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High-yield photovoltaic cells: achieving new levels of performance while lowering manufacturing costs

PV Photovoltaics

Published on 25 October 2016

The growth of photovoltaic solar energy conversion in the global energy mix has been unprecedented since the 2000s. The installed PV base increased tenfold from 2007 to 2012, and rising demand for energy will continue to drive increasing numbers of end users to solar worldwide. One of Liten’s key PV research areas is crystalline silicon, by far the leading material used in PV cells with 90% to 95% of the global market share. Our current research spans the entire value chain, from the material itself through to complete PV systems.


Our PV materials, cell, and module research focuses on overcoming two major hurdles:

  • Lowering manufacturing costs to ensure that PV energy costs are equivalent to or cheaper than the cost of “traditional” energy supplied by the grid.
  • Raising PV cell and system energy yields to generate more power at an affordable cost.


The growing proportion of PV in the global energy mix is proof that we are close to reaching these objectives. And yet, research must continue to keep brining costs down across the PV value chain. The result will be more affordable PV systems (cost per watt) and cheaper utility rates (cost per kWh).


We have a number of industrial partnerships covering everything from prototyping to scaling up new manufacturing processes so that our partners—multinational corporations and equipment manufacturers that export their products internationally, for example—can stay at the leading edge of the PV industry. “Our strategy is to develop wafer, cell, and module manufacturing technologies for companies in Europe and, ultimately, around the globe. We are poised to assist equipment and materials suppliers in penetrating global markets with high-performance solutions,” said the head of Liten’s PV materials and cells R&D.


The CEA Tech nanocharacterization platform provides equipment and know-how that are unique in Europe. Liten researchers and partners can use this world-class facility at any time to test the quality and reproducibility of the new materials and processes developed.


Our research and development work has resulted in yields of 18% to 19% for traditional monocrystalline silicon cells. For more advanced cell technologies, we have achieved yields of 22% to 23% at a cost that makes solar energy competitive with energy from other sources. In the coming years we will continue to focus our efforts on securing substantial additional improvements—25% to 26%—in operating yields. Higher yields are crucial to anchoring PV in a fast-paced business environment where changes like a three-fold reduction in PV panel costs in five years are not uncommon.


BENEFITS

Technologies that bring benefits to every link in the PV value chain

  • Our research covers the entire PV value chain, from materials to installed systems; we also study electrochemical energy storage. This holistic approach privileges actual operating conditions, keeping us in touch with the needs of our industrial partners.
  • We use firmly-established processes that have proven successful in real operating conditions, enabling us to make best use of new technologies developed alongside proven technologies.
  • We also develop new processes leveraging emerging technologies such as monolike Si and double-sided PV, for example.
  • We continue to invest in equipment to stay at the forefront of efforts to increase yields and develop new processes.
  • Our broad, deep experience cuts across several fields, positioning us to address the entire value chain holistically; this makes Liten unlike any other solar energy research institute in the world.



PROJECTS


Liten has developed, patented, and transferred to industrial partners several technologies along the value chain:


  • Silicon: Our researchers have developed alternative, lower-cost solutions for sourcing PV-grade silicon; these include a physical (fusion, aggregation, and plasma) process for purifying metallurgical-grade silicon.
  • Crystallization: We use a directed solidification process to obtain crystalline silicon (monolike); this is a flagship Liten technology that could potentially address 60% of the global market. In 2014 the furnace design and thermal treatment cycle developed for 60 kg (G2) monolike ingots were successfully tested on industrial-grade 450 kg (G5) and, subsequently, 600 kg (G6) completely-monocrystalline ingots—a world first. PV yields were also improved, getting closer to those of monocrystalline ingots, but at production costs that are far lower.
Our researchers also used a high-purity crucible coating—made from silazane, an inorganic polymer—to produce enhanced G2 (60 kg) ingots. Silicon quality at the core of the ingot was better, resulting in higher cell conversion yields. These improvements in yield more than offset the additional cost of the coating, which was patented in 2014.
- Wafer slicing: We continue to work with several industrial partners to improve the diamond-wire wafer-slicing process, for higher throughput, better quality, and thinner wafers. A prototype line was set up in 2013 and used to scale up a technology for an industrial partner.
  • Cells: We are developing high-temperature homojunction and heterojunction processes—which offer higher yields—at different degrees of industrial readiness in parallel. We are also looking at several ways to improve the cells’ optical confinement and, therefore, yields.
  • Modules: We are experimenting with copper wires to connect PV cells and with electrically-conductive adhesives to eliminate the welding step in the manufacturing process; we are also working on cell encapsulation to improve module performance over time. Module durability is studied via accelerated aging tests.
  • Manufacturing equipment: Liten researchers at INES (the French National Solar Energy Research Institute) worked with AET to develop a machine that automatically estimates the quality of monocrystalline wafers; the machine detects the main wafer defects caused by the presence of oxygen. A prototype was installed at Liten for testing in industrial conditions and for sales demonstrations in conjunction with our partner. A manually-loaded version was also developed for wafer and PV cell R&D. This product is now commercially available.
Liten is also involved in several EU research projects, including two major projects that will shape the future PV industry (Liten is coordinator):  
  • The Hercules project focuses on developing very-high-yield PV cells (heterojunction and backside contact). The project consortium includes some of Europe’s most prestigious research institutes (FhG-ISE, CSEM, ISFH); industrial partners include Meyer Burger and EDF R&D.
  • The Cabriss project aims to develop end-of-lifecycle recycling processes for PV panels taking into account all the environmental concerns inherent to this kind of process. The project brings together top-tier research institutes (SINTEF, IMCE, INES) and small European business seeking to carve out a position on this high-potential market. 
Find out more
    About Liten's PV modules that passed succesfully IEC 61215 certification testing (click here).
  About monolike silicon (click here).
  About  PV modules with advanced BIST (built-in self-test) capabilities (click here).

