Novel selective emitter process using non-acidic etch-back for inline-diffused silicon wafer solar cells

In this work, a novel etch-back approach for the fabrication of a selective emitter (SE) structure is reported for inline-diffused p-type monocrystalline silicon wafer solar cells. The complete SE process, named the ‘SERIS SE’ process, involves screen printing of an etch mask, use of a HF-free etch-back solution and screen-printed metallisation. Both the emitter etch-back and etch-mask dissolution are performed simultaneously in a single processing step, thereby reducing the number of processing steps as compared to other etch-back based SE technologies. For inline-diffused emitter (ILDE) solar cells, the ‘SERIS SE’ process actually requires only one additional processing step, as an emitter etch-back is typically applied to remove the detrimental top layer. An average cell efficiency gain of 0.4% (absolute) is reported for the SE cells fabricated using the single-step SERIS SE process, as compared to etch-back homogeneous-emitter (HE) solar cells. An average batch efficiency of 18.5% is achieved for screen-printed p-type 156 mm pseudo-square Cz mono-Si full-area aluminium back surface field (Al-BSF) SE solar cells. The minimal increase in the number of processing steps, reliance on the robust screen printing process, HF-free non-acidic chemical etch-back and applicability to both tube and inline-diffused emitters make the ‘SERIS SE’ process suitable for industrial application on both mono- and multicrystalline silicon wafers.