This report discusses the project results and lessons learnt to date for the UNSW Project, Improving World-Record Commercial High-Efficiency n-type Solar Cells through Recombination Analysis & Innovative Passivation.
The main focus of the project is to develop and commercialise technologies for hydrogen charge state control in n-type silicon to improve the material quality and improve the solar cell performance.
The formation of a solar cell using silicon relies on the addition of impurity atoms into silicon to change the electronic properties. In particular, dopant atoms are introduced to provide the material with conductivity. The type of impurity atoms added to the silicon determine whether the silicon is ‘p-type’ or ‘n-type’, and both are typically used in different regions of the device to allow the formation of a p-n junction and an electric field in the solar cell. Traditionally, silicon solar cells manufactured commercially have used silicon with a base-doping of boron atoms, which makes the silicon ‘p-type’. In recent years, many techniques have been developed that carefully control the charge state and movement of hydrogen atoms in p-type silicon, which has led to significant enhancement in the quality of p-type silicon. Such hydrogen passivation techniques have been adopted by industry and are being widely used today. In 2017, approximately 95% of silicon solar cells were fabricated using p-type silicon; it completely dominated the market. However, the International Technology Roadmap for Photovoltaics, compiled by experts, predicts a significant increase in the number of solar cells made using n-type silicon in the near future.