Future of high efficiency solar cells: low cost mono crystalline n-type Si devices

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1 Future of high efficiency solar cells: low cost mono crystalline n-type Si devices Valentin Mihailetchi, Andreas Halm, Razvan Roescu, Guiseppe Galbiati, Alexander Edler, Kristian Peter, Radovan Kopecek International Solar Energy Research Center Konstanz

2 content ISC Konstanz location, facts, research c-si solar cell history beginning n-type c-si solar cells present market n-type solar cells at ISC future market?

3 International Solar Energy Research Center Konstanz, e.v.

4 location within Germany solar cell manufacturers universities institutes

5 solar city Konstanz Konstanz

6 our sponsors and members Alice Wartemann-Stiftung, CH Prof. Dr. Ernst Bucher

7 our team 42 employees + 10 part time 5 directors, 15 scientists, 8 PhD students, 9 technicians, 5 administration international team: every 3rd from abroad

8 our goals research and development mc-si: >17% Cz-Si: >19% training and education 8 PhD students 2 Master students 5 Practice students development collaboration Cameroon: 4 projects India: 2 projects Guatemala, Tanzania

9 our partners AMERICA 1 Day4Energy, CA 2 Dow Corning, US 3 6Nsilicon, CA 4 University of Toronto, CA 5 Cali Solar, US 6 University of Santiago de Chile, CL 6 EUROPE 7 Isofotón, ES 8 Uni Valencia, ES 9 INES, FR 10 RENA, DE 11 centrotherm, DE 12 sunways, DE 13 PV Silicon, DE 14 BOSCH,DE 15 MP&L, DE 16 BASF, DE 17 GPsolar, DE 18 neonsee, DE 19 ipe Stuttgart, DE 20 Sefar, CH 21 Air Liquide, FR 22 ECN, NL 23 ELKEM Solar, NO 24 NTNU, NO 25 SINTEF, NO Polymer Kompositer, SE 27 Monocrystal, RU 28 semilab, HU 29 solartec, CZ 30 SilFab, IT 31 Baccini (Applied Materials), IT 32 N.M.B. Medical Applications Ltd., IL 33 B-solar, IL AUSTRALIA 33 UNSW, AU 34 Spark Solar, AU 34 33

10 our development work D F E A C B DEVELOPMENT AID A Cameroon (SLAK) B India (SUNI) C Tansania D Nepal E French Guyana F Guatemala 2012-

11 creating of solar villages and solar schools in Cameroon

12 pure water supply with solar for schools and hospitals

13 history of c-si solar cells

30 historic efficiency development (total area) efficiency (%) 25 20 15 10 5 best laboratory cells (schematic)

14 30 historic efficiency development (total area) efficiency (%) best laboratory cells (schematic) commercial modules (typical best, total area) year

15 historic efficiency development first cell: n-type n c-si c IBC cell

16 solar cell market till 2009 solar cells with total power of 12.3 GWp in 2009 (56% ) 83% still based on c-si solar cell production (89% on Si) no change expected within next years further increase of mono c-si share predicted financial crisis Si feedstock crisis source: Photon (4/2010)

17 future for c-si solar cells (ISC Konstanz) 17% on 156x156mm 2 mc-si (p-type SoG) 19% on 156x156mm 2 mono c-si (n-type poly-si)

18 why n-type mono c-si cells? material related advantages: lack of B-O B O pairs (no degradation) reduced SRH recombination in low purity c-sic D. Macdonald and L.J. Geerligs; APL 85, 4061 (2004) more tolerant to high temperature processing solar cell related advantages: bifacial process is suitable for thin wafers better performance at low light intensities C. Gong et al.; 23rd EUPVSEC 2008 G.E. Bunea et al.; IEEE 2006

19 commercial fabrication of (n-type) solar cells HIT solar cells (Sanyo) front, emitter: a-si a (p) back, BSF: a-si a (n) bifacial η 23%

20 commercial fabrication of (n-type) solar cells HIT solar cells (Sanyo) front, emitter: a-si a (p) back, BSF: a-si a (n) bifacial η 23% IBC solar cells (Sunpower( Sunpower) FSF/BSF: n + /n ++ diffusion emitter: p + diffusion η 24.2%

21 commercial fabrication of (n-type) solar cells HIT solar cells (Sanyo) front, emitter: a-si (p) back, BSF: a-si (n) bifacial η 23% IBC solar cells (Sunpower) FSF/BSF: n+/n++ diffusion emitter: p+ diffusion η 24.2% standard solar cells (Yingli) front, emitter: p+ diffusion back, BSF: n+ diffusion bifacial η 19%

22 n-type cells at ISC KN

23 schematic cross section H-pattern contact grid on front and back (bifacial) screen-printed and firing-through metallization

