3.3. Application in four terminal (4T) perovskite/c-Si tandem solar cells
The SST and DST poly-SiOx solar cells were deployed as bottom devices in high efficiency 4T tandem devices together with a previously processed and certified perovskite top device (bandgap 1.60 eV) [66]-[69]. The schematic sketches of the two 4T tandem devices alongside their constituting layers are presented in Figure 1. Following the method of measurement reported in [70] and with the certified measurements of both semi-transparent perovskite top and c-Si bottom devices, the combined results are summarized in Table 1. The 4T tandem devices based on SST and DST poly-SiOx bottom devices provide a PCE of 27.97% and 28.07%, respectively. Both SST and DST cells, after being illuminated with the transmitted light through the perovskite top device, experienced similar Jsclosses. Looking at the filtered EQE (see Figure 6(b)), the DST cell keeps the optical edge over the SST cell for every wavelength above 800 nm. The SST cell loses however more in Voc and FF than the DST cell. In fact, due to stronger Auger recombination at the p-type poly-SiOx / tunnelling SiOx / c-Si wafer side, the DST cell had poorer Voc, which is less sensitive to light-induced carriers’ injection, and FF more dominated by the low contact resistivity of the doped stack rather than an efficient extraction of light-induced majority carriers.