Solar Cell, Amorphous Silicon, Quintuple-Junction, Low Illuminance
Summary / Abstract:
Hydrogenated amorphous Si(a-Si:H) Quintuple-junction solar cells which consist of a-SiOx:H/aSiOx:H/a-Si:H/a-SiOx:H/a-SiOx:H were fabricated by plasma CVD method. The total thickness was 0.6-0.8 m. Irradiation intensity (Pin) dependence of the open circuit voltage (Voc) of quintuple-junction solar cells was measured. The decreasing amount Voc (1/10) of the open-circuit voltage when the irradiation intensity became 1/10 was 62mV/cell. Voc drops rapidly from around the irradiation intensity of 1mW/cm2 (approximately 1,000 lux). This large Voc reduction is due to leakage current. Then, we discussed the origin of the leakage current, and finally by improving the leakage current, a very high open-circuit voltage Voc of 3.5 V was demonstrated under LED light illumination. Furthermore, we theoretically analyzed Voc as a function of the irradiation intensity, including effects of the leakage current and the film quality of i-a-Si(O):H. It was found from the simulation results that it is necessary to increase the shunt resistance Rsh and to lower the defect density of i-a-Si(O):H in order to obtain a sufficient Voc-Pin characteristics for IoT devices application under low illuminance.