Determination of injection dependent recombination properties of locally processed surface regions

Abstract

High efficiency solar cell concepts typically depend upon highly localized processing technologies, such as partial rear contacts. In practice, characterizing these techniques is challenging and it has become increasingly popular to employ analytical expressions that fit the local surface recombination velocity (SRV) to area-averaged measurements of regularly arrayed test structures. However, this approach has numerous limitations imposed by the assumptions of the model and as a consequence significant inaccuracies can result. We present an alternative approach with improved accuracy and generality, which makes use of the recently developed fast 2D/3D device simulator Quokka. Quokka has been enhanced to predict luminescence as well as photoconductance (PC). Thus the recombination activity of the locally processed feature can be iteratively found to fit the measurement result of a test sample. The power of this technique is demonstrated by the derivation of the recombination current density as a function of the excess carrier density directly at the local feature from area-averaged photoluminescence (PL) signals. We apply the method to different laser-doped samples, which reveal accurate and consistent trends for a range of pitches and injection levels as well as a low sensitivity to the uncertainty of input parameters.