Impact of selective BSF on performance of bifacial npert cells with Ni/Ag co-plated contacts

Transcription

1 Impact of selective BSF on performance of bifacial npert cells with co-plated contacts Metallization Workshop, Konstanz, October 23-24, 2017 Loic Tous, Richard Russell, Emanuele Cornagliotti, Arvid van der Heide, Filip Duerinckx, and Jozef Szlufcik 1

2 Introduction: imec s bifacial npert with co-plating ARC SWCT TM Approach [see ref. 1-3]: bifacial npert cell design (high efficiency, high bifaciality) co-plated fingers (no busbars) designed for SWCT first bifacial single cell laminates shown to pass TC200 and DH1000 n-cz p + emitter n + BSF ARC Key features of co-plating: n & p surfaces are co-plated simultaneously batch process, compatible with >6000wph <10mg Ag required per cell (with SWCT) Silicon selective surface activation: After plating: References: [1] E. Cornagliotti et al, Proceedings of the 32 nd EUPVSEC, pages [2] L. Tous et al, Energy Procedia, Volume 124, Sep 2017, pages [3] R. Russell et al, Proceedings of the 33 rd EUPVSEC, 2BP.1.3 2

3 Motivation: Evaluate impact of selective BSF on performance of npert cells with contacts Al 2 O 3 /SiO x /SiN x n-cz p + emitter n + BSF Homogeneous or selective BSF? SiO x /SiN x 3

4 cell processing & results

5 npert with homogeneous BSF cell processing M2, n-cz, 180µm, 5Ω.cm batch SDR/texturing/cleaning BBr 3 p + diffusion (~120 Ω/sq) inline emitter removal PECVD diffusion mask POCl 3 n + diffusion (~50 Ω/sq) homo. n + etch-back to ~100 Ω/sq n + passivation = PECVD SiNx p + emitter: final Rsheet ~120 Ω/sq J 0p+,pass ~25 fa/cm 2 n-cz Al 2 O 3 /SiO x /SiN x p + emitter n + BSF p + passivation = ALD AL 2 O 3 + PECVD SiO x /SiN x n + laser ablation p + laser ablation + firing Homogeneous n + BSF: final Rsheet ~100 Ω/sq J 0n+,pass ~84 fa/cm 2 SiN x NiAg co-plating + sintering 5

6 npert with homogeneous BSF experimental J 0laser and J 0metal results test wafer with various contact fractions: Calc. V oc ~657mV QSSPC coil J 0,n+pass = 83 fa/cm 2 J 0,n+,metal = 9852 fa/cm 2 Calc. V oc ~668mV J 0,n+,laser = 2970 fa/cm 2 SiN x n-cz n + BSF J 0,ttttt = f J 0,ccccccc,fffff + 1 f J 0,pppp,fffff + J 0,pppp,rrrr = f (J 0,ccccccc,fffff J 0,pppp,fffff ) + 2 J 0,pppp QSSPC coil SiN x J 0total extraction from Sinton QSSPC (transient mode) npert cells with homogeneous BSF limited by n + metal recombination 6

7 npert with homogeneous BSF experimental light I-V results Gridtouch TM 5 Ωcm, 180 µm front STC (1000W/m 2, 25ºC) I-V data measured with lowly-reflective (black) Gridtouch comment npert with homogeneous BSF n-cz Al 2 O 3 /SiO x /SiN x p + emitter n + BSF cell area j sc V oc FF eta r s pff # cells meas. [cm 2 ] [ma/cm 2 ] [mv] [%] [%] [Ω.cm 2 ] [%] average STDEV SiN x Observations: average cell efficiency = 20.7±0.4 % limited by V oc = 652±6 mv due to recombination at n + BSF average pff = 82.5±0.6% limited by non-ideal recombination at n + BSF 7

8 npert with selective BSF cell processing compared to homogeneous BSF M2, n-cz, 180µm, 5Ω.cm M0, n-cz, 180µm, 5Ω.cm batch SDR/texturing/cleaning BBr 3 p + diffusion (~120 Ω/sq) inline emitter removal PECVD diffusion mask p + emitter: final Rsheet ~120 Ω/sq J 0p+,pass ~27 fa/cm 2 Al 2 O 3 /SiO x /SiN x POCl 3 n + diffusion (~50 Ω/sq) POCl 3 n + diffusion (~200 Ω/sq) homo. n + etch-back to ~100 Ω/sq dry oxidation n + passivation = PECVD SiNx n-cz p + emitter n + BSF n ++ BSF p + passivation = ALD AL 2 O 3 + PECVD SiO x /SiN x n + laser ablation n + laser doping (spin-on-dopant) p + laser ablation + firing NiAg plating + sintering selective n + BSF: final Rsheet ~350 Ω/sq J 0n+,pass ~6 fa/cm 2 SiO 2 /SiN x npert with homogeneous BSF npert with selective BSF References for laser doping from spin-on-dopant: [4] B. Hallam et al, Solar energy materials and solar cells. 2015;134: [5] A. Uruena et al, Progress in PV: Research & Applications. 2016; 24(8):

9 npert with selective BSF experimental J 0laser and J 0metal results comparison Calc. V oc ~657mV Calc. V oc ~668mV switch to npert with selective BSF drastic reduction of n + recombination thanks to: J 0n+pass ~ 6 fa/cm 2 J 0n++,contact ~ 2000 fa/cm 2 Calc. V oc ~689mV Calc. V oc ~681mV Al 2 O 3 /SiO x /SiN x Al 2 O 3 /SiO x /SiN x n-cz p + emitter n + BSF n-cz n ++ BSF p + emitter n + BSF SiN x SiO 2 /SiN x 9

