Investigations of high refractive silicon nitride layers for etched back emitters : enhanced surface passivation for selective emitter concept (SECT)

Abstract

The application of selective emitter solar cells via emitter etching has already shown its potential as an industrial type solar cell concept. Thereby the surface passivation of etched back emitters plays an important role. In this work the possibilities for enhanced surface passivation are investigated by using single and double layered high refractive PECVD SiNx layers. QSSPC, ellipsometry and FTIR measurements were performed on FZ wafers to determine the critical thickness of the high refractive SiNx for an improved hydrogen passivation. The studies were also focused on the firing stability of the passivation quality. Finally, optimized single as well as high refractive double SiNx layers were applied on selective emitter solar cells. The Selective Emitter ConcepT (SECT) solar cells show an increase of the open circuit voltage, which is related to the improved surface passivation. The highest Voc value of 642 mV was obtained with a high refractive double layered SiNx on large area screen printed Cz solar cells. Compared to reference solar cells an average gain of 0.6%abs. was achieved on SECT solar cells. The cell efficiency of 19.0% for screen printed SECT-solar cells with full area Al-BSF shows that a further improved surface passivation is possible and can increases cell performance of selective emitter solar cells.