Evaluation of Recombination Velocities of Grain Boundaries Measured by High Resolution Lock-in Thermography

Multicrystalline silicon solar cells include a high amount of crystal defects such as dislocations and grain boundaries, which are featured by different degrees of recombination activity. This contribution presents a method to investigate the recombination velocity at grain boundaries (GBs) by means of dark lock-in thermography (DLIT). The local diffusion current density j01 at the GB is evaluated by applying a spatial deconvolution algorithm and separating the dark current contributions due to their different voltage dependencies. Adopting a model of the GB developed by Lax enables an analysis of the recombination velocity from the local j01. In this contribution we firstly present an explicit expression for this calculation. It is shown that the dominant contribution to j01 at the investigated sample is caused by the recombination active GBs and that the intra-grain defects such as dislocations have just a lower influence.