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Abstract
Deployment of photovoltaic power generation is expected to accelerate over the next 10-20 years under the influence of reduced cost and increased power conversion efficiency. An important limiting factor to cell efficiency is carrier recombination at metal contacts, thus, to aid further improvements, an accurate and reliable measurement technique for this recombination is required.
This recombination is challenging to measure in isolation from other sources because measurements at the cell terminals convolve many types of recombination into a single measurement, and simplified test structures are not easily measured using traditional photoconductance based techniques for surface recombination measurement because the metal interferes with the conductance measurement. Photoluminescence (PL) measurements are ideally suited to studying recombination of metallised cells and test structures because they are contactless, applicable to arbitrarily size areas and minimally influenced by the presence of metal. Following other studies which apply PL imaging to this problem, this thesis investigates dynamic PL measurement techniques which are faster, simpler and do not require external calibration.
A dynamic PL measurement system is first developed and tested. The system is then used for detailed investigation of silicon-metal interface recombination.
A detailed study comparing dynamic open circuit voltage measurements (called Suns-Voc) and implied open circuit voltage measurements obtained from the developed PL system (called Suns-PL) shows that Suns-Voc data fail to accurately represent all of the recombination in a device at high illumination conditions due to lateral resistive effects but Suns-PL is unaffected by this effect and thus is well suited to measuring metallised cells and test structures.
Metal contact recombination measurements using dynamic PL and the subsequent data analysis are also investigated. It is concluded that because of the non-uniform recombination introduced by metal contacts, excess carriers tend to become non-uniformly distributed, and analysis techniques that assume uniform distribution are inaccurate. Analysis techniques that are based on the simulating the full device geometry such as the methods presented in this thesis can better account for the non-uniformity and are thus more accurate.