The abovementioned poly-SiOx passivated c-Si solar cell was integrated with the perovskite top device into a 2T perovskite/c-Si tandem device yielding an active area PCE of 23.18% (Voc = 1.76 V Jsc = 17.8 mA/cm2, FF = 74%, active area: 1 cm2, see Figure 8(a)). The 2T tandem efficiency is higher than the efficiency of its top device by 5%abs(with respect to an opaque analogous single junction perovskite solar cell efficiency [65],[74]) and the efficiency of its bottom device by 6.5%abs. This efficiency is higher than that of the earlier reported value of 21.3% for a monolithic 2T perovskite/PERC-POLO tandem device [29]. On the other hand, it is lower than that of the earlier reported value of 25.1% for monolithic 2T perovskite/c-Si tandem device where the bottom device is endowed with poly-SiCx CSPCs [43]. These three types of high-thermal budget devices exhibit similar Vocs (1.74 to 1.8 V) and FFs (74%) in 2T tandem devices while only the one with poly-SiCx CSPCs could achieve better current matching between the devices (19.5 mA/cm2). The EQE of the 2T tandem device (Figure 8(b)) shows that our bottom device can deliver 19.2 mA/cm2, but that the top device limits the short-circuit current density of the stack to 17.8 mA/cm2. By further optimizing the layer thickness and perovskite bandgap, the current generation of the two devices can be better matched and consequently the efficiency of the 2T tandem devices can be further increased.