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., 41, 134, 2014 Ref Mohamed M. Hilali et al., J. Electrochem. Soc., 1531, 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 Ωcm 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 Ωcm 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 2E20 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 4E20 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 1E20 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 2E20 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 2E20 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. mgkangkier.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 8.82E20 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 6.24E20 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 2.11E20 cm -3 20 21 N type Si P type, 1 - 3 Ωcm N type Si SiNx SiNx Ag crystalliteGlass frit Etching glass frit with HF N type Si P type, 1 - 3 Ωcm N type Si SiNx SiNx Ag crystallite Etching Ag crystallite with HNO3 N type Si P type, 1 - 3 Ωcm N type Si SiNx SiNx Ag dissolved HNO3