Status of Fluorinated Amorphous Silicon Alloy Multi-Junction Solar Cells
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STATUS OF FLUORINATED AMORPHOUS SILICON ALLOY MULTI-JUNCTION SOLAR CELLS JEFFREY YANG, ROBERT ROSS, RALPH MOHR, AND JEFFREY P. FOURNIER Energy Conversion Devices, Inc., 1675 West Maple Road, Troy, MI 48084 ABSTRACT We present in this paper updated solar cell performance data on fluorinated amorphous silicon and fluorinated amorphous silicon-germanium alloys. We have achieved a 9.7% conversion efficiency for a singlejunction device using a-Si:Ge:F:H alloy having an optical band gap of 1.5 eV. We have also achieved 12.5% and 13.0% efficiencies, respectively, for dual-band-gap tandem and triple devices using a-Si:F:H and a-Si:Ge:F:H alloys. These represent the highest values reported to date for their respective configurations. Multi-junction solar cells exhibit excellent stability not only in terms of light-induced effect but also in terms of prolonged heating at elevated temperatures. INTRODUCTION We have previously reported [1,2] high efficiency stable multijunction solar cells using fluorinated amorphous silicon and fluorinated amorphous silicon-germanium alloys. We have made further improvements on conversion efficiencies in various device configurations, and will report the results in this paper. Multi-band-gap, multi-junction solar cells fabricated in our laboratory exhibit higher efficiencies as well as superior stability than single-junction devices [E]. Multi-junction 0 devices also exhibit thermal stability after prolonged heating at 150 C in air. Dark characteristics of several device configurations will also be presented. RESULTS AND DISCUSSIONS All devices reported in this paper were fabricated using the conventional radio frequency glow discharge technique and deposited onto stainless steel substrates coated with a textured back reflector. Figure 1 shows the J-V characteristic of a single-junction device0 using 2 a-Si:Ge:F:H alloy measured under AMI (100 mW/cm ) illumination at 25C. SINGLE STRUCTURE a-S:Ge-.F:H Vo,
(177 volt
Jsc = 19.6 mA/cm 0.64 FF =
2
Area = 1.0 cm
2 2
Pin = 100 mW/cm 2 Pmax = 9.7 mW/cm
-4.5 E -9.0
Figure 1. J-V characteristic of a single a-Si:Ge:F:H device under AMl (100 mW/cm 2 ) illumination at 250C.
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