METALLIZATION MATERIAL QUALIFICATION IN TERMS OF DAMP HEAT INDUCED DEGRADATION (DHID)

Transcription

1 METALLIZATION MATERIAL QUALIFICATION IN TERMS OF DAMP HEAT INDUCED DEGRADATION (DHID) I. Dürr, S. Hoffmann, A. Kraft, J. Bartsch, Ch. Schmiga, D. Eberlein, U. Eitner, K.-A. Weiß, H. Wirth Fraunhofer Institute for Solar Energy Systems ISE Metallization Workshop Constance, October 21 th

2 AGENDA Introduction What is known so far? Experimental set-up Results Summary and conclusion 2

3 Introduction 3

4 Damp Heat induced degradation (DHID) What is DHID, when does it occur, how is it detectable? Power loss of c-si PV modules induced by degradation reaction between front metallization, encapsulation and moisture For Ag(Pb) metallization DHID commonly observed > 1700 h of DH testing Visible in electroluminescence (EL) image as blackening of image coming from corner and edges of cell EL EL after 2500 h DH 4

5 Looking in the future or the present? New encapsulation materials Ethylene vinyl acetate with lower VA content Reduced acetic acid formation? Innovative material, e.g. polyolefin encapsulation Cross-linked vs. thermoplastic material? What functional groups? Degradation by-products in terms of DHID? New metallization materials Ag paste with lead-free glass Plated metallization 5

6 What do we know so far? 6

7 Damp Heat testing at different temperatures P MPP, normalized 1,1 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 normalized power manufacturer H4 75 C / 85% rh 85 C / 85% rh 90 C / 85% rh 7 0, Kinetics of the DHID process time in h Results from long-term testing of one manufacturers PV modules Sigmoidal behavior of power losses for all three temperatures

8 How does acetic acid play a role? Hydrolysis of EVA Reaction of moisture with vinyl acetate functional side chain Reaction products most likely ethylene vinyl alcohol and acetic acid Diffusion coefficients (D) Very small D of acetic acid within EVA Out-diffusion is limited and time consumable Weber, U. et al.: Acetic Acid Production, Migration and Corrosion Effects in Ethylene-Vinyl-Acetate- (EVA-) Based PV Modules, 27th European Photovoltaic Solar Energy Conference and Exhibition (2012), S

9 EDX investigation on degradation products DHID effect of EVA/Si-Ag(Pb) modules Needle shaped crystallites visible on aged grid-finger EDX results indicate needles consists of lead acetate Pb(CH 3 COO) 2 * OK grid, position (1) grid, position (2) 2 1 counts CK NaK ZnL SiK PK PbM AgL (1) Needles (2) Normal grid 9 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 energy in kv *Peike, C. et al.: Origin of damp-heat induced cell degradation, Sol. Energ. Mat. Sol. Cells 116 (2013), S REM image (9000x) und EDX with 5 kev

10 Validation of lead acetate formation Validation of lead acetate as degradation product using water solubility Water extraction of cell fragments Filtration and drying of filtrate resulted in a powder (white/transparent) X-ray measurements showed: the obtained powder consists of elements Pb, C and O: Pb(CH 3 COO) 2 * 10 *Dürr, I. et al.: X-ray study of Damp-Heat Induced Cell degradation (DHID), 28 th EUPVSEC Paris 2013

11 The experimental set-up 11

12 Construction of modules Processing and manufacturing Materials: Mono c-si precursor cells SnPbAg cell interconnectors Tempered, white glass (200 x 200 mm²/3,2 mm) TPT back sheet material (ICOSOLAR 2442) Soldering manually Standard lamination process 12

13 What materials and set-ups were used? The materials Pb- or Bi-glass in Ag paste, screen printed Ag(Pb) paste with plated layer on top (Ag or Ni/Cu) Direct plated Ni/Cu/Ag metallization Ethylene vinyl acetate EVA (standard) Polyolefin elastomer POE (cross-linked) The set-ups Standard DH testing set-up (85 C/85% RH.) Biased sample DH testing set-up A and 85 C/85% RH.)* 13 *Kraft, A. et al.: Microstructure Analysis of the Interaction between Watts-Type Nickel Electrolyte and Sreen Printed Solar Cell Contacts, J Sol. State Sc. Techn., 3, (4 ) (2014) Q55-Q60

14 Results 14

15 Ag(Bi) metallization Problems with electrical contact formation Exemplary EL image () of module with Ag(Bi) metallization and EVA encapsulation Therefore no comparison between Ag(Pb) and Ag(Bi) possible in terms of EL images 15

16 EVA vs. POE Screen printed Ag(Pb) No DHID for Ag(Pb) observable with POE encapsulation after 1750 h DH With EVA encapsulation DHID slightly visible in EL image after 1750 h DH EVA 1750 h POE 1750 h 16