24 standard (industrial) n-type cell process Our solar cell process comprises of: front contacts; screen printing passivating layer/sin x ; ARC p + diffusion; 60 Ω/, BBr 3 tube n-type Si; mm 2 Cz from Bosch Solar Energy AG n + diffusion; 30 Ω/, POCl 3 tube SiN x passivation rear contacts; screen printing + damage etch/texturization texturization and standard cleaning

25 results: solar cells Solar cells results under standard test conditions material Cz (8 Ωcm) area [ cm 2 ] 241* J SC [ ma/cm 2 ] 38.3* * values measured by ISE CalLab. illumination V OC [ mv ] 637* IQE [%] Implied V OC [ mv ] 664 FF 76.5* pseudo-ff 82.5 Best cell: front illumination Best bifacial cell: front illumination back illumination η 18.6* Wavelength [µm]

26 results: solar cells Solar cells results under standard test conditions material Cz (8 Ωcm) area [ cm 2 ] 241* J SC [ ma/cm 2 ] 38.3* * values measured by ISE CalLab. illumination V OC [ mv ] 637* IQE [%] Implied V OC [ mv ] 664 FF 76.5* pseudo-ff 82.5 Best cell: front illumination Best bifacial cell: front illumination back illumination η 18.6* Wavelength [µm]

27 results: solar cells Solar cells results under standard test conditions material Cz (8 Ωcm) area [ cm 2 ] 241* J SC [ ma/cm 2 ] 38.3* * values measured by ISE CalLab. illumination V OC [ mv ] 637* IQE [%] Implied V OC [ mv ] 664 FF 76.5* pseudo-ff 82.5 Best cell: front illumination Best bifacial cell: front illumination back illumination η 18.6* Wavelength [µm]

OC [ mv ] FF pseudo-ff η screen printed 241 37.9 632 656±6 77.6 82.

28 results: solar cells Further work: towards more than 19% metallization area [ cm 2 ] J SC [ ma/cm 2 ] V OC [ mv ] Implied V OC [ mv ] FF pseudo-ff η screen printed ± Implied V OC V OC OC (screen printed contacts) or V OC (sputter contacts)

29 results: solar cells Further work: towards more than 19% metallization area [ cm 2 ] J SC [ ma/cm 2 ] V OC [ mv ] Implied V OC [ mv ] FF pseudo-ff η screen printed ± sputter & plated V OC [mv] implied V OC Sputter & Plated Screen printed 620 optimum contact Firing temperature (of screen-printed contacts) [ C]

30 results: solar cells Further work: towards more than 19% metallization area [ cm 2 ] J SC [ ma/cm 2 ] V OC [ mv ] Implied V OC [ mv ] FF pseudo-ff η screen printed ± sputter & plated V OC [mv] implied V OC Sputter & Plated Screen printed 620 optimum contact M.M. Hilali,, et. al., IEEE TED 51, 948 (2004) A. Richter et al., 35 th PVSEC (2010) Firing temperature (of screen-printed contacts) [ C]

31 IBC advanced cells with B-emitter both sided contacted n-type B-emitter solar cell 19% (19.5% possible) rear sided contacted n-type rear B-emitter IBC solar cell 19.5% (22% possible)

32 IBC advanced cells with B-emitter 19.5% efficiency with IBC solar cell in EU project LIMA

33 summary first solar cell was an n-type n IBC solar cell ISC Konstanz believes in SoG-Si Si (mc) and n-type n future (Cz( Cz) ISC is developing cell concepts based on screen printing ISC has reached efficiencies of 19% on front B-emitter B cell ISC has reached efficiencies of 19.5% on IBC B-emitter B cell Acknowledgements: ISC co-workers: Lejlja Hildebrand, Annette Helfricht, Stephan Eisert, Jens Theobald, Eckard Wefringhaus This work is financially supported by German government (BMU) within EnSol project, contract number A. Ales Poruba and Radim Barinka.

34 invitation date: 30./ place: Konstanz (Konzil( Konzil) participants: invited speakers; 250 visitors organisation: : ISC Konstanz, Fraunhofer ISE, ECN, ISFH information soon on: workshop.com

COMPARISON OF HIGH EFFICIENCY SOLAR CELLS ON LARGE AREA N-TYPE AND P-TYPE SILICON WAFERS WITH SCREEN-PRINTED ALUMINUM-ALLOYED REAR JUNCTION

COMPARISON OF HIGH EFFICIENCY SOLAR CELLS ON LARGE AREA N-TYPE AND P-TYPE SILICON WAFERS WITH SCREEN-PRINTED ALUMINUM-ALLOYED REAR JUNCTION D.S. Saynova, V.D. Mihailetchi, L.J. Geerligs, and A.W. Weeber