Generation of a Line Focus for Material Processing from an Array of High Power Diode Laser Bars R. Baettig, N. Lichtenstein, R. Brunner, J.

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1 Generation of a Line Focus for Material Processing from an Array of High Power Diode Laser Bars R. Baettig, N. Lichtenstein, R. Brunner, J. Müller, B. Valk, M. Kreijci, S. Weiss

2 Overview This slidepack discusses packaging of a linear arrays of laser bars Application : Laser Solid Phase Epitaxy (SPE) of photovoltaic cells Based on the use of next generation 808nm laser bars Sponsoring This work was sponsored by EU project HIGH-EF 7th technological framework program under contract Company Confidential 2

3 Laser-SPE Starting material Amorphous silicon [a-si] film deposited on glass substrate Growth of multi-crystalline silicon film 1. Scanning of the a-si film by line focus laser Formation of 100µm wide seed crystallites (mc-si) from the melt 2. Deposition of a-si onto the seed layer of mc-si 3. Furnace anneal Epitaxial growth from the solid phase of deposited a-si Starting from the seed layer formed by laser treatment LASER Furnace a-si mc-si (seed) a-si mc-si a-si mc-si mc-si mc-si Glass Company Confidential 3

4 Solution based on Diode Laser Bars Requirements for the annealing laser source Short emission wavelength Absorption in silicon decreases towards higher wavelengths High output power concentrated in a narrow (spatial) line Fast melting and cooling rates necessary in the silicon film Scalable concept L=5cm, 10cm,, 100cm Company Confidential 4

5 Solution based on diode laser bar Laser bars are an ideal source to meet the requirements 10 mm typ θ F =30 FWHM θ S =10 FWHM 1.2mm-2.4mm Technology available at short wavelengths 800nm-810nm High efficiency and power levels can be realized State of the art : 100W / bar at 800nm-810nm Demonstrated advancement in this project: 125W-140W CW / bar E2 facet passivation to avoid COMD Hard soldering of bars onto Micro-Channel Coolers Low bow assembly < 1µm achievable 1. Soft soldering : Disadvantage insufficient long term stability 2. Soldering onto stress buffer (CuW or CuMoCu) + hard solder (AuSn) 3. Use of expansion matched Micro Channel Coolers + hard solder (AuSn) Company Confidential 5

Bar Performance Power Conversion Efficiency (PCE) 200.0 180.0 160.0 140.0 120.0 100.0 80.0 60.0 40.0 20.0 2.000 1.800 1.600 1.400 1.200 1.000 0.800 0.600 0.400 0.

6 Bar Performance Power Conversion Efficiency (PCE) Power Conversion Efficiency [%] Forward Voltage [V] Current [A] 10mm 180W / 200A CW at 808nm, 600W / 500A quasi-cw (500µs) Hard-solder die attach with minimum smile onto Micro Channel Cooler <1µm bow Company Confidential 6

7 From the Laser Bar to the Line Focus Combine the output of 7x 808nm laser bars Hard soldered onto expansion matched Micro Channel Coolers Arranged in a linear geometry Up to 1.3kW of input power available Independently transform Slow and Fast Axis angle spectra Fast axis transformation defines the width 2w of the line focus Slow axis transformation defines the length L of the line focus Company Confidential 7

Aspheric Fast Axis Collimation (FAC) lenses High vertical divergence of bars

8 From Bar to Line Focus : Optical Concept Fast Axis transformation (define width 2w of line focus): 1. Aspheric Fast Axis Collimation (FAC) lenses High vertical divergence of bars Vertically collimated beam FAC FAC 2. Concentration via cylindrical Fast Axis Focusing (FAF) Lens Collimated beam Focus 2w FAF Company Confidential 8

9 From Bar to Line Focus : Optical Concept Slow Axis transformation (define length L of line focus): 1. Homogenizer Slow Axis angular spectrum of laser Top Hat angular distribution 2. Transform (Fourier) lens Top Hat angular distribution (after homogenizer) Top Hat intensity profile Transform Lens 7x 808nm Bar on Micro Channel Cooler 2β L = 2 β f TL Homogenizer 7x FAC lens Fast Axis Focusing Lens Company Confidential 9

10 Implementation : FAC attachment Bar on Micro Channel Cooler Glue point Laser Bars FAC Lens Company Confidential 10

11 Implementation : Homogenizer Transform optics Homogenizer Fast Axis Focusing Lens Company Confidential 11

12 Scaling of Line Length Industrial scale applications require annealing of 1m-panels Scale-up of the present approach Via joining of lines from multiple sources Angled stitching of 5 cm lines 100 mm Company Confidential 12

13 Electro-Optic Performance of Line Source 920W at 140A Throughput of optics = 87% <9nm spectral shift threshold to 130A Thermal resistance = 0.35K/W 1000 Electro-optic Characteristics 20 60% Spectral Shift 815 Power, W Output Power Voltage Wallplug Efficiency % Module Voltage, V 40% 30% 20% 10% 0% Wallplug Efficiency Drive Current, A Drive Current, A Company Confidential 13 Wavelength, nm

14 Parameters of Line Focus y Peak irradiance, 140A = 10kWcm -2 Length of line = 45mm Homogeneity = ±3% rms Variation of peak intensity B7 B6 B5 B4 B3 B2 B1 x Peak Irradiance, kwcm Peak Irradiance 140A Peak Irradiance Position, cm Company Confidential 14

film evaporated on glass Generation of domains>100µm achieved Peak irradiance during processing 6kWcm -2

15 Achieved Performance in Laser-ESP Successful application of developed line source demonstrated Collaboration with Institute for Photonic Technology HT Jena Seed crystals formed from the melt of a-si film evaporated on glass Generation of domains>100µm achieved Peak irradiance during processing 6kWcm -2 Scan speed 1cm sec -1 mc-si film formed by laser annealing IPHT Jena Setup realized at IPHT Jena Company Confidential 15

16 Conclusion Line source based on newly developed 808nm laser bars presented Field of application: Annealing of a-si films in Laser-ESP growth of mc-si for solar panels Presented line source combines the output of 7 bars on MCC Demonstrated peak irradiance 10kWcm -2 Length-scalable concept Successful application demonstrated in Laser-SPE process Length scaling via stitching presently under investigation Evaluation in the solar cell process scheduled as next step Company Confidential 16

High Brightness Laser Diode Bars

High Brightness Laser Diode Bars Norbert Lichtenstein *, Yvonne Manz, Jürgen Müller, Jörg Troger, Susanne Pawlik, Achim Thies, Stefan Weiß, Rainer Baettig, Christoph Harder Bookham (Switzerland) AG, Binzstrasse