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.