5 SERIS-Pradeep Padhamnath

1SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Analysis of LPCVD p+ poly-Si layer for applications in large area c-Si solar cells incorporating passivating contacts Pradeep PADHAMNATH, Kaylynn SEW, NAGARAJAN Balaji, Nitin NAMPALLI, Naomi NANDAKUMAR, Vinodh SHANMUGAM, Armin G. ABERLE, Shubham DUTTAGUPTA SNEC 2019 5 June 2019 2SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Outline ❑ Introduction ➢ Passivated contacts ➢ State-of-the-art result of p+ poly-Si ❑ Experiment ➢ Process flow ➢ Characterization details ❑ Results and Discussion ➢ Doping of poly-Si using BBr3-diffusion ➢ Passivation ➢ Contact-formation (screen-printing) ❖ SEM imaging ❑ Conclusion 3SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Introduction Passivating Contacts ❑ Passivated contacts is an obvious next-step after PERC ❑ High-efficiencies ~ 25.7% reached using n+ poly-Si contacts at the rear side of 2x2 cm2 cell [1] ❑ Efficiencies of ~ 23.5 % with rear n+ poly-Si contacts realized by inline PECVD + screen printed FT metallization [2] ❑ Efficiencies of ~21% (n-type, Rear junction) [3], 20.4% (p-type, front junction) [4] - using rear p+ poly-Si contacts - in-situ doped LPCVD p+ poly Si + screen printed FT metallization. [1] A.Richter et al., SolMat, 2017 [2] Nandakumar et al., PIP 2018; Nandakumar et. al. SiPV 2019. [3] Woo-Ok et al., APL, 2018 [4] Mack et al., PSS-RRl, 2019 4SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Introduction Relevant state-of-the-art properties of p+ poly-Si [01] Mack et al, PSSRRL, 2019 [02] Morisset et al, SolMat,2019 [03] Ingenito et al, Nat.Energy, 2018 [04] Mewe et al, proc. AIP conf., 2018 [05] Ok et al, AIP letters, 2018 [06] Stodolny et al, proc. EUPVSEC,2018 [07] Liu et al., SolMat,2018 [08] Ciftpinar et al, Proc. SiliconPV, 2017 [09] Mack et al, PSSRRL, 2017 [10] Larionova et al, PSS, 2017 [11] Wu et al, Proc. SiliconPV, 2016 [12] Romer et al, SolMat, 2014 0 10 20 30 40 50 60 670 680 690 700 710 720 730 740 pla nar tex tured iV oc [mV] J 0 [fA/ cm 2 ] 0 2 4 6 8 10 12 14 200 400 600 800 1000  contact [m − cm 2 ] J 0,meta l [f A/cm 2 ] 5SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Experimental details ❑ Surface morphology- Planar/Textured ❑ Five different thickness of iOx + LPCVD poly-Si (i) (50nm-250 nm) ❑ Ex-situ p+ doping with 2 different Boron recipes (Standard/Optimized) Diffusion test sample QSSPC test sample Metal test sample 6SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Experimental details Image of the test samples used for evaluating J0,metal An example of the fit obtained by Solar EYE to PL images of the samples J0,metal evaluated by fitting PL images at different intensities with the help of GriddlerTM based software. [1] J.Wong, IEEE PVSC 2013 [2] J.Wong et al, IEEE PVSC 2015 7SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Experimental details Characterization tool/Technique Parameters evaluated Ellipsometry Thickness of poly-Si 4 Point Probe Rsheet of doped poly-Si ECV Active dopant profile QSSPC teff, J0, iVoc TLM Specific contact resistivity PL imaging Evaluation of J0,metal SEM microscope Visual analysis of contacts 8SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Results – Boron-diffusion in poly-Si Doping Profiles Standard Recipe (T1000°C) Optimized Recipe (T1000°C) Optimized Recipe(T900°C) 50 100 150 200 250 20 40 60 80 100 120 140 160 180 200 Poly-Si t hicknes s [ nm] R shee t [  sq ] 50 100 150 200 250 0 100 200 300 400 500 600 700 800 Poly-Si t hicknes s [ nm] R shee t [  sq ] 10SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Results – surface passivation Standard Recipe- Deep emitter, High temp. Standard recipe on planar samples Standard recipe on textured samples ❑ Boron penetration into substrate for thinner poly-Si ❑ Deterioration of the passivating properties provided by the iOx layer 50 100 150 200 250 0 150 300 450 Poly-Si t hicknes s [ nm] J 0 [ fA/cm 2 ] 625 650 675 700 iV oc [ mV] 200 400 600 800 t eff [  s ] 50 100 150 200 250 0 150 300 450 Poly-Si t hicknes s [ nm] J 0 [ fA/cm 2 ] 625 650 