10 npert with selective BSF comparison of experimental light I-V results npert with homo. BSF Al 2 O 3 /SiO x /SiN x n-cz p + emitter n + BSF n-cz npert with selective BSF Al 2 O 3 /SiO x /SiN x p + emitter n ++ BSF n + BSF Gridtouch TM SiN x SiO 2 /SiN x front STC (1000W/m 2, 25ºC) I-V data measured with lowly-reflective (black) Gridtouch comment npert with homogeneous BSF cell area j sc V oc FF eta r s pff # cells meas. [cm 2 ] [ma/cm 2 ] [mv] [%] [%] [Ω.cm 2 ] [%] average STDEV npert with selective BSF average STDEV Observations: Selective BSF improves average V oc to 682±3 mv (in line with monitor wafers) and j sc to 40.4±0.1 ma/cm 2 Selective BSF reduces non-ideal recombination thereby improving pff values With selective BSF, average cell efficiency improves to 22.0±0.2 % 10

11 9-cells laminate results

12 Average 9-cells bifacial laminates results first trial (no optimization yet) 9-cells laminates making at imec: glass-glass (2x 3mm), no ARC 9-cells string, 18x300 µm SWCT foils encapsulant with Laminate front STC measured with rear black cover & I sc V oc FF Pmpp type of cells measurement average [A] [V] [] [W] 9 cells (Gridtouch TM ) 118 cells ±0.0 M2 npert 9-cells laminate front STC 7 laminates ±0.8 homogenous BSF cell-to-module (CTM) ratio M0 npert selective BSF 9 cells (Gridtouch TM ) 37 cells ±0.5 9-cells laminate front STC 2 laminates ±0.4 cell-to-module (CTM) ratio Poor CTM ratio of ~0.90 due to: I sc losses caused by : (1) no ARC glass, (2), UV cut-off, (3) SWCT shading (Gridtouch TM removes wire shading) FF losses caused by: (1) resistive losses in wires, (2) resistive losses in fingers (Gridtouch TM = 30 wires vs 18 SWCT), (3) cell mismatch further optimization required to improve CTM ratio 12

13 Best 9-cells bifacial laminate result first trial (no optimization yet) over-compensation method: Laminate front STC measured with rear black cover & BiFi10 and BiFi20 measured with over-compensation method type of cells M0 npert selective BSF Observations: calc. 60cells Irradiance I sc V oc FF P mpp measurement P mpp [W/m 2 ] [A] [V] [] [W] [W] front STC bifaciality 98.7% 100.1% 100.0% 98.8% 98.8% BiFi BiFi excellent Pmpp bifaciality of 98.8% (but having no front ARC glass helps) BiFi10 and BiFi20 values clearly show potential of bifacial npert with SWCT 13

14 Outlook

15 Roadmap bifacial npert NiAg + SWCT glass-glass laminate 60 cells front STC >340Wp appears feasible M4 cells (I sc +1.5%) M0 cells thin NiAg no ARC glass M2 cells (I sc +2.2%) thick NiAg (FF +3%) ARC glass (I sc +3.0%) reduced UV cut-off (Isc +2%) half-cells (FF +1.5%) Additional improvements possible as shown in references: [6] M. H. Saw et al, Energy Procedia 124 (2017) [7] M. Mrcarica et al. BiFi Workshop, Sep 2016, Miyazaki Japan. 15

16 Conclusions

17 Summary and conclusions Selective BSF in bifacial npert cells shown to result in: drastic reductions in both J 0n+,pass and J 0n+,metal average V oc of 682±3 mv (vs 652±6 mv with homo. BSF) average pff of 83.3±0.8 % (vs 82.5±0.6 % with homo. BSF) average cell efficiency of 22.0±0.2 % (vs 20.7±0.4 % with homo. BSF) First 9-cells bifacial glass-glass SWCT laminates made at imec. Based on own roadmap, 60 cells front STC >340Wp appears feasible 17

18 The authors gratefully acknowledge: the financial support of imec s industrial affiliation program for Si PV Alberto Pozza (Soltech) for the laminate measurements Yu Yao (Meyer Burger) for providing SWCT foils and valuable discussions This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg. 18

19 Annex slides

20 Lifetime evaluation n-cz Similar lifetimes for M0 and M2 wafers SDR POCl 3 diffusion (field effect) Dry oxidation (950 0 C) FGA (H 2 passivation) Lifetime (τ eff ) n-cz wafer type final wafer resistivity [Ω.cm] Average 1e15cm -3 [ms] 1e16cm -3 [fa/cm 2 ] Imec M ± Imec M ±

21 Estimated 72cells module level costs compared ($ct/wp) NiAg npert+ ~3% lower $/Wp than SP pperc+ Pmax & metallization cost advantage of NiAg npert+ reduced by increased module costs 33 rd EUPVSEC 2BP

22 Costs Compared for 3 cell types: SWCT= Smart Wire Connection Technology Show estimates for Cell metallization costs ($/cell) Module level cost ($/Wp) System level LCOE ($/kwh) 33 rd EUPVSEC 2BP

23 Estimated metallization costs ($/cell) Processes compared Screen-print (SP) 4500 wfr/hr 6000 wfr/hr Screen print front Dry Screen print rear Dry Fast-firing Test/sort Laser ablate front Laser dope rear Fast-firing anneal plating N 2 anneal Test/sort Estimate ~ 40% cheaper/cell than fine line 60mg Ag (metallization for smart wires no bus bars) 33 rd EUPVSEC 2BP

24