Low gap Amorphous (Si,Ge) Solar Cells

Abstract

ABSTRACTWe report on the growth and fabrication of low-gap a-(Si,Ge) solar cells, including cells made from a-Ge:H. The cells were deposited from silane and germane, or germane alone, using a high dilution of hydrogen in a remote ECR plasma reactor. We have been able to achieve a Tauc gap of as low as 1.15 eV with good device properties. The fill factors were in the 50%-60% range, and the Urbach energies measured in devices were in the range of 45 meV. The devices were of the p/i/n type with light entering the p layer. The devices were fabricated on stainless steel substrates. We also report on experiments to improve graded gap solar cells in a- (Si,Ge) using a novel combination of ppm-boron dopant and bandgap grading. It is shown that this grading significantly improves the device performance, both voltage and fill factor.