Detailed analysis of high sheet resistance emitters for selectively doped silicon solar cells

Abstract

A selective emitter structure is a promising approach to improve the cell efficiency of industrial type silicon solar cells by minimizing the losses at the front surface and in the emitter. Selective emitters can be produced by numerous processing sequences, resulting in different doping profiles. This work focuses on evaluating the potential of the high sheet resistance emitters that are created by the selective emitter processes developed at the University of Konstanz (UKN). In these processes, the high sheet resistance emitter is created by a heavy diffusion and an etchback of the heavily doped surface layer [1, 2], or by a weak diffusion with a subsequent drive-in step [4, 5]. QSSPC samples were fabricated to evaluate the emitter quality by measuring the emitter saturation current j0E. On some emitter profiles, SIMS measurements were performed. For the etchback emitter a strong improvement in j0E can be achieved by etching back a heavily doped emitter, resulting in a highest cell efficiency of 18.9%. For the drive-in emitter we have shown that the masking SiNX layer should be removed and redeposited after drive-in in order to obtain a good hydrogen passivation and a low emitter saturation current.