As described in Section 2.1, hydrogenation by FGA after SiNx layer capping is performed on p-type and n-type doped CSPCs to reintroduce the hydrogen that effused after high temperature annealing. Figure 4 shows the comparison in passivation of p-type and n-type doped poly-SiOx symmetric samples after thermal annealing and after hydrogenation. The optimum thermal oxidation and annealing conditions, as described in Figure 3, have been chosen for each type of CSPC. We observe that p-type and n-type doped poly-SiOx CSPCs applied on DSP and DST symmetric samples, respectively, gave the same iVoc of 690 mV after high-temperature annealing which improved to 710 mV after hydrogenation. Using the 2-step annealing technique, the symmetric p-type doped poly-SiOx applied on DST wafer exhibited an iVoc of 687 mV after hydrogenation. Applying the same 2-step annealing technique to symmetric n-type doped poly-SiOx on DST wafer (including the thermally grown tunnelling SiOx prepared at 675 °C for 3 minutes as in the p-type case), an iVoc of 690 mV was found after hydrogenation, resulting in lower passivation quality than the single step annealing case. Here, as the intrinsic poly-Si layer resulting from the first annealing got denser [73], we speculate that the phosphorus doping atoms do not easily reach the tunnelling SiOx/c-Si bulk interface to establish an effective electric field. In addition, as shown in Figure 3(b), the tunnelling SiOx prepared at 675 °C for 3 minutes is not the best condition for the n-type doped poly-SiOx on a textured surface. Still, this case is investigated (and later put forward in solar cell fabrication) to realize a neat flow chart in which both n-type and p-type doped poly-SiOx layers essentially undergo the same thermal processes at the same time.