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

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

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?

International Solar Energy Research Center Konstanz, e.v.

location within Germany solar cell manufacturers universities institutes

solar city Konstanz Konstanz 35 42 10 40 70 10

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

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

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

our partners 1 5 2 34 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 25 24 23 26 10 22 27-21 9 3029 28 7 8 33 32 26 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

our development work D F E A C B DEVELOPMENT AID A Cameroon (SLAK) 2009- B India (SUNI) 2010- C Tansania 2011- D Nepal 2012- E French Guyana 2012- F Guatemala 2012-

creating of solar villages and solar schools in Cameroon

pure water supply with solar for schools and hospitals

history of c-si solar cells

30 historic efficiency development (total area) efficiency (%) 25 20 15 10 5 best laboratory cells (schematic) commercial modules (typical best, total area) 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 year

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

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)

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)

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

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%

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%

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%

n-type cells at ISC KN

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

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; 156 156 156 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

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 100 90 80 70 60 50 40 30 20 [ mv ] 664 FF 76.5* pseudo-ff 82.5 Best cell: front illumination Best bifacial cell: front illumination back illumination η 18.6* 10 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Wavelength [µm]

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 100 90 80 70 60 50 40 30 20 [ mv ] 664 FF 76.5* pseudo-ff 82.5 Best cell: front illumination Best bifacial cell: front illumination back illumination η 18.6* 10 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Wavelength [µm]

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 100 90 80 70 60 50 40 30 20 [ mv ] 664 FF 76.5* pseudo-ff 82.5 Best cell: front illumination Best bifacial cell: front illumination back illumination η 18.6* 10 0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Wavelength [µm]

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 241 37.9 632 656±6 77.6 82.7 18.6 Implied V OC V OC OC (screen printed contacts) or V OC (sputter contacts)

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 241 37.9 632 656±6 77.6 82.7 18.6 sputter & plated 38.2 642 77.9 19.1 V OC [mv] 660 650 640 630 implied V OC Sputter & Plated Screen printed 620 optimum contact 785 800 815 830 845 Firing temperature (of screen-printed contacts) [ C]

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 241 37.9 632 656±6 77.6 82.7 18.6 sputter & plated 38.2 642 77.9 19.1 V OC [mv] 660 650 640 630 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) 785 800 815 830 845 Firing temperature (of screen-printed contacts) [ C]

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)

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

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 0325120A. Ales Poruba and Radim Barinka.

invitation date: 30./31.05. 2011 place: Konstanz (Konzil( Konzil) participants: invited speakers; 250 visitors organisation: : ISC Konstanz, Fraunhofer ISE, ECN, ISFH information soon on: www.npv-workshop.com workshop.com