Development of High, Stable-Efficiency Triple-Junction a-Si Alloy Solar Cells: Final Technical Report

This report summarizes Energy Conversion Devices, Inc.'s (ECD) research under this program. ECD researchers explored the deposition of a-Si at high rates using very- high-frequency plasma MHz, and compared these VHF i-layers with radio-frequency (RF) plasma-deposited i-layers. ECD conducted comprehensive research to develop a ..mu..c-Si p+ layer using VHF deposition process with the objectives ofestablishing a wider process window for the deposition of high-quality p+ materials and further enhancing their performance of a-Si solar cells by improving its p-layers. ECD optimized the deposition of the intrinsic a-Si layer and the boron-doped ..mu..c-Si p+ layer to improve the Voc. Researchers deposited wide-bandgap a-Si films using high hydrogen dilution; investigated the deposition of theZnO layer (for use in back-reflector) using a sputter deposition process involving metal Zn targets; and obtained a baseline fabrication for single-junction a-Si n-i-p devices with 10.6% initial efficiency and a baseline fabrication for triple-junction a-Si devices with 11.2% initial efficiency. ECD researchers also optimized the deposition parameters for a-SiGe with high Ge content; designed anovel structure for the p-n tunnel junction (recombination layer) in a multiple-junction solar cell; and demonstrated, in n-i-p solar cells, the improved stability of a-Si:H:F materials when deposited using a new fluorine precursor. Researchers investigated the use of c-Si(n+)/a-Si alloy/Pd Schottky barrier device as a tool for the effective evaluation of photovoltaic performance on a-Si alloymaterials. Through alterations in the deposition conditions and system hardware, researchers improved their understanding for the deposition of uniform and high-quality a-Si and a-SiGe films over large areas. ECD researchers also performed extensive research to optimize the deposition process of the newly constructed 5-MW back-reflector deposition machine.