Integrated Measurement of the Actual and Small Perturbation Lifetimes with Improved Accuracy

We have integrated the two main photoconductance decay (PCD) carrier lifetime measurement methods into one setup. This allows us to record both the actual carrier lifetime tau(alpha) and differential lifetime tau d in the function of injection level Delta n The two methods complement each other in terms of advantages. While the transient photoconductance (transient PC) is a very fast measurement not impacted by the optical properties of the given sample, the small-perturbation PCD (SP-PCD) 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 were designed to cover a 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 systematic error caused by lateral diffusion was investigated with computer simulations. Using the optimized integrated setup and corrected evaluation methods, consistent agreement between the recoded tau(alpha) (Delta n) curves was found, which confirms the accuracy of the reported values and the reliability of measuring tau(alpha) with the setup.