Abasifreke Ebong, Nirupama Bezawada, Veysel Unsur, Ren Keming and Ahrar Chowdhury Department of Electrical and Computer Engineering University of North Carolina at Charlotte 9201 University City Blvd, Charlotte NC 28223-0001, USA
(i) R 1 metal-semiconductor back contact (ii) R 2 bulk semiconductor (iii) R 3 emitter between two gridlines (iv) R 4 metal semiconductor contact on gridline (v) R 5 gridline (vi) R 6 - busbar 2
Sheet Resistance (ohm/sq.) 140 120 100 80 60 40 ITRPV 2017 Expected trend for sheet resistance 2024; 130 2017; 100 2016; 90 2015; 80 2014; 75 2013; 70 2012; 65 2011; 60 2008; 55 2005; 50 2000; 45 1995; 40 1990; 35 2021; 120 2019; 110 2027; 130 1980; 25 20 1970; 20 1970 1980 1990 2000 2010 2020 2030 Year
200 1970; 200 180 1980; 180 160 1990; 160 Gridline width (um) 140 120 2000; 140 2005; 120 100 80 ITRPV 2017 Expected trend for gridline width 2010; 100 2015; 70 60 2016; 48 40 2017; 45 2019; 38 2024; 30 2021; 30 20 2027; 25 1970 1980 1990 2000 2010 2020 2030 Year
2-5% 5-10% 85-90% [1] R. Prunchak, US patent 7,736,546B2, 2010. [2] Carroll et al, US Patent, 8,889,980 B2 [3] R. G. Rajendran, US 2013/0099177 A1
(i) SS (wwwww) + 2PPO (ggggg) SSO 2(ggggg) + 2PP (ii) SS (wwwww) + 2AA 2 O (ggggg) SSO 2 (ggggg) + 4AA (iii)ss 3 N 4(dddddddddd oo wwwww) + 6AA 2 O (ggggg) 3SSO 2 (ggggg) + 12AA + 2N 2 [1] C. Ballif, et al, App. Phys. Lett., 82 (12), 1878-1880, 2003. [2] Schubert et al, Solar Energy Materials and Solar Cells, 90, 33399-3406, 2006. [3] Hilali et al, J. Electrochem. Soc. 153, A5, 2006. [4] Li et al, J. Appl. Phys. 105, 066102, 2009 [5] Eberstein et al, Energy Proceedia 27, 522-530, 2012. [6] Tai et al, RSC Advances, 5, 92515-92521, 2015 p.7
TEM micrograph: overfired Ag/Si contact. The intermediate SiNx layer has been dissolved in the firing process. Ballif et al : Appl. Phys. Lett., Vol. 82, No. 12, 24 March 2003 p.8
SEM-picture of the interface of a silver thick film-finger on [1 0 0] orientated silicon. Silver crystallites grown into the silicon are clearly visible. Schubert et al., Solar Energy Materials & Solar Cells 90 (2006) 3399 3406 p.9
SEM micrographs of: contact layer, finger layer, full layer and elemental analysis Ag Crystallites Contact layers Top view of contact and finger layers after sintering Contact and Finger layers Ag Crystallites Si
Paste particle size Paste ID D10 D50 D90 Series Resistance (Ω-cm 2 ) Contact Resistance (Ω-cm 2 ) Fill factor (%) A 1.273 2.102 3.466 13.813 0.825 43.4 B 1.125 2.031 3.657 0.812 0.442 78.4 C 1.194 2.145 3.784 0.737 0.390 78.8 D 1.205 2.085 3.568 0.638 0.312 79.4 E 1.208 2.029 3.506 1.737 0.774 73.8 F 1.238 2.056 3.366 1.829 0.552 73.5 G 1.182 2.032 3.437 1.983 1.099 73.1 H 1.159 2.062 3.628 1.107 0.334 76.9 I 1.159 1.914 3.100 2.321 0.929 71.1 J 1.140 2.066 3.761 0.874 0.222 78.2 K 1.171 2.060 3.579 4.263 0.906 63.6 L 1.150 2.028 3.518 6.703 1.018 56.1 CP 1.545 3.456 4.965 5.876 0.967 60.3 p.11
