Investigation of various surface passivation schemes for silicon solar cells

In this work, we have investigated three different surface passivation technologies: classical thermal oxidation (CTO), rapid thermal oxidation (RTO) and silicon nitride by plasma enhanced chemical vapor deposition (PECVD). Eight different passivation properties including SiO₂/SiN_x stacks on phosphorus diffused (100 and 40 Ω/Sq) and non-diffused 1 Ω cm FZ silicon were compared. Both types of SiO₂ layers, CTO and RTO, yield a higher effective lifetime on the emitter surface than on the non-diffused surface. For the SiN_x layers the situation is reverted. On the other hand, with SiO₂/SiN_x stacks high lifetimes are obtained not only non-diffused surface but also on the diffused surface. Thus, we have chosen the RTO/SiN_x stack layers as front and rear surface passivation in solar cells, which passivate relatively good on the surface and has very low-weighted reflection. On planar cells passivated with RTO/SiN_x a very high V_oc of 675.6 mV and a J_sc of 35.1 mA/cm² was achieved. Compared to a planar cell using CTO the efficiency of RTO/SiN_x cell is 0.8% higher (4.5% relative). It can be concluded that the RTO/SiN_x layers are the optimal passivation for the front and rear surface. On the other hand, for textured cells, the J_sc and FF of RTO/SiN_x cells are lower than those of CTO cells. The main reasons of these J_sc and FF losses were also discussed systematically.