Etching of a-Si:H on c-Si absorber monitored by in situ photoluminescence measurements

Interdigitated rear contact concepts for amorphous (a-Si:H)/crystalline (c-Si) silicon heterojunction solar cells require structured amorphous layers of different doping on the rear side [1,2]. Such structures can be achieved by a wetchemical etching step. A monitoring of the etching process is required since the density of defects at the c-Si surface that are induced by the wet-chemical etching [3] should be minimal to avoid recombination induced losses. Therefore, in situ photoluminescence (PL) was used to investigate the a-Si:H etching velocities of different etching solutions and to monitor defect formation at the c-Si surfaces after the a-Si:H removal. A correlation between the decrease in PL intensity during the progressive etching of the a-Si:H layer and the remaining thickness of the a-Si:H layer as measured by vibrational spectroscopic techniques has been observed. First results on the etching induced defects measured by PL spectra are presented for the investigated etchants. It is thus concluded that in situ PL is ideally suited for fast and straightforward process monitoring of etching processes on c-Si surfaces for photovoltaic applications.