Contact characterization Paste D 34/66 PbO/TeO 2 Paste J 50/50 Pbo/TeO 2 SEM/EDX for Ag paste D and J after drying at 200 o C for 2-mins
EDX analyses of Contact Paste D Element Wt% At% CK 43.92 77.82 OK 06.10 08.12 MgK 03.62 03.17 AlK 02.81 02.22 SiK 03.86 02.92 PbM 13.51 01.39 TeL 26.19 04.37 Matrix Correction ZAF After 2-min drying at 200 o C Paste J Element Wt% At% CK 53.34 82.10 OK 07.53 08.70 MgK 03.39 02.58 SiK 04.52 02.97 PbM 15.72 01.40 TeL 15.50 02.25 Matrix Correction ZAF
Contact characterization Ag + Te + Pb Ag + Pb + Te K_Count Si Paste D K_Count Si Paste J SEM/EDX for Ag paste D and J after contact co-firing at 815 o C peak firing temperature in IR belt furnace.
EDX analyses of Contact Paste D Paste J After contact co-firing at 815 o C peak firing temperature in IR belt furnace.
Contact characterization 350 (111) 350 (111) 300 250 Paste D after 200 o C dry Paste D 300 250 Paste J after 200 o C dry Paste J Count per Sec 200 150 Counts per sec 200 150 (200) 100 50 (200) (220) Si peak (311) Paste D after 815 o C sintering (222) 0 30 40 50 60 70 80 90 100 2θ (degree) 100 50 (220) Paste J after 815 o C firing (311) Si Peak (222) 0 20 30 40 50 60 70 80 90 100 2Ѳ (degree) XRD pattern for Ag paste D and J after drying at 200 o C for 2-mins and after contact cofiring at 815 o C peak firing temperature in IR belt furnace. Before: All Ag phases are similar After: (111) phase in D doubles due to PbO/TeO 2 ratio difference
Raman Spectra of contact 15000 Si Intensity 124-D-HNO3-1 14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 Ag 2 Te TeO 2 Paste D 124-D-HNO3-1 124-D-HNO3-2 124-D-HF-1 124-D-HF-2 3000 2000 1000 100 200 300 400 500 600 700 800 900 1000 Wavenumber
1. Nano-sized metallic Zn additives - uniformly etch the non-conductive SiNx:H layer 2. TeO 2 additive - uniform etching of sinx:h layer - Decreases viscosity of molten glass and causes uniform wetting of SiNx:H - No Te after glass removal with HF (i) Ag, Te and Si form Ag-Te, Ag-Si and Ag-Te-Si alloys. (ii) Formation of Ag 2 Te a semimetal increases conductivity of glass low contact resistance and gridline resistance. 3. Both 66PbO-34TeO 2 and the 50PbO-50TeO 2 glasses enable higher isothermal conductivity. The resulting low melting nature of the glass facilitate diffusion process introducing ionic conductivity leading to high isothermal conductivity. 1. Li et al., J. Appl. Phys. 110, 074304 (2011) 2. Ionkin et al, ACS Appl. Mater. Interfaces 3, 606 (2011) 3. Ebong et al, JJAP, 56, 08MB07 (2017) 4. ] R. Prunchak, US patent 7,736,546B2, 2010 5. Vithal et al., J. Appl. Phys. 81 (12), 7922-7926, (1997) p.18
Abasifreke Ebong, Nirupama Bezawada, Veysel Unsur, Ren Keming and Ahrar Chowdhury Department of Electrical and Computer Engineering University of North Carolina at Charlotte 9201 University City Blvd, Charlotte NC 28223-0001, USA
Belt speed: 230 pm Peak Temp: 815 o C