Contacting and Recombination Analysis of Boron Emitters via Etch-back for Advanced N-type Si Solar Cells

In p-type c-Si solar cells, selective emitter structures generated by emitter etch-back (EEB) have been introduced in recent years in order to minimize electrical losses in the phosphorous emitter being one of the dominant factors limiting the performance of standard screen-printed p-type c-Si solar cells. In this work, a homogeneously or selectively etched-back boron emitter is demonstrated to provide additional benefits yielding an enhanced conversion efficiency in n-type Si solar cells. By means of subsequent B-EEB, contacting and recombination properties of B emitters dependent on their sheet resistance, surface concentration, and profile depth are studied indicating the latter to be the crucial parameter. Based on this, the characteristics of the optimal B emitter regarding low saturation current density and low specific contact resistivity are determined for the cases of homogeneous and selective etch-back. By employing the selectively etched-back B emitter in initial solar cells, a VOC gain of 5 mV and a significant shunting reduction compared with homogeneously doped devices is achieved.