Improving Silicon Solar Cell Efficiency by Measuring Carrier Lifetimes

02 Oct 2023

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- Alison Oliver

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The charge carrier lifetime is a key parameter that affects the efficiency of silicon photovoltaic cells. Carriers disappear upon recombination, and this mechanism takes place efficiently at the recombination centres. Hence, understanding their behaviour and reducing their concentration is important to improve the device efficiency. In the lab at Warwick, the team studies and improves the technique called passivation, which sticks atoms on the recombination centres and makes them inert. 

For their previous experiment,(Carrier lifetimes in high-lifetime silicon wafers and solar cells measured by photoexcited muon spin spectroscopy | Journal of Applied Physics | AIP Publishing)​ the team used the photoexcited mSR technique at HIFI Laser to measure carrier lifetimes in Si wafers with extremely long lifetime. Whilst analysing the data, they found interesting spatial dependence in muon spin relxation rates, which might be related to a gradient of impurity concentration (i.e. recombination centres) generated during the passivation process. This time at EMU, the scientists further investigate this finding using ZF-mSR (ZF for zero field), where muon spin is most sensitive to the presence of impurities. 

“This interesting behaviour was found as a side product of the previous experiment at HIFI Laser. One of the motivations this time is to try and measure the same sample on EMU as EMU is more sensitive to interactions between muons and carriers/impurities,” explains Dr Tim Niewalt, Research Fellow at the School of Engineering, University of Warwick. ​

Working with EMU Beamline Scientist Koji Yokoyama, the team carried out the experiment in Cycle 2023/2. Together with post-characterisation studies back at Warwick, they are now doing data analysis carefully because the signal can be very small. 

“Our time working on the EMU instrument has definitely been productive as we have been able to gather so much data. With results from this experiment, we wish to continue our carrier lifetime measurement at HIFI Laser and study beam damage by muons using RIKEN beamlines.” explains Dr Sophie Pain, Research Fellow at the School of Engineering, University of Warwick. 

We look forward to welcoming the team back to ISIS to continue their research.