Bifacial a-SiOx:H/a-SiOx:H/a-Si:H/a-SiOx:H/a-SiOx:H quintuple-junction and a-SiOx:H/a-SiOx:H/a-Si:H/a-Si:H/a-SiOx:H/a-SiOx:H sextuple-junction solar cells were prepared by the PE-CVD. The solar cell has a structure in which both sides are sandwiched between ITO layers, and the structure allows light irradiation from both sides. A total of 49 cells having an area of 0.25 cm2, 0.5 cm2, and 1 cm2 was fabricated on a 10 cm × 10 cm substrate. The distribution of open-circuit voltage, Voc, under low illumination in all 49 solar cells was investigated. As one example of applying bifacial multi-junction a-Si based solar cells as an independent power source for the Internet of Things (IoT) devices, a flexible bifacial quintuple-junction solar cell was also prepared. In the sextuple-junction solar cell, an open-circuit voltage of 4.1 and 3.5 V was obtained even at a low illuminance of 3000 and 100 lux, respectively. In the quintuple-junction solar cell formed on the polyimide film substrate, an open-circuit voltage of 3.2 and 2.7 V was obtained at 3000 and 100 lux, respectively. The decreasing amount of the open circuit voltage when the irradiation intensity became 1/10, ΔVoc (1/10), was 62–64 mV/cell.