FACTS AND FIGURES

  • ​More than 200 researchers
  • 30 patent applications per year (average)
  • Over 20 Publications:

Ribeyron PJ, Munoz D, Kleider JP, Favre W, Roca i Cabarrocas P, Labrune M, Geerligs B, Weeber A, Spaeth M, Olson C, Dekker N, van Sark GJHM, Schuetauf JA, Rath JK, Schropp REI, Tucci M, De Iullis S, Gordon I, O’Sullivan B, Descoeudres A, De Wolf S, Ballif C, Schulze T, Korte L, Madon F, Le Quang N, Scherff M, Doll R, Zemen Y, Zietek G. 2011. Proceedings of the 26th European Photovoltaic Solar Energy Conference.
Veschetti Y, Cabal R, Brand P, Sanzone V, Raymond G, Bettinelli A. Dec 2011. High efficiency on boron emitter n-type Cz silicon solar cells with industrial process. IEEE Journal of Photovoltaics 1 (2).
Dauzou F, Cabal R, Veschetti Y. 2012. Electrical behaviour of n-type silicon solar cells under reverse bias: Influence of the manufacturing process. Solar Energy Materials and Solar Cells 104: 175–179.
Cabal R, Veschetti Y, Sanzone V, Manuel S, Gall S, Barbier F, Ozanne F, Bettinelli A, Gillot C, Novel B, Ribeyron PJ. 2013. Industrial Process Leading to 19.8% on N-Type Cz Silicon. Energy Procedia 33: 11–17.
Veschetti Y, Manuel S, Sanzone V, Monna R, Fortin G, Pihan E, Lefillastre P, Novel B, Jouini A. Sept 2013. Potential of n-type Monolike silicon using PERT cell technology. Proceedings of the 28th EU PVSEC Conference, Paris.
Blevin T et al. 2014. Development of Industrial Processes for the Fabrication of High Efficiency N-type PERT Cells. Solar Energy Materials and Solar Cells 131: 24–29.
Lanterne A, Le Perchec J, Gall S, Manuel S, Coig M, Tauzin A, Veschetti Y. 2014. Understanding of the annealing temperature impact on ion implanted bifacial n-type solar cells to reach 20.3% efficiency. Progress in Photovoltaics: Research and Applications.
Schutz-Kuchly T, Sanzone V, Veschetti Y. 2013. N-type solar-grade silicon purified via the metallurgical route: Characterisation and fabrication of solar cells. Progress in Photovoltaics: Research and Applications 21 (5): 1214-1221.
Cabal R, Veschetti Y, Sanzone V, Manuel S, Gall S, Barbier F, Ozanne F, Bettinelli A, Gillot C, Novel B, Ribeyron PJ. 2013. Industrial process leading to 19.8% on n-type CZ silicon. Energy Procedia 33: 11–17.
Michel T, LePerchec J, Lanterne A, Monna R, Torregrosa F, Roux L, Commandré M. 2015. Phosphorus emitter engineering by plasma-immersion ion implantation for c-Si solar cells. Solar Energy Materials and Solar Cells 133: 194–200.
Veirman J, Dubois S, Martel B, Stendera J. 2014. Effect of dopant compensation on the temperature dependence of the transport properties in p-type monocrystalline Silicon. Journal of Applied Physics 115: 083703.
Huguet C, Dechamp C, Voytovych R, Drevet B, Camel D, Eustathopoulos N. 2014. Initial stages of silicon–crucible interactions in crystallisation of solar grade silicon: Kinetics of coating infiltration. Acta Materialia 76: 151.
Veirman J, Dubois S, Enjalbert N, Garandet JP, Lemiti M. 2011. A Fast and Easily Implemented Method for Interstitial Oxygen Concentration Mapping Through the Activation of Thermal Donors in Silicon. Energy Procedia 8: 41.
Veirman J, Dubois S, Enjalbert N, Garandet JP, Lemiti M. 2011. Electronic properties of highly-doped and compensated Solar-Grade Silicon wafers and solar cells. Journal of Applied Physics 109: 103711.
Tanay F, Dubois S, Veirman J, Enjalbert N. 2011. Low temperature-coefficient for solar cells processed from solar-grade silicon purified by metallurgical route. Progress in Photovoltaics: Research and Applications.
Jouini A, Ponthenier D, Lignier H, Enjalbert N, Marie B, Drevet B, Pihan E, Cayron C, Lafford T, Camel D. 2012.Improved multicrystalline silicon ingot crystal quality through seed growth for high efficiency solar cells. Progress in Photovoltaics: Research and Applications 20: 735–746.
Jay F, Muñoz D, Desrues T, Pihan E, Amaral de Oliveira V, Enjalbert N, Jouini A. 2014. Advanced process for n-type mono-like silicon a-Si:H/c-Si heterojunction solar cells with 21.5% efficiency. Solar Energy Materials and Solar Cells 130: 690–695.
Tsoutsouva MG, Oliveira VA, Camel D, Tran Thi TN, Baruchel J, Marie B, Lafford TA. 2013. Segregation, precipitation and dislocation generation between seeds in directionally solidified mono-like Si for PV application. Journal of Crystal Growth 401: 397.
Pihan E, Fortin G, Champliaud J, Enjalbert N, Veschetti Y, Jay F, Jouini A. September 30-October 4, 2013. Achievements and future potential of seeded directional solidification ingots. 28th European photovoltaic Solar Energy Conference, Paris, France.


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FACTS & FIGURES