Quantifying the effect of minority carrier diffusion and free carrier absorption on photoluminescence bulk lifetime imaging of silicon bricks

The spatially resolved bulk lifetimes of silicon bricks can be obtained by spectral photoluminescence intensity ratio imaging. The underlying principle of this method, relevant experimental data and studies discussing its residual artefacts and limitations were published recently. To further discuss the accuracy and drawbacks of the method, the impact of lateral carrier diffusion into grain boundaries and the influence of free carrier absorption are analysed theoretically. A criterion is given by which the impact of minority carrier diffusion on the bulk lifetime image can be rated depending on both the distance to the grain boundary and the local grain bulk lifetime. We find that the impact of free carrier absorption on the calculation of quantitative bulk lifetime can be neglected for bricks commonly used for solar cell fabrication. However, free carrier absorption needs to be accounted for bricks with lifetimes in the millisecond range such as can be found in Czochralski grown material.