Stability of front surface passivation of back-contact back-junction silicon solar cells under UV illumination
The performance of n-type silicon back-contact back-junction (BC-BJ) solar cells under the illumination with high energy ultraviolet (UV) photons was investigated and the impact of a phosphorus doped front surface field (FSF) layer on the UV-stability of the front surface passivation was analyzed. Solar cells without a FSF showed a significant performance reduction when exposed to UV light. The surface saturation current density (J0e), determined by lifetime measurements on test structures without a FSF, increased from 48 to 446 fA/cm2 after the UV exposure. At the same time the efficiency of the BC-BJ solar cells without a FSF decreased from 19.8 % to 14.3 %. On the other hand, the tested n+nn+ lifetime test structures and the BC-BJ solar cells with a FSF diffusion were stable under UV exposure, i.e. J0e increased only minimally and the efficiency of these cells was not affected by the UV illumination. The performance of the UV-degraded solar cells without FSF, could be improved during a forming gas anneal (FGA).