Boron and oxygen contamination in Czochralski-grown (Cz) silicon leads to a degradation of the minority charge carrier lifetime within short times due to the formation of recombination active complexes. The formation of these complexes is investigated for longer times showing a further development of the defect. This development called 'regeneration' is triggered by illumination or applied forward voltages and leads to a new state of the defect. This new state of the defect is proven to be less recombination active allowing higher stable minority carrier lifetimes and conversion efficiencies of solar cells. The influences of temperature and light intensity are discussed.
a b s t r a c tRecombination active boron oxygen related defects typically limit the efficiency of solar cells made from boron doped, oxygen rich silicon. This limitation can be overcome by applying a regeneration process that requires slightly elevated temperatures, carrier injection, and the presence of hydrogen in the silicon substrate in order to regenerate quickly and completely.The influence of mid temperature steps up to 400 1C on the regeneration kinetics is investigated and the results can be explained with the efficacy of the regeneration process depending on the hydrogen bonding states prior to regeneration. Boron hydrogen pairs are found to be good candidates to be the relevant hydrogen source during regeneration. The long term stability of the regenerated state is tested under solar cell operating conditions, and the thermal activation energy of its destabilization is determined to be 1.25 70.05 eV.Limiting factors for high speed regeneration processes are discussed, and a high temperature/high illumination procedure is presented, allowing complete regeneration in less than 10 s. This makes regeneration feasible as an in line process in solar cell production.
A new reaction model concerning the boron-oxygen related degradation is presented, introducing a third recombination inactive state, that stabilizes the electrical parameters of Cz-Si solar cells, and the transition to this new inactive state is proven by experimental data. Furthermore, the stability under solar cell working conditions and the formation kinetics of this additional state are discussed.
The formation of boron-oxygen complexes in boron-doped crystalline silicon can lead to a severe reduction in the minority charge carrier lifetime. This strongly influences, e.g., solar cell efficiencies if the material is used for photovoltaic application. Recent investigations have shown that a recovery of the carrier lifetime can be achieved by a subsequent thermally enhanced reaction induced by charge carriers. A model of the reaction dynamics of the boron-oxygen complex by means of rate equations is presented in this paper. Following a mathematical description of the reactions involved, the consequences based on the calculations are presented and allow a prediction of the observable electrical parameters. The fundamental agreement with measured data is proven experimentally for different phenomena.
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