xsi PV Technologies: Status and Outlook of Passivated Contacts and Rear Contacted Solar Cells

Transcription

1 xsi PV Technologies: Status and Outlook of Passivated Contacts and Rear Contacted Solar Cells Thematic session 4 Bart Macco, Jimmy Melskens, Bas van de Loo, Lachlan Black, Willem-Jan Berghuis & Erwin Kessels 1

2 Status and Outlook of Passivating Contacts Passivating contacts: Why and what? Requirements for passivating contacts Current status of various contacts Passivating contacts in TKI projects Outlook & Future trends 2 2

3 54% 52% 50% 49% 48% 49% 49% 50% 50% 48% 48% 48% 50% 48% 48% Average price ( /Wp) 61% 60% 62% 63% 61% 60% 56% 54% 56% 46% 48% 50% 51% 52% 51% 51% 50% 50% 52% 52% 52% 50% 52% 52% 63% 64% 67% 39% 40% 38% 37% 39% 40% 44% 46% 44% 69% 70% 71% 70% 70% 72% 74% 71% 72% 73% 74% 72% 37% 36% 28% 33% 31% 30% 29% 30% 30% 28% 26% 29% 28% 27% 26% Why passivating contacts? 5 4 Balance of system (BOS) (Inverter, cabling, labor,...) Module Year Balance of system is becoming dominant in PV system cost, strong driver to increase low complexity Source: Fraunhofer report,

4 Why passivating contacts? SiN x From Al-BSF towards higher efficiencies: c-si(p) Al-BSF n + Si Al-BSF Al SiN x SiN x TCOs: In 2 O 3 :H, IZO c-si(p) Al 2 O 3 /SiN x n + Si Local BSF SiO 2 /SiN x p + n + Si n + p + n + p + c-si(n) a-si:h (i/p) a-si:h (i/n) Al PERC Trina, Hanwha Q-Cells, Interdigitated back contact Sunpower, TCOs: doped ZnO Si heterojunction Panasonic, Kaneka, Tesla, 4 4

5 The passivating contact cell A simple concept: Just depositing stacks of thin films on silicon c-si(n or p) Hole contact (Stack of) thin films c-si Electron contact SiO x TiO x Many new materials: Doped poly-si, metal oxides, metal fluoriudes, organics, 5 5

6 Cell efficiency (%) Why passivating contacts? Steady increase of conventional technologies % UNSW PERL (1998) IBC 20 a-si:h (HIT) PERC n-pert Homojunctions: Interdigitated Back Contact (IBC) PERC (monocrystalline) n-pert Heterojunctions: a-si:h Year Source: PhD thesis Bart Macco,

7 Cell efficiency (%) Why passivating contacts? Steady increase of conventional technologies Rapid increase new contacts: Doped poly-si Already at 25.7%! % UNSW PERL (1998) IBC poly-si 20 a-si:h (HIT) PERC n-pert Homojunctions: Interdigitated Back Contact (IBC) PERC (monocrystalline) n-pert Heterojunctions: a-si:h poly-si Year Source: PhD thesis Bart Macco,

8 Cell efficiency (%) Why passivating contacts? Steady increase of conventional technologies Rapid increase new contacts: Doped poly-si Already at 25.7%! Novel materials, >22% MoO x, TiO 2, PEDOT, fluorides, % UNSW PERL (1998) IBC poly-si a-si:h (HIT) PERC n-pert MoO x Homojunctions: Interdigitated Back Contact (IBC) PERC (monocrystalline) n-pert Heterojunctions: a-si:h poly-si PEDOT-based contacts MoO x -based contacts TiO x -based contacts TiO x Year PEDOT Source: PhD thesis Bart Macco,

9 Why passivating contacts? High voltages (~750 mv) Fully passivated surfaces No highly-doped region Auger Full area contacts No patterning steps 1-D transport high FF Bifacial c-si(n or p) Hole contact Electron contact Source: PhD thesis Bart Macco,

10 What is a passivating contact? Back to basics for a second Light absorber c-si Electron membrane n-type Si a-si:h(n) poly-si(n) TiO 2,. Metal 10 10

11 What is a passivating contact? Light absorber c-si Electron membrane n-type Si a-si:h(n) poly-si(n) TiO 2,. Metal 11 11

12 What is a passivating contact? I. Interface passivation characterized by J 0 Light absorber c-si Electron membrane Metal 12 12

13 What is a passivating contact? I. Interface passivation characterized by J 0 II. Good e-conductivity characterized by ρ c Low R n Light absorber c-si Electron membrane Metal 13 13

14 What is a passivating contact? I. Interface passivation characterized by J 0 II. Good e-conductivity characterized by ρ c Low R n High R p Light absorber c-si Electron membrane III. Poor h-conductivity otherwise increase in J 0 Metal 14 14

15 Requirements of a passivating contact Stack of thin films Majority carrier extraction Low ρ c Well-passivated, selective layer Low J 0 c-si(n or p) Requirements: 1. Low recombination current J 0 2. Low contact resistance ρ c 16 16

16 Requirements of a passivating contact Lateral conductivity, R sheet Stack of thin films c-si(n or p) Requirements: 1. Low recombination current J 0 2. Low contact resistance ρ c 3. Lateral conductivity, R sheet 17 17

