Avoiding Parasitic Current Flow Through Point Contacts in Test Structures for QSSPC Contact Recombination Current Measurements

As saturation current densities of contacted junctions are critical figures of merit and design parameters for high-efficiency silicon solar cells, there is a great interest in methods for their characterization. We recently proposed a method for the characterization of contact recombination currents that is based on a specific test structure. The test structure consists of various areas with different contact fractions on which photoconductance measurements are done. Each area is a lattice of point contacts on a passivated wafer. A major added value of this method is that the metal contacts can be arbitrarily thick. A major drawback of this method is that injection levels and effective lifetimes measured using quasi-steady-state photoconductance measured on our test structure are significantly overestimated when current flows through the point contacts instead of through the semiconductor. We use a simple model to show that this effect can be avoided by designing the point contacts such that their characteristic size is smaller than the contact´s transfer length. We then experimentally verify our model calculation.