Modelling of Eddy-Current Measurement for Inhomogeneous Charge Carrier Depth Profile

We integrated the two main photoconductance decay (PCD) carrier lifetime measurement methods in one setup. It enables to record both the actual carrier lifetime 𝜏𝑎 and differential lifetime 𝜏𝑑 in the function of injection level Δ𝑛. The two methods complement each other in terms of advantages. While the transient PC is a very fast measurement not impacted by the optical properties of the given sample, the SP method is insensitive to sensor calibration issues, conductive layers, and does not rely on carrier mobility models. For proper measuring conditions, all parameters of the measurement setup were optimized aiming the accurate carrier lifetime measurement of modern solar cell structures featuring continuously improving performance. The optics was designed to provide large area, very homogenous spot of the steady-state and pulsed light beams to avoid the lateral diffusion effect. Both evaluation methods were critically reviewed and the effect of the systematic error caused by lateral diffusion was investigated by computer simulations. Using the optimized integrated setup, and corrected evaluation methods, consistent agreement between the recoded 𝜏𝑎(Δ𝑛) curves was found, which confirms the accuracy of the reported values and the reliability of measuring 𝜏𝑎 with the setup.