17 Requirements of a passivating contact Transparent front side Stack of thin films c-si(n or p) Requirements: 1. Low recombination current J 0 2. Low contact resistance ρ c 3. Lateral conductivity, R sheet 4. Transparency 5. Manufacturability Goal: To develop materials & processes to fulfill these 5 requirements Where are we now? 18 18

18 Current status of various contacts Recombination current J 0 and contact resistivity ρ c Kaneka a-si:h HIT 25.1% ANU TiO % IMEC npert 22.8% F-ISE Poly-Si 25.7% ISFH PEDOT 20.6% UNSW PERL 25.0% pperc 20.7% ECN n-pasha 21.0% ANU MoO x a-si:h - Excellent J 0 & ρ c Poly-Si - Excellent J 0 & ρ c TiO 2 - Good J 0 & reasonable ρ c MoO x - Reasonable J 0 & excellent ρ c - Often use a-si:h passivation layer B. Macco, B.W.H. van de Loo, W.M.M. Kessels, Atomic Layer Deposition for High Efficiency Crystalline Silicon Solar Cells, Wiley,

19 Absorption coefficient (10 4 cm -1 ) Photon flux (ma/m 2 /ev) Maximum J sc (ma/cm 2 ) Current status of various contacts Transparency AM 1.5g solar spectrum TiO a-si:h poly-si TiO 2 MoO x Photon energy (ev) MoO x 42 poly-si a-si:h 39 = typical minimal thickness Layer thickness d (nm) Metal oxides highly transparent Poly-Si data: Feldmann et al., SOLMAT 159, (2017) 20 20

20 Current status of various contacts Exploring new materials Requirement a-si:h (HIT) Poly-Si TiO 2 MoO x J ALD ZnO:Al, Nb 2 O 5, AlF, novel tunnel oxides ρ c Transparency R sheet Improving existing materials poly-sio x, poly-sic x, TiO 2 :Nb Note: Putting pluses and minuses can be subjective 21 21

21 COMPASS: The moly-poly cell Transparent front contact: MoO x hole contact High mobility TCOs Ag NW meshes n-poly rear Exploring PLD 22 22

22 Miracle: Si(n + ) or ALD TiO x front electron-contact Poly-Si (p) rear hole-contact 23 23

23 RADAR: Materials for bifacial pass-con cell WP 3 Cell and module integration, metallization ECN, TUD, Levitech, Solmates, AMOLF Industrial and economic assessment Levitech, Solmates, ECN WP 4 WP 1 Doped metal oxides ALD: TU/e, Levitech PLD: Solmates PVD: TUD WP Supporting layers 1&2 Transparent conductors Interface layers Capping & stability ALD: TU/e, Levitech PLD: Solmates Sputtering: TUD Transparent poly-sio x /SiC x PECVD: TUD WP 2 LPCVD: TUD Interface characterization Passivation: TU/e, TUD Contact resistance: TU/e, TUD Fixed charge: DST Wafer preparation: ECN WP 1,2 & 3 Develop novel material (combinations) that combine excellent selectivity, transparency & conductivity 24 24

24 Future trends Si passivating contact cells & perovskites are very alike Same nanomaterials in use! MoO x, TiO x,. Hole-selective contacts Electron-selective contacts Transparent conductors 25 25

25 Future trends Passivating contact Si cell + perovskite tandem! UV/VIS tuned perovskite with high IR transparency IR tuned Si cell Efficiency potential of ~30% 26 26

26 Outlook The Netherlands: A great eco-system for the ultimate passivating contact cell Material innovations Cell implementation c-si(n or p) Equipment manufacturers Efficient, lean processing, bifacial & NL-inside 27 27

27 Thank you for your attention! 28 28

28 Hierna extra slides 29 29

29 RADAR: Materials for bifacial passcon Among others: TU Eindhoven: Dope ALD TiO 2 with Nb Increase conductivity, reduce ρ c TiO 2 Nb TU Delft: Alloying poly-si with oxygen and/or carbon to enhance transparency 30 30

30 Opportunities for passivating contacts Novel materials Advanced materials Alloys, doping, ultrathin tunneloxides 31 31

31 Opportunities for passivating contacts Novel materials Advanced materials Alloys, doping, ultrathin tunneloxides Deposition techniques ALD, PLD Soft deposition! Manufacturers in NL! 32 32

32 How to make a passivating contact? How to achieve asymmetry in electron-hole conduction 33 33

33 How to make a passivating contact? How to achieve asymmetry in electron-hole conduction 34 34

34 35 35

35 Maximum J sc (ma/cm 2 ) TiO 2 MoO x poly-si 40 a-si:h 39 = typical minimal thickness Layer thickness d (nm) 36 36

36 Absorption coefficient (10 4 cm -1 ) Photon flux (ma/m 2 /ev) 10 AM 1.5g solar spectrum 40 8 ITO free carrier absorption In 2 O 3 :H Photon energy (ev) 37 37

37 Kaneka classical SHJ 25.1% ANU TiO % IMEC npert 22.8% F-ISE TOPCon 25.7% ISFH PEDOT 20.6% NREL SiO 2 /ITO UNSW PERL 25.0% pperc 20.7% ECN n-pasha 21.0% ANU MoO x 38 38