675 700 iV oc [ mV] 200 400 600 800 t eff [  s ] 11SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Results – surface passivation Optimized Recipe- Shallow emitter, Low temp. Optimized recipe on planar samples Optimized recipe on textured samples Thick [nm] J0 [fA/cm2] iVoc [mV] teff [µs] 50 10 720 3900 250 4.5 740 5300 Thick [nm] J0 [fA/cm2] iVoc [mV] teff [µs] 50 66 678 525 250 19 704 1200 3000 4000 5000 6000 t eff [  s ] 680 700 720 740 iV oc [ mV] Poly-Si t hicknes s [ nm] 50 100 150 200 250 4 8 12 16 J 0 [ fA/cm 2 ] 680 700 720 740 Poly-Si t hicknes s [ nm] iV oc [ mV] 300 600 900 1200 t eff [  s ] 50 100 150 200 250 0 20 40 60 80 J 0 [ fA/cm 2 ] 12SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). pl an tex pl an tex pl an tex pl an tex pl an tex 50 100 150 200 250 0.1 1 10 100 1000 Poly-Si thickne ss [nm]  co nta ct [ m  -cm 2 ] plan (1 0%~9 0%) tex (1 0%~9 0%) Me dian Lin e Results Specific Contact Resistivity Standard Recipe Optimized Recipe pl an tex pl an tex pl an tex pl an tex pl an tex 50 100 150 200 250 0.1 1 10 100 1000 Poly-Si thickne ss [nm]  co nta ct [ m  -cm 2 ] plan (1 0%~9 0%) tex (1 0%~9 0%) Me dian Lin e 13SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). 50 100 150 200 250 0 500 1000 1500 2000 2500 J 0,meta l [ fA/c m 2 ] poly-Si t hicknes s [ nm] Opt . Recip e ( plan ) Opt . Recip e ( tex ) 50 100 150 200 250 0 500 1000 1500 2000 2500 J 0,meta l [ fA/c m 2 ] poly-Si t hicknes s [ nm] Std. Re cipe (p lan) Std. Re cipe (te x ) Results Metal recombination ❑ Outstanding J0,metal ~ 300 fA/cm2 for 250 nm p+ poly-Si on textured surface ❑ Lower J0,metal values on planar samples – but it comes with poor contact resistivity 14SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Results: SEM images Top view - after 1st metal etch (planar surface, 250 nm poly-Si) (A) Recipe 1 | ρc= 8 mΩ-cm2 (B) Recipe 2 | ρc = 20 mΩ-cm2 ❑ Metal crystallites fraction vary with different recipes ❑ Lower metal crystallites in poly-Si samples with shallow emitter (B) A B 3µm 3µm 15SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Results SEM images – Top view - Etch pits (textured surface) ❑ Almost complete removal for thinner poly-Si with FT paste – high J0,metal ❑ Partial removal of poly-Si with FT paste – lower J0,metal 50 nm poly-Si 250 nm poly-Si 1µm 50 nm poly-Si 1µm 250 nm poly-Si 1µm 1µm 16SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Conclusion ❑ It is possible to dope poly-Si (BBr3,ex-situ) at lower temperatures (900°C) ❑ Lower temperature & optimized profile is required for better passivation with LPCVD based poly-Si ❑ Excellent passivation properties on both planar and textured surfaces ➢ J0 / iVoc = 4.5 fA/cm2 / 740 mV (planar), ➢ J0 / iVoc = 19 fA/cm2 / 704 mV (textured) ❑ J0,metal ~ 300 fA/cm2 (Tex)/120 fA/cm2 (Plan) for thick poly-Si layers with FT Ag-Al paste ❑ Retention of thick poly-Si (p+) layer under FT metal contacts, lower J0,metal 17SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). Conclusion Relevant state-of-the-art properties of p+ poly-Si [01] Mack et al, PSSRRL, 2019 [02] Morisset et al, SolMat,2019 [03] Ingenito et al, Nat.Energy, 2018 [04] Mewe et al, proc. AIP conf., 2018 [05] Ok et al, AIP letters, 2018 [06] Stodolny et al, proc. EUPVSEC,2018 [07] Liu et al., SolMat,2018 [08] Ciftpinar et al, Proc. SiliconPV, 2017 [09] Mack et al, PSSRRL, 2017 [10] Larionova et al, PSS, 2017 [11] Wu et al, Proc. SiliconPV, 2016 [12] Romer et al, SolMat, 2014 0 10 20 30 40 50 60 670 680 690 700 710 720 730 740 pla nar ( Lit) tex tured (Lit) pla nar ( SE RIS) tex tured (SER IS) iV oc [mv] J 0 [fA/ cm 2 ] 0 2 4 6 8 10 12 14 200 400 600 800 1000 Lite ra tur e SER IS J 0,meta l [f A/cm 2 ]  conta ct [m − cm 2 ] 18SERIS is a research institute at the National University of Singapore (NUS). SERIS is supported by the National University ofSingapore (NUS), National Research Foundation Singapore (NRF) and the Singapore Economic Development Board (EDB). 19SERIS is a research institute at the National University of Singapore (NUS). 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