Stabilized 9% efficiency of large-area (/spl sim/5000cm/sup 2/) a-Si/a-SiGe tandem submodules using high-rate deposition

High-rate deposition of photovoltaic layers of a-Si/a-SiGe tandem solar cells has been investigated using RF (13.56 MHz) plasma-CVD method while keeping the substrate temperature below 200/spl deg/C. A remarkable improvement in film quality and device performance can be attained at a high deposition rate of /spl ges/3 /spl Aring//s by optimizing hydrogen dilution and other deposition conditions. It is of great importance to utilize the effect of hydrogen dilution which can reduce the incorporation of excess hydrogen in the films. The world's highest stabilized efficiency of 9.3% has been achieved for a large-area (5150cm/sup 2/) a-Si/a-SiGe tandem submodule whose top and bottom photovoltaic layers are deposited at /spl sim/3 /spl Aring//s using an optimized hydrogen dilution. A smart back reflector, with a high light scattering effect, and other approaches to enhance the optical confinement effect, are also proposed for further improvement of cell performance.