17 EVA vs. POE Ag(Pb)/Ag Screen printed bottom contact Ag(Pb) and Ag capping (plated) Both encapsulants trigger degradation induced during 1750 h DH testing EVA 1750 h POE 1750 h 17

18 Investigation on Ag(Pb)/Ag with EVA SEM investigations on reference cell and extracted aged cell SEM images of reference cell, stored under inert gas SEM images of extracted cell part after 1750 h DH testing Grid: dense surface DH aged grid: pitted surface Reference Extracted cell part after DH testing 18

19 Investigation on Ag(Pb)/Ag with EVA EDX investigation on pitted surface and reference sample Aged grid hole : C, N, O and Na detectable (pos. 1) Aged grid surface : Ag and C detectable (pos. 2) Reference grid: Ag and C detectable (pos. 3) SEM image DH aged grid CK DH aged grid, position 1 DH aged grid, position 2 reference grid, position counts 3000 SEM image reference grid OK NaK AgL NK AgL AgL AgL 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 energy in kev 19 3

20 Investigation on Ag(Pb)/Ag with EVA Raman investigation on pitted surface Raman measurement: WITEC confocal microscope with 532 nm laser Detection of Ag 2 CO 3 and AgNO 3 phase on 1750 h DH aged cell part 5000 NO h DH aged Ag(Pb)/Ag grid 4000 NO - 3 intensity in a.u CO 2-3 NO - 3 CO 2-3 CO 2-3 CO 2-3 CO 1000 wavenumber in cm

21 EVA vs. POE Ag(Pb)/Ni/Cu Screen printed bottom contact Ag(Pb) and Ni/Cu capping (plated) Both encapsulants trigger degradation induced during 1750 h DH testing EVA 1750 h POE 1750 h 21

22 Comparison of Ag(Pb)/Ni/Cu with EVA or POE Microscope images/raman results Ag(Pb)/Ni/Cu: reaction with EVA and POE after 1750 h DH testing visible Raman investigation showed existence of CuO (EVA) and CuO/Cu 2 O (POE) EVA POE 22

23 EVA vs. POE Direct plated Ni/Cu/Ag No degradation visible in EL image after 1750 h DH testing with EVA No degradation visible in EL image after 1750 h DH testing with POE EVA 1750 h POE 1750 h 23

24 Fast, faster,? Biased vs. standard : Ag(Pb) Biased sample set-up: 8A and DH condition No acceleration of DHID for Ag(Pb) metallization for biased sample compared to standard testing after 1500 h testing biased standard 1500 h 1500 h 24

25 Fast, faster,? Biased vs. standard : Ag(Pb)/Ag Biased sample set-up: 8A and DH condition DHID of Ag(Pb)/Ag metallization accelerated due to biased DH after 1500 h testing biased standard 1500 h 1500 h 25

26 Fast, faster,? Biased vs. standard : Ag(Pb)/Ni/Cu Biased sample set-up: 8A and DH condition No acceleration of DHID for Ag(Pb)/Ni/Cu metallization for biased sample compared to standard testing after 1500 h testing biased standard 1500 h 1500 h 26

27 Fast, faster,? Biased vs. standard : Ni/Cu/Ag Biased sample set-up: 8A and DH condition No acceleration of DHID for Ni/Cu/Ag metallization for biased sample compared to standard testing after 1500 h testing biased standard 1500 h 1500 h 27

28 Results with a little twinkle Bad contacts?! Biased DH testing (@8 A and 85 C/85% RH.) of screen printed Ag-paste metallization with Bi-glass Most probably decreasing contact resistance between metallization and cell biased 500 h 1000 h 28

29 Results with a little twinkle Bad contacts?! Biased DH testing (@8 A and 85 C/85% RH.) of screen printed Ag-paste metallization with Bi-glass Most probably decreasing contact resistance between metallization and cell biased 500 h 1000 h? xxxx h standard 29

30 Summary and conclusion Biased set-up accelerated DHID only in terms of Ag(Pb)/Ag metallization Why is this so? Biased cell vs. module testing EVA vs. POE: For Ag(Pb) metallization no DHID with POE visible (1750 h DH), next: looking for other degradation pattern in next time frames For Ag(Pb) with capping for both encapsulation materials degradation detectable Process-induced degradation (electrolyte, ph) or DHID? What happened chemically at the interface Ag(Pb) / cell? After enhancing electrical contacts for Ag(Bi) metallization during biased DH testing (< 1000 h), next: looking for degradation in next time frames 30

31 Special thanks to J. Metzger, N. Mahmoud, K. Krüger, G. Cimiotti, J. Zielonka & E. Schäffer Fraunhofer Institute for Solar Energy Systems ISE Ines Dürr 31

32 Thank you for your attention! Fraunhofer Institute for Solar Energy Systems ISE Ines Dürr 32