February 2005 • NREL/SR-520-37660 Implementation of a Comprehensive On-Line Closed-Loop Diagnostic System for Roll-to-Roll Amorphous Silicon Solar Cell Production Annual Report, Year Two 1 September 2003—31 August 2004 T. Ellison Energy Conversion Devices, Inc. Troy, Michigan National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 February 2005 • NREL/SR-520-37660 Implementation of a Comprehensive On-Line Closed-Loop Diagnostic System for Roll-to-Roll Amorphous Silicon Solar Cell Production Annual Report, Year Two 1 September 2003—31 August 2004 T. Ellison Energy Conversion Devices, Inc. Troy, Michigan NREL Technical Monitor: R. Matson Prepared under Subcontract No. ZDO-2-30628-11 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 This publication was reproduced from the best available copy submitted by the subcontractor and received no editorial review at NREL NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste CONTENTS BACKGROUND and EXECUTIVE SUMMARY 1 TASK 5: Development of Closed-Loop Control of Film Thickness – II .................... 4 1.1 Introduction....................................................................................................... 4 1.2 2nd Generation ITO/ZnO CLTC System ............................................................ 4 1.3 3rd Generation ITO/ZnO CLTC System............................................................. 9 1.4 2nd and 3rd Generation a-Si Spectrometers ...................................................... 12 1.5 1st Generation a-Si CLTC System .................................................................... 15 TASK 6: PV Capacitive Diagnostic (PVCD) for Bottom and Middle Cells................ 18 2.1 Introduction and Background............................................................................ 18 2.2. Bottom (Component) Cell PVCD ...................................................................... 20 2.3 Middle Component Cell PVCD Status .............................................................. 25 2.4 PVCD Temperature Stabilization System......................................................... 28 2.5 Using the PVCD’s for Optimization................................................................... 31 2.6 The Diagnostics Data Display [DDD] and Alarm Package................................ 33 TASKS 7: Deposition Optimization and Plasma Diagnostics................................... 35 3.1 Introduction....................................................................................................... 35 3.2 Improved p-Deposition Hardware..................................................................... 36 3.3 Residual Gas Analyzer (RGA) for Production Monitoring ................................. 39 3.4 OIS and RGA for Plasma Characterization ...................................................... 40 3.5. “Moving-Wire” Langmuir Probe......................................................................... 44 TASKS 8: Yield Improvements: Substrate Quality..................................................... 45 4.1 Introduction, Background and Summary .......................................................... 45 4.2 Evaluation of Plasma Cleaning Versus Chemical Cleaning.............................. 46 4.3 Evaluation Of On Line Techniques for Measuring Substrate Cleanliness ........ 53 4.4 Implementation of Plasma Cleaning System into the 30 MW Roll-To-Roll Production Manufacturing Process............................................... 57 4.5 Off-Line Vacuum Testing of the OSEE Monitor for Implementation in BR........ 64 iii BACKGROUND and EXECUTIVE SUMMARY Energy Conversion Devices, Inc. (ECD) has developed and built 7 generations of roll-to-roll amorphous silicon PV production equipment. In the ECD/United Solar Ovonic production process we deposit about a 1 µm-thick 12-layer coating consisting of a metal/oxide backreflector, a 9 layer a-Si/a-SiGe alloy triple junction solar cell, and a top transparent conductive oxide coating onto 125 µm thick, 35.5 cm wide stainless steel webs in a series of three roll-to-roll deposition machines. Figure 1 shows a schematic of the United Solar 30 MW a-Si deposition machine; a photograph of the machine is shown in Fig. 2. Ovonic a-Si Triple Junction Solar Cell Processor Top View I1 I2 I3 P1 P2 P3 N1 N2 N3 P3 6 Pay-Off Chambers I3 6 Take-Up Chambers 6 Rolls of Stainless 6 Rolls of Stainless 2.6 km long x 36 cm N3 Steel Subtrate wide x 0.13 mm thick P2 Coated with < 1 um thick thin film triple I2 junction photovoltaics Gas N2 Gate P1 I1 N1 Al/ZnO Stainless Steel Side View I1 I2 I3 P1 P2 P3 N1 N2 N3 Fig. 1. Schematic of the United Solar 30 MW/yr a-Si deposition equipment. All the developments of the PVMaT 5A program have been incorporated into this machine: • A substrate heating and monitoring system, using durable NiChrome heater elements; • Reactive sputtering for low-cost deposition of the Al/ZnO backreflector; • A new PECVD cathode providing uniform deposition over large areas and reduced germane usage; • “Pinch Valves” that allow the rolls of substrate to be installed and removed while keeping the deposition regions of the machine under vacuum; and 1 • Hardware for online diagnostic systems, including the non-contacting PV Capacitive Diagnostic (PVCD) system, which can measure the a-Si solar cell electrical properties in-situ without an ITO top coating[4], and reflection spectrometers to measure the cell thickness. “Included in the machine” might be an understatement: many of these technologies are essential to the machine. For example, the a-Si machine processes about ½ MW of material in a single “batch” of six 2500 m long coils. Offline Q/A-Q/C may not be available for another 1 – 2 batch-cycles: it is difficult envisioning operating such a machine without the online diagnostic systems (e.g. PVCD and spectrometers) developed in the PVMaT 5A program. Fig. 2. Side view of the United Solar 30 MW/yr a Si processor. In the PV Manufacturing R&D Inline Diagnostics Solicitation, ECD is building upon these accomplishments to enhance the operation of the present production machine, and lay the foundation for improvements in the next generation machine. The four major work areas undertaken by ECD and United Solar in the present PV Manufacturing R&D program are described below: 1. Development of closed loop thickness control systems for the ZnO, ITO layers, and a-Si component layer thicknesses (the last is an expansion of this program) (Tasks 1, 5 and 9); 2. Continued development of the PVCD, and the initiation of online optimization using these devices (Tasks 2, 6 and 10); 3. The development of plasma monitoring systems to further optimize the i-layer deposition process, and for possible online implementation (Tasks 3, 7 and 11); 4. Yield improvements by investigating online yield measurement systems, investigations into sources of reduced yield, and mitigation of these sources (Tasks 4, 8 and 12). 2 United Solar has been expanding its manufacturing capability at a rate of about 30%/yr – doubling capacity every 3 years. The PV Manufacturing R&D Program is playing a key roll in the incubation of this Roll-to-Roll manufacturing technology allowing ECD/United Solar to develop new technologies to enhance the present equipment and lay the foundation for the next generation machines. 35 28%/yr growth rate 20022002 3030 MWMW 30 25 20 15 10 19961996 55 MWMW(3-jnct,(3-jnct, 33 bandgap)bandgap) 5 19861986 0.60.6 MWMW 19911991 2.02.0 MWMW (2(2 junction,junction, 11 bandgap)bandgap) Production Capacity [MW/yr] 0 1985 1990 1995 2000 2005 Year Fig. 3. ECD/United Solar Joint Venture