Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Industrial aspects of silicon material research for photovoltaic applications Hans Joachim Möller

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg General development of photovoltaics Crystalline silicon technology Thin film technologies Feedstock ressources Summary Outline

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg General development of photovoltaics Crystalline silicon technology Thin film technologies Feedstock ressources Summary Outline

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Market share of different solar cell technologies EU - Prognosis for future development 2010c - Si %multi, Cz, ribbons 2020c - Si 50%multi, ribbons, thin films PV - market based on the silicon technology

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg System cost 1, €/Wp Module cost €/Wp System lifetime years System efficiency 15% - 30% Electricity cost €/kWh Source: Study of M. Green 2002 Goals of future developments Grid parity for < 0.1 €/kWh Peak current parity for €/kWh PV goals for ,50 €/Wp 1,00 €/Wp 0,50 €/Wp 2,00 €/Wp 0,20 €/Wp c-Si Thin film PV - system cost depend on efficiency and cost per area

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Cost and efficiency per area for different technologies Source: I. Schwirtlich, Schott Solar Cost per m 2 Cost per W p New concepts Nanocryst. Dye Efficiency Technologies EFG CIS New concepts Thin films

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg General development of photovoltaics Crystalline silicon technology Thin film technologies Feedstock ressources Summary

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Formation of defects during crystal growth Dislocations Melt precipitation Transition elements Solid impurity precipitation Carbon Oxygen New Donors Thermal Donors Dislocations Oxygen Nitrogen Carbon Boron Metals Defect interactions

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Internal quantum efficiency (IQE) - topogram Dislocation density - topogram Correlation between dislocations and lifetime Analysis of dislocation activity in solar cells requires a modified Donolato model

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Theoretical description with modified Donolato's theory Experimental results yield similar recombination strengths  compared to wafers but higher volume - diffusion lengths L

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Cost reduction through more efficient use of silicon

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Cost distribution Wafer Solar cell Ingot crystal

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg spec. Si-consumption [g/W p ] Development of wafer thickness and silicon consumption Wafers below 100 µm thickness become very flexible and fragile 60 µm wafer

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Radial/median cracks Lateral cracks Subsurface microcracks from multi-wire sawing SEM images of wafer cross sections 1 µm 3 µm

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Etch removal  [µm]  0 [MPa] as-sawn 83 etched etched etched etched etched Surface damage by microcracks determines fracture toughness Weibull distribution and fracture strength Biaxial bending test

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg General development of photovoltaics Crystalline silicon technology Thin film technologies Feedstock ressources Summary

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg front cover foil substrate active layer a-Si or CIS back side cover foil superstrate active layer a-Si or CdTe Substrate: glass, metal, polymer Foil: EVA or PVB Front cover: glass, polmer, varnish Superstrate: glass Foil: EVA or PVB Back side cover: glass, polmer, metal 3 mm mm µm 3 mm mm µm 3 mm SubstrateSuperstrate Principle of thin film cells

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Thin film solar cells Flexible CIS - cell Today‘s thin film materials Cadmium telluride CdTe Kupfer-Indium/Gallium-Diselenide CIGS Amorphous Silicon a-Si:H Application

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Status thin film efficiencies Module efficiency only about % of cell efficiency

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Analyses of the cost reduction potential From 1.5 to 1.0 €/kW p Material and energy Yield increase Reduction of glass fracture Efficiency From 8% to 12% Production optimization From 1.0 to 0.5 €/kW p cheaper TCO and foils new substrate glass New absorber material Efficiency From 20% to 40% Production optimization  Normal cost reduction and efficiency increases are not suffcient to reach the goals of the EU roadmap  Cost per W p converges to fixed cost  Material and energy cost cannot be reduced arbitrarily  Efficiency has to be increased disproportionately

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg New generation thin film cells Losses in the solar spectrum More efficient use of the spectrum by multi-junction solar cells with different band gap Tandem-junction efficiency (theoretical) > 45% (Si: 33%) Triple-junction cell > 51% (WR 41,1%) Four junction cell > 54% Thin film technologies allow flexible formation of multi-junction cells

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg General development of photovoltaics Crystalline silicon technology Thin film technologies Feedstock ressources Summary

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Comparison of material consumption for c-Si and thin films Wafer technologySi - wafer thickness150 µm (mono- or multi-Si)Wafer size 0.01 m 2 to 0.04 m 2 3 kg silicon for 1 kW p solar power Thin filmsdeposition on substrate (a-Si/µ-Si,tf-cSi,CdTe, CIS) µm layer thickness Substrate size 0.5 m 2 to 1.43 m kg material for 1 kW p solar power Cost advantage for electronic metals only, if prices are below Euro/kg

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Silicon Massive expansion of the crystalline technology requires separate feedstock supply. Long term supply secured CIGS, CdTe und GaInAs/GaInP/Ge Feedstock shortage for In Problem with toxicity of Cd and As-compounds Prices for electronic materialsare high because of small markets Development of new solar cell concepts necessary Technological development of the thin film technology in industrial scale still difficult Summary

Fraunhofer Technology Center Semiconductor Materials Institute for Experimental Physics TU Bergakademie Freiberg Thank you for your attention