Flexible bifacial amorphous Si quintuple‐ and sextuple‐junction solar cells for Internet of Things devices

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. 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. As one example of applying bifacial multi‐junction a‐Si based solar cells as an independent power source for the Internet of Things (loT) devices, a flexible bifacial quintuple‐junction solar cell was also prepared. In the sextuple‐junction solar cell, Voc of 3.5 V was obtained at 100 lux. In the quintuple‐junction solar cell formed on the polyimide film, Voc of 2.7 V was obtained at 100 lux.