ω·cm N type Si SiNx SiNx Ag dissolved HNO3