Experimental study on the role of parameters affecting surface recombination and emitter passivation

A multifunction metrology platform for silicon photovoltaics introduced about 3 years ago has helped generate experimental data demonstrating the importance of different electrical parameters that affect the surface recombination and corresponding passivation of PV emitters for advanced solar cells. In this paper we outline unique capabilities provided by mapping of multiple electrical properties. Interface trap density data are presented for Si passivated with Al₂O₃ and for a-Si/SiN_x heterointerfaces. Using examples of corresponding multi-parameter data it is also shown that surface recombination can be increased or decreased depending on the value of the silicon space charge barrier, interface trapped charge and dielectric charge. For emitter structures the latter effect determines the effectiveness of field effect passivation and the value of the emitter saturation current, J₀. The results reviewed in this paper illustrate potential paths to cell efficiency improvements by elimination of defective wafer areas with high D_it or with dielectric charge values away from low J₀ field effect saturation. In this respect, the wafer mapping approach offers significant practical advantages as compared to a study involving multi-sample preparation and single point measurements.