UNSW Sydney has received a funding grant from ARENA to develop new recently patented techniques for trapping and controlling hydrogen within highly defective silicon to enable higher solar cell efficiencies while using cheaper silicon wafer sources.
Defects in silicon solar cells harm the efficiency but can be passivated (deactivated or healed) by hydrogen. This Development of Novel Hydrogen Trapping Techniques project will investigate the defects present in two heavily defected cheap sources of silicon wafer that cannot be passivated by existing hydrogenation processes. Techniques will be developed to use the defects themselves to get more hydrogen into the cell, control the hydrogen to trap it within the defects and subsequently passivate the defects.
The project aimed to improve the understanding of defects in quasi-mono silicon (QM-Si) also known as cast-mono silicon, and small-grain mc-Si wafers in order to develop and optimise the new patented hydrogen trapping processes. As a result, the project has been able to significantly improve the electrical quality of these wafers / improve materials and effectively mitigate light-induced defects resulting in stable cell efficiencies.
Report: Development of Novel Hydrogen Trapping Techniques for Breakthrough Si Casting and Wafering Technologies
This report discusses the project results and lessons learnt to date for the UNSW Project, Development of Novel Hydrogen Trapping Techniques for Breakthrough Si Casting and Wafering Technologies.
How the project works
Initial results have shown that in heavily defected silicon, certain hydrogenation conditions can actually enable defected regions to be better quality than nearby non-defected regions. The mechanisms are not yet fully understood. In conjunction with ANU researchers (Canberra) who specialise in defect analysis, the mechanisms will be investigated. The team at UNSW Sydney has extensive experience controlling hydrogen within silicon and will use a combination of techniques to develop a multi-step process to (i) increase the amount of hydrogen in the silicon; (ii) trap the hydrogen in the defected regions; (iii) passivate the harmful defects.
One of the key outcomes for the project is to develop a process suitable for commercial manufacturing to enable the use of cheap heavily defected silicon for stable and higher efficiency solar cells.
Area of innovation
New hydrogen trapping techniques, recently patented, will be developed to enable hydrogen passivation of cheap defective wafers that cannot be effectively passivated by existing Advanced Hydrogenation techniques.
The Development of Novel Hydrogen Trapping Techniques project will enable the use of cheaper sources of silicon wafers in solar cells, while enabling higher efficiencies and stable cells. The wafers will be direct replacements for typical wafers used in over 90% of solar cells. The overall benefit is therefore reduced $/Watt and cheaper solar energy.
The study will add knowledge on hydrogen behaviour in cheap highly defective silicon wafers, as well as understanding the mechanisms of hydrogen and defect interaction, and the mechanisms causing cell degradation and instabilities.