Preparation of a-Si:H and a-SiGe:H I-Layers for Nip Solar Cells at High Deposition Rates Using a Very High Frequency Technique

Abstract

The 70 MHz Plasma Enhance Chemical Vapor Deposition (PECVD) technique has been tested as a high deposition rate (10 Å/s) process for the fabrication of a-Si:H and a-SiGe:H alloy ilayers for high efficiency nip solar cells. As a prelude to multi-junction cell fabrication, the deposition conditions used to make single-junction a-Si:H and a-SiGe:H cells using this Very High Frequency (VHF) method have been varied to optimize the material quality and the cell efficiencies. It was found that the efficiencies and the light stability for a-Si:H single-junction cells can be made to remain relatively constant as the i-layer deposition rate is varied from 1 to 10 Å/s. Also these stable efficiencies are similar to those for cells made at low deposition rates (1 Å/s) using the standard 13.56 MHz PECVD technique. For the a-SiGe:H cells of the same i-layer thickness, use of the VHF technique leads to cells with higher currents and an ability to more easily current match triple-junction cells prepared at high deposition rates which should lead to higher multi-junction efficiencies. Thus, use of this VHF method in the production of large area a- Si:H based multi-junction solar modules will allow for higher i-layer deposition rates, higher manufacturing throughput and reduced module cost.